A comparative study of the magnetic properties and phase separation behavior of the rare earth cobaltates, Ln0.5Sr0.5CoO3 (Ln=rare earth)

A comparative study of the magnetic properties of a few members of the Ln0.5Sr0.5CoO3 family with different radii of the A-site cations, 〈rA〉, in the range 1.19–1.40 Å has been carried out. The apparent Tc (where the magnetization undergoes an abrupt increase) decreases markedly with 〈rA〉 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 〈rA〉 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 La0.5Sr0.5CoO3 as well. The variation of the FM/PM ratio with 〈rA〉 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 Ln0.5Sr0.5CoO3 type cobaltates, with the nature of the different magnetic species in the phase-separated system varying with 〈rA〉 and size disorder.