A comparative study of the magnetic properties and phase separation behavior of the rare earth cobaltates, Ln0.5Sr 0.5CoO 3 ( Ln=rare earth)

Abstract

A comparative study of the magnetic properties of a few members of the Ln 0.5Sr 0.5CoO 3 family with different radii of the A-site cations, 〈 r A 〉, in the range 1.19–1.40 Å has been carried out. The apparent T c (where the magnetization undergoes an abrupt increase) decreases markedly with 〈 r A 〉 as well as the size-disorder arising from the mismatch in the size of the A-site cations. The value of the magnetization at low temperatures decreases markedly with decrease in 〈 r A 〉 or increase in size-disorder, suggesting that the relative proportion of the ferromagnetic (FM) species decreases relative to that of the paramagnetic (PM) species. Such a variation of the FM/PM ratio with composition and temperature is evidenced from the Mössbauer spectra of La 0.5Sr 0.5CoO 3 as well. The variation of the FM/PM ratio with 〈 r A 〉 and size-disorder, as well as a local-probe study using 59Co Nuclear magnetic resonance spectroscopy suggest that electronic phase separation is an inherent feature of the Ln 0.5Sr 0.5CoO 3 type cobaltates, with the nature of the different magnetic species in the phase-separated system varying with 〈 r A 〉 and size disorder.