Spin Glass Order by Antisite Disorder in the Highly Frustrated Spinel Oxide CoAl₂O₄

Abstract

We experimentally studied the effects of the intersite mixing disorder between the \(A\)-site and \(B\)-site on the magnetic properties of the highly frustrated spinel oxide CoAl2O4 by measuring DC and AC susceptibilities. We controlled the inversion parameter η systematically from 0.0467 to 0.153 for (Co1-η Alη)[Al2-ηCoη]O4 by changing the heat treatment condition of the sample preparation. For η 0.0643, no magnetic transition is observed down to 2 K, indicating a spin liquid (SL) regime for η 0.0643, whereas for η 0.101, a spin glass (SG) transition emerges at about \(T_{\text{g}} = 4.5\) K, which is almost independent of η. In addition, the coefficient of the \(H\)–\(T_{\text{g}}\) relation is fairly large compared with that of a conventional SG. Our results suggest that some degrees of additional exchange randomness and local distortion by the quenched antisite disorder lead to degeneracy breaking in the SL state and induce SG order.