1,518 results on '"van der Laan, G"'
Search Results
2. Evidence of temperature-dependent interplay between spin and orbital moment in van der Waals ferromagnet VI3
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De Vita, A., Sant, R., Polewczyk, V., van der Laan, G., Brookes, N. B., Kong, T., Cava, R. J., Rossi, G., Vinai, G., and Panaccione, G.
- Subjects
Condensed Matter - Materials Science - Abstract
Van der Waals materials provide a versatile toolbox for the emergence of new quantum phenomena and the fabrication of functional heterostructures. Among them, the trihalide VI3 stands out for its unique magnetic and structural landscape. Here we investigate the spin and orbital magnetic degrees of freedom in the layered ferromagnet VI3 by means of temperature-dependent x-ray absorption spectroscopy and x-ray magnetic circular and linear dichroism. We detect localized electronic states and reduced magnetic dimensionality, due to electronic correlations. We furthermore provide experimental evidence of (a) an unquenched orbital magnetic moment (up to 0.66(7)) in the ferromagnetic state, and (b) an instability of the orbital moment in proximity of the spin reorientation transition. Our results support a coherent picture where electronic correlations give rise to a strong magnetic anisotropy and a large orbital moment, and establish VI3 as a prime candidate for the study of orbital quantum effects.
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- 2024
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3. Templates for magnetic symmetry and altermagnetism in hexagonal MnTe
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Lovesey, S. W., Khalyavin, D. D., and van der Laan, G.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
The symmetry of long-range magnetic order in manganese telluride (alpha-MnTe) is unknown. Likewise, its standing as an altermagnet. To improve the situation, we present symmetry informed Bragg diffraction patterns based on a primary magnetic order parameter for antiferromagnetic alignment between Mn dipoles. It does not break translation symmetry in a centrosymmetric structure, in keeping with an accepted definition of altermagnetism. Our templates serve x-ray diffraction that benefits from signal enhancement using a Mn atomic resonance, and neutron scattering. Even rank multipoles in magnetic neutron diffraction reflect a core requirement of altermagnetism, because they are zero for strong spin-orbit coupling. Symmetry in the templates demands that nuclear and magnetic contributions possess the same phase, which enables standard neutron polarization analysis on Bragg spots with overlapping contributions. However, three of the four templates generate Bragg spots that do not appear in the lattice (nuclear) diffraction pattern, i.e., Bragg spots that are basis-forbidden and purely magnetic in origin. On the other hand, identical symmetry demands a 90 deg phase shift between magnetic (time-odd) and charge-like (time-even, Templeton-Templeton) contributions to x-ray scattering amplitudes. Consequently, circular polarization in the primary beam of x-rays is rotated. The difference in the intensities of a Bragg spot measured with right- and left-handed circular primary polarization defines a chiral signature. Further tests include predictions in three out four templates of zero intensity in a specified channel of x-ray polarization. Diffraction properties of a template are radically different from those of a parity-time (PT)-symmetric antiferromagnet, for its symmetry allows a linear ME effect and prohibits both a PM effect and a chiral signature.
- Published
- 2023
4. A magnetic structure of ruthenium dioxide (RuO2) and altermagnetism
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Lovesey, S. W., Khalyavin, D. D., and van der Laan, G.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
The magnetic structure of RuO2 and the Ru atomic configuration are unknown. A magnetic structure is inferred by confronting measured and calculated Bragg diffraction patterns and adjusting the latter to achieve satisfactory agreement. An accepted pattern, a magnetic symmetry, includes symmetry of sites occupied by the magnetic ions. As a realistic starting point, we provide diffraction patterns for a magnetic symmetry of RuO2, a descendent of the tetragonal parent structure, which accommodates a departure of Ru axial dipoles from the crystal c axis. A chiral signal and piezomagnetic effect are permitted, and a linear magnetoelectric effect forbidden. Features of the neutron diffraction pattern test the non-relativistic requirement of altermagnetism, and we scrutinize published room-temperature data. Specifically, one Bragg point is consistent with Ru orbital angular momentum and magnetic quadrupole both zero, and the latter result is not expected from non-relativistic altermagnetism. Azimuthal angle scans in resonant x-ray diffraction are sensitive to the Ru site symmetry and the atomic configuration. Acid tests of the studied magnetic symmetry include a chiral signature and null intensity for unrotated photon polarization.
- Published
- 2023
5. Anisotropic hybridization probed by polarization dependent x-ray absorption spectroscopy in VI3 van der Waals Mott ferromagnet
- Author
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Sant, R., De Vita, A., Polewczyk, V., Pierantozzi, G., Mazzola, F., Vinai, G., van der Laan, G., Panaccione, G., and Brookes, N. B.
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Condensed Matter - Strongly Correlated Electrons - Abstract
Polarization dependent x-ray absorption spectroscopy was used to study the magnetic ground state and the orbital occupation in bulk-phase VI$_3$ van der Waals crystals below and above the ferromagnetic and structural transitions. X-ray natural linear dichroism and X-ray magnetic circular dichroism spectra acquired at the V $L_{2,3}$ edges are compared against multiplet cluster calculations within the frame of the ligand field theory to quantify the intra-atomic electronic interactions at play and evaluate the effects of symmetry reduction occurring in a trigonally distorted VI$_6$ unit. We observed a non zero linear dichroism proving the presence of an anisotropic charge density distribution around the V$^{3+}$ ion due to the unbalanced hybridization between the Vanadium and the ligand states. Such hybridization acts as an effective trigonal crystal field, slightly lifting the degeneracy of the $t_{2g}^2$ ground state. However, the energy splitting associated to the distortion underestimates the experimental band gap, suggesting that the insulating ground state is stabilized by Mott correlation effects rather than via a Jahn-Teller mechanism. Our results clarify the role of the distortion in VI$_3$ and establish a benchmark for the study of the spectroscopic properties of other van der Waals halides, including emerging 2D materials with mono and few-layers thickness, whose fundamental properties might be altered by reduced dimensions and interface proximity.
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- 2023
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6. Synchrotron Radiation Techniques and their Application to Actinide Materials
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Caciuffo, R., Lander, G. H., and van der Laan, G.
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Condensed Matter - Materials Science - Abstract
Research on actinide materials, both basic and applied, has been greatly advanced by the general techniques available from high-intensity photon beams from x-ray synchrotron sources. The most important single reason is that such x-ray sources can work with minute (e.g., microgram) samples, and at this level, the radioactive hazards of actinides are much reduced. We start by discussing the form and encapsulation procedures used for different techniques, then discuss the basic theory for interpreting the results. By reviewing a selection of x-ray diffraction (XRD), resonant elastic x-ray scattering (REXS), x-ray magnetic circular dichroism (XMCD), resonant and non-resonant inelastic scattering (RIXS, NIXS), dispersive inelastic x-ray scattering (IXS), and conventional and resonant photoemission experiments, we demonstrate the potential of synchrotron radiation techniques in studying lattice and electronic structure, hybridization effects, multipolar order, and lattice dynamics in actinide materials., Comment: To be published in Reviews of Modern Physics; 57 pages, 36 figures, 475 references
- Published
- 2022
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7. Depth-dependent magnetic crossover in a room-temperature skyrmion-hosting multilayer
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Hicken, T. J., Wilson, M. N., Salman, Z., Zhang, S. L., Holt, S. J. R., Prokscha, T., Suter, A., Pratt, F. L., van der Laan, G., Hesjedal, T., and Lancaster, T.
