Local electronic structure and magnetic properties of double-perovskite LaCo₀.₅Ni₀.₅O₃ and PrCo₀.₅Ni₀.₅O₃

With x-ray absorption spectroscopy and x-ray magnetic circular dichroism, the element-specific electronic structure and the magnetic interactions of the double perovskite compounds PrCo$_{0.5}$⁢Ni$_{0.5}$⁢O$_3$ and LaCo$_{0.5}$⁢Ni$_{0.5}$⁢O$_3$ were studied. In both compounds, Co and Ni depart from their nominal valence state of +3, implying a charge transfer from Ni to Co. XMCD measurements clearly reveal a ferromagnetic behavior of Co and Ni in both samples. The substitution of La by Pr is isovalent but leads to a partial spin-state transition of Co$^{3+}$ from high spin to low spin, resulting in a significant decrease in the magnetic moment of Co. Furthermore, a magnetic moment is found on the Pr site as well, with the Pr spin moment oriented antiparallel to those of Co and Ni. This antiferromagnetic coupling is induced by the superexchange interaction between the Pr 4⁢𝑓 and Co/Ni 3⁢𝑑 states.