Field-induced crossover from cluster-glass to ferromagnetic state in La0.7Sr0.3Mn0.7Co0.3O3

The thermodynamics and kinetics of the magnetic states of the semiconductor-like compound La0.7Sr0.3Mn0.7Co0.3O3 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 Mn4+-O- Mn3+ 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. (C) 1999 American Institute of Physics. [S0021-8979(99)09703-0].