First order transitions and multicritical points in weak itinerant ferromagnets

TL;DR

This paper demonstrates that phase transitions in low-temperature clean itinerant ferromagnets are typically first order due to correlation effects, with a tricritical point and disorder effects influencing the transition nature.

Contribution

It introduces the concept that correlation effects cause first order transitions in weak itinerant ferromagnets and discusses the impact of disorder and experimental implications.

Findings

First order transition in clean itinerant ferromagnets due to correlation effects.

Existence of a tricritical point separating first order and critical behavior.

Disorder suppresses first order transition, leading to a critical endpoint.

Abstract

It is shown that the phase transition in low-T_c clean itinerant ferromagnets is generically of first order, due to correlation effects that lead to a nonanalytic term in the free energy. A tricritical point separates the line of first order transitions from Heisenberg critical behavior at higher temperatures. Sufficiently strong quenched disorder suppresses the first order transition via the appearance of a critical endpoint. A semi-quantitative discussion is given in terms of recent experiments on MnSi, and predictions for other experiments are made.