Enhancement of the Curie temperature in small particles of weak itinerant ferromagnets

TL;DR

This paper uses self-consistent renormalization theory and random matrix models to show that small clusters of weak itinerant ferromagnets can have higher Curie temperatures than bulk materials due to quantum level repulsion effects.

Contribution

It introduces a novel approach combining renormalization theory with random matrix models to predict enhanced Curie temperatures in small ferromagnetic clusters.

Findings

Curie temperature increases in clusters smaller than 100 atoms.

Level repulsion suppresses spin fluctuations, stabilizing magnetic order.

Contradicts naive Stoner model expectations.

Abstract

Self consistent renormalization theory of itinerant ferromagnets is used to calculate the Curie temperature of clusters down to approximately 100 atoms in size. In these clusters the electrons responsible for the magnetic properties are assumed to be (weakly) itinerant. It is shown that the Curie temperature can be larger than in the bulk. The effect originates from the phenomenon of level repulsion in chaotic quantum systems, which suppresses spin fluctuations. Since the latter destroy the magnetic order the resulting Curie temperature increases, contrary to expectations of the naive Stoner picture. The calculations are done assuming that the energy levels of the cluster are described by the Gaussian Orthogonal Ensemble of random matrix theory.