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Condensed Matter - Strongly Correlated Electrons - Abstract
Skyrmion-hosting multilayer stacks are promising avenues for applications, although little is known about the depth dependence of the magnetism. We address this by reporting the results of circular dichroic resonant elastic x-ray scattering (CD-REXS), micromagnetic simulations, and low-energy muon-spin rotation (LE-$\mu^+$SR) measurements on a stack comprising [Ta/CoFeB/MgO]$_{16}$/Ta on a Si substrate. Energy-dependent CD-REXS shows a continuous, monotonic evolution of the domain-wall helicity angle with incident energy, consistent with a three-dimensional hybrid domain-wall-like structure that changes from N\'eel-like near the surface to Bloch-like deeper within the sample. LE-$\mu^+$SR reveals that the magnetic field distribution in the trilayers near the surface of the stack is distinct from that in trilayers deeper within the sample. Our micromagnetic simulations support a quantitative analysis of the $\mu^+$SR results. By increasing the applied magnetic field, we find a reduction in the volume occupied by domain walls at all depths, consistent with a crossover into a region dominated by skyrmions above approximately 180 mT., Comment: 9 pages, 4 figures
- Published
- 2022
8. Robust Kagome Electronic Structure in Topological Quantum Magnets XMn6Sn6 (X = Dy, Tb, Gd, Y)
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Gu, X., Chen, C., Wei, W. S., Liu, J. Y., Du, X., Pei, D., Zhou, J. S., Xu, R. Z., Yin, Z. X., Zhao, W. X., Li, Y. D., Jozwiak, C., Bostwick, A., Rotenberg, E., Backes, D., Veiga, L. S. I., Dhesi, S., Hesjedal, T., van der Laan, G., Du, H. F., Jiang, W. J., Qi, Y. P., Li, G., Shi, W. J., Liu, Z. K., Chen, Y. L., and Yang, L. X.
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Condensed Matter - Strongly Correlated Electrons - Abstract
Crystal geometry can greatly influence the emergent properties of quantum materials. As an example, the kagome lattice is an ideal platform to study the rich interplay between topology, magnetism, and electronic correlation. In this work, combining high-resolution angle-resolved photoemission spectroscopy and ab-initio calculation, we systematically investigate the electronic structure of XMn6Sn6 (X = Dy, Tb, Gd, Y) family compounds. We observe the Dirac fermion and the flat band arising from the magnetic kagome lattice of Mn atoms. Interestingly, the flat band locates in the same energy region in all compounds studied, regardless of their different magnetic ground states and 4f electronic configurations. These observations suggest a robust Mn magnetic kagome lattice across the XMn6Sn6 family, thus providing an ideal platform for the search and investigation on new emergent phenomena in magnetic topological materials., Comment: PRB accepted
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- 2022
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9. Ligand-metal covalency effects in resonance enhanced x-ray Bragg diffraction
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Lovesey, S. W. and van der Laan, G.
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Condensed Matter - Strongly Correlated Electrons - Abstract
Chlorine covalently bonded to an open shell metal is present in many materials with desirable or intriguing physical properties. Materials include highly luminescent nontoxic alternatives to lead halide perovskites for optoelectronic applications K2CuCl3 and Rb2CuCl3, enantiomorphic CsCuCl3 that presents magneto-chiral dichroism at a low temperature, and cubic K2RuCl6 that possesses a singlet ground state generated by antiparallel spin and orbital angular momenta. Structural chirality of CsCuCl3 has been confirmed by resonant x-ray Bragg diffraction. We explore likely benefits of the technique at the chlorine K-edge using a symmetry inspired method of calculation applied to chlorine multipoles. Already, a low energy feature in corresponding x-ray absorption spectra of many compounds has been related to the chlorine-metal bond. Bragg diffraction from chlorine in cubic K2RuCl6 is treated in detail. Diffraction patterns for rhombohedral compounds that present space-group forbidden Bragg spots are found to be relatively simple.
- Published
- 2021
10. Robust kagome electronic structure in the topological quantum magnets XMn6Sn6 (X=Dy,Tb,Gd,Y)
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Gu, X, Chen, C, Wei, WS, Gao, LL, Liu, JY, Du, X, Pei, D, Zhou, JS, Xu, RZ, Yin, ZX, Zhao, WX, Li, YD, Jozwiak, C, Bostwick, A, Rotenberg, E, Backes, D, Veiga, LSI, Dhesi, S, Hesjedal, T, van der Laan, G, Du, HF, Jiang, WJ, Qi, YP, Li, G, Shi, WJ, Liu, ZK, Chen, YL, and Yang, LX
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Quantum Physics ,Physical Sciences ,Condensed Matter Physics ,Chemical sciences ,Engineering ,Physical sciences - Abstract
Crystal geometry can greatly influence the emergent properties of quantum materials. As an example, the kagome lattice is an ideal platform to study the rich interplay between topology, magnetism, and electronic correlation. In this work, combining high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we systematically investigate the electronic structure of XMn6Sn6 (X=Dy,Tb,Gd,Y) family compounds. We observe the Dirac fermion and the flat band arising from the magnetic kagome lattice of Mn atoms. Interestingly, the flat band locates in the same energy region in all compounds studied, regardless of their different magnetic ground states and 4f electronic configurations. These observations suggest a robust Mn magnetic kagome lattice across the XMn6Sn6 family, thus providing an ideal platform for the search for, and investigation of, new emergent phenomena in magnetic topological materials.
- Published
- 2022
11. Magnetic properties of ruthenium dioxide (RuO2) and charge-magnetic interference in Bragg diffraction of circularly polarized x-rays
- Author
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Lovesey, S. W., Khalyavin, D. D., and van der Laan, G.
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Condensed Matter - Strongly Correlated Electrons - Abstract
Rutile-type RuO2 likely supports a simple antiferromagnetic structure which can be verified by x-ray Bragg diffraction. Three magnetic motifs that do not break translation symmetry are explored in calculations of amplitudes suitable for diffraction enhanced by tuning the primary x-ray energy to a ruthenium atomic resonance. Coupling to x-ray helicity through a charge-magnetic interference is common to all motifs, together with magnetic and charge intensities in quadrature in the rotated channel of polarization. Necessary conditions for these diffraction phenomena are a centrosymmetric crystal structure, null magnetic propagation vector, and absence of a linear magnetoelectric effect. Published x-ray diffraction data for RuO2 was analysed by the authors against a magnetic motif that does not satisfy the conditions. A polarized neutron study of antiferromagnetic domains can be achieved with a sample that meets the stated crystal and magnetic symmetries.
