Dynamics of the Magnetic Susceptibility Deep in the Coulomb Phase of the Dipolar Spin Ice Material Ho2Ti2O7

TL;DR

This study investigates the low-temperature magnetic susceptibility dynamics of Ho2Ti2O7, revealing temperature-activated behavior and complex spectra that challenge existing monopole models, with careful correction for demagnetization effects.

Contribution

It extends susceptibility measurements to lower temperatures and frequencies, providing new insights into the dynamics and challenging current theoretical models of spin ice behavior.

Findings

Susceptibility follows an Arrhenius law with activation energy near 6J_eff

Susceptibility spectra are nontrivial and differ from standard glassy relaxation

Demagnetization effects significantly influence the measured spectra

Abstract

Low temperature measurements of the ac magnetic susceptibility along the [110] direction of a single crystal of the dipolar spin ice material Ho2Ti2O7, in zero static field, are presented. While behavior that is qualitatively consistent with previous work on Ho2Ti2O7 and the related material Dy2Ti2O7 is observed, this work extends measurements to appreciably lower temperatures and frequencies. In the freezing regime, below 1 K, the dynamics are found to be temperature activated, thus well described by an Arrhenius law with an activation energy close to 6J_eff, a result that is not easily explained with the current model of magnetic monopole excitations in dipolar spin ice. The form and temperature dependence of the ac susceptibility spectra are found to be nontrivial and distinct from standard glassy relaxation. Particular attention has been paid to correcting for the demagnetization effect, which is quite significant in these materials and has important, even qualitative, effects on the susceptibility spectra.