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Register a new userSpin-orbit coupling control of anisotropy, ground state and frustration in 5d2 Sr2MgOsO6
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The influence of spin-orbit coupling (SOC) on the physical properties of the 5d2 system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d2 system of 0.60(2) muB - a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the size of the local moment in this compound. Through comparison to Sr2ScOsO6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d2 systems relative to their 5d3 counterparts, providing an explanation of the high TN found in Sr2MgOsO6.
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Magnetic anisotropy (MA) is one of the most important material properties for modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e. magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry. Extrinsic control over the MA is usually achieved by introducing shape anisotropy or exchange bias from another magnetically ordered material. Here we demonstrate a pathway to manipulate MA of 3d transition metal oxides (TMOs) by digitally inserting non-magnetic 5d TMOs with pronounced spin-orbit coupling (SOC). High quality superlattices comprised of ferromagnetic La2/3Sr1/3MnO3 (LSMO) and paramagnetic SrIrO3 (SIO) are synthesized with the precise control of thickness at atomic scale. Magnetic easy axis reorientation is observed by controlling the dimensionality of SIO, mediated through the emergence of a novel spin-orbit state within the nominally paramagnetic SIO.
We report neutron scattering experiments which reveal a large spin gap in the magnetic excitation spectrum of weakly-monoclinic double perovskite Sr2ScOsO6. The spin gap is demonstrative of appreciable spin-orbit-induced anisotropy, despite nominally orbitally-quenched 5d3 Os5+ ions. The system is successfully modeled including nearest neighbor interactions in a Heisenberg Hamiltonian with exchange anisotropy. We find that the presence of the spin-orbit-induced anisotropy is essential for the realization of the type I antiferromagnetic ground state. This demonstrates that physics beyond the LS or JJ coupling limits plays an active role in determining the collective properties of 4d3 and 5d3 systems, and that theoretical treatments must include spin-orbit coupling.
The intertwined charge, spin, orbital, and lattice degrees of freedom could endow 5d compounds with exotic properties. Current interest is focused on electromagnetic interactions in these materials, whereas the important role of lattice geometry remains to be fully recognized. For this sake, we investigate pressure-induced phase transitions in the spin-orbit Mott insulator Sr3Ir2O7 with Raman, electrical resistance, and x-ray diffraction measurements. We reveal an interesting magnetic transition coinciding with a structural transition at 14.4 GPa, but without a concurrent insulator-metal transition. The conventional correlation between magnetic and Mott insulating states is thereby absent. The observed softening of the one-magnon mode can be explained by a reduced tetragonal distortion, while the actual magnetic transition is associated with tilting of the IrO6 octahedra. This work highlights the critical role of lattice frustration in determining the high-pressure phases of Sr3Ir2O7. The ability to control electromagnetic properties via manipulating the crystal structure with pressure promises a new way to explore new quantum states in spin-orbit Mott insulators.
The electronic ground state of Ca3LiOsO6 was recently considered within an intermediate coupling regime that revealed J=3/2 spin-orbit entangled magnetic moments. Through inelastic neutron scattering and density functional theory we investigate the magnetic interactions and probe how the magnetism is influenced by the change in hierarchy of interactions as we move from Ca3LiOsO6 (5d3) to Ca3LiRuO6 (4d3). An alteration of the spin-gap and ordered local moment is observed, however the magnetic structure, Neel temperature and exchange interactions are unaltered. To explain this behavior it is necessary to include both spin-orbit coupling and hybridization, indicating the importance of an intermediate coupling approach when describing 5$d$ oxides.
X-ray scattering by multiferroic LuFe2O4 is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to (1/3,1/3,3/2). The corresponding charge configuration, also found by electronic structure calculations as most stable, contains polar Fe/O double-layers with antiferroelectric stacking. Diffuse scattering at 360 K, with (1/3,1/3,0) propagation, indicates ferroelectric short-range correlations between neighboring double-layers. The temperature dependence of the incommensuration indicates that charge order and magnetism are coupled.
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