Zero-point entropy of the spinel spin glasses CuGa_2O_4 and CuAl_2O_4

TL;DR

This study experimentally measures the zero-point entropy of CuGa2O4 and CuAl2O4 spinel spin glasses, revealing higher degeneracy in their ground states than predicted by existing models, thus challenging current spin glass theories.

Contribution

First experimental determination of zero-point entropy for these spinel spin glasses, providing new insights into their ground state degeneracy and theoretical predictions.

Findings

Zero-point entropies are higher than all theoretical predictions.

Spin glass freezing temperatures are approximately 2.89 K and 2.30 K.

Results suggest greater ground state degeneracy than existing models.

Abstract

The zero-point entropy of a spin glass is a difficult property to experimentally determine and interpret. Spin glass theory provides various predictions, including unphysical ones, for the value of the zero-point entropy, however experimental results have been lacking. We have investigated the magnetic properties and zero-point entropy of two spinel Cu2+ based spin glasses, CuGa2O4 and CuAl2O4. Dc- and ac-susceptibility and specific heat measurements show many characteristic spin glass features for both materials. The spin glass freezing temperature is determined to be Tf = 2.89 +/- 0.05 K for CuGa2O4 and Tf = 2.30 +/- 0.05 K for CuAl2O4. By integrating the specific heat data we have found that CuGa2O4 and CuAl2O4 have zero-point entropies of S0 = 4.96 JK-1mol-1 and S0 = 4.76 JK-1mol-1 respectively. These values are closest to the prediction for a Sherrington-Kirkpatrick XY spin glass, however they are notably higher than all of the theoretical predictions. This indicates that CuGa2O4 and CuAl2O4 have a greater degeneracy in their ground states than any of the spin glass models.