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Tula T, Möller G, Quintanilla J, Giblin SR, Hillier AD, McCabe EE, Ramos S, Barker DS, Gibson S. Machine learning approach to muon spectroscopy analysis. J Phys Condens Matter 2021; 33:194002. [PMID: 33545697 DOI: 10.1088/1361-648x/abe39e] [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] [Received: 11/20/2020] [Accepted: 02/05/2021] [Indexed: 06/12/2023]
Abstract
In recent years, artificial intelligence techniques have proved to be very successful when applied to problems in physical sciences. Here we apply an unsupervised machine learning (ML) algorithm called principal component analysis (PCA) as a tool to analyse the data from muon spectroscopy experiments. Specifically, we apply the ML technique to detect phase transitions in various materials. The measured quantity in muon spectroscopy is an asymmetry function, which may hold information about the distribution of the intrinsic magnetic field in combination with the dynamics of the sample. Sharp changes of shape of asymmetry functions-measured at different temperatures-might indicate a phase transition. Existing methods of processing the muon spectroscopy data are based on regression analysis, but choosing the right fitting function requires knowledge about the underlying physics of the probed material. Conversely, PCA focuses on small differences in the asymmetry curves and works without any prior assumptions about the studied samples. We discovered that the PCA method works well in detecting phase transitions in muon spectroscopy experiments and can serve as an alternative to current analysis, especially if the physics of the studied material are not entirely known. Additionally, we found out that our ML technique seems to work best with large numbers of measurements, regardless of whether the algorithm takes data only for a single material or whether the analysis is performed simultaneously for many materials with different physical properties.
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Affiliation(s)
- T Tula
- School of Physical Sciences, University of Kent, Park Wood Rd, Canterbury CT2 7NH, United Kingdom
| | - G Möller
- School of Physical Sciences, University of Kent, Park Wood Rd, Canterbury CT2 7NH, United Kingdom
| | - J Quintanilla
- School of Physical Sciences, University of Kent, Park Wood Rd, Canterbury CT2 7NH, United Kingdom
| | - S R Giblin
- School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, United Kingdom
| | - A D Hillier
- ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot Oxon, OX11 0QX, United Kingdom
| | - E E McCabe
- School of Physical Sciences, University of Kent, Park Wood Rd, Canterbury CT2 7NH, United Kingdom
| | - S Ramos
- School of Physical Sciences, University of Kent, Park Wood Rd, Canterbury CT2 7NH, United Kingdom
| | - D S Barker
- School of Physical Sciences, University of Kent, Park Wood Rd, Canterbury CT2 7NH, United Kingdom
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - S Gibson
- School of Physical Sciences, University of Kent, Park Wood Rd, Canterbury CT2 7NH, United Kingdom
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Freeman PG, Giblin SR, Skoulatos M, Mole RA, Prabhakaran D. Wave Vector Difference of Magnetic Bragg Reflections and Low Energy Magnetic Excitations in Charge-stripe Ordered La2NiO4.11. Sci Rep 2019; 9:14468. [PMID: 31594985 PMCID: PMC6783545 DOI: 10.1038/s41598-019-50904-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Accepted: 09/10/2019] [Indexed: 11/09/2022] Open
Abstract
We report on the magnetism of charge-stripe ordered La2NiO4.11±0.01 by neutron scattering and μSR. On going towards zero energy transfer there is an observed wave vector offset in the centring of the magnetic excitations and magnetic Bragg reflections, meaning the excitations cannot be described as Goldstone modes of the magnetic order. Weak transverse field μSR measurements determine the magnetically order volume fraction is 87% from the two stripe twins, and the temperature evolution of the magnetic excitations is consistent with the low energy excitations coming from the magnetically ordered volume of the material. We will discuss how these results contrast with the proposed origin of a similar wave vector offset recently observed in a La-based cuprate, and possible origins of this effect in La2NiO4.11.
