A comparative study of the magnetic properties and phase separation behavior of the rare earth cobaltates, Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} (Ln=rare earth)

A comparative study of the magnetic properties of a few members of the Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} family with different radii of the A-site cations, , in the range 1.19-1.40 A has been carried out. The apparent T {sub c} (where the magnetization undergoes an abrupt increase) decreases markedly with 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 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 Moessbauer spectra of La{sub 0.5}Sr{sub 0.5}CoO{sub 3} as well. The variation of the FM/PM ratio with and size-disorder, as well as a local-probe study using {sup 59}Co Nuclear magnetic resonance spectroscopy suggest that electronic phase separation is an inherent feature of the Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} type cobaltates, with the nature of the different magnetic species in the phase-separated system varying with and size disorder. - Graphical abstract: Variation of (a) T {sub c} and (b) FC magnetization at 1000 Oe with at 120 K in Ln {sub 0.5}Sr{sub 0.5}CoO{sub 3} and Dy{sub 0.34}Nd{sub 0.16}Sr{sub 0.40}Ca{sub 0.10}CoO{sub 3}.