Non-equilibrium hysteresis and spin relaxation in the mixed-anisotropy dipolar coupled spin-glass LiHo$_{0.5}$Er$_{0.5}$F$_{4}$

TL;DR

This study investigates the microscopic spin dynamics and hysteresis behavior in the dipolar-coupled spin-glass LiHo$_{0.5}$Er$_{0.5}$F$_4$ at sub-Kelvin temperatures using multiple experimental techniques and simulations.

Contribution

It combines experimental measurements with mean-field simulations to reveal the microscopic mechanisms driving hysteresis and avalanches in a mixed-anisotropy spin-glass.

Findings

Avalanche driven by Zeeman energy release heats the sample.

Hysteresis involves a depletion of intermediate cluster sizes.

Microscopic spin reconfiguration tracked via SANS and simulations.

Abstract

We present a study of the model spin-glass LiHo$_{0.5}$Er$_{0.5}$F$_4$ using simultaneous AC susceptibility, magnetization and magnetocaloric effect measurements along with small angle neutron scattering (SANS) at sub-Kelvin temperatures. All measured bulk quantities reveal hysteretic behavior when the field is applied along the crystallographic c axis. Furthermore avalanche-like relaxation is observed in a static field after ramping from the zero-field-cooled state up to $200 - 300$ Oe. SANS measurements are employed to track the microscopic spin reconfiguration throughout both the hysteresis loop and the related relaxation. Comparing the SANS data to inhomogeneous mean-field calculations performed on a box of one million unit cells provides a real-space picture of the spin configuration. We discover that the avalanche is being driven by released Zeeman energy, which heats the sample and creates positive feedback, continuing the avalanche. The combination of SANS and mean-field simulations reveal that the conventional distribution of cluster sizes is replaced by one with a depletion of intermediate cluster sizes for much of the hysteresis loop.