Magnetization process of spin ice in a [111] magnetic field

TL;DR

This paper investigates the magnetization process of spin ice in a [111] magnetic field, revealing non-monotonic entropy behavior and phase crossovers through analytical and simulation methods, with implications for cooling techniques.

Contribution

The study develops an analytical theory for the nearest-neighbor spin ice model and explores defect interactions and entropy spikes, advancing understanding of spin ice behavior under magnetic fields.

Findings

Identification of two magnetization plateaux with finite entropy.

Discovery of a giant entropy spike between the plateaux.

Development of an RG treatment for string defects at low fields.

Abstract

Spin ice in a magnetic field in the [111] direction displays two magnetization plateaux, one at saturation and an intermediate one with finite entropy. We study the crossovers between the different regimes from a point of view of (entropically) interacting defects. We develop an analytical theory for the nearest-neighbor spin ice model, which covers most of the magnetization curve. We find that the entropy is non-monotonic, exhibiting a giant spike between the two plateaux. This regime is described by a monomer-dimer model with tunable fugacities. At low fields, we develop an RG treatment for the extended string defects, and we compare our results to extensive Monte Carlo simulations. We address the implications of our results for cooling by adiabatic (de)magnetization.