- Published
- 2021
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12. Spin-current mediated exchange coupling in MgO-based magnetic tunnel junctions
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Gladczuk, L., Dluzewski, P., Lasek, K., Aleshkevych, P., Burn, D. M., van der Laan, G., and Hesjedal, T.
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Condensed Matter - Materials Science - Abstract
Heterostructures composed of ferromagnetic layers that are mutually interacting through a nonmagnetic spacer are at the core of magnetic sensor and memory devices. In the present study, layer-resolved ferromagnetic resonance was used to investigate the coupling between the magnetic layers of a Co/MgO/Permalloy magnetic tunnel junction. Two magnetic resonance peaks were observed for both magnetic layers, as probed at the Co and Ni L3 x-ray absorption edges, showing a strong interlayer interaction through the insulating MgO barrier. A theoretical model based on the Landau-Lifshitz-Gilbert-Slonczewski equation was developed, including exchange coupling and spin pumping between the magnetic layers. Fits to the experimental data were carried out, both with and without a spin pumping term, and the goodness of the fit was compared using a likelihood ratio test. This rigorous statistical approach provides an unambiguous proof of the existence of interlayer coupling mediated by spin pumping., Comment: 11 pages, 7 figures
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- 2021
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13. Absence of magnetic-proximity effect at the interface of Bi$_2$Se$_3$ and (Bi,Sb)$_2$Te$_3$ with EuS
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Figueroa, A. I., Bonell, F., Cuxart, M. G., Valvidares, M., Gargiani, P., van der Laan, G., Mugarza, A., and Valenzuela, S. O.
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Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
We performed x-ray magnetic circular dichroism (XMCD) measurements on heterostructures comprising topological insulators (TIs) of the (Bi,Sb)$_2$(Se,Te)$_3$ family and the magnetic insulator EuS. XMCD measurements allow us to investigate element-selective magnetic proximity effects at the very TI/EuS interface. A systematic analysis reveals that there is neither significant induced magnetism within the TI nor an enhancement of the Eu magnetic moment at such interface. The induced magnetic moments in Bi, Sb, Te, and Se sites are lower than the estimated detection limit of the XMCD measurements of $\sim\!10^{-3}$ $\mu_\mathrm{B}$/at., Comment: 7 pages, 3 figures, published in Physical Review Letters
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- 2020
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14. Electronic multipoles in second harmonic generation and neutron scattering
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van der Laan, G. and Lovesey, S. W.
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Condensed Matter - Strongly Correlated Electrons ,Physics - Optics - Abstract
Nonlinear optics, and particularly second harmonic generation (SHG), is increasingly used in many modern disciplines from material characterization in physical sciences to bio-imaging in medicine and optical signal processing in information technology. We present a theoretical analysis providing a strong estimate for the energy-integrated SHG response. Requirements of symmetry in time and space are fully respected in the calculation, and estimates of natural and magnetic circular dichroic signals are superior to previous ones. Like symmetry requirements are traced in the amplitude for magnetic neutron scattering, which includes all axial and polar (Dirac) contributions. Our method of working, in terms of spherical multipoles and implementation of symmetry, could be of use in a variety of other probes of electronic properties.
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- 2020
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15. Diffraction by multipoles in a 5d2 rhenium double perovskite
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Lovesey, S. W., Khalyavin, D. D., van der Laan, G., and Nilsen, G. J.
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Condensed Matter - Strongly Correlated Electrons - Abstract
A recent polarized neutron diffraction experiment on the 5d2 rhenium double perovskite Ba2YReO6 held at a low temperature uncovered weak magnetic diffraction peaks. Data analysis inferred a significantly reduced Re dipole moment, and long-range order compatible with an antiferromagnet, non-collinear motif. To interpret the experimental findings, we present a model wavefunction for Re ions derived from the crystal field potential, Coulomb interaction, and spin-orbit coupling that fully respects the symmetry of the low-temperature ordered state. It is used to calculate in analytic form all multipole moments visible in neutron and resonance enhanced x-ray diffraction. A minimal model consistent with available neutron diffraction data predicts significant multipolar moments up to the hexadecapole, and, in particular, a dominant charge-like quadrupole moment. Calculated diffraction patterns embrace single crystal x-ray diffraction at the Re L-edge, and renewed neutron diffraction, to probe the presumed underlying multipolar order.
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- 2020
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16. Magnetic multipoles and correlation shortage in pyrochlore cerium stannate
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Lovesey, S. W. and van der Laan, G.
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Condensed Matter - Strongly Correlated Electrons - Abstract
Cerium electronic multipoles in trigonal symmetry viewed in magnetic neutron diffraction are investigated. Analytic expressions for all the magnetic multipoles, and radial integrals calculated with an established atomic code, are used to scrutinize a recent claim to have observed an octupole-ice configuration in a powder sample of pyrochlore Ce2Sn2O7. Three equally plausible suites of multipoles belonging to uncorrelated cerium ions give equally satisfactory accounts of the available diffraction pattern. Our multipoles are suitable for future experiments using Bragg diffraction from a compound that supports long-range magnetic order.
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- 2020
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17. Canted standing spin-wave modes of permalloy thin films observed by ferromagnetic resonance
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Dąbrowski, M, Hicken, RJ, Frisk, A, Newman, DG, Klewe, C, N'Diaye, AT, Shafer, P, Van Der Laan, G, Hesjedal, T, and Bowden, GJ
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ferromagnetic resonance ,standing spin waves ,XFMR ,canted magnetization ,exchange spring magnet ,Fluids & Plasmas ,Physical Sciences - Abstract
Non-collinear spin structures in materials that combine perpendicular and in-plane magnetic anisotropies are of great technological interest for microwave and spin wave-assisted magnetization switching. [Co/Pt] multilayers are well-known perpendicular anisotropy materials that have the potential to pin the magnetization of a soft magnetic layer, such as permalloy (Py), that has in-plane anisotropy, thereby forming a magnetic exchange spring. Here we report on multilayered [Co/Pt]/Pt/Py films, where an additional ultrathin Pt spacer has been included to control the coupling between the sub-units with in-plane and perpendicular magnetic anisotropy. Vector network analyser (VNA)-ferromagnetic resonance (FMR) measurements were made to obtain a complete picture of the resonant conditions, while the dynamical response of the sub-units was probed by synchrotron-based element- and phase selective x-ray detected FMR (XFMR). For all samples, only slight pinning of the dynamic magnetization of the Py by the [Co/Pt] was noted, and the FMR results were dominated by the 50 nm thick Py layer. Out-of-plane VNA-FMR maps reveal the presence of additional modes, e.g. a perpendicular standing spin-wave (PSSW) state. However, as the magnetic field is reduced below the saturation field, the PSSW state morphs continuously through a series of canted standing spin-wave (CSSW) states into a horizontal standing spin-wave (HSSW) state. The PSSW, CSSW and HSSW states are well described using a multilayer model of the Py film. The observation of CSSW modes is of particular relevance to microwave assisted magnetic recording, where microwave excitation stimulates precession of a soft layer canted out of plane by a pulsed magnetic field.
