Electronic and magnetic phase diagram of La0.5Sr0.5Co1−xFexO3(⩽x⩽0.6) perovskites

Spin dynamics and magnetic frustration effects in La0.5Sr0.5Co1−xFexO3 (0⩽x⩽0.6) compounds were systematically studied by means of resistivity, dc magnetization, ac susceptibility, and electron-spin-resonance spectra. The Fe substitution caused a metal-semiconductor transition for x⩽0.3 compositions whereas the only semiconducting state behaved for x>0.3 compositions. With increasing Fe-doping levels, the ferromagnetic–paramagnetic transition temperature, TC, decreased from 250 (x=0) to 166K (x=0.4). A spin-glass behavior was observed for x>0.4 compositions and is attributed to the frustration of random competing exchange interactions, namely, the ferromagnetic Co3+–Co4+ double-exchange interaction and the antiferromagnetic interactions such as Co–O–Fe and Fe–O–Fe. The internal dynamic properties of the samples were elucidated by the electron-paramagnetic-resonance spectra. An electronic and magnetic phase diagram of La0.5Sr0.5Co1−xFexO3 is drawn up.