Quantum magnets with large single-ion easy-plane anisotropy in transverse magnetic field

TL;DR

This paper develops a theoretical framework to understand the low-temperature magnetic properties of integer-spin quantum magnets with large easy-plane anisotropy under transverse magnetic fields, matching experimental data for DTN.

Contribution

It introduces a perturbative approach considering exchange interactions as a correction, deriving expressions for excitation spectrum, magnetization, specific heat, and phase boundary near quantum critical points.

Findings

Derived the boundary field $h_{c1}(T)$ between phases.

Calculated effective interactions near quantum critical point.

The theory aligns well with experimental data for DTN.

Abstract

We discuss low-temperature properties of magnets with integer spin and large single-ion easy-plane anisotropy $D$ in transverse magnetic field $h$. Considering the exchange interaction between spins as a perturbation and using the diagram technique we derive at $h\sim D$ in the first nonvanishing orders of the perturbation theory thermal corrections to the elementary excitation spectrum, magnetization and specific heat. An expression for the boundary $h_{c1}(T)$ is found in the $h$-$T$ plane between the paramagnetic phase and that with the long range magnetic order. The effective interaction is derived between bosons near the quantum critical point $h_{c1}(0)$. The proposed theory describes well experimental data obtained in $\rm NiCl_2$-$\rm 4SC(NH_2)_2$ (DTN).