Field-induced vortex-like textures as a probe of the critical line in reentrant spin glasses

TL;DR

This study investigates vortex-like magnetic defects in reentrant spin glasses using neutron scattering and simulations, revealing their potential to probe phase transitions between different magnetic states.

Contribution

It introduces the observation of vortex-like defects in reentrant spin glasses and demonstrates their evolution with magnetic field and composition, linking defect morphology to phase boundaries.

Findings

Vortex-like defects resemble quasi-bidimensional spin vortices.

Defects decrease in size with increasing magnetic field.

Defects disappear in the true spin glass phase.

Abstract

We study the evolution of the low-temperature field-induced magnetic defects observed under an applied magnetic field in a series of frustrated amorphous ferromagnets (Fe$_{1-x}$Mn$_{x}$)$_{75}$P$_{16}$B$_{3}$Al$_{3}$ (a-FeMn). Combining small-angle neutron scattering and Monte Carlo simulations, we show that the morphology of these defects resemble that of quasi-bidimensional spin vortices. They are observed in the reentrant spin-glass (RSG) phase, up to the critical concentration $x_{\rm C} \approx 0.36$ which separates the RSG and "true" spin glass (SG) within the low temperature part of the magnetic phase diagram of a-FeMn. These vortices systematically decrease in size with increasing magnetic field or decreasing the average exchange interaction, and they finally disappear in the SG sample ($x = 0.41$), being replaced by field-induced correlations over finite length scales. We argue that the study of these nanoscopic defects could be used to probe the nature of the critical line between the RSG and SG phases.