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- 2021
18. Circular dichroism of second harmonic generation response
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Lovesey, S. W. and van der Laan, G.
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Condensed Matter - Strongly Correlated Electrons - Abstract
Polarization-dependent photon spectroscopy (dichroism) of the second-harmonic generation (SHG) response is shown to reveal chiral and magnetic properties of a sample. Two dichroic signals are allowed with electric-dipole (E1) and electric-quadrupole (E2) scattering events, and both require circular polarization in the primary beam. Explicit expressions for electronic multipoles, which benefit from equivalent electronic operators, in NCD and MCD of the SHG response are derived using theoretical techniques from atomic physics.
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- 2019
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19. Magnetic Multipoles in a Ruthenate Ca3Ru2O7
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Lovesey, S W, Khalyavin, D D, and van der Laan, G
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Condensed Matter - Strongly Correlated Electrons - Abstract
Compulsory Dirac multipoles in the bilayer perovskite Ca3Ru2O7 are absent in published analyses of experimental data. In a first step at correcting knowledge of the magnetic structure, we have analysed existing Bragg diffraction patterns gathered on samples held well below the N\'eel temperature at which A-type antiferromagnetic order of axial dipoles spontaneously develops. Patterns were gathered with neutrons, and linearly polarized x-rays tuned in energy to a ruthenium atomic resonance. Neutron diffraction data contains solid evidence of Dirac dipoles (anapoles or toroidal moments). No such conclusion is reached with existing x-ray diffraction data, which instead is ambiguous on the question. To address this shortcoming by future experiments, we calculated additional diffraction patterns. Chiral order of Dirac multipoles is allowed by magnetic space-group PCna21, and it can be exposed in Bragg diffraction using circularly polarized x-rays. Likewise, a similar experiment can expose a chiral order of axial dipoles. A magnetic field applied parallel to the b-axis creates a ferrimagnetic structure in which bulk magnetization arises from field-induced nonequivalent Ru sites (magnetic space-group Pm'c'21)., Comment: 5 fig
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- 2019
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20. Element- and Time-Resolved Measurements of Spin Dynamics Using X-ray Detected Ferromagnetic Resonance
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Klewe, C, Li, Q, Yang, M, N’Diaye, AT, Burn, DM, Hesjedal, T, Figueroa, AI, Hwang, C, Li, J, Hicken, RJ, Shafer, P, Arenholz, E, van der Laan, G, and Qiu, Z
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Optical Physics - Published
- 2020
21. Direct observation of anapoles by neutron diffraction
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Lovesey, S. W., Chatterji, T., Stunault, A., Khalyavin, D. D., and van der Laan, G.
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Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons - Abstract
The scope of magnetic neutron scattering has been expanded by the observation of electronic Dirac dipoles (anapoles) that are polar (parity-odd) and magnetic (time-odd). A zero-magnetization ferromagnet Sm0.976Gd0.024Al2 with a diamond-type structure presents Dirac multipoles at basis-forbidden reflections that include the standard (2, 2, 2) reflection. Magnetic amplitudes measured at four such reflections are in full accord with a structure factor calculated from the appropriate magnetic space group., Comment: 4 pages, 3 figures
- Published
- 2018
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22. Depth-dependent magnetic crossover in a room-temperature skyrmion-hosting multilayer
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Hicken, T. J., primary, Wilson, M. N., additional, Salman, Z., additional, Zhang, S. L., additional, Holt, S. J. R., additional, Prokscha, T., additional, Suter, A., additional, Pratt, F. L., additional, van der Laan, G., additional, Hesjedal, T., additional, and Lancaster, T., additional
- Published
- 2024
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23. Microscopic effects of Dy-doping in the topological insulator Bi2Te3
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Duffy, L. B., Steinke, N. -J., Krieger, J. A., Figueroa, A. I., Kummer, K., Lancaster, T., Giblin, S. R., Pratt, F. L., Blundell, S. J., Prokscha, T., Suter, A., Langridge, S., Strocov, V. N., Salman, Z., van der Laan, G., and Hesjedal, T.
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Condensed Matter - Materials Science - Abstract
Magnetic doping with transition metal ions is the most widely used approach to break timereversal symmetry in a topological insulator, a prerequisite for unlocking the TIs exotic potential. Recently, we reported the doping of Bi2Te3 thin films with rare earth ions, which, owing to their large magnetic moments, promise commensurately large magnetic gap openings in the topological surface states. However, only when doping with Dy has a sizable gap been observed in angle-resolved photoemission spectroscopy, which persists up to room-temperature. Although disorder alone could be ruled out as a cause of the topological phase transition, a fundamental understanding of the magnetic and electronic properties of Dy:Bi2Te3 remained elusive. Here, we present an X-ray magnetic circular dichroism, polarized neutron reflectometry, muon spin rotation, and resonant photoemission study of the microscopic magnetic and electronic properties. We find that the films are not simply paramagnetic but that instead the observed behavior can be well explained by the assumption of slowly fluctuating, inhomogeneous magnetic patches with increasing volume fraction as the temperature decreases. At liquid helium temperatures, a large effective magnetization can be easily introduced by the application of moderate magnetic fields, implying that this material is very suitable for proximity coupling to an underlying ferromagnetic insulator or in a heterostructure with transition metal-doped layers. However, the introduction of some charge carriers by the dopants cannot be excluded at least in these highly doped samples. Nevertheless, we find that the magnetic order is not mediated via the conduction channel in these rare earth doped samples and therefore magnetic order and carrier concentration are expected to be independently controllable. This is not generally the case for transition metal doped topological insulators., Comment: 9 pages, 5 figures
- Published
- 2018
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24. Field-induced magnetic charge in a cubic Laves compound UAl2
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Lovesey, S. W., Khalyavin, D. D., and van der Laan, G.
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Condensed Matter - Strongly Correlated Electrons - Abstract
Magnetic diffraction of polarized neutrons by the cubic Laves compound UAl2 in a magnetic field has unveiled weak Bragg spots that are nominally forbidden. On the one hand, they can be viewed as magnetic analogues of the basis-forbidden (2, 2, 2) reflection in diamond-type structures that has been painstakingly and frequently investigated over almost a century. Alternatively, the pattern of weak intensities can be assigned to Dirac multipoles imbedded in field-induced magnetic charge. To this end, a published diffraction pattern is successfully confronted with intensities calculated from the appropriate magnetic space-group that includes Dirac dipoles (anapoles) to describe the basis-forbidden magnetic reflections, and conventional (axial) dipole and octupole multipoles to describe basis-allowed magnetic reflections.
