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MacKinnon CR, Zeissler K, Finizio S, Raabe J, Marrows CH, Mercer T, Bissell PR, Lepadatu S. Collective skyrmion motion under the influence of an additional interfacial spin-transfer torque. Sci Rep 2022; 12:10786. [PMID: 35750744 PMCID: PMC9232533 DOI: 10.1038/s41598-022-14969-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Accepted: 06/15/2022] [Indexed: 11/26/2022] Open
Abstract
Here we study the effect of an additional interfacial spin-transfer torque, as well as the well-established spin–orbit torque and bulk spin-transfer torque, on skyrmion collections—group of skyrmions dense enough that they are not isolated from one another—in ultrathin heavy metal/ferromagnetic multilayers, by comparing modelling with experimental results. Using a skyrmion collection with a range of skyrmion diameters and landscape disorder, we study the dependence of the skyrmion Hall angle on diameter and velocity, as well as the velocity as a function of diameter. We show that inclusion of the interfacial spin-transfer torque results in reduced skyrmion Hall angles, with values close to experimental results. We also show that for skyrmion collections the velocity is approximately independent of diameter, in marked contrast to the motion of isolated skyrmions, as the group of skyrmions move together at an average group velocity. Moreover, the calculated skyrmion velocities are comparable to those obtained in experiments when the interfacial spin-transfer torque is included. Our results thus show the significance of the interfacial spin-transfer torque in ultrathin magnetic multilayers, which helps to explain the low skyrmion Hall angles and velocities observed in experiment. We conclude that the interfacial spin-transfer torque should be considered in numerical modelling for reproduction of experimental results.
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Affiliation(s)
- Callum R MacKinnon
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE, UK.
| | - Katharina Zeissler
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK.,Bragg Center for Materials Research, University of Leeds, Leeds, LS2 9JT, UK
| | - Simone Finizio
- Swiss Light Source, Paul Scherrer Institut, 5232, Villigen, Switzerland
| | - Jörg Raabe
- Swiss Light Source, Paul Scherrer Institut, 5232, Villigen, Switzerland
| | - Christopher H Marrows
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK.,Bragg Center for Materials Research, University of Leeds, Leeds, LS2 9JT, UK
| | - Tim Mercer
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE, UK
| | - Philip R Bissell
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE, UK
| | - Serban Lepadatu
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE, UK.
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2
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Franke KJA, Ophus C, Schmid AK, Marrows CH. Switching between Magnetic Bloch and Néel Domain Walls with Anisotropy Modulations. Phys Rev Lett 2021; 127:127203. [PMID: 34597075 DOI: 10.1103/physrevlett.127.127203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Revised: 07/08/2021] [Accepted: 08/09/2021] [Indexed: 06/13/2023]
Abstract
It has been shown previously that the presence of a Dzyaloshinskii-Moriya interaction in perpendicularly magnetized thin films stabilizes Néel type domain walls. We demonstrate, using micromagnetic simulations and analytical modeling, that the presence of a uniaxial in plane magnetic anisotropy can also lead to the formation of Néel walls in the absence of a Dzyaloshinskii-Moriya interaction. It is possible to abruptly switch between Bloch and Néel walls via a small modulation of the in plane, but also the perpendicular, magnetic anisotropy. This opens up a route toward electric field control of the domain wall type with small applied voltages through electric field controlled anisotropies.
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Affiliation(s)
- Kévin J A Franke
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Colin Ophus
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Andreas K Schmid
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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Morley SA, Porro JM, Hrabec A, Rosamond MC, Venero DA, Linfield EH, Burnell G, Im MY, Fischer P, Langridge S, Marrows CH. Author Correction: Thermally and field-driven mobility of emergent magnetic charges in square artificial spin ice. Sci Rep 2020; 10:3328. [PMID: 32076092 PMCID: PMC7031501 DOI: 10.1038/s41598-020-60497-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022] Open
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5
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Mergia K, Tsompopoulou EO, Dellis S, Marrows CH, Michelakaki I, Kinane C, Caruana A, Langridge S, Douvalis AP, Cabet C, Messoloras S. Phase stability of Fe-5at%Cr and Fe-10at%Cr films under Fe + ion irradiation. J Phys Condens Matter 2020; 32:185702. [PMID: 31918418 DOI: 10.1088/1361-648x/ab69a1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
This work is within the objective of understanding the effects caused to Fe-Cr alloys by fast Fe ion irradiation. As the penetration length of Fe ion is of the order of hundreds of nanometers, 70 nm Fe-5at%C and Fe-10at%Cr films were irradiated at room temperature with 490 keV Fe+ ions at increasing fluence corresponding to a maximum damage of 50 displacements per atom (dpa). In Fe-5at%Cr alloy the Cr solute concentration remains unaltered even after a damage of 50 dpa. In the 10at%Cr the Cr solute concentration is reduced, with the increase of damage, asymptotically to a value of 7.2 at%.
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Affiliation(s)
- K Mergia
- Institute for Nuclear and Radiological Science and Technology, Safety and Energy, National Centre for Scientific Research 'Demokritos', 15310 Agia Paraskevi, Greece
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6
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Fallon K, Hughes S, Zeissler K, Legrand W, Ajejas F, Maccariello D, McFadzean S, Smith W, McGrouther D, Collin S, Reyren N, Cros V, Marrows CH, McVitie S. Controlled Individual Skyrmion Nucleation at Artificial Defects Formed by Ion Irradiation. Small 2020; 16:e1907450. [PMID: 32141234 DOI: 10.1002/smll.201907450] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 02/14/2020] [Accepted: 02/17/2020] [Indexed: 06/10/2023]
Abstract
Magnetic skyrmions are particle-like deformations in a magnetic texture. They have great potential as information carriers in spintronic devices because of their interesting topological properties and favorable motion under spin currents. A new method of nucleating skyrmions at nanoscale defect sites, created in a controlled manner with focused ion beam irradiation, in polycrystalline magnetic multilayer samples with an interfacial Dzyaloshinskii-Moriya interaction, is reported. This new method has three notable advantages: 1) localization of nucleation; 2) stability over a larger range of external field strengths, including stability at zero field; and 3) existence of skyrmions in material systems where, prior to defect fabrication, skyrmions were not previously obtained by field cycling. Additionally, it is observed that the size of defect nucleated skyrmions is uninfluenced by the defect itself-provided that the artificial defects are controlled to be smaller than the inherent skyrmion size. All of these characteristics are expected to be useful toward the goal of realizing a skyrmion-based spintronic device. This phenomenon is studied with a range of transmission electron microscopy techniques to probe quantitatively the magnetic behavior at the defects with applied field and correlate this with the structural impact of the defects.
