Unified theory of magnetization temperature dependence in ferrimagnets

TL;DR

This paper extends a unified theoretical framework to describe the temperature dependence of magnetization in multi-sublattice ferrimagnets, successfully matching experimental data across the entire temperature range from low to Curie temperature.

Contribution

It generalizes existing models to multi-sublattice ferrimagnets and combines Bloch's law with mean-field approximation for comprehensive $M(T)$ prediction.

Findings

The combined model accurately fits experimental $M(T)$ data.

Magnetization follows the mean-field $ oot{T_c - T}{}$ dependence across temperatures.

The approach is validated on Yttrium Iron Garnet and similar materials.

Abstract

Recent advancements in spintronics and fundamental physical research have brought increased attention to the rare-earth-based magnetically ordered materials. One of the important properties of these materials is the temperature dependence of the spontaneous magnetization $M(T)$. Recently, a successful framework was proposed for the theoretical description of M(T) across the entire temperature range from zero to the Curie temperature in simple cubic ferromagnets, EuO and EuS. We extend this approach to compute and analyze $M(T)$ for multi-sublattice collinear ferrimagnets such as Yttrium Iron Garnet $Y_3Fe_5 O_{12}$. We analyzed and generalized for multi-sublattice collinear ferrimagnets two well-known approximations describing $M(T)$. The first approach is the Bloch-3/2 law, which describes the suppression of $M(T)$ due to spin-wave excitation, and is valid in the low-temperature limit $T << T_c$. The second one is Weiss's mean-field approximation, which provides a reasonable description of $M(T)$ near $T_c$. Using a single tuning parameter, we combine these two approaches to describe $M(T)$ for any $0<T<T_c$. The theoretical result for $M(T)$ aligns well with our measurements and the previously available experimental data across the entire temperature range. We also demonstrate that experimental and theoretical dependences $M(T)$ follow the mean-field prediction $\sqrt{T_c - T }$ for almost all temperatures.