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Nan T, Quintela CX, Irwin J, Gurung G, Shao DF, Gibbons J, Campbell N, Song K, Choi SY, Guo L, Johnson RD, Manuel P, Chopdekar RV, Hallsteinsen I, Tybell T, Ryan PJ, Kim JW, Choi Y, Radaelli PG, Ralph DC, Tsymbal EY, Rzchowski MS, Eom CB. Controlling spin current polarization through non-collinear antiferromagnetism. Nat Commun 2020; 11:4671. [PMID: 32938910 PMCID: PMC7494910 DOI: 10.1038/s41467-020-17999-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [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: 02/15/2020] [Accepted: 07/22/2020] [Indexed: 11/09/2022] Open
Abstract
The interconversion of charge and spin currents via spin-Hall effect is essential for spintronics. Energy-efficient and deterministic switching of magnetization can be achieved when spin polarizations of these spin currents are collinear with the magnetization. However, symmetry conditions generally restrict spin polarizations to be orthogonal to both the charge and spin flows. Spin polarizations can deviate from such direction in nonmagnetic materials only when the crystalline symmetry is reduced. Here, we show control of the spin polarization direction by using a non-collinear antiferromagnet Mn3GaN, in which the triangular spin structure creates a low magnetic symmetry while maintaining a high crystalline symmetry. We demonstrate that epitaxial Mn3GaN/permalloy heterostructures can generate unconventional spin-orbit torques at room temperature corresponding to out-of-plane and Dresselhaus-like spin polarizations which are forbidden in any sample with two-fold rotational symmetry. Our results demonstrate an approach based on spin-structure design for controlling spin-orbit torque, enabling high-efficient antiferromagnetic spintronics. In the typical spin-hall effect, spin-current, charge current, and spin polarisation are all mutually perpendicular, a feature enforced by symmetry. Here, using an anti-ferromagnet with a triangular spin structure, the authors demonstrate a spin-hall effect without a perpendicular spin alignment.
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Affiliation(s)
- T Nan
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - C X Quintela
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - J Irwin
- Department of Physics, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - G Gurung
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, 68588, USA
| | - D F Shao
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, 68588, USA
| | - J Gibbons
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, 14853, USA
| | - N Campbell
- Department of Physics, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - K Song
- Department of Materials Modeling and Characterization, KIMS, Changwon, 51508, South Korea
| | - S -Y Choi
- Department of Materials Science and Engineering, POSTECH, Pohang, 37673, South Korea
| | - L Guo
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - R D Johnson
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UK.,ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK.,Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
| | - P Manuel
- Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
| | - R V Chopdekar
- Advanced Light Source, Lawrence Berkeley National Laboratory (LBNL), 1 Cyclotron Road, Berkeley, CA, 94720, USA
| | - I Hallsteinsen
- Advanced Light Source, Lawrence Berkeley National Laboratory (LBNL), 1 Cyclotron Road, Berkeley, CA, 94720, USA.,Department of Electronic Systems, Norwegian University of Science and Technology, Trondheim, 7491, Norway
| | - T Tybell
- Department of Electronic Systems, Norwegian University of Science and Technology, Trondheim, 7491, Norway
| | - P J Ryan
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439, USA.,School of Physical Sciences, Dublin City University, Dublin, 11, Ireland
| | - J -W Kim
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439, USA
| | - Y Choi
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439, USA
| | - P G Radaelli
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UK
| | - D C Ralph
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, 14853, USA.,Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, 14853, USA
| | - E Y Tsymbal
- Department of Physics and Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE, 68588, USA
| | - M S Rzchowski
- Department of Physics, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - C B Eom
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA.
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Reynolds MF, Guimarães MHD, Gao H, Kang K, Cortese AJ, Ralph DC, Park J, McEuen PL. MoS 2 pixel arrays for real-time photoluminescence imaging of redox molecules. Sci Adv 2019; 5:eaat9476. [PMID: 31723596 PMCID: PMC6839941 DOI: 10.1126/sciadv.aat9476] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2018] [Accepted: 09/17/2019] [Indexed: 05/22/2023]
Abstract
Measuring the behavior of redox-active molecules in space and time is crucial for understanding chemical and biological systems and for developing new technologies. Optical schemes are noninvasive and scalable, but usually have a slow response compared to electrical detection methods. Furthermore, many fluorescent molecules for redox detection degrade in brightness over long exposure times. Here, we show that the photoluminescence of "pixel" arrays of monolayer MoS2 can image spatial and temporal changes in redox molecule concentration. Because of the strong dependence of MoS2 photoluminescence on doping, changes in the local chemical potential substantially modulate the photoluminescence of MoS2, with a sensitivity of 0.9 mV / Hz on a 5 μm × 5 μm pixel, corresponding to better than parts-per-hundred changes in redox molecule concentration down to nanomolar concentrations at 100-ms frame rates. This provides a new strategy for visualizing chemical reactions and biomolecules with a two-dimensional material screen.
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Affiliation(s)
- M. F. Reynolds
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA
| | - M. H. D. Guimarães
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA
- Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY, USA
| | - H. Gao
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
- Department of Chemistry, Institute for Molecular Engineering, and James Franck Institute, University of Chicago, Chicago, IL, USA
| | - K. Kang
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
- Department of Chemistry, Institute for Molecular Engineering, and James Franck Institute, University of Chicago, Chicago, IL, USA
| | - A. J. Cortese
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA
| | - D. C. Ralph
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA
- Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY, USA
| | - J. Park
- Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY, USA
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
- Department of Chemistry, Institute for Molecular Engineering, and James Franck Institute, University of Chicago, Chicago, IL, USA
| | - P. L. McEuen
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA
- Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY, USA
- Corresponding author.