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Riordan E, Blomgren J, Jonasson C, Ahrentorp F, Johansson C, Margineda D, Elfassi A, Michel S, Dell'ova F, Klemencic GM, Giblin SR. Design and implementation of a low temperature, inductance based high frequency alternating current susceptometer. Rev Sci Instrum 2019; 90:073908. [PMID: 31370440 DOI: 10.1063/1.5074154] [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] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Accepted: 07/09/2019] [Indexed: 06/10/2023]
Abstract
We report on the implementation of an induction based, low temperature, high frequency ac susceptometer capable of measuring at frequencies up to 3.5 MHz and at temperatures between 2 K and 300 K. Careful balancing of the detection coils and calibration allow a sample magnetic moment resolution of 5 × 10-10 Am2 at 1 MHz. We discuss the design and characterization of the susceptometer and explain the calibration process. We also include some example measurements on the spin ice material CdEr2S4 and iron oxide based nanoparticles to illustrate functionality.
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Affiliation(s)
- E Riordan
- Department of Physics & Astronomy, Cardiff University, Cardiff CF24 3AA, United Kingdom
| | - J Blomgren
- RISE Acreo, Arvid Hedvalls Backe 4, Box 53071, SE-400 14 Göteborg, Sweden
| | - C Jonasson
- RISE Acreo, Arvid Hedvalls Backe 4, Box 53071, SE-400 14 Göteborg, Sweden
| | - F Ahrentorp
- RISE Acreo, Arvid Hedvalls Backe 4, Box 53071, SE-400 14 Göteborg, Sweden
| | - C Johansson
- RISE Acreo, Arvid Hedvalls Backe 4, Box 53071, SE-400 14 Göteborg, Sweden
| | - D Margineda
- Department of Physics & Astronomy, Cardiff University, Cardiff CF24 3AA, United Kingdom
| | - A Elfassi
- INSA, Institut National des Sciences Appliques, Toulouse, 135 Avenue de Rangueil, 31077 Toulouse Cedex 4, France
| | - S Michel
- INSA, Institut National des Sciences Appliques, Toulouse, 135 Avenue de Rangueil, 31077 Toulouse Cedex 4, France
| | - F Dell'ova
- INSA, Institut National des Sciences Appliques, Toulouse, 135 Avenue de Rangueil, 31077 Toulouse Cedex 4, France
| | - G M Klemencic
- Department of Physics & Astronomy, Cardiff University, Cardiff CF24 3AA, United Kingdom
| | - S R Giblin
- Department of Physics & Astronomy, Cardiff University, Cardiff CF24 3AA, United Kingdom
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Paulsen C, Giblin SR, Lhotel E, Prabhakaran D, Matsuhira K, Balakrishnan G, Bramwell ST. Nuclear spin assisted quantum tunnelling of magnetic monopoles in spin ice. Nat Commun 2019; 10:1509. [PMID: 30944307 PMCID: PMC6447640 DOI: 10.1038/s41467-019-09323-6] [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] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Accepted: 03/04/2019] [Indexed: 12/03/2022] Open
Abstract
Extensive work on single molecule magnets has identified a fundamental mode of relaxation arising from the nuclear-spin assisted quantum tunnelling of nearly independent and quasi-classical magnetic dipoles. Here we show that nuclear-spin assisted quantum tunnelling can also control the dynamics of purely emergent excitations: magnetic monopoles in spin ice. Our low temperature experiments were conducted on canonical spin ice materials with a broad range of nuclear spin values. By measuring the magnetic relaxation, or monopole current, we demonstrate strong evidence that dynamical coupling with the hyperfine fields bring the electronic spins associated with magnetic monopoles to resonance, allowing the monopoles to hop and transport magnetic charge. Our result shows how the coupling of electronic spins with nuclear spins may be used to control the monopole current. It broadens the relevance of the assisted quantum tunnelling mechanism from single molecular spins to emergent excitations in a strongly correlated system. Spin ice compounds have localised excitations that behave as magnetic monopoles which move by hopping from site to site, creating a chain of spins. Here the authors show that the hyperfine coupling between electron and nuclear spins is an important part of the mechanism underlying monopole motion.