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Affiliation(s)
- Kayla Fallon
- SUPA School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Sean Hughes
- SUPA School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Katharina Zeissler
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, 91767, France
| | - William Legrand
- National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK
| | - Fernando Ajejas
- National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK
| | | | - Samuel McFadzean
- SUPA School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
| | - William Smith
- SUPA School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Damien McGrouther
- SUPA School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Sophie Collin
- National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK
| | - Nicolas Reyren
- National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK
| | - Vincent Cros
- National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK
| | | | - Stephen McVitie
- SUPA School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
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7
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Finizio S, Zeissler K, Wintz S, Mayr S, Weßels T, Huxtable AJ, Burnell G, Marrows CH, Raabe J. Deterministic Field-Free Skyrmion Nucleation at a Nanoengineered Injector Device. Nano Lett 2019; 19:7246-7255. [PMID: 31525983 DOI: 10.1021/acs.nanolett.9b02840] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Magnetic skyrmions are topological solitons promising for applications as encoders for digital information. A number of different skyrmion-based memory devices have been recently proposed. In order to demonstrate a viable skyrmion-based memory device, it is necessary to reliably and reproducibly nucleate, displace, detect, and delete the magnetic skyrmions, possibly in the absence of external applied magnetic fields, which would needlessly complicate the device design. While the skyrmion displacement and detection have both been thoroughly investigated, much less attention has been dedicated to the study of the skyrmion nucleation process and its sub-nanosecond dynamics. In this study, we investigate the nucleation of magnetic skyrmions from a dedicated nanoengineered injector, demonstrating the reliable magnetic skyrmion nucleation at the remnant state. The sub-nanosecond dynamics of the skyrmion nucleation process were also investigated, allowing us to shine light on the physical processes driving the nucleation.
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Affiliation(s)
- Simone Finizio
- Paul Scherrer Institut , 5232 Villigen PSI , Switzerland
| | - Katharina Zeissler
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Sebastian Wintz
- Paul Scherrer Institut , 5232 Villigen PSI , Switzerland
- Institute of Ion Beam Physics and Materials Research , Helmholtz-Zentrum Dresden-Rossendorf , 01328 Dresden , Germany
| | - Sina Mayr
- Paul Scherrer Institut , 5232 Villigen PSI , Switzerland
- Laboratory for Mesoscopic Systems, Department of Materials , ETH Zürich , 8093 Zürich , Switzerland
| | - Teresa Weßels
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute , Forschungszentrum Jülich GmbH , 52425 Jülich , Germany
| | - Alexandra J Huxtable
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Gavin Burnell
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Christopher H Marrows
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Jörg Raabe
- Paul Scherrer Institut , 5232 Villigen PSI , Switzerland
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8
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Hrabec A, Shahbazi K, Moore TA, Martinez E, Marrows CH. Tuning spin-orbit torques at magnetic domain walls in epitaxial Pt/Co/Pt 1-x Au x trilayers. Nanotechnology 2019; 30:234003. [PMID: 30780146 DOI: 10.1088/1361-6528/ab087b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Magnetic domain walls (DWs) in perpendicularly magnetised thin films are attractive for racetrack memories, but technological progress still requires further reduction of the operationing currents. To efficiently drive these objects by the means of electric current, one has to optimize the damping-like torque which is caused by the spin Hall effect (SHE). This not only requires a high net spin Hall angle but also the presence of a Dzyaloshinskii-Moriya interaction (DMI) to produce magnetic textures sensitive to this type of the torque. In this work, we explore the coexistence and importance of these two phenomena in epitaxial Pt/Co/Pt1-x Au x films in which we control the degree of inversion symmetry-breaking between the two interfaces by varying x. Gold is used as a material with negligible induced magnetic moment and SHE and the interface between Co/Au as a source of a small DMI. We find no current-induced DW motion in the symmetric Pt/Co/Pt (x = 0) trilayer. By fitting a one-dimensional model to the DW velocity as a function of drive current density and in-plane applied field in samples with non-zero values of x, we find that both net DMI strength and spin Hall angle rise monotonically as Au is introduced. They reach values of 0.75 ± 0.05 mJ m-2 and 0.10 ± 0.01, respectively, for Pt/Co/Au (x = 1).
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Affiliation(s)
- Aleš Hrabec
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, United Kingdom
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9
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Li Y, Paterson GW, Macauley GM, Nascimento FS, Ferguson C, Morley SA, Rosamond MC, Linfield EH, MacLaren DA, Macêdo R, Marrows CH, McVitie S, Stamps RL. Superferromagnetism and Domain-Wall Topologies in Artificial "Pinwheel" Spin Ice. ACS Nano 2019; 13:2213-2222. [PMID: 30588800 DOI: 10.1021/acsnano.8b08884] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
For over ten years, arrays of interacting single-domain nanomagnets, referred to as artificial spin ices, have been engineered with the aim to study frustration in model spin systems. Here, we use Fresnel imaging to study the reversal process in "pinwheel" artificial spin ice, a modified square ASI structure obtained by rotating each island by some angle about its midpoint. Our results demonstrate that a simple 45° rotation changes the magnetic ordering from antiferromagnetic to ferromagnetic, creating a superferromagnet which exhibits mesoscopic domain growth mediated by domain wall nucleation and coherent domain propagation. We observe several domain-wall configurations, most of which are direct analogues to those seen in continuous ferromagnetic films. However, charged walls also appear due to the geometric constraints of the system. Changing the orientation of the external magnetic field allows control of the nature of the spin reversal with the emergence of either one- or two-dimensional avalanches. This property of pinwheel ASI could be employed to tune devices based on magnetotransport phenomena such as Hall circuits.
