Magnetic Phase Diagrams of R_1–xSr_x(Mn_1–x/2Sb_x/2)O₃ (R = La, Pr, Nd, Sm, Eu) with Trivalent Manganese Ions

The results of neutron-diffraction, magnetic, and magnetotransport studies of La_1‒xSr_x(Mn_1-x/2³⁺Sb_x/2⁵⁺)O₃ (x ≤ 0.7) pervoskites, which contain only Mn³⁺ ions, are reported. It is demonstrated that the system undergoes a transition from the antiferromagnetic state to the ferromagnetic one at x ∼ 0.2. Its structure then changes from O′-orthorombic to O-orthorombic, which is attributable to orbital disordering. At x ≥ 0.6, the competition between antiferromagnetic and ferromagnetic interactions and strong diamagnetic dilution trigger the emergence of the cluster spin-glass phase. As the ionic radius of rare-earth ions in R_0.7Sr_0.3Mn_0.85Sb_0.15O₃ decreases, the ferromagnetic state transforms gradually into spin glass (R = Sm). All ferromagnetic compositions are dielectric in the magnetically ordered phase with strong magnetoresistive effects. It is assumed that ferromagnetism is induced by the strong covalency and orbital disordering.