Induced Random Fields in the LiHo$_x$Y$_{1-x}$F$_4$ Quantum Ising Magnet in a Transverse Magnetic Field

TL;DR

This paper demonstrates that applying a transverse magnetic field to LiHo$_x$Y$_{1-x}$F$_4$ induces random fields along the Ising axis, revealing it as a new random field Ising system and explaining observed quantum critical behavior.

Contribution

The study shows that transverse magnetic fields induce random fields in LiHo$_x$Y$_{1-x}$F$_4$, providing a new understanding of its quantum phase transitions and disordered magnetic properties.

Findings

Random fields are generated along the Ising axis due to transverse field and local disorder.

Rapid decrease of critical temperature with increasing transverse field.

Smearing of nonlinear susceptibility at the spin glass transition.

Abstract

The LiHo$_x$Y$_{1-x}$F$_4$ magnetic material in a transverse magnetic field $B_{x}\hat x$ perpendicular to the Ising spin direction has long been used to study tunable quantum phase transitions in a random disordered system. We show that the $B_{x}-$induced magnetization along the $\hat x$ direction, combined with the local random dilution-induced destruction of crystalline symmetries, generates, via the predominant dipolar interactions between Ho$^{3+}$ ions, {\it random fields} along the Ising $\hat z$ direction. This identifies LiHo$_x$Y$_{1-x}$F$_4$ in $B_x$ as a new random field Ising system. The random fields explain the rapid decrease of the critical temperature in the diluted ferromagnetic regime and the smearing of the nonlinear susceptibility at the spin glass transition with increasing $B_{x}$, and render the $B_{x}-$induced quantum criticality in LiHo$_x$Y$_{1-x}$F$_4$ likely inaccessible.