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Affiliation(s)
- Yue Li
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Gary W Paterson
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Gavin M Macauley
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Fabio S Nascimento
- Departamento de Física , Universidade Federal de Viçosa , Viçosa 36570-900 , Minas Gerais , Brazil
| | - Ciaran Ferguson
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Sophie A Morley
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , United Kingdom
- Department of Physics , University of California , Santa Cruz , California 95064 , United States
| | - Mark C Rosamond
- School of Electronic and Electrical Engineering , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Edmund H Linfield
- School of Electronic and Electrical Engineering , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Donald A MacLaren
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Rair Macêdo
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Christopher H Marrows
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Stephen McVitie
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Robert L Stamps
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
- Department of Physics and Astronomy , University of Manitoba , Manitoba R3T 2N2 , Canada
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10
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Finizio S, Wintz S, Zeissler K, Sadovnikov AV, Mayr S, Nikitov SA, Marrows CH, Raabe J. Dynamic Imaging of the Delay- and Tilt-Free Motion of Néel Domain Walls in Perpendicularly Magnetized Superlattices. Nano Lett 2019; 19:375-380. [PMID: 30517003 DOI: 10.1021/acs.nanolett.8b04091] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We report on the time-resolved investigation of current- and field-induced domain wall motion in the flow regime in perpendicularly magnetized microwires exhibiting antisymmetric exchange interaction by means of scanning transmission X-ray microscopy with a 200 ps time step. The sub-ns time step of the dynamical images allowed us to observe the absence of incubation times for the motion of the domain wall within an uncertainty of 200 ps, together with indications for a negligible inertia of the domain wall. Furthermore, we observed that, for short current and magnetic field pulses, the magnetic domain walls do not exhibit a tilting during their motion, providing a mechanism for the fast, tilt-free, current-induced motion of magnetic domain walls.
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Affiliation(s)
- Simone Finizio
- Swiss Light Source , Paul Scherrer Institut , 5232 Villigen PSI , Switzerland
| | - Sebastian Wintz
- Swiss Light Source , Paul Scherrer Institut , 5232 Villigen PSI , Switzerland
- Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf , 01328 Dresden , Germany
| | - Katharina Zeissler
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Alexandr V Sadovnikov
- Laboratory Metamaterials , Saratov State University , Saratov 410012 , Russia
- Kotel'nikov Institute of Radioengineering and Electronics , Russian Academy of Sciences , Moscow 125009 , Russia
| | - Sina Mayr
- Swiss Light Source , Paul Scherrer Institut , 5232 Villigen PSI , Switzerland
- Department of Materials, Laboratory for Mesoscopic Systems , ETH Zürich , 8093 Zürich , Switzerland
| | - Sergey A Nikitov
- Laboratory Metamaterials , Saratov State University , Saratov 410012 , Russia
- Kotel'nikov Institute of Radioengineering and Electronics , Russian Academy of Sciences , Moscow 125009 , Russia
| | - Christopher H Marrows
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Jörg Raabe
- Swiss Light Source , Paul Scherrer Institut , 5232 Villigen PSI , Switzerland
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11
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Shahbazi K, Kim JV, Nembach HT, Shaw JM, Bischof A, Rossell MD, Jeudy V, Moore TA, Marrows CH. Domain-wall motion and interfacial Dzyaloshinskii-Moriya interactions in Pt/Co/Ir( t Ir)/Ta multilayers. Phys Rev B 2019; 99:10.1103/PhysRevB.99.094409. [PMID: 33336122 PMCID: PMC7739563 DOI: 10.1103/physrevb.99.094409] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The interfacial Dzyaloshinskii-Moriya interaction (DMI) is important for chiral domain walls (DWs) and for stabilizing magnetic skyrmions. We study the effects of introducing increasing thicknesses of Ir, from zero to 2 nm, into a Pt/Co/Ta multilayer between the Co and Ta layers. There is a marked increase in magnetic moment, due to the suppression of the dead layer at the interface with Ta, but the perpendicular anisotropy is hardly affected. All samples show a universal scaling of the field-driven DW velocity across the creep and depinning regimes. Asymmetric bubble expansion shows that DWs in all of the samples have the left-handed Néel form. The value of in-plane magnetic field at which the creep velocity shows a minimum drops markedly on the introduction of Ir, as does the frequency shift of the Stokes and anti-Stokes peaks in Brillouin light scattering (BLS) measurements. Despite this qualitative similarity, there are quantitative differences in the DMI strength given by the two measurements, with BLS often returning higher values. Many features in bubble expansion velocity curves do not fit simple models commonly used, namely a lack of symmetry about the velocity minimum and no difference in velocities at high in-plane fields. These features are explained by the use of a new model in which the depinning field is allowed to vary with in-plane field in a way determined from micromagnetic simulations. This theory shows that the velocity minimum underestimates the DMI field, consistent with BLS giving higher values. Our results suggest that the DMI at an Ir/Co interface has the same sign as the DMI at a Pt/Co interface.
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Affiliation(s)
- Kowsar Shahbazi
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Joo-Von Kim
- Centre for Nanoscience and Nanotechnology (C2N), CNRS, Université Paris-Sud, Université Paris-Saclay, 91120 Palaiseau, France
| | - Hans T. Nembach
- Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA
| | - Justin M. Shaw
- Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA
| | - Andreas Bischof
- IBM Research-Zurich, Säumerstrasse 4, CH-8803 Rüschlikon, Switzerland
| | - Marta D. Rossell
- IBM Research-Zurich, Säumerstrasse 4, CH-8803 Rüschlikon, Switzerland
- Electron Microscopy Center, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dubendorf, Switzerland
| | - Vincent Jeudy
- Laboratoire de Physique des Solides, CNRS, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay Cedex, France
| | - Thomas A. Moore
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, United Kingdom
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12
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Zeissler K, Finizio S, Shahbazi K, Massey J, Ma'Mari FA, Bracher DM, Kleibert A, Rosamond MC, Linfield EH, Moore TA, Raabe J, Burnell G, Marrows CH. Discrete Hall resistivity contribution from Néel skyrmions in multilayer nanodiscs. Nat Nanotechnol 2018; 13:1161-1166. [PMID: 30275493 DOI: 10.1038/s41565-018-0268-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Accepted: 08/28/2018] [Indexed: 06/08/2023]
Abstract
Magnetic skyrmions are knot-like quasiparticles. They are candidates for non-volatile data storage in which information is moved between fixed read and write terminals. The read-out operation of skyrmion-based spintronic devices will rely on the electrical detection of a single magnetic skyrmion within a nanostructure. Here we present Pt/Co/Ir nanodiscs that support skyrmions at room temperature. We measured the Hall resistivity and simultaneously imaged the spin texture using magnetic scanning transmission X-ray microscopy. The Hall resistivity is correlated to both the presence and size of the skyrmion. The size-dependent part matches the expected anomalous Hall signal when averaging the magnetization over the entire disc. We observed a resistivity contribution that only depends on the number and sign of skyrmion-like objects present in the disc. Each skyrmion gives rise to 22 ± 2 nΩ cm irrespective of its size. This contribution needs to be considered in all-electrical detection schemes applied to skyrmion-based devices. Not only the area of Néel skyrmions but also their number and sign contribute to their Hall resistivity.
