Spin state and magnetic ordering of half-doped Nd_0.5Sr_0.5CoO₃ cobaltite

Cobaltites show intriguing magnetic and transport properties, when compared with manganites for instance, as they exhibit an additional degree of freedom: the spin state of the Co ions. For Nd_0.5Sr_0.5CoO₃ this spin configuration is not well-established, as well as the magnetic ordering below the Curie temperature. Thus, in the present effort, magnetization measurements and a mean-field theoretical model were developed in order to understand in detail these aspects of the half-doped Nd_0.5Sr_0.5CoO₃ cobaltite. These results show that the Co and Nd magnetic sub-lattices couple antiferromagnetically below Curie temperature T_c=215 K down to very low temperature. These findings clarify the presence of the plateau observed at 80 K on M(T) curve, which is erroneously attributed, in the literature, to the onset of an antiferromagnetic ordering. Magnetization data also clearly shows that Co³⁺ and Co⁴⁺ are in an intermediate spin state. In addition, experimental and theoretical magnetic entropy changes were determined and a comparative analysis among these two leads to ratify the results above claimed. Finally, from all those results, a magnetic phase diagram for Nd_0.5Sr_0.5CoO₃. could be drawn.