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Affiliation(s)
- C Paulsen
- Institut Néel, C.N.R.S-Université Grenoble Alpes, BP 166, 38042, Grenoble, France.
| | - S R Giblin
- School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, UK.
| | - E Lhotel
- Institut Néel, C.N.R.S-Université Grenoble Alpes, BP 166, 38042, Grenoble, France
| | - D Prabhakaran
- Clarendon Laboratory, Physics Department, Oxford University, Oxford, OX1~3PU, UK
| | - K Matsuhira
- Kyushu Institute of Technology, Kitakyushu, 804-8550, Japan
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
| | - S T Bramwell
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London, WC1H 0AJ, UK
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Klemencic GM, Fellows JM, Werrell JM, Mandal S, Giblin SR, Smith RA, Williams OA. Observation of a superconducting glass state in granular superconducting diamond. Sci Rep 2019; 9:4578. [PMID: 30872614 PMCID: PMC6418110 DOI: 10.1038/s41598-019-40306-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Accepted: 02/11/2019] [Indexed: 11/13/2022] Open
Abstract
The magnetic field dependence of the superconductivity in nanocrystalline boron doped diamond thin films is reported. Evidence of a superconducting glass state is presented, as demonstrated by the observation of a quasi de Almeida-Thouless line in the phase diagram and a logarithmic time dependence of the magnetism. The position of the phase boundary in the H-T plane is determined from electrical transport data by detailed fitting to quasi-zero-dimensional fluctuation conductivity theory. This allows determination of the boundary between resistive and non-resistive behaviour to be made with greater precision than the standard ad hoc onset/midpoint/offset criterion. We attribute the glassy superconductivity to the morphological granularity of the diamond films.
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Affiliation(s)
- G M Klemencic
- School of Physics and Astronomy, Cardiff University, Queen's Buildings, The Parade, Cardiff, CF24 3AA, UK.
| | - J M Fellows
- School of Physics, HH Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL, UK
| | - J M Werrell
- School of Physics and Astronomy, Cardiff University, Queen's Buildings, The Parade, Cardiff, CF24 3AA, UK
| | - S Mandal
- School of Physics and Astronomy, Cardiff University, Queen's Buildings, The Parade, Cardiff, CF24 3AA, UK
| | - S R Giblin
- School of Physics and Astronomy, Cardiff University, Queen's Buildings, The Parade, Cardiff, CF24 3AA, UK
| | - R A Smith
- School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
| | - O A Williams
- School of Physics and Astronomy, Cardiff University, Queen's Buildings, The Parade, Cardiff, CF24 3AA, UK
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Giblin SR, Twengström M, Bovo L, Ruminy M, Bartkowiak M, Manuel P, Andresen JC, Prabhakaran D, Balakrishnan G, Pomjakushina E, Paulsen C, Lhotel E, Keller L, Frontzek M, Capelli SC, Zaharko O, McClarty PA, Bramwell ST, Henelius P, Fennell T. Pauling Entropy, Metastability, and Equilibrium in Dy_{2}Ti_{2}O_{7} Spin Ice. Phys Rev Lett 2018; 121:067202. [PMID: 30141658 DOI: 10.1103/physrevlett.121.067202] [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] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Indexed: 06/08/2023]
Abstract
Determining the fate of the Pauling entropy in the classical spin ice material Dy_{2}Ti_{2}O_{7} with respect to the third law of thermodynamics has become an important test case for understanding the existence and stability of ice-rule states in general. The standard model of spin ice-the dipolar spin ice model-predicts an ordering transition at T≈0.15 K, but recent experiments by Pomaranski et al. suggest an entropy recovery over long timescales at temperatures as high as 0.5 K, much too high to be compatible with the theory. Using neutron scattering and specific heat measurements at low temperatures and with long timescales (0.35 K/10^{6} s and 0.5 K/10^{5} s, respectively) on several isotopically enriched samples, we find no evidence of a reduction of ice-rule correlations or spin entropy. High-resolution simulations of the neutron structure factor show that the spin correlations remain well described by the dipolar spin ice model at all temperatures. Furthermore, by careful consideration of hyperfine contributions, we conclude that the original entropy measurements of Ramirez et al. are, after all, essentially correct: The short-time relaxation method used in that study gives a reasonably accurate estimate of the equilibrium spin ice entropy due to a cancellation of contributions.
