Quantum critical behavior of itinerant ferromagnets

TL;DR

This paper studies the quantum phase transition in itinerant ferromagnets, revealing how correlation effects induce long-range interactions that influence the nature of the transition, which can be first order or continuous depending on disorder.

Contribution

It introduces a theoretical framework showing how correlation effects cause singularities leading to long-range interactions, affecting the order of the quantum phase transition in itinerant ferromagnets.

Findings

Correlation effects induce long-range interactions between spin fluctuations.

Clean systems exhibit first order quantum phase transitions, matching experimental observations.

Disordered systems display complex phase diagrams with multiple transition types.

Abstract

We investigate the quantum phase transition of itinerant ferromagnets. It is shown that correlation effects in the underlying itinerant electron system lead to singularities in the order parameter field theory that result in an effective long-range interaction between the spin fluctuations. This interaction turns out to be generically {\em antiferromagnetic} for clean systems. In disordered systems analogous correlation effects lead to even stronger singularities. The resulting long-range interaction is, however, generically ferromagnetic. We discuss two possibilities for the ferromagnetic quantum phase transition. In clean systems, the transition is generically of first order, as is experimentally observed in MnSi. However, under certain conditions the transition may be continuous with non-mean field critical behavior. In disordered systems, one finds a very rich phase diagram showing first order and continuous phase transitions and several multicritical points.