CLUSTER PHASE-TRANSITION IN INSULATING SPIN-GLASS GA0.4FE0.6NIALO4

Mossbauer effect, a.c. susceptibility and magnetisation studies (4.2 less-than-or-equal-to T less-than-or-equal-to 350 K, -20 less-than-or-equal-to H less-than-or-equal-to 20 kOe) show that in the mixed spinel ferrite Ga0.4Fe0.6NiAlO4, spin freezing occurs via cluster formation. As in some other insulating spin glasses, the spin glass phase diagram transitions occur not for individual spins but for clusters whose effective spins' transverse and longitudinal components successively freeze. The presence of entropic spins and the centre shifts of the field cooled hysteresis loop confirm the system's frustrated nature.