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Affiliation(s)
- S R Giblin
- School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, United Kingdom
| | - M Twengström
- Department of Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - L Bovo
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London, WC1H OAH, United Kingdom
- Department of Innovation and Enterprise, University College London, 90 Tottenham Court Road, Fitzrovia, London W1T 4TJ, United Kingdom
| | - M Ruminy
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Bartkowiak
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - P Manuel
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom
| | - J C Andresen
- Department of Physics, Ben Gurion University of the Negev, Beer Sheva 84105, Israel
| | - D Prabhakaran
- Clarendon Laboratory, Physics Department, Oxford University, Oxford, OX1 3PU, United Kingdom
| | - G Balakrishnan
- Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
| | - E Pomjakushina
- Laboratory for Scientific Developments, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - C Paulsen
- Institut Néel, C.N.R.S-Université Joseph Fourier, B.P. 166, 38042 Grenoble, France
| | - E Lhotel
- Institut Néel, C.N.R.S-Université Joseph Fourier, B.P. 166, 38042 Grenoble, France
| | - L Keller
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Frontzek
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - S C Capelli
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom
| | - O Zaharko
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - P A McClarty
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Strasse 38, 01187 Dresden, Germany
| | - S T Bramwell
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London, WC1H OAH, United Kingdom
| | - P Henelius
- Department of Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - T Fennell
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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Gao S, Zaharko O, Tsurkan V, Prodan L, Riordan E, Lago J, Fåk B, Wildes AR, Koza MM, Ritter C, Fouquet P, Keller L, Canévet E, Medarde M, Blomgren J, Johansson C, Giblin SR, Vrtnik S, Luzar J, Loidl A, Rüegg C, Fennell T. Dipolar Spin Ice States with a Fast Monopole Hopping Rate in CdEr_{2}X_{4} (X=Se, S). Phys Rev Lett 2018; 120:137201. [PMID: 29694199 DOI: 10.1103/physrevlett.120.137201] [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: 05/30/2017] [Indexed: 06/08/2023]
Abstract
Excitations in a spin ice behave as magnetic monopoles, and their population and mobility control the dynamics of a spin ice at low temperature. CdEr_{2}Se_{4} is reported to have the Pauling entropy characteristic of a spin ice, but its dynamics are three orders of magnitude faster than the canonical spin ice Dy_{2}Ti_{2}O_{7}. In this Letter we use diffuse neutron scattering to show that both CdEr_{2}Se_{4} and CdEr_{2}S_{4} support a dipolar spin ice state-the host phase for a Coulomb gas of emergent magnetic monopoles. These Coulomb gases have similar parameters to those in Dy_{2}Ti_{2}O_{7}, i.e., dilute and uncorrelated, and so cannot provide three orders faster dynamics through a larger monopole population alone. We investigate the monopole dynamics using ac susceptometry and neutron spin echo spectroscopy, and verify the crystal electric field Hamiltonian of the Er^{3+} ions using inelastic neutron scattering. A quantitative calculation of the monopole hopping rate using our Coulomb gas and crystal electric field parameters shows that the fast dynamics in CdEr_{2}X_{4} (X=Se, S) are primarily due to much faster monopole hopping. Our work suggests that CdEr_{2}X_{4} offer the possibility to study alternative spin ice ground states and dynamics, with equilibration possible at much lower temperatures than the rare earth pyrochlore examples.
