UCL Discovery

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 spina Cu2+ based spin glasses, CuGa2O4 and CuAl2O4. Dc- and ac-susceptibility. The spin glass freezing temperature is determined to be T-f = 2.89 +/- 0.05 K for CuGa2O4 and T-f = 2.30 +/- 0.05 K for CuAl2O4. By integrating of S0 = 4.96 JK(-1)mol(-1) and S-0 = 4.76 JK(-1)mol(-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 theorectical predictions. This indicates that CuGa2O4 and CuAl2O4 have a greater degeneracy in their ground states than any of the spin glass models.