Specific Heat of the Dilute Ising Magnet LiHo$_x$Y$_{1-x}$F$_4$

TL;DR

This study measures the specific heat of dilute LiHo$_x$Y$_{1-x}$F$_4$ samples, revealing broad features consistent with a spin glass state and showing increased residual entropy at lower Ho concentrations.

Contribution

It provides new specific heat data for dilute LiHo$_x$Y$_{1-x}$F$_4$ samples, contrasting previous findings and supporting the absence of a spin glass transition at low concentrations.

Findings

Broad specific heat features suggest spin glass behavior.

Residual entropy increases as Ho concentration decreases.

No sharp features observed in specific heat measurements.

Abstract

We present specific heat data on three samples of the dilute Ising magnet $\HoYLF$ with $x = 0.018$, 0.045 and 0.080. Previous measurements of the ac susceptibility of an $x = 0.045$ sample showed the Ho$^{3+}$ moments to remain dynamic down to very low temperatures and the specific heat was found to have unusually sharp features. In contrast, our measurements do not exhibit these sharp features in the specific heat and instead show a broad feature, for all three samples studied, which is qualitatively consistent with a spin glass state. Integrating $C/T$, however, reveals an increase in residual entropy with lower Ho concentration, consistent with recent Monte Carlo simulations showing a lack of spin glass transition for low x.