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- 2018
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25. Observation of magnetic vortex pairs at room temperature in a planar {\alpha}-Fe2O3/Co heterostructure
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Chmiel, F. P., Price, N. Waterfield, Johnson, R. D., Lamirand, A. D., Schad, J., van der Laan, G., Harris, D. T., Irwin, J., Rzchowski, M. S., Eom, C. -B., and Radaelli, P. G.
- Subjects
Condensed Matter - Materials Science - Abstract
Vortices are among the simplest topological structures, and occur whenever a flow field `whirls' around a one-dimensional core. They are ubiquitous to many branches of physics, from fluid dynamics to superconductivity and superfluidity, and are even predicted by some unified theories of particle interactions, where they might explain some of the largest-scale structures seen in today's Universe. In the crystalline state, vortex formation is rare, since it is generally hampered by long-range interactions: in ferroic materials (ferromagnetic and ferroelectric), vortices are only observed when the effects of the dipole-dipole interaction is modified by confinement at the nanoscale, or when the parameter associated with the vorticity does not couple directly with strain. Here, we present the discovery of a novel form of vortices in antiferromagnetic (AFM) hematite ($\alpha$-Fe$_2$O$_3$) epitaxial films, in which the primary whirling parameter is the staggered magnetisation. Remarkably, ferromagnetic (FM) topological objects with the same vorticity and winding number of the $\alpha$-Fe$_2$O$_3$ vortices are imprinted onto an ultra-thin Co ferromagnetic over-layer by interfacial exchange. Our data suggest that the ferromagnetic vortices may be merons (half-skyrmions, carrying an out-of-plane core magnetisation), and indicate that the vortex/meron pairs can be manipulated by the application of an in-plane magnetic field, H$_{\parallel}$, giving rise to large-scale vortex-antivortex annihilation., Comment: 16 pages, 4 figures
- Published
- 2018
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26. Imaging and manipulation of skyrmion lattice domains in Cu2OSeO3
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Zhang, S. L., Bauer, A., Berger, H., Pfleiderer, C., van der Laan, G., and Hesjedal, T.
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Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
Nanoscale chiral skyrmions in noncentrosymmetric helimagnets are promising binary state variables in high-density, low-energy nonvolatile memory. Skyrmions are ubiquitous as an ordered, single-domain lattice phase, which makes it difficult to write information unless they are spatially broken up into smaller units, each representing a bit. Thus, the formation and manipulation of skyrmion lattice domains is a prerequisite for memory applications. Here, using an imaging technique based on resonant magnetic x-ray diffraction, we demonstrate the mapping and manipulation of skyrmion lattice domains in Cu2OSeO3. The material is particularly interesting for applications owing to its insulating nature, allowing for electric field-driven domain manipulation., Comment: 4 pages, 3 figures
- Published
- 2016
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27. Strain in epitaxial MnSi films on Si(111) in the thick film limit studied by polarization-dependent extended x-ray absorption fine structure
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Figueroa, A. I., Zhang, S. L., Baker, A. A., Chalasani, R., Kohn, A., Speller, S. C., Gianolio, D., Pfleiderer, C., van der Laan, G., and Hesjedal, T.
- Subjects
Condensed Matter - Materials Science - Abstract
We report a study of the strain state of epitaxial MnSi films on Si(111) substrates in the thick film limit (100-500~\AA) as a function of film thickness using polarization-dependent extended x-ray absorption fine structure (EXAFS). All films investigated are phase-pure and of high quality with a sharp interface between MnSi and Si. The investigated MnSi films are in a thickness regime where the magnetic transition temperature $T_\mathrm{c}$ assumes a thickness-independent enhanced value of $\geq$43~K as compared with that of bulk MnSi, where $T_\mathrm{c} \approx 29~{\rm K}$. A detailed refinement of the EXAFS data reveals that the Mn positions are unchanged, whereas the Si positions vary along the out-of-plane [111]-direction, alternating in orientation from unit cell to unit cell. Thus, for thick MnSi films, the unit cell volume is essentially that of bulk MnSi --- except in the vicinity of the interface with the Si substrate (thin film limit). In view of the enhanced magnetic transition temperature we conclude that the mere presence of the interface, and its specific characteristics, strongly affects the magnetic properties of the entire MnSi film, even far from the interface. Our analysis provides invaluable information about the local strain at the MnSi/Si(111) interface. The presented methodology of polarization dependent EXAFS can also be employed to investigate the local structure of other interesting interfaces., Comment: 11 pages, 10 figures
- Published
- 2016
- Full Text
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28. Dependence of spin pumping and spin transfer torque upon Ni81Fe19 thickness in Ta/Ag/Ni81Fe19/Ag/Co2MnGe/Ag/Ta spin-valve structures
- Author
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Durrant, CJ, Shelford, LR, Valkass, RAJ, Hicken, RJ, Figueroa, AI, Baker, AA, Van Der Laan, G, Duffy, LB, Shafer, P, Klewe, C, Arenholz, E, Cavill, SA, Childress, JR, and Katine, JA
- Abstract
Spin pumping has been studied within Ta / Ag / Ni81Fe19 (0-5 nm) / Ag (6 nm) / Co2MnGe (5 nm) / Ag / Ta large-area spin-valve structures, and the transverse spin current absorption of Ni81Fe19 sink layers of different thicknesses has been explored. In some circumstances, the spin current absorption can be inferred from the modification of the Co2MnGe source layer damping in vector network analyzer ferromagnetic resonance (VNA-FMR) experiments. However, the spin current absorption is more accurately determined from element-specific phase-resolved x-ray ferromagnetic resonance (XFMR) measurements that directly probe the spin transfer torque (STT) acting on the sink layer at the source layer resonance. Comparison with a macrospin model allows the real part of the effective spin mixing conductance to be extracted. We find that spin current absorption in the outer Ta layers has a significant impact, while sink layers with thicknesses of less than 0.6 nm are found to be discontinuous and superparamagnetic at room temperature, and lead to a noticeable increase of the source layer damping. For the thickest 5-nm sink layer, increased spin current absorption is found to coincide with a reduction of the zero frequency FMR linewidth that we attribute to improved interface quality. This study shows that the transverse spin current absorption does not follow a universal dependence upon sink layer thickness but instead the structural quality of the sink layer plays a crucial role.
- Published
- 2017
29. Aerotoxic syndrome: A new occupational disease caused by contaminated cabin air?
- Author
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Hageman, G., primary, Mackenzie Ross, S.J., additional, Nihom, J., additional, and van der Laan, G., additional
- Published
- 2022
- Full Text
- View/download PDF
30. Resonant Elastic X-ray Scattering from the Skyrmion Lattice in Cu$_{2}$OSeO$_{3}$
- Author
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Zhang, S. L., Bauer, A., Berger, H., Pfleiderer, C., van der Laan, G., and Hesjedal, T.
