Magnetic phase diagrams of R$_{1-x}$Sr$_{x}$(Mn$_{1-x/2}$Sb$_{x/2}$)O$_{3}$ ($R$ = La, Pr, Nd, Sm, Eu) with trivalent manganese ions

The results of neutron-diffraction, magnetic, and magnetotransport studies of La$_{1-x}$Sr$_{x}$(Mn$_{1-x/2}^{3+}$Sb$_{x/2}^{5+}$)O$_{3}$ ($x\le$ 0.7) pervoskites, which contain only Mn$^{3+}$ ions, are reported. It is demonstrated that the system undergoes a transition from the antiferromagnetic state to the ferromagnetic one at $x\sim$ 0.2. Its structure then changes from $O'$-orthorombic to $O$-orthorombic, which is attributable to orbital disordering. At $x\ge$ 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 $R_{0.7}$Sr$_{0.3}$Mn$_{0.85}$Sb$_{0.15}$O$_{3}$ 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.