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Affiliation(s)
- Shang Gao
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- Department of Quantum Matter Physics, University of Geneva, CH-1211 Geneva, Switzerland
| | - O Zaharko
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - V Tsurkan
- Experimental Physics V, University of Augsburg, D-86135 Augsburg, Germany
- Institute of Applied Physics, Academy of Sciences of Moldova, MD-2028 Chisinau, Republic of Moldova
| | - L Prodan
- Institute of Applied Physics, Academy of Sciences of Moldova, MD-2028 Chisinau, Republic of Moldova
| | - E Riordan
- School of Physics and Astronomy, Cardiff University, CF24 3AA Cardiff, United Kingdom
| | - J Lago
- Department of Inorganic Chemistry, Universidad del País Vasco (UPV-EHU), 48080 Bilbao, Spain
| | - B Fåk
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - A R Wildes
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - M M Koza
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - C Ritter
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - P Fouquet
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - L Keller
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - E Canévet
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
| | - M Medarde
- Laboratory for Scientific Developments and Novel Materials, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - J Blomgren
- RISE Acreo AB, SE-411 33 Göteborg, Sweden
| | | | - S R Giblin
- School of Physics and Astronomy, Cardiff University, CF24 3AA Cardiff, United Kingdom
| | - S Vrtnik
- Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia
| | - J Luzar
- Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia
| | - A Loidl
- Experimental Physics V, University of Augsburg, D-86135 Augsburg, Germany
| | - Ch Rüegg
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- Department of Quantum Matter Physics, University of Geneva, CH-1211 Geneva, Switzerland
| | - T Fennell
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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Foronda FR, Lang F, Möller JS, Lancaster T, Boothroyd AT, Pratt FL, Giblin SR, Prabhakaran D, Blundell SJ. Anisotropic local modification of crystal field levels in Pr-based pyrochlores: a muon-induced effect modeled using density functional theory. Phys Rev Lett 2015; 114:017602. [PMID: 25615502 DOI: 10.1103/physrevlett.114.017602] [Citation(s) in RCA: 6] [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: 08/06/2014] [Indexed: 06/04/2023]
Abstract
Although muon spin relaxation is commonly used to probe local magnetic order, spin freezing, and spin dynamics, we identify an experimental situation in which the measured response is dominated by an effect resulting from the muon-induced local distortion rather than the intrinsic behavior of the host compound. We demonstrate this effect in some quantum spin ice candidate materials Pr(2)B(2)O(7) (B=Sn, Zr, Hf), where we detect a static distribution of magnetic moments that appears to grow on cooling. Using density functional theory we show how this effect can be explained via a hyperfine enhancement arising from a splitting of the non-Kramers doublet ground states on Pr ions close to the muon, which itself causes a highly anisotropic distortion field. We provide a quantitative relationship between this effect and the measured temperature dependence of the muon relaxation and discuss the relevance of these observations to muon experiments in other magnetic materials.
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Affiliation(s)
- F R Foronda
- Oxford University Department of Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - F Lang
- Oxford University Department of Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - J S Möller
- Oxford University Department of Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - T Lancaster
- Durham University, Centre for Materials Physics, South Road, Durham DH1 3LE, United Kingdom
| | - A T Boothroyd
- Oxford University Department of Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - F L Pratt
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxfordshire OX11 0QX, United Kingdom
| | - S R Giblin
- School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, United Kingdom
| | - D Prabhakaran
- Oxford University Department of Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
| | - S J Blundell
- Oxford University Department of Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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Ernsting D, Billington D, Haynes TD, Millichamp TE, Taylor JW, Duffy JA, Giblin SR, Dewhurst JK, Dugdale SB. Calculating electron momentum densities and Compton profiles using the linear tetrahedron method. J Phys Condens Matter 2014; 26:495501. [PMID: 25390292 DOI: 10.1088/0953-8984/26/49/495501] [Citation(s) in RCA: 3] [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: 06/04/2023]
Abstract
A method for computing electron momentum densities and Compton profiles from ab initio calculations is presented. Reciprocal space is divided into optimally-shaped tetrahedra for interpolation, and the linear tetrahedron method is used to obtain the momentum density and its projections such as Compton profiles. Results are presented and evaluated against experimental data for Be, Cu, Ni, Fe3Pt, and YBa2Cu4O8, demonstrating the accuracy of our method in a wide variety of crystal structures.
