Low-temperature properties of the dilute dipolar magnet LiHo_xY_(1-x)F_4

TL;DR

This study uses Monte Carlo simulations to analyze the low-temperature magnetic properties of dilute LiHo_xY_(1-x)F_4, comparing theoretical predictions with experimental data and examining the phase diagram and spin-glass behavior.

Contribution

It provides a detailed theoretical analysis of the dilute dipolar magnet LiHo_xY_(1-x)F_4, highlighting discrepancies with recent experiments and re-evaluating the phase diagram and spin-glass phase.

Findings

Susceptibility follows Curie-Weiss law at high T, with T_cw scaling with x

Specific heat peak scales linearly with dilution, conflicting with experiments

Spin-glass susceptibility does not diverge below critical dilution, contrary to experimental evidence

Abstract

We analyze recent experiments on the dilute rare-earth compound LiHo_xY_(1-x)F_4 in the context of an effective Ising dipolar model. Using a Monte Carlo method we calculate the low-temperature behavior of the specific heat and linear susceptibility, and compare our results to measurements. In our model the susceptibility follows a Curie-Weiss law at high temperature, chi ~ 1/(T-T_cw), with a Curie-Weiss temperature that scales with dilution, T_cw ~ x, consistent with early experiments. We also find that the peak in the specific heat scales linearly with dilution, C_max(T) ~ x, in disagreement with recent experiments. Experimental studies do not reach a consensus on the functional form of these quantities, and in particular we do not see reported scalings of the form chi ~ T^-0.75 and chi ~ exp(-T/T_0). Furthermore we calculate the ground state magnetization as a function of dilution, and re-examine the phase diagram around the critical dilution x_c=0.24(3). We find that the spin glass susceptibility for the Ising model does not diverge below x_c, while recent experiments give strong evidence for a stable spin-glass phase in LiHo_0.167Y_0.833F_4.