Ezana Negusse | Searcharxiv

arXiv2026

Cr3+ spin dynamics under the octahedral crystal field in van der Waals antiferromagnets

The magnetic moment in van der Waals (vdW) materials containing 3d transition metals originates from unpaired d-electron spins and their interaction with surrounding ligands. The interplay between exchange interactions and magnetic anisotropy stabilizes long-range ordering of such moments. The compound CuCrP2S6 (CCPS) presents an interesting class of vdW solids where the coupling of Cr3+ moments and ordering of Cu1+ ions give rise to a multiferroic ground state. Here we investigate the spin dynamics of Cr3+ ions in CCPS through magnetization and broadband as well as single sub-THz magnetic resonance measurements. The orbital moment of Cr3+ is quenched under the octahedral crystal field of surrounding chalcogen ions, resulting in negligible magnetic anisotropy-a feature common to Cr-based vdW antiferromagnets (AFM). Resonance spectra over a wide frequency-field-temperature range reveal quasi-2D AFM dynamics governed mainly by isotropic Cr-Cr exchange interactions, which determine the magnetic order, spin reorientation, and damping. Sub-THz resonance spectra also uncover a field-induced ferromagnetic polarization, highlighting the universal role of Cr-Cr exchange in layered Cr compounds. Moreover, persistent magnetic correlations far above the Néel temperature (TN ~ 32 K) points to short-range magnetic order in CCPS and motivates future studies of a possible interplay between AFM and antiferroelectric orders. These results establish CCPS as an exemplary system for exploring 2D magnetism and electric-field-tunable spintronic functionalities in layered multiferroics.

cond-mat.mtrl-sci↗

arXiv2022

Magneto-transport and magnetic textures in Ho/FeCoGd/β-W multilayers

The enhancement of interfacial Dzyaloshinskii-Moriya Interaction (DMI) in magnetic multilayers results in the stabilization of topological spin textures like chiral domain walls and skyrmions. Here we report on the evaluation of interface-driven magnetic interactions in a uniquely designed multilayer where each magnetic layer of two AFM coupled sublattices of 3d and 4f moments is sandwiched between the layers of β-tungsten and holmium whose spin Hall angles are large but opposite in sign. The atomic and magnetic periodicity of these multilayers is established by polarized neutron reflectivity measurements and the presence of a labyrinth domain spin texture of zero remanence with x-ray photoelectron microscopy. Measurements of the Hall resistivity (ρ_{xy}(T, H)) together with static magnetization (M(T,H)) over a broad range of temperature (T) and magnetic field (H) indicate impending compensation between 3d and 4f sublattices at T>350 K. These multilayers are characterized by a small (0.04 %) but positive magnetoresistance indicative of interface enhance scattering and a large (40 nΩ.m) and negative anomalous ρ_{xy}(T,H) which results from a parallel alignment of 4f moments with the external magnetic field. No distinct scaling is seen between ρ_{xy}(T,H), ρ_{xx}(T, H) and M(T,H) at temperatures above 200K where the magnetization develops out-of-plane anisotropy. The field scans of ρ_{xy} at T>200K show a distinct cusp in the vicinity of magnetic saturation. These Hall data have been analyzed in the framework of a model where a distinct topological contribution to ρ_{xy} rides over the anomalous Hall resistivities of the 3d and 4f magnetic sublattices. It is suggested that this apparent topological effect results from an interfacial DMI and dominates ρ_{xy}(T,H) in the temperature regime where the 3d and 4f lattices are nearly compensated.

cond-mat.mtrl-sci↗