Spin-glass behavior in Pr0.7Ca0.3CoO3 and Nd0.7Ca0.3CoO3

With a view to investigate the effect of small size of A-site cations on the magnetic properties of the rare earth cobaltates, Ln 1− xAx CoO3 (Ln=rare earth, A=alkaline earth), we have investigated Pr0.7Ca0.3CoO3 and Nd0.7Ca0.3CoO3 in detail. For this purpose, we have carried out low-field DC magnetization and ac susceptibility measurements including a study of magnetic relaxation and memory effects. Both Pr0.7Ca0.3CoO3 and Nd0.7Ca0.3CoO3 show frequency-dependent transitions at 70 and 55K respectively in the ac susceptibility data, due to the onset of spin-glass like behavior. Their relaxation behavior exhibits aging effects. In addition, memory effects are found in the magnetization behavior. These characteristics establish spin-glass behavior in both these cobaltates, a behavior that is distinctly different from that of La0.7Ca0.3CoO3 and La0.5Sr0.5CoO3 which show well-defined ferromagnetic transitions, albeit without long-range ordering.