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Affiliation(s)
- D Ernsting
- H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL, UK
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Calder S, Giblin SR, Parker DR, Deen PP, Ritter C, Stewart JR, Rols S, Fennell T. Neutron scattering and μSR investigations of the low temperature state of LuCuGaO₄. J Phys Condens Matter 2013; 25:356002. [PMID: 23917326 DOI: 10.1088/0953-8984/25/35/356002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
LuCuGaO₄ has magnetic Cu(2+) and diamagnetic Ga(3+) ions distributed on a triangular bilayer and is suggested to undergo a spin glass transition at Tg ∼ 0.4 K. Using μSR (muon spin rotation) and neutron scattering measurements, we show that at low temperature the spins form a short range correlated state with spin fluctuations detectable over a wide range of timescales: at 0.05 K magnetic fluctuations can be detected in both the μSR time window and also extending beyond 7 meV in the inelastic neutron scattering response, indicating magnetic fluctuations spanning timescales between ∼10(-5) and ∼10(-10) s. The dynamical susceptibility scales according to the form χ″(ω)T(α), with α = 1, throughout the measured temperature range (0.05-50 K). These effects are associated with quantum fluctuations and some degree of structural disorder in ostensibly quite different materials, including certain heavy fermion alloys, kagome spin liquids, quantum spin glasses, and valence bond glasses. We therefore suggest that LuCuGaO₄ is an interesting model compound for the further examination of disorder and quantum magnetism.
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Affiliation(s)
- S Calder
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
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Giblin SR, Taylor JW, Duffy JA, Butchers MW, Utfeld C, Dugdale SB, Nakamura T, Visani C, Santamaria J. Measurement of magnetic exchange in ferromagnet-superconductor La2/3Ca1/3MnO3/YBa2Cu3O7 bilayers. Phys Rev Lett 2012; 109:137005. [PMID: 23030115 DOI: 10.1103/physrevlett.109.137005] [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: 04/03/2012] [Indexed: 06/01/2023]
Abstract
The existence of coherent magnetic correlations in the normal phase of cuprate high-temperature superconductors has proven difficult to measure directly. Here we report on a study of ferromagnetic-superconductor bilayers of La2/3Ca1/3MnO3/YBa2Cu3O7 (LCMO/YBCO) with varying YBCO layer thicknesses. Using x-ray magnetic circular dichroism, we demonstrate that the ferromagnetic layer induces a Cu magnetic moment in the adjacent high-temperature superconductor. For thin samples, this moment exists at all temperatures below the Curie temperature of the LCMO layer. However, for a YBCO layer thicker than 12 unit cells, the Cu moment is suppressed for temperatures above the superconducting transition, suggesting this to be a direct measurement of magnetic coherence in the normal state of a superconducting oxide.
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Affiliation(s)
- S R Giblin
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxfordshire, United Kingdom
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Lord JS, McKenzie I, Baker PJ, Blundell SJ, Cottrell SP, Giblin SR, Good J, Hillier AD, Holsman BH, King PJC, Lancaster T, Mitchell R, Nightingale JB, Owczarkowski M, Poli S, Pratt FL, Rhodes NJ, Scheuermann R, Salman Z. Design and commissioning of a high magnetic field muon spin relaxation spectrometer at the ISIS pulsed neutron and muon source. Rev Sci Instrum 2011; 82:073904. [PMID: 21806196 DOI: 10.1063/1.3608114] [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] [Indexed: 05/31/2023]
Abstract
The high magnetic field (HiFi) muon instrument at the ISIS pulsed neutron and muon source is a state-of-the-art spectrometer designed to provide applied magnetic fields up to 5 T for muon studies of condensed matter and molecular systems. The spectrometer is optimised for time-differential muon spin relaxation studies at a pulsed muon source. We describe the challenges involved in its design and construction, detailing, in particular, the magnet and detector performance. Commissioning experiments have been conducted and the results are presented to demonstrate the scientific capabilities of the new instrument.