- Subjects
Condensed Matter - Materials Science - Abstract
We report the study of the skyrmion state near the surface of Cu$_2$OSeO$_3$ using soft resonant elastic x-ray scattering (REXS) at the Cu $L_3$ edge. Within the lateral sampling area of $200 \times 200$ $\mu$m$^2$, we found a long-range-ordered skyrmion lattice phase as well as the formation of skyrmion domains via the multiple splitting of the diffraction spots. In a recent REXS study of the skyrmion phase of Cu$_2$OSeO$_3$ [Phys. Rev. Lett. 112, 167202 (2014)], Langner et al. reported the observation of the unexpected existence of two distinct skyrmion sublattices that arise from inequivalent Cu sites, and that the rotation and superposition of the two periodic structures leads to a moir\'{e} pattern. However, we find no energy splitting of the Cu peak in x-ray absorption measurements and, instead, discuss alternative origins of the peak splitting. In particular, we find that for magnetic field directions deviating from the major cubic axes, a multidomain skyrmion lattice state is obtained, which consistently explains the splitting of the magnetic spots into two - and more - peaks., Comment: 6 pages, 3 figures
- Published
- 2016
- Full Text
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31. Multidomain Skyrmion Lattice State in Cu$_2$OSeO$_3$
- Author
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Zhang, S. L., Bauer, A., Burn, D. M., Milde, P., Neuber, E., Eng, L. M., Berger, H., Pfleiderer, C., van der Laan, G., and Hesjedal, T.
- Subjects
Condensed Matter - Materials Science - Abstract
Magnetic skyrmions in chiral magnets are nanoscale, topologically-protected magnetization swirls that are promising candidates for spintronics memory carriers. Therefore, observing and manipulating the skyrmion state on the surface level of the materials are of great importance for future applications. Here, we report a controlled way of creating a multidomain skyrmion state near the surface of a Cu$_{2}$OSeO$_{3}$ single crystal, observed by soft resonant elastic x-ray scattering. This technique is an ideal tool to probe the magnetic order at the $L_{3}$ edge of $3d$ metal compounds giving a depth sensitivity of ${\sim}50$ nm. The single-domain sixfold-symmetric skyrmion lattice can be broken up into domains overcoming the propagation directions imposed by the cubic anisotropy by applying the magnetic field in directions deviating from the major cubic axes. Our findings open the door to a new way to manipulate and engineer the skyrmion state locally on the surface, or on the level of individual skyrmions, which will enable applications in the future., Comment: 19 pages, 5 figures
- Published
- 2016
- Full Text
- View/download PDF
32. XMCD and XMCD-PEEM Studies on Magnetic-Field-Assisted Self-Assembled 1D Nanochains of Spherical Ferrite Particles
- Author
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Zhang, W, Wong, PKJ, Zhang, D, Yue, J, Kou, Z, van der Laan, G, Scholl, A, Zheng, JG, Lu, Z, and Zhai, Y
- Subjects
Materials ,Chemical Sciences ,Engineering ,Physical Sciences - Abstract
Quasi-1D nanochains of spherical magnetic ferrite particles with a homogeneous particle size of ≈200 nm and a micrometer-sized chain length are fabricated via a self-assembly method under an external magnetic field. This assisting magnetic field (Hassist), applied during synthesis, significantly modifies the distribution of the Fe2+Oh, Fe3+Td, and Fe3+Oh cations in the chains, as demonstrated by X-ray magnetic circular dichroism (XMCD) combined with theoretical analysis. This provides direct evidence of the nontrivial role of external synthetic conditions for defining the crystal chemistry of nanoscale ferrites and in turn their magnetic properties, providing an extra degree of freedom for intentional control over the performances of 1D magnetic nanodevices for various applications. Magnetic imaging, performed via XMCD in photoemission electron microscopy, further shows the possibility of creating and trapping a series of adjacent magnetic domain walls in a single chain, suggesting that there is great application potential for these nanochains in 1D magnetic nanodevices, as determined by field- or current-driven domain wall motions. Practical control over the magnetic properties of the nanochains is also achieved by extrinsic dopants of cobalt and zinc, which are observed to occupy the ferrite ionic sites in a selective manner.
- Published
- 2017
33. Direct detection of pure spin-current by x-ray pump-probe measurements
- Author
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Li, J., Shelford, L. R., Shafer, P., Tan, A., Deng, J. X., Keatley, P. S., Hwang, C., Arenholz, E., van der Laan, G., Hicken, R. J., and Qiu, Z. Q.
- Subjects
Condensed Matter - Materials Science - Abstract
By synchronizing a microwave waveform with the synchrotron x-ray pulses, we use the ferromagnetic resonance (FMR) of the Py (Ni81Fe19) layer in a Py/Cu/Cu75Mn25/Cu/Co multilayer to pump a pure spin current into the Cu75Mn25 spacer layer, and then directly probe the spin current in the Cu75Mn25 layer by a time-resolved x-ray magnetic circular dichroism (XMCD). This element-specific pump-probe measurement unambiguously identifies the AC spin current in the Cu75Mn25 layer. In addition, phase resolved x-ray measurements reveal a characteristic bipolar phase behavior of the Co spins that is a fingerprint of spin-current driven spin precession.
- Published
- 2015
- Full Text
- View/download PDF
34. Direct Detection of Pure ac Spin Current by X-Ray Pump-Probe Measurements
- Author
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Li, J, Shelford, LR, Shafer, P, Tan, A, Deng, JX, Keatley, PS, Hwang, C, Arenholz, E, van der Laan, G, Hicken, RJ, and Qiu, ZQ
- Subjects
cond-mat.mtrl-sci ,Mathematical Sciences ,Physical Sciences ,Engineering ,General Physics - Abstract
Despite recent progress in spin-current research, the detection of spin current has mostly remained indirect. By synchronizing a microwave waveform with synchrotron x-ray pulses, we use the ferromagnetic resonance of the Py (Ni_{81}Fe_{19}) layer in a Py/Cu/Cu_{75}Mn_{25}/Cu/Co multilayer to pump a pure ac spin current into the Cu_{75}Mn_{25} and Co layers, and then directly probe the spin current within the Cu_{75}Mn_{25} layer and the spin dynamics of the Co layer by x-ray magnetic circular dichroism. This element-resolved pump-probe measurement unambiguously identifies the ac spin current in the Cu_{75}Mn_{25} layer.
