Spin Dynamics at Very Low Temperature in Spin Ice Dy$_2$Ti$_2$O$_7$

TL;DR

This study investigates the spin dynamics of Dy$_2$Ti$_2$O$_7$ spin ice at very low temperatures, revealing a transition from thermal activation to quantum relaxation below 0.5 K.

Contribution

It provides detailed measurements of relaxation times down to 0.08 K and identifies a crossover from thermal to quantum spin dynamics in Dy$_2$Ti$_2$O$_7$.

Findings

Relaxation times increase with cooling, fitting an Arrhenius law between 0.5-1 K.

Below 0.5 K, relaxation becomes temperature independent, indicating quantum effects.

Two distinct relaxation processes are identified, characterized by short and long times.

Abstract

We have performed AC susceptibility and DC magnetic relaxation measurements on the spin ice system Dy$_2$Ti$_2$O$_7$ down to 0.08 K. The relaxation time of the magnetization has been estimated below 2 K down to 0.08 K. The spin dynamics of Dy$_2$Ti$_2$O$_7$ is well described by using two relaxation times ($\tau_{\rm S}$ (short time) and $\tau_{\rm L}$ (long time)). Both $\tau_{\rm S}$ and $\tau_{\rm L}$ increase on cooling. Assuming the Arrhenius law in the temperature range 0.5-1 K, we obtained an energy barrier of 9 K. Below 0.5 K, both $\tau_{\rm S}$ and $\tau_{\rm L}$ show a clear deviation from the thermal activated dynamics toward temperature independent relaxation, suggesting a quantum dynamics.