Determination of the universality class of Gadolinium

TL;DR

This paper identifies a new dynamic universality class, model J*, for the spin dynamics of Gadolinium, by combining theoretical analysis and experimental data, resolving a longstanding puzzle in its critical behavior.

Contribution

It introduces the novel universality class model J* for Gadolinium's spin dynamics, integrating exchange and dipole interactions with experimental validation.

Findings

Identification of a new universality class, model J*.

Quantitative agreement between theory and hyperfine probe experiments.

Elucidation of the crossover scenario involving three length scales.

Abstract

We resolve a longstanding puzzle for the static and dynamic critical behavior of Gadolinium by a combined theoretical and experimental investigation. It is shown that the spin dynamics of a three dimensional ferromagnet with hcp lattice structure and a spin-spin interaction given by both exchange and dipole-dipole interaction belongs to a new dynamic universality class, model J$^*$. Comparing results from mode coupling theory with results from three different hyperfine interaction probes we find quantitative agreement. The crossover scenario for the wavevector dependence of the hyperfine relaxation rate is determined by a subtle interplay between three length scales: the correlation length, the dipolar and the uniaxial wave vector.