- Published
- 2016
35. Templates for magnetic symmetry and altermagnetism in hexagonal MnTe
- Author
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Lovesey, S. W., primary, Khalyavin, D. D., additional, and van der Laan, G., additional
- Published
- 2023
- Full Text
- View/download PDF
36. Periodically modulated skyrmion strings in Cu2OSeO3
- Author
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Burn, D. M., Brearton, R., Ran, K. J., Zhang, S. L., van der Laan, G., and Hesjedal, T.
- Published
- 2021
- Full Text
- View/download PDF
37. Deriving the skyrmion Hall angle from skyrmion lattice dynamics
- Author
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Brearton, R., Turnbull, L. A., Verezhak, J. A. T., Balakrishnan, G., Hatton, P. D., van der Laan, G., and Hesjedal, T.
- Published
- 2021
- Full Text
- View/download PDF
38. Oxidation and crystal field effects in uranium
- Author
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Tobin, JG, Yu, SW, Booth, CH, Tyliszczak, T, Shuh, DK, Van Der Laan, G, Sokaras, D, Nordlund, D, Weng, TC, and Bagus, PS
- Subjects
Fluids & Plasmas ,Physical Sciences ,Chemical Sciences ,Engineering - Abstract
An extensive investigation of oxidation in uranium has been pursued. This includes the utilization of soft x-ray absorption spectroscopy, hard x-ray absorption near-edge structure, resonant (hard) x-ray emission spectroscopy, cluster calculations, and a branching ratio analysis founded on atomic theory. The samples utilized were uranium dioxide (UO2), uranium trioxide (UO3), and uranium tetrafluoride (UF4). A discussion of the role of nonspherical perturbations, i.e., crystal or ligand field effects, will be presented.
- Published
- 2015
39. Identifying the electronic character and role of the Mn states in the valence band of (Ga,Mn)As
- Author
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Fujii, J., Salles, B. R., Sperl, M., Ueda, S., Kobata, M., Kobayashi, K., Yamashita, Y., Torelli, P., Utz, M., Fadley, C. S., Gray, A. X., Minar, J., Braun, J., Ebert, H., Di Marco, I., Eriksson, O., Thunström, P., Fecher, G. H., Ouardi, S., Stryhanyuk, H., Ikenaga, E., Back, C. H., van der Laan, G., and Panaccione, G.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We report high-resolution hard x-ray photoemission spectroscopy results on (Ga,Mn)As films as a function of Mn doping. Supported by theoretical calculations we identify, over the entire 1% to 13% Mn doping range, the electronic character of the states near the top of the valence band. Magnetization and temperature dependent core-level photoemission spectra reveal how the delocalized character of the Mn states enables the bulk ferromagnetic properties of (Ga,Mn)As., Comment: prl submitted
- Published
- 2013
- Full Text
- View/download PDF
40. Magnetostrictive thin films for microwave spintronics
- Author
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Parkes, D. E., Shelford, L. R., Wadley, P., Holý, V., Wang, M., Hindmarch, A. T., van der Laan, G., Campion, R. P., Edmonds, K. W., Cavill, S. A., and Rushforth, A. W.
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
Multiferroic composite materials, consisting of coupled ferromagnetic and piezoelectric phases, are of great importance in the drive towards creating faster, smaller and more energy efficient devices for information and communications technologies. Such devices require thin ferromagnetic films with large magnetostriction and narrow microwave resonance linewidths. Both properties are often degraded, compared to bulk materials, due to structural imperfections and interface effects in the thin films. We report the development of single crystal thin films of Galfenol (Fe81Ga19) with magnetostriction as large as the best reported values for bulk material. This allows the magnetic anisotropy and microwave resonant frequency to be tuned by voltage-induced strain, with a larger magnetoelectric response and a narrower linewidth than any previously reported Galfenol thin films. The combination of these properties make the single crystal thin films excellent candidates for developing tunable devices for magnetic information storage, processing and microwave communications.
- Published
- 2013
41. Absence of spin-mixed states in ferrimagnet Yttrium iron garnet.
- Author
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Cheshire, D., Bencok, P., Gianolio, D., Cibin, G., Lazarov, V. K., van der Laan, G., and Cavill, S. A.
- Subjects
YTTRIUM iron garnet ,MAGNETIC circular dichroism ,NUCLEAR magnetic resonance spectroscopy ,FERROMAGNETIC resonance ,SPIN-orbit interactions ,INSULATING materials - Abstract
The spectroscopic g-factor of epitaxial thin film Yttrium Iron Garnet (YIG) has been studied using a combination of ferromagnetic resonance spectroscopy and x-ray magnetic circular dichroism. The values obtained by the two techniques are found, within experimental error, to be in agreement using Kittel's original derivation for the g-factor. For an insulating material with an entirely Fe
3+ configuration, a spin mixing correction to Kittel's derivation of the spectroscopic g-factor, as recently shown by Shaw et al. [Phys. Rev. Lett. 127, 207201 (2021)] for metallic systems, is not required and demonstrates that the spin mixing parameter is small in YIG due to negligible spin–orbit coupling. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
42. Magnetization reversal processes in ErFe2/YFe2 exchange spring multilayer studied by xray magnetic circular dichroism
- Author
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Stenning, G. B. G., Buckingham, A. R., Bowden, G. J., Ward, R. C. C., van der Laan, G., Shelford, L. R., Maccherozzi, F., Dhesi, S. S., and de Groot, P. A. J.
