Magnetotransport and magnetic textures in Ho/FeCoGd/ β -W multilayers

Abstract

The enhancement of interfacial Dzyaloshinskii-Moriya Interaction (DMI) in magnetic multilayers results in the stabilization of topological spin textures such as 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 antiferromagnetically coupled sublattices of $3d$ and $4f$ moments is sandwiched between the layers of \ensuremath{\beta}-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 $[{\ensuremath{\rho}}_{xy}(T,H)]$ 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 $T>350\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. These multilayers are characterized by a small (0.04%) but positive magnetoresistance indicative of interface enhanced scattering, and a large (40 n\ensuremath{\Omega} m) and negative anomalous ${\ensuremath{\rho}}_{xy}(T,H)$ which results from a parallel alignment of $4f$ moments with the external magnetic field. No distinct scaling is seen between ${\ensuremath{\rho}}_{xy}(T,H), {\ensuremath{\rho}}_{xx}(T,H)$, and $M$($T, H$) at temperatures above 200 K where the magnetization develops out of plane anisotropy. The field scans of ${\ensuremath{\rho}}_{xy}$ at $T>200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ 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 ${\ensuremath{\rho}}_{xy}$ 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 ${\ensuremath{\rho}}_{xy}(T,H)$ in the temperature regime where the $3d$ and $4f$ lattices are nearly compensated.