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Affiliation(s)
| | - Simone Finizio
- Swiss Light Source, Paul Scherrer Institut, Villigen PSI, Switzerland
| | - Kowsar Shahbazi
- School of Physics and Astronomy, University of Leeds, Leeds, UK
| | - Jamie Massey
- School of Physics and Astronomy, University of Leeds, Leeds, UK
| | - Fatma Al Ma'Mari
- School of Physics and Astronomy, University of Leeds, Leeds, UK
- Department of Physics, Sultan Qaboos University, Muscat, Oman
| | - David M Bracher
- Swiss Light Source, Paul Scherrer Institut, Villigen PSI, Switzerland
| | - Armin Kleibert
- Swiss Light Source, Paul Scherrer Institut, Villigen PSI, Switzerland
| | - Mark C Rosamond
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, UK
| | - Edmund H Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, UK
| | - Thomas A Moore
- School of Physics and Astronomy, University of Leeds, Leeds, UK
| | - Jörg Raabe
- Swiss Light Source, Paul Scherrer Institut, Villigen PSI, Switzerland
| | - Gavin Burnell
- School of Physics and Astronomy, University of Leeds, Leeds, UK
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13
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McVitie S, Hughes S, Fallon K, McFadzean S, McGrouther D, Krajnak M, Legrand W, Maccariello D, Collin S, Garcia K, Reyren N, Cros V, Fert A, Zeissler K, Marrows CH. A transmission electron microscope study of Néel skyrmion magnetic textures in multilayer thin film systems with large interfacial chiral interaction. Sci Rep 2018; 8:5703. [PMID: 29632330 PMCID: PMC5890272 DOI: 10.1038/s41598-018-23799-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Accepted: 03/21/2018] [Indexed: 12/05/2022] Open
Abstract
Skyrmions in ultrathin ferromagnetic metal (FM)/heavy metal (HM) multilayer systems produced by conventional sputtering methods have recently generated huge interest due to their applications in the field of spintronics. The sandwich structure with two correctly-chosen heavy metal layers provides an additive interfacial exchange interaction which promotes domain wall or skyrmion spin textures that are Néel in character and with a fixed chirality. Lorentz transmission electron microscopy (TEM) is a high resolution method ideally suited to quantitatively image such chiral magnetic configurations. When allied with physical and chemical TEM analysis of both planar and cross-sectional samples, key length scales such as grain size and the chiral variation of the magnetisation variation have been identified and measured. We present data showing the importance of the grain size (mostly < 10 nm) measured from direct imaging and its potential role in describing observed behaviour of isolated skyrmions (diameter < 100 nm). In the latter the region in which the magnetization rotates is measured to be around 30 nm. Such quantitative information on the multiscale magnetisation variations in the system is key to understanding and exploiting the behaviour of skyrmions for future applications in information storage and logic devices.
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Affiliation(s)
- S McVitie
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom.
| | - S Hughes
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - K Fallon
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - S McFadzean
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - D McGrouther
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - M Krajnak
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom.,Department of Materials Science and Engineering, Monash University, Clayton, Victoria, 3800, Australia
| | - W Legrand
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - D Maccariello
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - S Collin
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - K Garcia
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - N Reyren
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - V Cros
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - A Fert
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, 91767, Palaiseau, France
| | - K Zeissler
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - C H Marrows
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom
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14
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Almeida TP, Temple R, Massey J, Fallon K, McGrouther D, Moore T, Marrows CH, McVitie S. Quantitative TEM imaging of the magnetostructural and phase transitions in FeRh thin film systems. Sci Rep 2017; 7:17835. [PMID: 29259255 PMCID: PMC5736605 DOI: 10.1038/s41598-017-18194-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Accepted: 12/07/2017] [Indexed: 11/26/2022] Open
Abstract
Equi-atomic FeRh is a very interesting material as it undergoes a magnetostructural transition from an antiferromagnetic (AF) to a ferromagnetic (FM) phase between 75-105 °C. Its ability to present phase co-existence separated by domain walls (DWs) above room temperature provides immense potential for exploitation of their DW motion in spintronic devices. To be able to effectively control the DWs associated with AF/FM coexistence in FeRh thin films we must fully understand the magnetostructural transition and thermomagnetic behaviour of DWs at a localised scale. Here we present a transmission electron microscopy investigation of the transition in planar FeRh thin-film samples by combining differential phase contrast (DPC) magnetic imaging with in situ heating. We perform quantitative measurements from individual DWs as a function of temperature, showing that FeRh on NiAl exhibits thermomagnetic behaviour consistent with the transition from AF to FM. DPC imaging of an FeRh sample with HF-etched substrate reveals a state of AF/FM co-existence and shows the transition from AF to FM regions proceeds via nucleation of small vortex structures, which then grow by combining with newly nucleated vortex states into larger complex magnetic domains, until it is in a fully-FM state.
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Affiliation(s)
- Trevor P Almeida
- SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK.
| | - Rowan Temple
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
| | - Jamie Massey
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
| | - Kayla Fallon
- SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Damien McGrouther
- SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Thomas Moore
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
| | | | - Stephen McVitie
- SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
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15
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Zeissler K, Mruczkiewicz M, Finizio S, Raabe J, Shepley PM, Sadovnikov AV, Nikitov SA, Fallon K, McFadzean S, McVitie S, Moore TA, Burnell G, Marrows CH. Pinning and hysteresis in the field dependent diameter evolution of skyrmions in Pt/Co/Ir superlattice stacks. Sci Rep 2017; 7:15125. [PMID: 29123144 PMCID: PMC5680206 DOI: 10.1038/s41598-017-15262-3] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 10/17/2017] [Indexed: 11/09/2022] Open
Abstract
We have imaged Néel skyrmion bubbles in perpendicularly magnetised polycrystalline multilayers patterned into 1 µm diameter dots, using scanning transmission x-ray microscopy. The skyrmion bubbles can be nucleated by the application of an external magnetic field and are stable at zero field with a diameter of 260 nm. Applying an out of plane field that opposes the magnetisation of the skyrmion bubble core moment applies pressure to the bubble and gradually compresses it to a diameter of approximately 100 nm. On removing the field the skyrmion bubble returns to its original diameter via a hysteretic pathway where most of the expansion occurs in a single abrupt step. This contradicts analytical models of homogeneous materials in which the skyrmion compression and expansion are reversible. Micromagnetic simulations incorporating disorder can explain this behaviour using an effective thickness modulation between 10 nm grains.
