Effects of Spin Fluctuations and Anomalous Thermal Expansion of delta-Plutonium

TL;DR

This paper presents a model linking spin fluctuations to anomalous thermal expansion in delta-plutonium, explaining negative thermal expansion and Invar behavior through magneto-elastic coupling and magnetic dynamics.

Contribution

It introduces a novel model connecting spin fluctuations and thermal expansion anomalies in delta-plutonium, emphasizing the role of magneto-elastic coupling and magnetic moments.

Findings

Spin fluctuations contribute negatively to volume strain.

The model explains the Invar anomaly in delta-plutonium.

Results align with experimental thermal expansion data for Pu-Ga alloys.

Abstract

We suggest a model for the magnetic dynamics of - plutonium and its alloys in order to show that the dynamical fluctuations of the magnetization density, or spin fluctuations, may be responsible for the anomalies of their observed thermal expansion. We show that due to strong magneto-elastic coupling, spin fluctuations may essentially contribute to the volume strain by giving a negative magneto-volume contribution that is proportional to the squared local magnetic moment and the magnetic Gruneisen constant which is negative in - plutonium. In the presented model, the local magnetic moment increases as the temperature rises, resulting in the interplay between the positive contributions to the volume strain from the lattice and the negative contribution from spin fluctuations, and finally leads to the Invar anomaly or to the negative coefficient of thermal expansion. Our results agree closely with the measured thermal expansion data for Pu-Ga alloys.