Spin Textures induced by Quenched Disorder in a Reentrant Spin Glass: Vortices versus "Frustrated" Skyrmions

TL;DR

This study investigates vortex-like spin textures in reentrant spin glasses, revealing their disordered nature, internal structure, and how they can be controlled by magnetic field and composition, offering new insights into quenched disorder effects.

Contribution

It provides the first detailed characterization of vortex textures in reentrant spin glasses, distinguishing them from skyrmions and demonstrating control over their properties.

Findings

Spin textures are randomly distributed and vary with magnetic field.

Vortex internal structure is strongly distorted and differs from skyrmions.

Vortex size and number can be independently tuned by field and composition.

Abstract

Reentrant spin glasses are frustrated disordered ferromagnets developing vortex-like textures under an applied magnetic field. Our study of a Ni$_{0.81}$Mn$_{0.19}$ single crystal by small angle neutron scattering clarifies their internal structure and shows that these textures are randomly distributed. Spin components transverse to the magnetic field rotate over length scales of 3-15 nm in the explored field range, decreasing as field increases according to a scaling law. Monte-Carlo simulations reveal that the internal structure of the vortices is strongly distorted and differs from that assumed for "frustrated" skyrmions, built upon a competition between symmetric exchange interactions. Isolated vortices have small non-integer topological charge. The vortices keep an anisotropic shape on a 3 dimensional lattice, recalling "croutons" in a "ferromagnetic soup". Their size and number can be tuned independently by the magnetic field and concentration x (or heat treatment), respectively. This opens an original route to understand and control the influence of quenched disorder in systems hosting non trivial spin textures.