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Affiliation(s)
- K Zeissler
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom.
| | - M Mruczkiewicz
- Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04, Bratislava, Slovak Republic
| | - S Finizio
- Swiss Light Source, Paul Scherrer Institute, 5232, Villigen, Switzerland
| | - J Raabe
- Swiss Light Source, Paul Scherrer Institute, 5232, Villigen, Switzerland
| | - P M Shepley
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - A V Sadovnikov
- Laboratory "Metamaterials", Saratov State University, Saratov, 410012, Russia.,Kotel'nikov Institute of Radioengineering and Electronics, Russian Academy of Sciences, Moscow, 125009, Russia
| | - S A Nikitov
- Laboratory "Metamaterials", Saratov State University, Saratov, 410012, Russia.,Kotel'nikov Institute of Radioengineering and Electronics, Russian Academy of Sciences, Moscow, 125009, Russia
| | - K Fallon
- School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - S McFadzean
- School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - S McVitie
- School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - T A Moore
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - G Burnell
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - C H Marrows
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom
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16
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Temple RC, McLaren M, Brydson RMD, Hickey BJ, Marrows CH. Long spin lifetime and large barrier polarisation in single electron transport through a CoFe nanoparticle. Sci Rep 2016; 6:28296. [PMID: 27329575 PMCID: PMC4916452 DOI: 10.1038/srep28296] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 05/25/2016] [Indexed: 11/09/2022] Open
Abstract
We have investigated single electron spin transport in individual single crystal bcc Co30Fe70 nanoparticles using scanning tunnelling microscopy with a standard tungsten tip. Particles were deposited using a gas-aggregation nanoparticle source and individually addressed as asymmetric double tunnel junctions with both a vacuum and a MgO tunnel barrier. Spectroscopy measurements on the particles show a Coulomb staircase that is correlated with the measured particle size. Field emission tunnelling effects are incorporated into standard single electron theory to model the data. This formalism allows spin-dependent parameters to be determined even though the tip is not spin-polarised. The barrier spin polarisation is very high, in excess of 84%. By variation of the resistance, several orders of magnitude of the system timescale are probed, enabling us to determine the spin relaxation time on the island. It is found to be close to 10 μs, a value much longer than previously reported.
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Affiliation(s)
- R C Temple
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
| | - M McLaren
- Institute for Materials Research, School of Chemical and Process Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - R M D Brydson
- Institute for Materials Research, School of Chemical and Process Engineering, University of Leeds, Leeds, LS2 9JT, UK
| | - B J Hickey
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
| | - C H Marrows
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
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17
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Benitez MJ, Hrabec A, Mihai AP, Moore TA, Burnell G, McGrouther D, Marrows CH, McVitie S. Magnetic microscopy and topological stability of homochiral Néel domain walls in a Pt/Co/AlOx trilayer. Nat Commun 2015; 6:8957. [PMID: 26642936 PMCID: PMC4686874 DOI: 10.1038/ncomms9957] [Citation(s) in RCA: 105] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Accepted: 10/20/2015] [Indexed: 11/09/2022] Open
Abstract
The microscopic magnetization variation in magnetic domain walls in thin films is a crucial property when considering the torques driving their dynamic behaviour. For films possessing out-of-plane anisotropy normally the presence of Néel walls is not favoured due to magnetostatic considerations. However, they have the right structure to respond to the torques exerted by the spin Hall effect. Their existence is an indicator of the interfacial Dzyaloshinskii-Moriya interaction (DMI). Here we present direct imaging of Néel domain walls with a fixed chirality in device-ready Pt/Co/AlOx films using Lorentz transmission electron and Kerr microscopies. It is shown that any independently nucleated pair of walls in our films form winding pairs when they meet that are difficult to annihilate with field, confirming that they all possess the same topological winding number. The latter is enforced by the DMI. The field required to annihilate these winding wall pairs is used to give a measure of the DMI strength. Such domain walls, which are robust against collisions with each other, are good candidates for dense data storage.
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Affiliation(s)
- M J Benitez
- School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland
| | - A Hrabec
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
| | - A P Mihai
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
| | - T A Moore
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
| | - G Burnell
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
| | - D McGrouther
- School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland
| | - C H Marrows
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
| | - S McVitie
- School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland
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18
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Le Graët C, de Vries MA, McLaren M, Brydson RMD, Loving M, Heiman D, Lewis LH, Marrows CH. Sputter growth and characterization of metamagnetic B2-ordered FeRh epilayers. J Vis Exp 2013. [PMID: 24145690 PMCID: PMC3938335 DOI: 10.3791/50603] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Chemically ordered alloys are useful in a variety of magnetic nanotechnologies. They are most conveniently prepared at an industrial scale using sputtering techniques. Here we describe a method for preparing epitaxial thin films of B2-ordered FeRh by sputter deposition onto single crystal MgO substrates. Deposition at a slow rate onto a heated substrate allows time for the adatoms to both settle into a lattice with a well-defined epitaxial relationship with the substrate and also to find their proper places in the Fe and Rh sublattices of the B2 structure. The structure is conveniently characterized with X-ray reflectometry and diffraction and can be visualised directly using transmission electron micrograph cross-sections. B2-ordered FeRh exhibits an unusual metamagnetic phase transition: the ground state is antiferromagnetic but the alloy transforms into a ferromagnet on heating with a typical transition temperature of about 380 K. This is accompanied by a 1% volume expansion of the unit cell: isotropic in bulk, but laterally clamped in an epilayer. The presence of the antiferromagnetic ground state and the associated first order phase transition is very sensitive to the correct equiatomic stoichiometry and proper B2 ordering, and so is a convenient means to demonstrate the quality of the layers that can be deposited with this approach. We also give some examples of the various techniques by which the change in phase can be detected.
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19
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Abstract
We report the observation of a large linear magnetoresistance in the ohmic regime in commonplace commercial n-type silicon wafer with a P dopant density of (1.4±0.1) ×1015 cm–3, and report measurements of it in the temperature range 30–200 K. It arises from the deformation of current paths, which causes a part of the Hall field to be detected at the voltage probes. In short, wide samples we found linear magnetoresistance as large as 4707% in an 8 tesla field at 35 K. Sample geometry effects like these are commonplace in commercial Hall sensors. However, we found that the effect persisted in long, thin samples where the macroscopic current flow should be uniform between the voltage probes: we observed a magnetoresistance of 445% under the same conditions as above. We interpret this result as arising due to spatial fluctuations in the donor density, in the spirit of the Herring model.
