Magnetism and the Weiss Exchange Field - A Theoretical Analysis Inspired by Recent Experiments

TL;DR

This paper provides a theoretical analysis of the Weiss exchange field's role in magnetism, explaining recent experimental observations of high spin precession frequencies and proposing new experimental and theoretical insights into exchange interactions and magnetic phase transitions.

Contribution

It offers a microscopic derivation of Weiss exchange field dynamics and introduces proofs of phase transitions in quantum XY-models and antiferromagnets based on exchange field distributions.

Findings

Interpretation of high spin precession frequencies via Weiss exchange field

Proposal of a Stern-Gerlach experiment for exchange fields

Proofs of phase transitions in quantum magnetic models

Abstract

The huge spin precession frequency observed in recent experiments with spin-polarized beams of hot electrons shot through magnetized films is interpreted as being caused by Zeeman coupling of the electron spins to the so-called Weiss exchange field in the film. A "Stern-Gerlach experiment" for electrons moving through an inhomogeneous exchange field is proposed. The microscopic origin of exchange interactions and of large mean exchange fields, leading to different types of magnetic order, is elucidated. A microscopic derivation of the equations of motion of the Weiss exchange field is presented. Novel proofs of the existence of phase transitions in quantum XY-models and antiferromagnets, based on an analysis of the statistical distribution of the exchange field, are outlined.