- Subjects
Condensed Matter - Materials Science - Abstract
X-ray magnetic circular dichroism at the Er M4,5 edge is used to study the switching behavior of the hard ErFe2 layers in an epitaxial [ErFe2(70{\AA})/YFe2 (150{\AA})]{\times}25 exchange-spring superlattice. Magnetic hysteresis loops for the Er magnetization, at temperatures T < 200 K, reveal a switching behavior with a single type of irreversible switch corresponding to vertical exchange spring states. Experiments at T > 200 K reveal a crossover to a regime with two types of switching processes. Computational modelling for this system gives a semi-quantitative agreement with the experiment and reveals that the observed high temperature switching behavior is due to a spin-flop like reorientation transition. In contrast to conventional spin-flop transitions in antiferromagnets, in this exchange spring system the increase in anisotropy energy of the hard magnetic layers is overcome by the decrease in Zeeman energy of the soft layers. Computational studies also reveal the presence of transitions between vertical exchange spring and spin-flop states with a first-order character as well as continuous transitions between these states., Comment: 10 Pages 5 Figures
- Published
- 2011
43. RASOR: An advanced instrument for soft x-ray reflectivity and diffraction
- Author
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Beale, T. A. W., Hase, T. P. A., Iida, T., Endo, K., Steadman, P., Marshall, A. R., Dhesi, S. S., van der Laan, G., and Hatton, P. D.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Physics - Instrumentation and Detectors - Abstract
We report the design and construction of a novel soft x-ray diffractometer installed at Diamond Light Source. The beamline endstation RASOR is constructed for general users and designed primarily for the study of single crystal diffraction and thin film reflectivity. The instrument is comprised of a limited three circle ({\theta}, 2{\theta}, {\chi}) diffractometer with an additional removable rotation ({\phi}) stage. It is equipped with a liquid helium cryostat, and post-scatter polarization analysis. Motorised motions are provided for the precise positioning of the sample onto the diffractometer centre of rotation, and for positioning the centre of rotation onto the x-ray beam. The functions of the instrument have been tested at Diamond Light Source, and initial test measurements are provided, demonstrating the potential of the instrument., Comment: 10 pages, 9 figures
- Published
- 2010
- Full Text
- View/download PDF
44. Element-resolved orbital polarization in (III,Mn)As ferromagnetic semiconductors from $K$ edge x-ray magnetic circular dichroism
- Author
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Wadley, P., Freeman, A. A., Edmonds, K. W., van der Laan, G., Chauhan, J. S., Campion, R. P., Rushforth, A. W., Gallagher, B. L., Foxon, C. T., Wilhelm, F., Smekhova, A. G., and Rogalev, A.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
Using x-ray magnetic circular dichroism (XMCD), we determine the element-specific character and polarization of unoccupied states near the Fermi level in (Ga,Mn)As and (In,Ga,Mn)As thin films. The XMCD at the As K absorption edge consists of a single peak located on the low-energy side of the edge, which increases with the concentration of ferromagnetic Mn moments. The XMCD at the Mn K edge is more detailed and is strongly concentration-dependent, which is interpreted as a signature of hole localization for low Mn doping. The results indicate a markedly different character of the polarized holes in low-doped insulating and high-doped metallic films, with a transfer of the hole orbital magnetic moment from Mn to As sites on crossing the metal-insulator transition., Comment: 5 figures, to be published in Physical Review B
- Published
- 2010
- Full Text
- View/download PDF
45. 5d-5f Electric-multipole Transitions in Uranium Dioxide Probed by Non-resonant Inelastic X-ray Scattering
- Author
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Caciuffo, R., van der Laan, G., Simonelli, L., Vitova, T., Mazzoli, C., Denecke, M. A., and Lander, G. H.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Physics - Atomic Physics - Abstract
Non-resonant inelastic x ray scattering (NIXS) experiments have been performed to probe the 5d-5f electronic transitions at the uranium O(4,5) absorption edges in uranium dioxide. For small values of the scattering vector q, the spectra are dominated by dipole-allowed transitions encapsulated within the giant resonance, whereas for higher values of q the multipolar transitions of rank 3 and 5 give rise to strong and well-defined multiplet structure in the pre-edge region. The origin of the observed non-dipole multiplet structures is explained on the basis of many-electron atomic spectral calculations. The results obtained demonstrate the high potential of NIXS as a bulk-sensitive technique for the characterization of the electronic properties of actinide materials., Comment: Submitted to Physical Review Letters on 31 December 2009
- Published
- 2010
- Full Text
- View/download PDF
46. Exchange bias of a ferromagnetic semiconductor by a ferromagnetic metal
- Author
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Olejnik, K., Wadley, P., Haigh, J. A, Edmonds, K. W., Campion, R. P., Rushforth, A. W., Gallagher, B. L., Foxon, C. T., Jungwirth, T., Wunderlich, J., Dhesi, S. S., Cavill, S., van der Laan, G., and Arenholz, E
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
We demonstrate an exchange bias in (Ga,Mn)As induced by antiferromagnetic coupling to a thin overlayer of Fe. Bias fields of up to 240 Oe are observed. Using element-specific x-ray magnetic circular dichroism measurements, we distinguish a strongly exchange coupled (Ga,Mn)As interface layer in addition to the biassed bulk of the (Ga,Mn)As film. The interface layer remains polarized at room temperature., Comment: 3 figures, submitted to Physical Review B
- Published
- 2010
- Full Text
- View/download PDF
47. Magnetic structure of RuO2 in view of altermagnetism
- Author
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Lovesey, S. W., primary, Khalyavin, D. D., additional, and van der Laan, G., additional
- Published
- 2023
- Full Text
- View/download PDF
48. Anisotropic hybridization probed by polarization dependent x-ray absorption spectroscopy in VI3 van der Waals Mott ferromagnet
- Author
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Sant, R, primary, De Vita, A, additional, Polewczyk, V, additional, Pierantozzi, G M, additional, Mazzola, F, additional, Vinai, G, additional, van der Laan, G, additional, Panaccione, G, additional, and Brookes, N B, additional
- Published
- 2023
- Full Text
- View/download PDF
49. Magnetic structure of actinide metals
- Author
-
van der Laan, G. and Moore, K. T.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
In comparison to 3d or 4f metals, magnetism in actinides remains poorly understood due to experimental complications and the exotic behavior of the 5f states. In particular, plutonium metal is most especially vexing. Over the last five decades theories proposed the presence of either ordered or disordered local moments at low temperatures. However, experiments such as magnetic susceptibility, electrical resistivity, nuclear magnetic resonance, specific heat, and elastic and inelastic neutron scattering show no evidence for ordered or disordered magnetic moments in any of the six phases of plutonium. Beyond plutonium, the magnetic structure of other actinides is an active area of research given that temperature, pressure, and chemistry can quickly alter the magnetic structure of the 5f states. For instance, curium metal has an exceedingly large spin polarization that results in a total moment of about 8 Bohr magneton/atom, which influences the phase stability of the metal. Insight in the actinide ground state can be obtained from core-level x-ray absorption spectroscopy (XAS) and electron energy-loss spectroscopy (EELS). A sum rule relates the branching ratio of the core-level spectra measured by XAS or EELS to the expectation value of the angular part of the spin-orbit interaction., Comment: 32 pages, 8 figs, Mittelwihr 2008, Magnetism and Synchrotron Radiation
- Published
- 2008
50. Determination of the single-ion anisotropy energy in a S = 5/2 kagome antiferromagnet using X-ray absorption spectroscopy
- Author
-
de Vries, M. A., Johal, T. K., Mirone, A., Claydon, J. S., Nilsen, G. J., Ronnow, H. M., van der Laan, G., and Harrison, A.
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
We report x-ray absorption and x-ray linear dichroism measurements at the Fe L2,3 edges of the geometrically frustrated systems of potassium and hydronium iron jarosite. Comparison with simulated spectra, involving ligand-field multiplet calculations modelling the 3d-2p hybridization between the iron ion and the oxygen ligands, has yielded accurate estimates for the ligand metal-ion hybridization and the resulting single-ion crystal field anisotropy energy. Using this method we provide an experimentally verified scenario for the appearance of a single-ion anisotropy in this nominally high-spin 3d5 orbital singlet 6S system, which accounts for features of the spin-wave dispersion in the long-range ordered ground state of potassium iron jarosite., Comment: minor changes in text, captions and table 1. Accepted for publication in Phys. Rev. B
- Published
- 2008
- Full Text
- View/download PDF
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