Basics of the magnetocaloric effect

TL;DR

This chapter explains the fundamental physics and thermodynamics behind magnetocaloric materials, focusing on entropy changes, phase transitions, and hysteresis effects relevant to magnetic cooling technologies.

Contribution

It provides a comprehensive review of the thermodynamics, microscopic origins, and hysteresis modeling of magnetocaloric effects in magnetic materials.

Findings

Analysis of entropy sources in magnetic materials.

Discussion of first order magnetic phase transitions.

Insights into irreversibility and hysteresis in magnetocaloric materials.

Abstract

This chapter reviews the basic physics and thermodynamics that govern magnetocaloric materials. The thermodynamics of magnetic materials is discussed by introducing relevant free energy terms together with their microscopic origin leading to a discussion of the sources of entropy that can change in an applied magnetic field. Such entropies account for measurable magnetocaloric effects, especially in the vicinity of magnetic phase transitions. Particular attention is devoted to first order magnetic transitions that involve the coupling of spin, lattice, electronic and anisotropic magneto-crystalline degrees of freedom. The problem of irreversibility and hysteresis, present in magnetocaloric materials with first order phase transitions is discussed in the context of out-of-equilibrium thermodynamics and hysteresis modeling.