: A ferromagnet with strong irreversibility

This paper presents a summary of measurements of the field and temperature dependence of the ac susceptibility, magnetic hysteresis isotherms, and the zero field cooled (ZFC) and field cooled (FC) moment. These results demonstrate that La0.5Sr0.5CoO3 is consistently and comprehensively described as a ferromagnet with strong irreversibility. Analysis of the ac susceptibility demonstrates unequivocally the occurrence of a continuous (second order) paramagnetic to ferromagnetic phase transition with mean-field-like effective exponents (although estimates for the true, asymptotic critical exponents appear precluded by the substantial anisotropy/coercivity, linked to the presence of Co ions). The behaviour of the irreversible response is analyzed within the framework of a Preisach model which decomposes the magnetizing process into a sequence of two-state Barkhausen excitations. The model is able to replicate the field and temperature dependence of the hysteresis isotherms and the FC and ZFC moments, and shows that these response functions are a product of field activated transitions over a spectrum of temperature dependent metastable state excitation barriers, with a negligible contribution from thermal fluctuations.