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−xA_xCoO₃ (Ln=rare earth, A=alkaline earth), we have investigated Pr_0.7Ca_0.3CoO₃ and Nd_0.7Ca_0.3CoO₃ 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 Pr_0.7Ca_0.3CoO₃ and Nd_0.7Ca_0.3CoO₃ show frequency-dependent transitions at 70 and 55 K 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 La_0.7Ca_0.3CoO₃ and La_0.5Sr_0.5CoO₃ which show well-defined ferromagnetic transitions, albeit without long-range ordering.