Real-space observation of fluctuating antiferromagnetic domains

Magnetic domains play a fundamental role in physics of magnetism and its technological applications. Dynamics of antiferromagnetic domains is poorly understood, although antiferromagnets are expected to be extensively used in future electronic devices wherein it determines the stability and operational speed. Dynamics of antiferromagnets also features prominently in the studies of topological quantum matter. Real-space imaging of fluctuating antiferromagnetic domains is therefore highly desired but has never been demonstrated. We use coherent x-ray diffraction to obtain videos of fluctuating micrometer-scale antiferromagnetic domains in Ni2MnTeO6 on time scales from 10-1 to 103 s. In the collinear phase, thermally activated domain wall motion is observed in the vicinity of the Néel temperature. Unexpectedly, the fluctuations persist through the full range of the higher-temperature helical phase. These observations illustrate the high potential significance of the dynamic domain imaging in phase transition studies and in magnetic device research

Seeing is believing: visualization of antiferromagnetic domains

Understanding and utilizing novel antiferromagnetic (AFM) materials has been recently one of the central issues in condensed matter physics, as well as in materials science and engineering. The relevant contemporary topics include multiferroicity, topological magnetism and AFM spintronics. The ability to image magnetic domains in AFM materials is of key importance for the success of these exciting fields. While imaging techniques of magnetic domains on the surfaces of ferro-(ferri)magnetic materials with, for example, magneto-optical Kerr microscopy and magnetic force microscopy have been available for a number of decades, AFM domain imaging is a relatively new development. We review various experimental techniques utilizing scanning, optical, and synchrotron X-ray probes to visualize AFM domains and domain walls, and to unveil their physical properties. We also discuss the existing challenges and opportunities in these techniques, especially with further increase of spatial and temporal resolution.ISSN:2397-464

Incommensurate Structural Correlations in the Disordered Spin-Dimer State Induced by X-Ray and Electron Irradiation in CuIr₂S₄

Irradiation with ~10keV x rays or medium-energy electrons destroys long-range order of Ir spin dimers in CuIr2S4 while preserving the dimers locally. We find that as the order is destroyed, a new type of incommensurate structural correlations appears. This represents an intriguing example of order from disorder phenomenon, in which a previously unknown incommensurate order appears in the radiation-induced disordered state. These results suggest that two competing instabilities, one of which can be suppressed by radiation, are present in the system. Otherwise unrealized structural or electronic states can, therefore, be revealed in correlated systems by x-ray or electron irradiation

Noncollinear magnetic order, in-plane anisotropy, and magnetoelectric coupling in the pyroelectric honeycomb antiferromagnet Ni2Mo3 O8

©2023 American Physical Society. Ni2Mo3O8 is a pyroelectric honeycomb antiferromagnet exhibiting peculiar changes in its electric polarization at magnetic transitions. Ni2Mo3O8 stands out from isostructural magnetic compounds, showing an anomalously low magnetic transition temperature and unique magnetic anisotropy. We determine the magnetic structure of Ni2Mo3O8 utilizing high-resolution powder and single-crystal neutron diffraction. A noncollinear stripy antiferromagnetic order is found in the honeycomb planes. The magnetic space group is PCna21. The in-plane magnetic connection is of the stripy type for both the ab-plane and c-axis spin components. This is a simpler connection than the one proposed previously. The ferromagnetic interlayer order of the c-axis spin components in our model is also distinct. The magnetic anisotropy of Ni2Mo3O8 is characterized by orientation-dependent magnetic susceptibility measurements on a single crystal, consistent with neutron diffraction analysis. The local magnetoelectric tensor analysis using our magnetic models provides insights into its magnetoelectric coupling and polarization. Thus, our results deliver essential information for understanding both the unusual magnetoelectric properties of Ni2Mo3O8 and the prospects for observing exotic nonreciprocal, Hall, and magnonic effects characteristic of this compound family. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.11Nscopu

Metal-Insulator Transition in CuIr2S4: XAS Results on the Electronic Structure

S K and Ir L3 x-ray absorption measurements across the temperature-induced metal (M) to insulator (I) transition in Culr2S4 are presented. Dramatic S K-edge changes reflect the Ir d-electronic state redistribution across this transition. These changes, along with a detailed consideration of the I-phase structure, motivate a model in which the I-phase stabilization involves an interplay of charge and d-orbital orientation ordering along Ir chains, a quadrupling of the Ir-chain repeat unit, and correlated dimer spin-singlet formation

Spin-phonon interactions and magnetoelectric coupling in Co4 B 2 O9 (B = Nb, Ta)

In order to explore the consequences of spin-orbit coupling on spin-phonon interactions in a set of chemically similar mixed metal oxides, we measured the infrared vibrational properties of Co 4 B 2 O9 (B = Nb, Ta) as a function of temperature and compared our findings with lattice dynamics calculations and several different models of spin-phonon coupling. Frequency vs temperature trends for the Co2+ shearing mode near 150 cm−1 reveal significant shifts across the magnetic ordering temperature that are especially large in relative terms. Bringing these results together and accounting for noncollinearity, we obtain spin-phonon coupling constants of −3.4 and −4.3 cm−1 for Co4Nb2O9 and the Ta analog, respectively. Analysis reveals that these coupling constants are derived from interlayer (rather than intralayer) exchange interactions and that the interlayer interactions contain competing antiferromagnetic and ferromagnetic contributions. At the same time, beyond-Heisenberg terms are minimized due to fortuitous symmetry considerations, different from most other 4d- and 5d-containing oxides. Comparison with other contemporary oxides shows that spin-phonon coupling in this family of materials is among the strongest ever reported, suggesting an origin for magnetoelectric coupling. © 2023 Author(s).11Nsciescopu

Formation of isomorphic Ir3+ and Ir4+ octamers and spin dimerization in the spinel CuIr2S4.

Inorganic compounds with the AB2X4 spinel structure have been studied for many years, because of their unusual physical properties. The spinel crystallographic structure, first solved by Bragg in 1915, has cations occupying both tetrahedral (A) and octahedral (B) sites. Interesting physics arises when the B-site cations become mixed in valence. Magnetite (Fe3O4) is a classic and still unresolved example, where the tendency to form ordered arrays of Fe2+ and Fe3+ ions competes with the topological frustration of the B-site network. The CuIr2S4 thiospinel is another example, well known for the presence of a metal-insulator transition at 230 K with an abrupt decrease of the electrical conductivity on cooling accompanied by the loss of localized magnetic moments. Here, we report the determination of the crystallographic structure of CuIr2S4 below the metal-insulator transition. Our results indicate that CuIr2S4 undergoes a simultaneous charge-ordering and spin-dimerization transition-a rare phenomenon in three-dimensional compounds. Remarkably, the charge-ordering pattern consists of isomorphic octamers of Ir83+S24 and Ir84+S24 (as isovalent bi-capped hexagonal rings). This extraordinary arrangement leads to an elegant description of the spinel structure, but represents an increase in complexity with respect to all the known charge-ordered structures, which are typically based on stripes, slabs or chequerboard patterns