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Zhu L, Ralph DC, Buhrman RA. Spin-Orbit Torques in Heavy-Metal-Ferromagnet Bilayers with Varying Strengths of Interfacial Spin-Orbit Coupling. Phys Rev Lett 2019; 122:077201. [PMID: 30848626 DOI: 10.1103/physrevlett.122.077201] [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] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Revised: 12/17/2018] [Indexed: 06/09/2023]
Abstract
Despite intense efforts it has remained unresolved whether and how interfacial spin-orbit coupling (ISOC) affects spin transport across heavy-metal (HM)-ferromagnet (FM) interfaces. Here we report conclusive experiment evidence that the ISOC at HM/FM interfaces is the dominant mechanism for "spin memory loss". An increase in ISOC significantly reduces, in a linear manner, the dampinglike spin-orbit torque (SOT) exerted on the FM layer via degradation of the spin transparency of the interface for spin currents generated in the HM. In addition, the fieldlike SOT is also dominated by the spin Hall contribution of the HM and decreases with increasing ISOC. This work reveals that ISOC at HM/FM interfaces should be minimized to advance efficient SOT devices through atomic layer passivation of the HM/FM interface or other means.
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Affiliation(s)
- Lijun Zhu
- Cornell University, Ithaca, New York 14850, USA
| | - D C Ralph
- Cornell University, Ithaca, New York 14850, USA
- Kavli Institute at Cornell, Ithaca, New York 14853, USA
| | - R A Buhrman
- Cornell University, Ithaca, New York 14850, USA
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Ou Y, Ralph DC, Buhrman RA. Strong Enhancement of the Spin Hall Effect by Spin Fluctuations near the Curie Point of Fe_{x}Pt_{1-x} Alloys. Phys Rev Lett 2018; 120:097203. [PMID: 29547325 DOI: 10.1103/physrevlett.120.097203] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2017] [Revised: 11/19/2017] [Indexed: 06/08/2023]
Abstract
Robust spin Hall effects (SHE) have recently been observed in nonmagnetic heavy metal systems with strong spin-orbit interactions. These SHE are either attributed to an intrinsic band-structure effect or to extrinsic spin-dependent scattering from impurities, namely, side jump or skew scattering. Here we report on an extraordinarily strong spin Hall effect, attributable to spin fluctuations, in ferromagnetic Fe_{x}Pt_{1-x} alloys near their Curie point, tunable with x. This results in a dampinglike spin-orbit torque being exerted on an adjacent ferromagnetic layer that is strongly temperature dependent in this transition region, with a peak value that indicates a lower bound 0.34±0.02 for the peak spin Hall ratio within the FePt. We also observe a pronounced peak in the effective spin-mixing conductance of the FM/FePt interface, and determine the spin diffusion length in these Fe_{x}Pt_{1-x} alloys. These results establish new opportunities for fundamental studies of spin dynamics and transport in ferromagnetic systems with strong spin fluctuations, and a new pathway for efficiently generating strong spin currents for applications.
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Affiliation(s)
- Yongxi Ou
- Cornell University, Ithaca, New York 14853, USA
| | - D C Ralph
- Cornell University, Ithaca, New York 14853, USA
- Kavli Institute at Cornell, Ithaca, New York 14853, USA
| | - R A Buhrman
- Cornell University, Ithaca, New York 14853, USA
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5
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Aradhya SV, Rowlands GE, Oh J, Ralph DC, Buhrman RA. Nanosecond-Timescale Low Energy Switching of In-Plane Magnetic Tunnel Junctions through Dynamic Oersted-Field-Assisted Spin Hall Effect. Nano Lett 2016; 16:5987-5992. [PMID: 27327619 DOI: 10.1021/acs.nanolett.6b01443] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We investigate fast-pulse switching of in-plane-magnetized magnetic tunnel junctions (MTJs) within 3-terminal devices in which spin-transfer torque is applied to the MTJ by the giant spin Hall effect. We measure reliable switching, with write error rates down to 10-5, using current pulses as short as just 2 ns in duration. This represents the fastest reliable switching reported to date for any spin-torque-driven magnetic memory geometry and corresponds to a characteristic time scale that is significantly shorter than predicted possible within a macrospin model for in-plane MTJs subject to thermal fluctuations at room temperature. Using micromagnetic simulations, we show that in the three-terminal spin-Hall devices the Oersted magnetic field generated by the pulse current strongly modifies the magnetic dynamics excited by the spin-Hall torque, enabling this unanticipated performance improvement. Our results suggest that in-plane MTJs controlled by Oersted-field-assisted spin-Hall torque are a promising candidate for both cache memory applications requiring high speed and for cryogenic memories requiring low write energies.