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20
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Budrikis Z, Morgan JP, Akerman J, Stein A, Politi P, Langridge S, Marrows CH, Stamps RL. Disorder strength and field-driven ground state domain formation in artificial spin ice: experiment, simulation, and theory. Phys Rev Lett 2012; 109:037203. [PMID: 22861890 DOI: 10.1103/physrevlett.109.037203] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2011] [Indexed: 06/01/2023]
Abstract
Quenched disorder affects how nonequilibrium systems respond to driving. In the context of artificial spin ice, an athermal system comprised of geometrically frustrated classical Ising spins with a twofold degenerate ground state, we give experimental and numerical evidence of how such disorder washes out edge effects and provide an estimate of disorder strength in the experimental system. We prove analytically that a sequence of applied fields with fixed amplitude is unable to drive the system to its ground state from a saturated state. These results should be relevant for other systems where disorder does not change the nature of the ground state.
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Affiliation(s)
- Zoe Budrikis
- School of Physics, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia.
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21
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Lepadatu S, Mihai AP, Claydon JS, Maccherozzi F, Dhesi SS, Kinane CJ, Langridge S, Marrows CH. The increase of the spin-transfer torque threshold current density in coupled vortex domain walls. J Phys Condens Matter 2012; 24:024210. [PMID: 22173240 DOI: 10.1088/0953-8984/24/2/024210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We have studied the dependence on the domain wall structure of the spin-transfer torque current density threshold for the onset of wall motion in curved, Gd-doped Ni(80)Fe(20) nanowires with no artificial pinning potentials. For single vortex domain walls, for both 10% and 1% Gd-doping concentrations, the threshold current density is inversely proportional to the wire width and significantly lower compared to the threshold current density measured for transverse domain walls. On the other hand for high Gd concentrations and large wire widths, double vortex domain walls are formed which require an increase in the threshold current density compared to single vortex domain walls at the same wire width. We suggest that this is due to the coupling of the vortex cores, which are of opposite chirality, and hence will be acted on by opposing forces arising through the spin-transfer torque effect.
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Affiliation(s)
- S Lepadatu
- School of Physics and Astronomy, E C Stoner Laboratory, University of Leeds, Leeds, UK
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22
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Affiliation(s)
- C H Marrows
- School of Physics and Astronomy, University of Leeds, Leeds, UK
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23
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Abstract
Single electron electronics is now well developed, and allows the manipulation of electrons one-by-one as they tunnel on and off a nanoscale conducting island. In the past decade or so, there have been concerted efforts in several laboratories to construct single electron devices incorporating ferromagnetic components in order to introduce spin functionality. The use of ferromagnetic electrodes with a non-magnetic island can lead to spin accumulation on the island. On the other hand, making the dot also ferromagnetic introduces new physics such as tunnelling magnetoresistance enhancement in the cotunnelling regime and manifestations of the Kondo effect. Such nanoscale islands are also found to have long spin lifetimes. Conventional spintronics makes use of the average spin-polarization of a large ensemble of electrons: this new approach offers the prospect of accessing the quantum properties of the electron, and is a candidate approach to the construction of solid-state spin-based qubits.
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Affiliation(s)
- Kari J Dempsey
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
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24
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Abstract
Conventional microelectronics exploits only the charge degree of freedom of the electron. Bringing the spin degree of freedom to bear on sensing, radio frequency, memory and logic applications opens up new possibilities for 'more than Moore' devices incorporating magnetic components that can couple to an external field, store a bit of data or represent a Boolean state. Moreover, the electron spin is an archetypal two-state quantum system that is an excellent candidate for a solid-state realization of a qubit.
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Affiliation(s)
- C H Marrows
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK.
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25
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San Emeterio Alvarez L, Wang KY, Lepadatu S, Landi S, Bending SJ, Marrows CH. Spin-transfer-torque-assisted domain-wall creep in a Co/Pt multilayer wire. Phys Rev Lett 2010; 104:137205. [PMID: 20481911 DOI: 10.1103/physrevlett.104.137205] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2009] [Revised: 02/10/2010] [Indexed: 05/29/2023]
Abstract
We have studied field- and current-driven domain-wall (DW) creep motion in a perpendicularly magnetized Co/Pt multilayer wire by real-time Kerr microscopy. The application of a dc current of density of approximately < 10(7) A/cm2 assisted only the DW creeping under field in the same direction as the electron flow, a signature of spin-transfer torque effects. We develop a model dealing with both bidirectional spin-transfer effects and Joule heating, with the same dynamical exponent mu=1/4 for both field- and current-driven creep, and use it to quantify the spin-transfer efficiency as 3.6+/-0.6 Oe cm2/MA in our wires, confirming the significant nonadiabatic contribution to the spin torque.
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26
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Seemann KM, Mokrousov Y, Aziz A, Miguel J, Kronast F, Kuch W, Blamire MG, Hindmarch AT, Hickey BJ, Souza I, Marrows CH. Spin-orbit strength driven crossover between intrinsic and extrinsic mechanisms of the anomalous hall effect in the epitaxial L1{0}-ordered ferromagnets FePd and FePt. Phys Rev Lett 2010; 104:076402. [PMID: 20366900 DOI: 10.1103/physrevlett.104.076402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2009] [Indexed: 05/29/2023]
Abstract
We determine the composition of intrinsic as well as extrinsic contributions to the anomalous Hall effect (AHE) in the isoelectronic L1_{0} FePd and FePt alloys. We show that the AHE signal in our 30 nm thick epitaxially deposited films of FePd is mainly due to an extrinsic side jump, while in the epitaxial FePt films of the same thickness and degree of order the intrinsic contribution is dominating over the extrinsic mechanisms of the AHE. We relate this crossover to the difference in spin-orbit strength of Pt and Pd atoms and suggest that this phenomenon can be used for tuning the origins of the AHE in complex alloys.
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Affiliation(s)
- K M Seemann
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom.
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27
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Aziz A, Wessely OP, Ali M, Edwards DM, Marrows CH, Hickey BJ, Blamire MG. Nonlinear giant magnetoresistance in dual spin valves. Phys Rev Lett 2009; 103:237203. [PMID: 20366169 DOI: 10.1103/physrevlett.103.237203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2009] [Indexed: 05/29/2023]
Abstract
Giant magnetoresistance (GMR) arises from differential scattering of the majority and minority spin electrons by a ferromagnet (FM) so that the resistance of a heterostructure depends on the relative magnetic orientation of the FM layers within it separated by nonmagnetic spacers. Here, we show that highly nonequilibrium spin accumulation in metallic heterostructures results in a current-dependent nonlinear GMR which is not predicted within the present understanding of GMR. The behavior can be explained by allowing the scattering asymmetries in an ultrathin FM layer to be current dependent.
