Magnetic frustration effects in Fe-doped cobalt oxides

A thorough study of electron paramagnetic resonance (EPR) spectra of La0.5Sr0.5Co1−xFexO3 (0⩽x⩽0.6) compounds has been made. It is shown that, in the paramagnetic region, the EPR signal decreased considerably with increasing Fe-doped content. Cluster-glass (CG) behavior for 0⩽x⩽0.4 compositions was realized near the phase transition temperature TC, but almost disappeared with further iron addition. This feature is a direct consequence of the magnetic frustration of random competing interactions, namely the ferromagnetic Co3+-Co4+ double-exchange interactions and the antiferromagnetic interactions like Co-O-Fe and Fe-O-Fe. For x>0.4 compositions, spin-glass (SG) behavior was observed and, this phase emerged and competed strongly with the CG phase. The results obtained from the EPR spectra are consistent with those obtained from the magnetization and resistivity measurements.