# Magnetization beyond the Ising limit of Ho$_2$Ti$_2$O$_7$

## TL;DR

This study demonstrates that high magnetic fields can break the local Ising anisotropy in Ho$_2$Ti$_2$O$_7$, leading to magnetization beyond the Ising limit and revealing complex spin dynamics and cross-over phenomena.

## Contribution

It shows that the Ising anisotropy in spin-ice Ho$_2$Ti$_2$O$_7$ can be overcome with ultra-high magnetic fields, revealing new magnetization behavior and spin relaxation effects.

## Key findings

- Magnetization exceeds the Ising limit at high fields up to 120 T.
- Level crossing causes magnetization steps at 55 T and 100 T.
- A susceptibility peak indicates a crossover between spin-ice and polarized states.

## Abstract

We report that the local Ising anisotropy in pyrochlore oxides - the crucial requirement for realizing the spin-ice state - can be broken by means of high magnetic fields. For the case of the well-established classical spin-ice compound Ho$_2$Ti$_2$O$_7$ the magnetization exceeds the angle-dependent saturation value of the Ising limit using ultra-high fields up to 120 T. However, even under such extreme magnetic fields full saturation cannot be achieved. Crystal-electric-field calculations reveal that a level crossing for two of the four ion positions leads to magnetization steps at 55 and 100 T. In addition, we show that by using a field sweep rate in the range of the spin-relaxation time the dynamics of the spin system can be probed. Exclusively at 25 ns/T a new peak of the susceptibility appears around 2 T. We argue, this signals the cross-over between spin-ice and polarized correlations.