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Affiliation(s)
- A Aziz
- Department of Materials Science, Cambridge University, Pembroke Street, Cambridge CB2 3QZ, United Kingdom
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28
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Tettamanzi GC, Pakes CI, Potenza A, Rubanov S, Marrows CH, Prawer S. Superconducting transition in Nb nanowires fabricated using focused ion beam. Nanotechnology 2009; 20:465302. [PMID: 19843991 DOI: 10.1088/0957-4484/20/46/465302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Making use of focused Ga-ion beam (FIB) fabrication technology, the evolution with device dimension of the low-temperature electrical properties of Nb nanowires has been examined in a regime where crossover from Josephson-like to insulating behaviour is evident. Resistance-temperature data for devices with a physical width of order 100 nm demonstrate suppression of superconductivity, leading to dissipative behaviour that is shown to be consistent with the activation of phase-slip below T(c). This study suggests that by exploiting the Ga-impurity poisoning introduced by the FIB into the periphery of the nanowire, a central superconducting phase-slip nanowire with sub-10 nm dimensions may be engineered within the core of the nanowire.
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Affiliation(s)
- G C Tettamanzi
- School of Physics, University of Melbourne, Victoria 3010, Australia.
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29
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Lepadatu S, Vanhaverbeke A, Atkinson D, Allenspach R, Marrows CH. Dependence of domain-wall depinning threshold current on pinning profile. Phys Rev Lett 2009; 102:127203. [PMID: 19392318 DOI: 10.1103/physrevlett.102.127203] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2007] [Indexed: 05/27/2023]
Abstract
We have investigated the threshold current density required for depinning a domain wall from constrictions in NiFe nanowires, which give rise to pinning potentials of fixed amplitude but variable profile. We observed it to vary linearly with the angle of the triangular constriction. These results are reproduced using micromagnetic simulations including the adiabatic and nonadiabatic spin-torque terms. By curve-fitting the calculated variations to the experimental results, we obtain the nonadiabaticity parameter beta=0.04(+/-0.005) and current spin polarization P=0.51(+/-0.02).
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Affiliation(s)
- S Lepadatu
- E. C. Stoner Laboratory, University of Leeds, Leeds LS2 9JT, UK.
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30
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Baltz V, Naylor AD, Seemann KM, Elder W, Sheen S, Westerholt K, Zabel H, Burnell G, Marrows CH, Hickey BJ. Conductance features in point contact Andreev reflection spectra. J Phys Condens Matter 2009; 21:095701. [PMID: 21817404 DOI: 10.1088/0953-8984/21/9/095701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Point contact Andreev reflection (PCAR) spectroscopy is a common technique for determining the spin polarization of a ferromagnetic sample. The polarization is extracted by measuring the bias dependence of the conductance of a metallic/superconducting point contact. Under ideal conditions, the conductance is dominated by Andreev reflection and the Blonder-Tinkham-Klapwijk (BTK) model can be used to extract a value for the polarization. However, PCAR spectra often exhibit unwanted features in the conductance that cannot be appropriately modelled with the BTK theory. In this paper we isolate some of these unwanted features and show that any further extraction of the spin polarization from these non-ideal spectra proves unreliable. Understanding the origin of these features provides an objective criterion for rejection of PCAR spectra unsuitable for fitting with the modified BTK model.
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Affiliation(s)
- V Baltz
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
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31
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Wu MC, Aziz A, Witt JDS, Hickey MC, Ali M, Marrows CH, Hickey BJ, Blamire MG. Structural and functional analysis of nanopillar spin electronic devices fabricated by 3D focused ion beam lithography. Nanotechnology 2008; 19:485305. [PMID: 21836299 DOI: 10.1088/0957-4484/19/48/485305] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We discuss the fabrication of nanopillar spin electronic devices from metal multilayered heterostructures, utilizing a novel three-dimensional focused ion beam lithography process. Finite element simulation was performed to optimize the geometry of the nanopillar device and to demonstrate that current flow is perpendicular to the plane within the active region of the device. Clear zero-field current induced magnetization switching is observed in our nanopillar devices at room temperature.
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Affiliation(s)
- M C Wu
- Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK
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32
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Neal JS, Milosević MV, Bending SJ, Potenza A, San Emeterio L, Marrows CH. Competing symmetries and broken bonds in superconducting vortex-antivortex molecular crystals. Phys Rev Lett 2007; 99:127001. [PMID: 17930542 DOI: 10.1103/physrevlett.99.127001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2007] [Indexed: 05/25/2023]
Abstract
Hall probe microscopy has been used to image vortex-antivortex molecules induced in superconducting Pb films by the stray fields from square arrays of magnetic dots. We have directly observed spontaneous vortex-antivortex pairs and studied how they interact with added free (anti)fluxons in an applied magnetic field. We observe a variety of phenomena arising from competing symmetries which either drive added antivortices to join antivortex shells around dots or stabilize the translationally symmetric antivortex lattice between the dots. Added vortices annihilate antivortex shells, leading first to a stable "nulling state" with no free fluxons and then, at high densities, to vortex shells around the dots stabilized by the asymmetric antipinning potential. Our experimental findings are in good agreement with Ginzburg-Landau calculations.
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Affiliation(s)
- J S Neal
- Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
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Blamire MG, Ali M, Leung CW, Marrows CH, Hickey BJ. Exchange bias and blocking temperature in Co/FeMn/CuNi trilayers. Phys Rev Lett 2007; 98:217202. [PMID: 17677802 DOI: 10.1103/physrevlett.98.217202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2007] [Indexed: 05/16/2023]
Abstract
Aspects of exchange bias between antiferromagnets and ferromagnets remain unclear despite recent research. An outstanding issue is the relationship between exchange bias and enhanced coercivity in the ferromagnetic layer. This Letter reports the unexpected finding that a substantial exchange bias can be generated between an antiferromagnet (FeMn) with a higher ordering temperature than that of the ferromagnet (CuNi). We interpret the result in terms of a temperature-dependent competition between interfacial exchange and antiferromagnet anisotropy energies. Crossover of these energies during cooling is responsible for the onset of exchange bias at the blocking temperature.