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Affiliation(s)
- S V Aradhya
- Cornell University , Ithaca, New York 14853, United States
| | - G E Rowlands
- Cornell University , Ithaca, New York 14853, United States
| | - J Oh
- Cornell University , Ithaca, New York 14853, United States
| | - D C Ralph
- Cornell University , Ithaca, New York 14853, United States
- Kavli Institute at Cornell , Ithaca, New York 14853, United States
| | - R A Buhrman
- Cornell University , Ithaca, New York 14853, United States
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6
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Nguyen MH, Ralph DC, Buhrman RA. Spin Torque Study of the Spin Hall Conductivity and Spin Diffusion Length in Platinum Thin Films with Varying Resistivity. Phys Rev Lett 2016; 116:126601. [PMID: 27058088 DOI: 10.1103/physrevlett.116.126601] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Indexed: 06/05/2023]
Abstract
We report measurements of the spin torque efficiencies in perpendicularly magnetized Pt/Co bilayers where the Pt resistivity ρ_{Pt} is strongly dependent on thickness t_{Pt}. The dampinglike spin Hall torque efficiency per unit current density ξ_{DL}^{j} varies significantly with t_{Pt}, exhibiting a peak value ξ_{DL}^{j}=0.12 at t_{Pt}=2.8-3.9 nm. In contrast, ξ_{DL}^{j}/ρ_{Pt} increases monotonically with t_{Pt} and saturates for t_{Pt}>5 nm, consistent with an intrinsic spin Hall effect mechanism, in which ξ_{DL}^{j} is enhanced by an increase in ρ_{Pt}. Assuming the Elliott-Yafet spin scattering mechanism dominates, we estimate that the spin diffusion length λ_{s}=(0.77±0.08)×10^{-15} Ω·m^{2}/ρ_{Pt}.
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Affiliation(s)
| | - D C Ralph
- Cornell University, Ithaca, New York 14853, USA
- Kavli Institute at Cornell, Ithaca, New York 14853, USA
| | - R A Buhrman
- Cornell University, Ithaca, New York 14853, USA
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7
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Mellnik AR, Lee JS, Richardella A, Grab JL, Mintun PJ, Fischer MH, Vaezi A, Manchon A, Kim EA, Samarth N, Ralph DC. Spin-transfer torque generated by a topological insulator. Nature 2014; 511:449-51. [DOI: 10.1038/nature13534] [Citation(s) in RCA: 945] [Impact Index Per Article: 94.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Accepted: 05/27/2014] [Indexed: 11/09/2022]
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8
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Liu L, Pai CF, Ralph DC, Buhrman RA. Magnetic oscillations driven by the spin Hall effect in 3-terminal magnetic tunnel junction devices. Phys Rev Lett 2012; 109:186602. [PMID: 23215306 DOI: 10.1103/physrevlett.109.186602] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2012] [Indexed: 06/01/2023]
Abstract
We show that a direct current in a tantalum microstrip can induce steady-state magnetic oscillations in an adjacent nanomagnet through spin torque from the spin Hall effect (SHE). The oscillations are detected electrically via a magnetic tunnel junction (MTJ) contacting the nanomagnet. The oscillation frequency can be controlled using the MTJ bias to tune the magnetic anisotropy. In this 3-terminal device, the SHE torque and the MTJ bias therefore provide independent controls of the oscillation amplitude and frequency, enabling new approaches for developing tunable spin torque nano-oscillators.
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Affiliation(s)
- Luqiao Liu
- Cornell University, Ithaca, New York 14853, USA
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9
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Liu L, Lee OJ, Gudmundsen TJ, Ralph DC, Buhrman RA. Current-induced switching of perpendicularly magnetized magnetic layers using spin torque from the spin Hall effect. Phys Rev Lett 2012; 109:096602. [PMID: 23002867 DOI: 10.1103/physrevlett.109.096602] [Citation(s) in RCA: 299] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Indexed: 06/01/2023]
Abstract
We show that in a perpendicularly magnetized Pt/Co bilayer the spin-Hall effect (SHE) in Pt can produce a spin torque strong enough to efficiently rotate and switch the Co magnetization. We calculate the phase diagram of switching driven by this torque, finding quantitative agreement with experiments. When optimized, the SHE torque can enable memory and logic devices with similar critical currents and improved reliability compared to conventional spin-torque switching. We suggest that the SHE torque also affects current-driven magnetic domain wall motion in Pt/ferromagnet bilayers.
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Affiliation(s)
- Luqiao Liu
- Cornell University, Ithaca, New York 14853, USA
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Xue L, Wang C, Cui YT, Liu L, Swander A, Sun JZ, Buhrman RA, Ralph DC. Resonance measurement of nonlocal spin torque in a three-terminal magnetic device. Phys Rev Lett 2012; 108:147201. [PMID: 22540819 DOI: 10.1103/physrevlett.108.147201] [Citation(s) in RCA: 2] [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: 11/28/2011] [Indexed: 05/31/2023]
Abstract
A pure spin current generated within a nonlocal spin valve can exert a spin-transfer torque on a nanomagnet. This nonlocal torque enables new design schemes for magnetic memory devices that do not require the application of large voltages across tunnel barriers that can suffer electrical breakdown. Here we report a quantitative measurement of this nonlocal spin torque using spin-torque-driven ferromagnetic resonance. Our measurement agrees well with the prediction of an effective circuit model for spin transport. Based on this model, we suggest strategies for optimizing the strength of nonlocal torque.
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Affiliation(s)
- Lin Xue
- Cornell University, Ithaca, New York 14853, USA
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12
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Ralph DC, Cui YT, Liu LQ, Moriyama T, Wang C, Buhrman RA. Spin-transfer torque in nanoscale magnetic devices. Philos Trans A Math Phys Eng Sci 2011; 369:3617-3630. [PMID: 21859725 DOI: 10.1098/rsta.2011.0169] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We discuss recent highlights from research at Cornell University, Ithaca, New York, regarding the use of spin-transfer torques to control magnetic moments in nanoscale ferromagnetic devices. We highlight progress on reducing the critical currents necessary to produce spin-torque-driven magnetic switching, quantitative measurements of the magnitude and direction of the spin torque in magnetic tunnel junctions, and single-shot measurements of the magnetic dynamics generated during thermally assisted spin-torque switching.
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Affiliation(s)
- D C Ralph
- Cornell University, Ithaca, New York, NY 14853, USA.
