Evolution of the spin dynamics during freezing in the spin-glass Fe$_{x}$Cr$_{1-x}$

TL;DR

This study investigates how spin dynamics evolve during the freezing process in Fe$_{x}$Cr$_{1-x}$ spin-glass systems, revealing different relaxation behaviors and dispersive characteristics across various iron concentrations.

Contribution

It provides a detailed analysis of spin relaxation processes in Fe$_{x}$Cr$_{1-x}$, highlighting the persistence of stretched exponential behavior and momentum-dependent relaxation across different regimes.

Findings

Reentrant cluster-glass regime shows stretched exponential relaxation up to high temperatures.

Superparamagnetic regime exhibits a single relaxation time at elevated temperatures.

Spin relaxation displays a power-law momentum dependence, indicating dispersive behavior.

Abstract

In the iron--chromium system, Fe$_{x}$Cr$_{1-x}$, a wide dome of spin-glass behavior emerges when the ferromagnetism of iron is suppressed and the antiferromagnetism of chromium emerges as a function of increasing iron content $x$. As both, the high-temperature state and the characteristic cluster size vary as a function of $x$, different regimes of spin-glass behavior may be compared in a single, isostructural material system. Here, we report a study of the spin dynamics across the freezing process into the spin-glass state for different iron concentrations ($x = 0.145$, $0.175$, $0.21$) using Modulation of IntEnsity with Zero Effort (MIEZE) spectroscopy. In the parameter range studied, the relaxation process observed experimentally may be described well in terms of a stretched exponential. In the reentrant cluster-glass regime, $x = 0.145$, this behavior persists up to high temperatures. In comparison, in the superparamagnetic regime, $x = 0.175$ and $x = 0.21$, a single relaxation time at elevated temperatures is observed. For all samples studied, the spin relaxation exhibits a momentum dependence consistent with a power law, providing evidence of a dispersive character of the spin relaxation.