Role of the rare-earth ion on the strength of the ferromagnetic exchange interactions inRMn0.5M0.5O3 (M = Co,Ni)

Abstract

The role of the trivalent rare-earth ion on the paramagnetic to ferromagnetic transition temperature(Tc) of the substituted perovskite-type rare-earth (R) manganese oxides,RMn0.5Co0.5O3 and RMn0.5Ni0.5O3 (R = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er and Yb), is compared. For a particularR3+ with largerionic size, the Tc of RMn0.5Ni0.5O3 is largerthan that of RMn0.5Co0.5O3 and vice versa for smaller ionic size, though the ionic sizes of trivalent low-spin Co and Ni ions are comparable.Tc values of both Co and Ni containing compositions decrease with the decrease in the ionic size ofR3+, showing a faster decrease for heavier rare-earth ions beyondGd3+. Though the decreasing size of the rare-earth ion is responsible for the decrease in the magnetictransition temperature, due to structural distortions, an anomalous change in the rate of decrease ofTc beyondGd3+ is due to contributions from the single-ion anisotropy of the heavier rare-earth ions.