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Yu XW, Pribiag VS, Acremann Y, Tulapurkar AA, Tyliszczak T, Chou KW, Bräuer B, Li ZP, Lee OJ, Gowtham PG, Ralph DC, Buhrman RA, Stöhr J. Images of a spin-torque-driven magnetic nano-oscillator. Phys Rev Lett 2011; 106:167202. [PMID: 21599407 DOI: 10.1103/physrevlett.106.167202] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2010] [Indexed: 05/30/2023]
Abstract
We present the first space- and time-resolved images of the spin-torque-induced steady-state oscillation of a magnetic vortex in a spin-valve nanostructure. We find that the vortex structure in a nanopillar is considerably more complicated than the 2D idealized structure often-assumed, which has important implications for the driving efficiency. The sense of the vortex gyration is uniquely determined by the vortex core polarity, confirming that the spin-torque acts as a source of negative damping even in such a strongly nonuniform magnetic system. The orbit radius is ∼10 nm, in agreement with micromagnetic simulations.
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Affiliation(s)
- X W Yu
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
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15
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Shi SF, Xu X, Ralph DC, McEuen PL. Plasmon resonance in individual nanogap electrodes studied using graphene nanoconstrictions as photodetectors. Nano Lett 2011; 11:1814-8. [PMID: 21434673 DOI: 10.1021/nl200522t] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We achieve direct electrical readout of the wavelength and polarization dependence of the plasmon resonance in individual gold nanogap antennas by positioning a graphene nanoconstriction within the gap as a localized photodetector. The polarization sensitivities can be as large as 99%, while the plasmon-induced photocurrent enhancement is 2-100. The plasmon peak frequency, polarization sensitivity, and photocurrent enhancement all vary between devices, indicating the degree to which the plasmon resonance is sensitive to nanometer-scale irregularities.
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Affiliation(s)
- S-F Shi
- Physics Department, Cornell University, Ithaca, New York 14853, United States
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Liu L, Moriyama T, Ralph DC, Buhrman RA. Spin-torque ferromagnetic resonance induced by the spin Hall effect. Phys Rev Lett 2011; 106:036601. [PMID: 21405285 DOI: 10.1103/physrevlett.106.036601] [Citation(s) in RCA: 281] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2010] [Indexed: 05/17/2023]
Abstract
We demonstrate that the spin Hall effect in a thin film with strong spin-orbit scattering can excite magnetic precession in an adjacent ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer generates an oscillating transverse spin current in the Pt, and the resultant transfer of spin angular momentum to the NiFe induces ferromagnetic resonance dynamics. The Oersted field from the current also generates a ferromagnetic resonance signal but with a different symmetry. The ratio of these two signals allows a quantitative determination of the spin current and the spin Hall angle.
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Affiliation(s)
- Luqiao Liu
- Cornell University, Ithaca, New York 14853, USA
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17
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Parks JJ, Champagne AR, Costi TA, Shum WW, Pasupathy AN, Neuscamman E, Flores-Torres S, Cornaglia PS, Aligia AA, Balseiro CA, Chan GKL, Abruna HD, Ralph DC. Mechanical Control of Spin States in Spin-1 Molecules and the Underscreened Kondo Effect. Science 2010; 328:1370-3. [DOI: 10.1126/science.1186874] [Citation(s) in RCA: 358] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Cui YT, Finocchio G, Wang C, Katine JA, Buhrman RA, Ralph DC. Single-shot time-domain studies of spin-torque-driven switching in magnetic tunnel junctions. Phys Rev Lett 2010; 104:097201. [PMID: 20367007 DOI: 10.1103/physrevlett.104.097201] [Citation(s) in RCA: 4] [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: 06/11/2009] [Indexed: 05/29/2023]
Abstract
We report single-shot measurements of resistance versus time for thermally assisted spin-torque switching in magnetic tunnel junctions. We achieve the sensitivity to resolve the magnetic dynamics prior to as well as during switching, yielding detailed views of switching modes and variations between events. Analyses of individual traces allow measurements of coherence times, nonequilibrium excitation spectra, and variations in magnetization precession amplitude. We find that with a small in-plane hard-axis magnetic field the switching dynamics are more spatially coherent than for a zero field.
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Affiliation(s)
- Y-T Cui
- Cornell University, Ithaca, New York 14853, USA
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Ozatay O, Gowtham PG, Tan KW, Read JC, Mkhoyan KA, Thomas MG, Fuchs GD, Braganca PM, Ryan EM, Thadani KV, Silcox J, Ralph DC, Buhrman RA. Sidewall oxide effects on spin-torque- and magnetic-field-induced reversal characteristics of thin-film nanomagnets. Nat Mater 2008; 7:567-73. [PMID: 18536721 DOI: 10.1038/nmat2204] [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: 01/03/2008] [Accepted: 05/06/2008] [Indexed: 05/13/2023]
Abstract
The successful operation of spin-based data storage devices depends on thermally stable magnetic bits. At the same time, the data-processing speeds required by today's technology necessitate ultrafast switching in storage devices. Achieving both thermal stability and fast switching requires controlling the effective damping in magnetic nanoparticles. By carrying out a surface chemical analysis, we show that through exposure to ambient oxygen during processing, a nanomagnet can develop an antiferromagnetic sidewall oxide layer that has detrimental effects, which include a reduction in the thermal stability at room temperature and anomalously high magnetic damping at low temperatures. The in situ deposition of a thin Al metal layer, oxidized to completion in air, greatly reduces or eliminates these problems. This implies that the effective damping and the thermal stability of a nanomagnet can be tuned, leading to a variety of potential applications in spintronic devices such as spin-torque oscillators and patterned media.
