Microscopic spin Hamiltonian for a dipolar-Heisenberg magnet LiGdF4 from EPR measurements

TL;DR

This study uses EPR measurements to determine the microscopic spin Hamiltonian parameters of LiGdF4, revealing magnetic frustration and potential for low-temperature magnetocaloric applications.

Contribution

The paper provides precise microscopic parameters of LiGdF4's spin Hamiltonian derived from EPR spectra, including the exchange constant, and links these to magnetic frustration phenomena.

Findings

Determined microscopic spin Hamiltonian parameters for LiGdF4.

Identified a balance of magnetic interactions leading to frustration.

Observed enhanced magnetocaloric effect at low temperatures.

Abstract

Low-temperature electron paramagnetic resonance measurements are performed on single crystals of LiY_{1-x}Gd_xF_4 with weak x=0.005 and moderate x=0.05 concentration of Gd ions. Modeling of the experimental spectra allows us to precisely determine microscopic parameters of the spin Hamiltonian of the parent LiGdF4 material, including the nearest-neighbor exchange constant. The obtained parameters are further tested by comparing a strongly anisotropic Curie-Weiss temperature obtained for LiGdF4 in our static magnetization measurements with theoretically computed values. We find a fine balance between principal magnetic interactions in LiGdF4, which results in a hidden magnetic frustration presumably leading to a delayed magnetic ordering and an enhanced magnetocaloric effect at low temperatures.