Abstract
The thermodynamics and kinetics of the magnetic states of the semiconductor-like compound La 0.7 Sr 0.3 Mn 0.7 Co 0.3 O 3 were studied by detailed magnetic measurements. The spontaneous magnetic state was found to be a cluster-glass phase which can cross over to a ferromagnetic state under an external magnetic field H. The defreezing temperature T f for the cluster-glass phase and the merging temperature T m for zero field cooled and field cooled magnetizations are related to the field H by H j = H 0j (1 - T j /T c ) nj , where H 0j and n j are constants and j = f, m. Codoping tends to destroy the double exchange in Mn 4+ -O-Mn 3+ and broadens the coexistence region of the cluster-glass and ferromagnetic states. The magnetic relaxation was found to deviate from the usual logarithmic time dependence and follow a power law. © 1999 American Institute of Physics.