Significance of the Hyperfine Interactions in the Phase Diagram of ${\rm LiHo_xY_{1-x}F_4}$

TL;DR

This paper demonstrates that hyperfine interactions in LiHo_xY_{1-x}F_4 critically influence its phase diagram, explaining peculiar experimental features of the spin glass to paramagnet transition under varying temperature and magnetic field.

Contribution

It reveals the dominant role of hyperfine interactions in shaping the phase diagram and interpreting experimental results in LiHo_xY_{1-x}F_4.

Findings

Hyperfine interactions dominate the phase behavior.

Spin glass order is more sensitive to thermal fluctuations.

The size of the nonlinear susceptibility cusp decreases at lower temperatures.

Abstract

We consider the quantum magnet $\rm LiHo_xY_{1-x}F_4$ at $x = 0.167$. Experimentally the spin glass to paramagnet transition in this system was studied as a function of the transverse magnetic field and temperature, showing peculiar features: for example (i) the spin glass order is destroyed much faster by thermal fluctuations than by the transverse field; and (ii) the cusp in the nonlinear susceptibility signaling the glass state {\it decreases} in size at lower temperature. Here we show that the hyperfine interactions of the Ho atom must dominate in this system, and that along with the transverse inter-Ho dipolar interactions they dictate the structure of the phase diagram. The experimental observations are shown to be natural consequences of this.