Magnetic ordering in Ln$_{0.7}$Sr$_{0.3}$Mn$_{0.85}$Sb$_{0.15}$O$_3$ (Ln = La, Nd, Sm, Eu)

The crystal structure and magnetic properties of stoichiometric compounds Ln$_{0.7}$Sr$_{0.3}$Mn$_{0.85}$Sb$_{0.15}$O$_3$, in which manganese ions are in a trivalent state, have been investigated. No cooperative orbital ordering has been found in the Ln = La composition, but structural parameters of the Ln = Nd composition indicate Jahn–Teller distortions. It has been shown that, as the ionic radius of lanthanide (Ln) decreases, structural distortions of the MnO$_6$ octahedron increase and the ferromagnetic component weakens due to a decrease in hybridization of manganese and oxygen orbitals. An increase in the covalent component of the chemical bond along with the orbital disorder promotes an increase in the role of positive superexchange interactions Mn$^{3+}$–O–Mn$^{3+}$.