EVIDENCE FOR A NEW STATE IN ALUMINOSILICATE SPIN-GLASSES IN VERY WEAK MAGNETIC-FIELDS

The dc magnetic susceptibility of CoO•Al2O3•SiO2 (14.3 at.% Co) below Tg=5.7 K decreases markedly with reduction in field for H<150 mOe. The observation of this field sensitivity, equilibrium behavior, and a sharp cusp at Tg in this very weak field range is evidence for a cooperative transition at Tg below which correlations extend over many spins. This state is characterized by an energy scale per spin comparable to that of magnetic dipolar coupling between nearest-neighbor spins. © 1979 The American Physical Society.