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 Ln(0.5)Sr(0.5)CoO(3) family with different radii of the A-site cations, < r(A) >, in the range 1.19-1.40 A has been carried out. The apparent Tc (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 Mossbauer 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 Co-59 Nuclear magnetic resonance spectroscopy suggest that electronic phase separation is an inherent feature of the Ln(0.5)Sr(0.5)CoO(3) type cobaltates, with the nature of the different magnetic species in the phase-separated system varying with < r(A) > and size disorder. (c) 2007 Elsevier Inc. All rights reserved.