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Affiliation(s)
- O Ozatay
- Cornell University, Ithaca, New York 14853-2501, USA.
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Kuemmeth F, Ilani S, Ralph DC, McEuen PL. Coupling of spin and orbital motion of electrons in carbon nanotubes. Nature 2008; 452:448-52. [DOI: 10.1038/nature06822] [Citation(s) in RCA: 482] [Impact Index Per Article: 30.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2007] [Accepted: 02/05/2008] [Indexed: 11/09/2022]
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22
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Parks JJ, Champagne AR, Hutchison GR, Flores-Torres S, Abruña HD, Ralph DC. Tuning the Kondo effect with a mechanically controllable break junction. Phys Rev Lett 2007; 99:026601. [PMID: 17678242 DOI: 10.1103/physrevlett.99.026601] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2006] [Indexed: 05/16/2023]
Abstract
We study electron transport through C(60) molecules in the Kondo regime using a mechanically controllable break junction. By varying the electrode spacing, we are able to change both the width and the height of the Kondo resonance, indicating modification of the Kondo temperature and the relative strength of coupling to the two electrodes. The linear conductance as a function of T/T(K) agrees with the scaling function expected for the spin-1/2 Kondo problem. We are also able to tune finite-bias Kondo features which appear at the energy of the first C(60) intracage vibrational mode.
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Affiliation(s)
- J J Parks
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
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23
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Bolotin KI, Kuemmeth F, Ralph DC. Anisotropic magnetoresistance and anisotropic tunneling magnetoresistance due to quantum interference in ferromagnetic metal break junctions. Phys Rev Lett 2006; 97:127202. [PMID: 17025993 DOI: 10.1103/physrevlett.97.127202] [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: 02/09/2006] [Revised: 06/30/2006] [Indexed: 05/12/2023]
Abstract
We measure the low-temperature resistance of permalloy break junctions as a function of contact size and the magnetic field angle in applied fields large enough to saturate the magnetization. For both nanometer-scale metallic contacts and tunneling devices we observe large changes in resistance with the angle, as large as 25% in the tunneling regime. The pattern of magnetoresistance is sensitive to changes in bias on a scale of a few mV. We interpret the effect as a consequence of conductance fluctuations due to quantum interference.
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Affiliation(s)
- Kirill I Bolotin
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853, USA
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24
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Jo MH, Grose JE, Baheti K, Deshmukh MM, Sokol JJ, Rumberger EM, Hendrickson DN, Long JR, Park H, Ralph DC. Signatures of molecular magnetism in single-molecule transport spectroscopy. Nano Lett 2006; 6:2014-20. [PMID: 16968018 DOI: 10.1021/nl061212i] [Citation(s) in RCA: 151] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
We report single-molecule-transistor measurements on devices incorporating magnetic molecules. By studying the electron-tunneling spectrum as a function of magnetic field, we are able to identify signatures of magnetic states and their associated magnetic anisotropy. A comparison of the data to simulations also suggests that sequential electron tunneling may enhance the magnetic relaxation of the magnetic molecule.
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Affiliation(s)
- Moon-Ho Jo
- Department of Chemistry & Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA
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25
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Emley NC, Krivorotov IN, Ozatay O, Garcia AGF, Sankey JC, Ralph DC, Buhrman RA. Time-resolved spin-torque switching and enhanced damping in permalloy/Cu/permalloy spin-valve nanopillars. Phys Rev Lett 2006; 96:247204. [PMID: 16907277 DOI: 10.1103/physrevlett.96.247204] [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: 11/01/2005] [Indexed: 05/11/2023]
Abstract
We report time-resolved measurements of current-induced reversal of a free magnetic layer in Permalloy/Cu/Permalloy elliptical nanopillars at temperatures T=4.2 K to 160 K. Comparison of the data to Landau-Lifshitz-Gilbert macrospin simulations of the free layer switching yields numerical values for the spin torque and the Gilbert damping parameters as functions of T. The damping is strongly T dependent, which we attribute to the presence of an antiferromagnetic oxide layer around the perimeter of the Permalloy free layer. This adventitious antiferromagnetic oxide can have a major impact on spin-torque phenomena.
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Affiliation(s)
- N C Emley
- Cornell University, Ithaca, New York 14853-2501, USA
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26
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Sankey JC, Braganca PM, Garcia AGF, Krivorotov IN, Buhrman RA, Ralph DC. Spin-transfer-driven ferromagnetic resonance of individual nanomagnets. Phys Rev Lett 2006; 96:227601. [PMID: 16803344 DOI: 10.1103/physrevlett.96.227601] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2006] [Indexed: 05/10/2023]
Abstract
We demonstrate a technique that enables ferromagnetic resonance measurements of the normal modes for magnetic excitations in individual nanoscale ferromagnets, smaller in volume by more than a factor of 50 compared to individual ferromagnetic samples measured by other resonance techniques. Studies of the resonance frequencies, amplitudes, linewidths, and line shapes as a function of microwave power, dc current, and magnetic field provide detailed new information about the exchange, damping, and spin-transfer torques that govern the dynamics in magnetic nanostructures.