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Affiliation(s)
- M G Blamire
- Department of Materials Science, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, United Kingdom
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Ali M, Adie P, Marrows CH, Greig D, Hickey BJ, Stamps RL. Exchange bias using a spin glass. Nat Mater 2007; 6:70-5. [PMID: 17173030 DOI: 10.1038/nmat1809] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2006] [Accepted: 11/15/2006] [Indexed: 05/13/2023]
Abstract
Exchange bias is commonly manifested as the hysteresis-loop shift observed when a ferromagnet is in contact with an antiferromagnet. Here, we report observations of exchange bias with unusual features of a ferromagnet in contact with a spin glass, demonstrating that this is a phenomenon of greater generality. The easily measured properties of the ferromagnet allow access to the internal magnetic degrees of freedom of the glass to which they are coupled. Our results show that a Co/CuMn bilayer system exhibits all the rich phenomena of coercivity enhancement, bias-field shifts and training effects associated with a conventional ferromagnet/antiferromagnet system. Nevertheless, striking differences arise, such as an orientation reversal of the bias field in a small temperature range just below the blocking temperature. We argue that all features can be understood within the context of a random-field model for long-ranged oscillatory Ruderman-Kittel-Kasuya-Yosida (RKKY) coupled spins.
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Affiliation(s)
- Mannan Ali
- School of Physics and Astronomy, E. C. Stoner Laboratory, University of Leeds, Leeds LS2 9JT, UK.
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Aziz A, Bending SJ, Roberts HG, Crampin S, Heard PJ, Marrows CH. Angular dependence of domain wall resistivity in artificial magnetic domain structures. Phys Rev Lett 2006; 97:206602. [PMID: 17155700 DOI: 10.1103/physrevlett.97.206602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2006] [Indexed: 05/12/2023]
Abstract
We exploit the ability to precisely control the magnetic domain structure of perpendicularly magnetized Pt/Co/Pt trilayers to fabricate artificial domain wall arrays and study their transport properties. The scaling behavior of this model system confirms the intrinsic domain wall origin of the magnetoresistance, and systematic studies using domains patterned at various angles to the current flow are excellently described by an angular-dependent resistivity tensor containing perpendicular and parallel domain wall resistivities. We find that the latter are fully consistent with Levy-Zhang theory, which allows us to estimate the ratio of minority to majority spin carrier resistivities, rho downward arrow/rho upward arrow approximately 5.5, in good agreement with thin film band structure calculations.
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Affiliation(s)
- A Aziz
- Department of Physics, University of Bath, Bath BA2 7AY, UK
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Rozatian ASH, Marrows CH, Hase TPA, Tanner BK. The relationship between interface structure, conformality and perpendicular anisotropy in CoPd multilayers. J Phys Condens Matter 2005; 17:3759-3770. [PMID: 21690694 DOI: 10.1088/0953-8984/17/25/004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The relationship between the interface structure and perpendicular anisotropy in sputtered Co/Pd multilayers has been investigated using grazing incidence x-ray scattering and vibrating sample magnetometry. Using fits to a self-affine fractal model of the interfaces, the variation in in-plane correlation length, fractal parameter and conformality has been determined as a function of the number of repeats in the Co/Pd bilayers. As the number of interfaces rises, the roughness becomes predominantly non-conformal and the in-plane length scale associated with the roughness increases as a power law with multilayer thickness. It is suggested that the loss of conformality, characterized by a relatively short out-of-plane correlation length, may be the cause of the reduction in anisotropy energy per interface observed for high numbers of bilayer repeats. There is a weak association between fractal parameter and interface anisotropy; a reduction in the fractal dimension of the interface appears to result in a higher surface anisotropy.
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Affiliation(s)
- A S H Rozatian
- Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK
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Marrows CH, Dalton BC. Spin mixing and spin-current asymmetry measured by domain wall magnetoresistance. Phys Rev Lett 2004; 92:097206. [PMID: 15089510 DOI: 10.1103/physrevlett.92.097206] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2003] [Indexed: 05/24/2023]
Abstract
By making a straightforward reformulation of the Levy-Zhang spin-mistracking model, we show that it is possible to extract the spin asymmetry of a current from measurements of domain wall resistance. Experiments on epitaxial films of L1(0) FePd are reported, showing that, while the micromagnetic structure of the sample is stable, the resistivity and the domain wall resistance change by a factor approximately 3 between helium and room temperature. The temperature dependence of the spin asymmetry of the current has been determined over a wide range in a single material.
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Affiliation(s)
- C H Marrows
- School of Physics and Astronomy, E.C. Stoner Laboratory, University of Leeds, Leeds LS2 9JT, United Kingdom.
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Steadman P, Ali M, Hindmarch AT, Marrows CH, Hickey BJ, Langridge S, Dalgliesh RM, Foster S. Exchange bias in spin-engineered double superlattices. Phys Rev Lett 2002; 89:077201. [PMID: 12190551 DOI: 10.1103/physrevlett.89.077201] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2002] [Indexed: 05/23/2023]
Abstract
Exchange bias has been observed in sputtered magnetic double superlattices which consist of a ferromagnetically coupled superlattice grown on an antiferromagnetically (AF) coupled superlattice. This system exhibits a parallel domain wall, a spin flop transition, and exchange bias when the anisotropy is large in the AF block. This work shows that neither the domain wall nor the spin flop are directly related to exchange bias but that the anisotropy is essential.
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Affiliation(s)
- P Steadman
- Department of Physics and Astronomy, E. C. Stoner Laboratory, University of Leeds, United Kingdom.
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Langridge S, Schmalian J, Marrows CH, Dekadjevi DT, Hickey BJ. Quantification of magnetic domain disorder and correlations in antiferromagnetically coupled multilayers by neutron reflectometry. Phys Rev Lett 2000; 85:4964-4967. [PMID: 11102162 DOI: 10.1103/physrevlett.85.4964] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/1999] [Indexed: 05/23/2023]
Abstract
The in-plane correlation lengths and angular dispersion of magnetic domains in a transition metal multilayer have been studied using off-specular neutron reflectometry techniques. A theoretical framework considering both structural and magnetic disorder has been developed, quantitatively connecting the observed scattering to the in-plane correlation length and the dispersion of the local magnetization vector about the mean macroscopic direction. The antiferromagnetic domain structure is highly vertically correlated throughout the multilayer. We are easily able to relate the neutron determined magnetic domain dispersion to magnetization and magnetoresistance experiments.
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Affiliation(s)
- S Langridge
- Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom
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