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Affiliation(s)
- J S Lord
- ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX, United Kingdom
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Utfeld C, Giblin SR, Taylor JW, Duffy JA, Shenton-Taylor C, Laverock J, Dugdale SB, Manno M, Leighton C, Itou M, Sakurai Y. Bulk spin polarization of Co(1-x)Fe(x)S2. Phys Rev Lett 2009; 103:226403. [PMID: 20366116 DOI: 10.1103/physrevlett.103.226403] [Citation(s) in RCA: 1] [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: 04/01/2009] [Indexed: 05/29/2023]
Abstract
We report on a new method to determine the degree of bulk spin polarization in single crystal Co(1-x)Fe(x)S2 by modeling magnetic Compton scattering with ab initio calculations. Spin-dependent Compton profiles were measured for CoS2 and Co0.9Fe0.1S2. The ab initio calculations were then refined by rigidly shifting the bands to provide the best fit between the calculated and experimental directional profiles for each sample. The bulk spin polarizations, P, corresponding to the spin-polarized density of states at the Fermi level, were then extracted from the refined calculations. The values were found to be P=-72+/-6% and P=18+/-7% for CoS2 and Co0.9Fe0.1S2, respectively. Furthermore, determinations of P weighted by the Fermi velocity (v(F) or v(F)2) were obtained, permitting a rigorous comparison with other experimental data and highlighting the experimental dependence of P on v(F).
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Affiliation(s)
- C Utfeld
- H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom
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Prando G, Carretta P, Giblin SR, Lago J, Pin S, Ghigna P. Dilution effects in Ho2-xYxSn2O7: From the spin ice to the single-ion magnet. ACTA ACUST UNITED AC 2009. [DOI: 10.1088/1742-6596/145/1/012033] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Giblin SR, Champion JDM, Zhou HD, Wiebe CR, Gardner JS, Terry I, Calder S, Fennell T, Bramwell ST. Static magnetic order in Tb2Sn2O7 revealed by muon spin relaxation with exterior muon implantation. Phys Rev Lett 2008; 101:237201. [PMID: 19113586 DOI: 10.1103/physrevlett.101.237201] [Citation(s) in RCA: 1] [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: 09/16/2008] [Revised: 10/16/2008] [Indexed: 05/27/2023]
Abstract
Tb2Sn2O7 has been proposed as an ordered spin ice, but the precise nature of the low temperature magnetic state remains uncertain. Recent independent muon spin relaxation (microSR) investigations suggest the possibility of exotic ground states with static order precluded on time scales longer than 10(-6) s. Here the more conventional hypothesis of canted ferromagnetism is tested by means of microSR with the muons stopped outside the sample, as well as ultralow field bulk magnetization measurements. The field cooled state shows conventional static order, while the zero field cooled state may be interpreted in terms of conventional closed domains. These results rule out purely dynamical ground states and illustrate the value of exterior muon implantation as a complement to the conventional technique.
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Affiliation(s)
- S R Giblin
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom.
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Graf MJ, Lago J, Lascialfari A, Amato A, Baines C, Giblin SR, Lord JS, Tkachuk AM, Barbara B. Muon spin rotation studies of spin dynamics at avoided level crossings in LiY0.998Ho0.002F4. Phys Rev Lett 2007; 99:267203. [PMID: 18233602 DOI: 10.1103/physrevlett.99.267203] [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: 09/05/2007] [Indexed: 05/25/2023]
Abstract
We have studied the Ho3+ spin dynamics for LiY0.998Ho0.002F4 via the positive muon (mu+) transverse field depolarization rate lambdaTF as a function of temperature and magnetic field. We find sharp minima in lambdaTF(H) at fields for which the Ho3+ ion system has field-induced (avoided) level crossings. The reduction scales with calculated level repulsions, suggesting that mu+ depolarization by slow fluctuations of nonresonant Ho3+ spin states is partly suppressed when resonant tunneling opens new fluctuation channels at frequencies much greater than the muon precession frequency.
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Affiliation(s)
- M J Graf
- Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA
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