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Affiliation(s)
- J C Sankey
- Cornell University, Ithaca, New York 14853, USA
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27
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Fuchs GD, Katine JA, Kiselev SI, Mauri D, Wooley KS, Ralph DC, Buhrman RA. Spin torque, tunnel-current spin polarization, and magnetoresistance in MgO magnetic tunnel junctions. Phys Rev Lett 2006; 96:186603. [PMID: 16712385 DOI: 10.1103/physrevlett.96.186603] [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: 10/28/2005] [Indexed: 05/09/2023]
Abstract
We employ the spin-torque response of magnetic tunnel junctions with ultrathin MgO tunnel barrier layers to investigate the relationship between spin transfer and tunnel magnetoresistance (TMR) under finite bias, and find that the spin torque per unit current exerted on the free layer decreases by < 10% over a bias range where the TMR decreases by > 40%. This is inconsistent with free-electron-like spin-polarized tunneling and reduced-surface-magnetism models of the TMR bias dependence, but is consistent with magnetic-state-dependent decay lengths in the tunnel barrier.
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Affiliation(s)
- G D Fuchs
- Cornell University, Ithaca, New York 14853-2501, USA
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28
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Bolotin KI, Kuemmeth F, Pasupathy AN, Ralph DC. From ballistic transport to tunneling in electromigrated ferromagnetic breakjunctions. Nano Lett 2006; 6:123-7. [PMID: 16402799 DOI: 10.1021/nl0522936] [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: 05/06/2023]
Abstract
We fabricate ferromagnetic nanowires with constrictions whose cross section can be reduced gradually from 100 x 30 nm(2) to the atomic scale and eventually to the tunneling regime by means of electromigration. The contacts are mechanically and thermally stable. We measure low-temperature magnetoresistances (MR) < 3% for contacts < 400 Omega, reproducible MR variations that are nonmonotonic in the regime 400 Omega - 25 kOmega, and a maximum MR of 80% for atomic-scale widths. These results for devices > 400 Omega differ from previous room-temperature studies of electrodeposited devices. For samples in the tunneling regime, we observe large fluctuations in MR, between -10 and 85%.
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Affiliation(s)
- Kirill I Bolotin
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
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29
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Pasupathy AN, Park J, Chang C, Soldatov AV, Lebedkin S, Bialczak RC, Grose JE, Donev LAK, Sethna JP, Ralph DC, McEuen PL. Vibration-assisted electron tunneling in C140 transistors. Nano Lett 2005; 5:203-207. [PMID: 15794596 DOI: 10.1021/nl048619c] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We measure electron tunneling in transistors made from C(140), a molecule with a mass-spring-mass geometry chosen as a model system to study electron-vibration coupling. We observe vibration-assisted tunneling at an energy corresponding to the stretching mode of C(140). Molecular modeling provides explanations for why this mode couples more strongly to electron tunneling than to the other internal modes of the molecule. We make comparisons between the observed tunneling rates and those expected from the Franck-Condon model.
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Affiliation(s)
- A N Pasupathy
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853, USA
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30
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Krivorotov IN, Emley NC, Sankey JC, Kiselev SI, Ralph DC, Buhrman RA. Time-Domain Measurements of Nanomagnet Dynamics Driven by Spin-Transfer Torques. Science 2005; 307:228-31. [PMID: 15653496 DOI: 10.1126/science.1105722] [Citation(s) in RCA: 463] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
We present time-resolved measurements of gigahertz-scale magnetic dynamics caused by torque from a spin-polarized current. By working in the time domain, we determined the motion of the magnetic moment throughout the process of spin-transfer-driven switching, and we measured turn-on times of steady-state precessional modes. Time-resolved studies of magnetic relaxation allow for the direct measurement of magnetic damping in a nanomagnet and prove that this damping can be controlled electrically using spin-polarized currents.
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31
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Krivorotov IN, Emley NC, Garcia AGF, Sankey JC, Kiselev SI, Ralph DC, Buhrman RA. Temperature dependence of spin-transfer-induced switching of nanomagnets. Phys Rev Lett 2004; 93:166603. [PMID: 15525019 DOI: 10.1103/physrevlett.93.166603] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2004] [Indexed: 05/24/2023]
Abstract
We measure the temperature, magnetic-field, and current dependence for the switching of nanomagnets by a spin-polarized current. Depending on current bias, switching can occur between either two static magnetic states or a static state and a current-driven precessional mode. In both cases, the switching is thermally activated and governed by the sample temperature, not a higher effective magnetic temperature. The activation barriers for switching between static states depend linearly on current, with a weaker dependence for dynamic to static switching.
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32
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Abstract
We present measurements of magnetic tunnel junctions made using a self-assembled-monolayer molecular barrier. Ni-octanethiol-Ni samples were fabricated in a nanopore geometry. The devices exhibit significant changes in resistance as the angle between the magnetic moments in the two electrodes is varied, demonstrating that low-energy electrons can traverse the molecular barrier while remaining spin polarized. An analysis of the voltage and temperature dependence of the data suggests that the spin-polarized transport signals can be degraded by localized states in the molecular barriers.
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Affiliation(s)
- J R Petta
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
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33
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Kiselev SI, Sankey JC, Krivorotov IN, Emley NC, Rinkoski M, Perez C, Buhrman RA, Ralph DC. Current-induced nanomagnet dynamics for magnetic fields perpendicular to the sample plane. Phys Rev Lett 2004; 93:036601. [PMID: 15323848 DOI: 10.1103/physrevlett.93.036601] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2004] [Indexed: 05/24/2023]
Abstract
We present electrical measurements of high-frequency magnetic dynamics excited by spin-polarized currents in Co/Cu/Ni(80)Fe20 nanopillar devices, with a magnetic field applied perpendicular to the sample layers. As a function of current and magnetic field, the dynamical phase diagram contains several distinguishable precessional modes and also static magnetic states. Using detailed comparisons with numerical simulations, we provide rigorous tests of the theory of spin-transfer torques.
