Magnetostatic modes and criticality in quantum-Ising materials

TL;DR

This paper investigates magnetostatic modes in quantum-Ising materials, revealing how shape effects influence quantum criticality and identifying specific modes through theoretical analysis and experimental evidence in LiHoF4.

Contribution

It introduces the concept that a magnetostatic mode governs quantum criticality in non-ellipsoidal samples, accounting for shape effects in quantum-Ising materials.

Findings

The soft mode is a magnetostatic mode nulling dynamic-demagnetization effects.

Two additional modes are identified based on the sample's demagnetization factor.

Experimental analysis in LiHoF4 supports the theoretical predictions.

Abstract

We analyze modes in a dipole-dipole coupled quantum-Ising material, taking into consideration shape effects present in any real magnet. We find that the soft mode governing quantum criticality in a non-ellipsoidal sample is a magnetostatic mode which nulls out the effects of dynamic-demagnetization-field fluctuations. The demagnetization field is analyzed from a microscopic perspective. Two additional modes are calculated relying solely on knowledge of the demagnetization factor of the sample, one of which has lower energy than the soft mode governing quantum criticality in the bulk of the magnet. Experimental evidence for these theoretical results is provided by analysis of electronuclear modes in LiHoF$_4$, an archetypal quantum-Ising material.