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Affiliation(s)
- S I Kiselev
- Cornell University, Ithaca, New York 14853, USA
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34
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Kiselev SI, Sankey JC, Krivorotov IN, Emley NC, Schoelkopf RJ, Buhrman RA, Ralph DC. Microwave oscillations of a nanomagnet driven by a spin-polarized current. Nature 2003; 425:380-3. [PMID: 14508483 DOI: 10.1038/nature01967] [Citation(s) in RCA: 1694] [Impact Index Per Article: 80.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2003] [Accepted: 07/28/2003] [Indexed: 11/09/2022]
Abstract
The recent discovery that a spin-polarized electrical current can apply a large torque to a ferromagnet, through direct transfer of spin angular momentum, offers the possibility of manipulating magnetic-device elements without applying cumbersome magnetic fields. However, a central question remains unresolved: what type of magnetic motions can be generated by this torque? Theory predicts that spin transfer may be able to drive a nanomagnet into types of oscillatory magnetic modes not attainable with magnetic fields alone, but existing measurement techniques have provided only indirect evidence for dynamical states. The nature of the possible motions has not been determined. Here we demonstrate a technique that allows direct electrical measurements of microwave-frequency dynamics in individual nanomagnets, propelled by a d.c. spin-polarized current. We show that spin transfer can produce several different types of magnetic excitation. Although there is no mechanical motion, a simple magnetic-multilayer structure acts like a nanoscale motor; it converts energy from a d.c. electrical current into high-frequency magnetic rotations that might be applied in new devices including microwave sources and resonators.
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Affiliation(s)
- S I Kiselev
- Cornell University, Ithaca, New York 14853, USA
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35
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Deshmukh MM, Ralph DC. Using single quantum states as spin filters to study spin polarization in ferromagnets. Phys Rev Lett 2002; 89:266803. [PMID: 12484848 DOI: 10.1103/physrevlett.89.266803] [Citation(s) in RCA: 3] [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: 07/10/2002] [Indexed: 05/24/2023]
Abstract
By measuring electron tunneling between a ferromagnet and individual energy levels in an aluminum quantum dot, we show how spin-resolved quantum states can be used as filters to determine spin-dependent tunneling rates. We also observe magnetic-field-dependent shifts in the magnet's electrochemical potential relative to the dot's energy levels. The shifts vary between samples and are generally smaller than expected from the magnet's spin-polarized density of states. We suggest that they are affected by field-dependent charge redistribution at the magnetic interface.
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Affiliation(s)
- Mandar M Deshmukh
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
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36
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Albert FJ, Emley NC, Myers EB, Ralph DC, Buhrman RA. Quantitative study of magnetization reversal by spin-polarized current in magnetic multilayer nanopillars. Phys Rev Lett 2002; 89:226802. [PMID: 12485091 DOI: 10.1103/physrevlett.89.226802] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2002] [Indexed: 05/24/2023]
Abstract
We have studied magnetic switching by spin-polarized currents and also the magnetoresistance in sub-100-nm-diam thin-film Co/Cu/Co nanostructures, with the current flowing perpendicular to the plane of the films. By independently varying the thickness of all three layers and measuring the change of the switching currents, we test the theoretical models for spin-transfer switching. In addition, the changes in the switching current and magnetoresistance as a function of the Cu layer thickness give two independent measurements of the room-temperature spin-diffusion length in Cu.
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Affiliation(s)
- F J Albert
- Cornell University, Ithaca, New York 14853-2501, USA
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37
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Myers EB, Albert FJ, Sankey JC, Bonet E, Buhrman RA, Ralph DC. Thermally activated magnetic reversal induced by a spin-polarized current. Phys Rev Lett 2002; 89:196801. [PMID: 12443138 DOI: 10.1103/physrevlett.89.196801] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2002] [Indexed: 05/24/2023]
Abstract
We have measured the statistical properties of magnetic reversal in nanomagnets driven by a spin-polarized current. Like reversal induced by a magnetic field, spin-transfer-driven reversal near room temperature exhibits the properties of thermally activated escape over an effective barrier. However, the spin-transfer effect produces qualitatively different behaviors than an applied magnetic field. We discuss an effective current vs field stability diagram. If the current and field are tuned so that their effects oppose one another, the magnet can exhibit telegraph-noise switching.
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Affiliation(s)
- E B Myers
- Cornell University, Ithaca, New York 14853, USA
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38
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Petta JR, Ralph DC. Measurements of strongly anisotropic g factors for spins in single quantum states. Phys Rev Lett 2002; 89:156802. [PMID: 12366011 DOI: 10.1103/physrevlett.89.156802] [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: 06/20/2002] [Indexed: 05/23/2023]
Abstract
We have measured the full angular dependence, as a function of the direction of magnetic field, for the Zeeman splitting of individual energy states in copper nanoparticles. The g factors for spin splitting are highly anisotropic, with angular variations as large as a factor of 5. The angular dependence fits well to ellipsoids. Both the principal-axis directions and g-factor magnitudes vary between different energy levels within one nanoparticle. The variations agree quantitatively with random-matrix theory predictions which incorporate spin-orbit coupling.
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Affiliation(s)
- J R Petta
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
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39
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Petta JR, Ralph DC. Studies of spin-orbit scattering in noble-metal nanoparticles using energy-level tunneling spectroscopy. Phys Rev Lett 2001; 87:266801. [PMID: 11800850 DOI: 10.1103/physrevlett.87.266801] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2001] [Indexed: 05/23/2023]
Abstract
The effects of spin-orbit scattering on discrete electronic energy levels are studied in copper, silver, and gold nanoparticles. Level-to-level fluctuations of the effective g-factor for Zeeman splitting are characterized, and the statistics are found to be well described by random matrix theory predictions. The strength of spin-orbit scattering increases with atomic number and also varies between nanoparticles made of the same metal. We compare the spin-orbit scattering rates in the nanoparticles to weak-localization measurements on larger samples.
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Affiliation(s)
- J R Petta
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
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40
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Deshmukh MM, Kleff S, Guéron S, Bonet E, Pasupathy AN, von Delft J, Ralph DC. Magnetic anisotropy variations and nonequilibrium tunneling in a cobalt nanoparticle. Phys Rev Lett 2001; 87:226801. [PMID: 11736415 DOI: 10.1103/physrevlett.87.226801] [Citation(s) in RCA: 8] [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: 06/04/2001] [Indexed: 05/23/2023]
Abstract
We present detailed measurements of the discrete electron-tunneling level spectrum within nanometer-scale cobalt particles as a function of magnetic field and gate voltage, in this way probing individual quantum many-body eigenstates inside ferromagnetic samples. Variations among the observed levels indicate that different quantum states within one particle are subject to different magnetic anisotropy energies. Gate-voltage studies demonstrate that the low-energy tunneling spectrum is affected dramatically by the presence of nonequilibrium spin excitations.
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Affiliation(s)
- M M Deshmukh
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
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41
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Vegge T, Sethna JP, Cheong SA, Jacobsen KW, Myers CR, Ralph DC. Calculation of quantum tunneling for a spatially extended defect: the dislocation kink in copper has a low effective mass. Phys Rev Lett 2001; 86:1546-1549. [PMID: 11290189 DOI: 10.1103/physrevlett.86.1546] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2000] [Indexed: 05/23/2023]
Abstract
Several experiments indicate that there are atomic tunneling defects in plastically deformed metals. How this is possible has not been clear, given the large mass of the metal atoms. Using a classical molecular-dynamics calculation, we determine the structures, energy barriers, effective masses, and quantum tunneling rates for dislocation kinks and jogs in copper screw dislocations. We find that jogs are unlikely to tunnel, but the kinks should have large quantum fluctuations. The kink motion involves hundreds of atoms each shifting a tiny amount, leading to a small effective mass and tunneling barrier.
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42
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Katine JA, Albert FJ, Buhrman RA, Myers EB, Ralph DC. Current-driven magnetization reversal and spin-wave excitations in Co /Cu /Co pillars. Phys Rev Lett 2000; 84:3149-3152. [PMID: 11019034 DOI: 10.1103/physrevlett.84.3149] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/1999] [Indexed: 05/23/2023]
Abstract
Using thin film pillars approximately 100 nm in diameter, containing two Co layers of different thicknesses separated by a Cu spacer, we examine the process by which the scattering from the ferromagnetic layers of spin-polarized currents flowing perpendicular to the layers causes controlled reversal of the moment direction in the thin Co layer. The well-defined geometry permits a quantitative analysis of this spin-transfer effect, allowing tests of competing theories for the mechanism and also new insight concerning magnetic damping. When large magnetic fields are applied, the spin-polarized current no longer fully reverses the magnetic moment, but instead stimulates spin-wave excitations.
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Affiliation(s)
- JA Katine
- School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
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43
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Abstract
Current-induced switching in the orientation of magnetic moments is observed in cobalt/copper/cobalt sandwich structures, for currents flowing perpendicularly through the layers. Magnetic domains in adjacent cobalt layers can be manipulated controllably between stable parallel and antiparallel configurations by applying current pulses of the appropriate sign. The observations are in accord with predictions that a spin-polarized current exerts a torque at the interface between a magnetic and nonmagnetic metal, due to local exchange interactions between conduction electrons and the magnetic moments.
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Affiliation(s)
- EB Myers
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853, USA. School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA
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44
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Black CT, Ralph DC, Tinkham M. Spectroscopy of the superconducting gap in individual nanometer-scale aluminum particles. Phys Rev Lett 1996; 76:688-691. [PMID: 10061522 DOI: 10.1103/physrevlett.76.688] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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45
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46
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Ralph DC, Black CT, Tinkham M. Spectroscopic measurements of discrete electronic states in single metal particles. Phys Rev Lett 1995; 74:3241-3244. [PMID: 10058147 DOI: 10.1103/physrevlett.74.3241] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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47
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Hergenrother JM, Lu JG, Tuominen MT, Ralph DC, Tinkham M. Photon-activated switch behavior in the single-electron transistor with a superconducting island. Phys Rev B Condens Matter 1995; 51:9407-9410. [PMID: 9977600 DOI: 10.1103/physrevb.51.9407] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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48
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Ralph DC, Buhrman RA. Kondo scattering from atomic two-level tunneling systems in metals: Enhanced conductance, critical-bias transitions, and the non-Fermi-liquid electronic state. Phys Rev B Condens Matter 1995; 51:3554-3568. [PMID: 9979165 DOI: 10.1103/physrevb.51.3554] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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49
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Ralph DC, Buhrman RA. Kondo-assisted and resonant tunneling via a single charge trap: A realization of the Anderson model out of equilibrium. Phys Rev Lett 1994; 72:3401-3404. [PMID: 10056189 DOI: 10.1103/physrevlett.72.3401] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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50
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Ralph DC, Ludwig AW, Buhrman RA. 2-channel Kondo scaling in conductance signals from 2 level tunneling systems. Phys Rev Lett 1994; 72:1064-1067. [PMID: 10056608 DOI: 10.1103/physrevlett.72.1064] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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