Phase separation and stability in Sm_0.50Sr_0.50MnO₃: effects of cation dopants

The Sm(0.50)Sr(0.50)MnO(3) system has been studied with respect to identifying the various electronic and magnetic phases and the effects of introducing different cation dopants on these phases and their respective stabilities. Magnetic, resistive and thermoelectric studies have been performed as a function of temperature in Sm(0.50)Sr(0.50)MnO(3), (Sm(0.50)Nd(0.50))(0.50)Sr(0.50)MnO(3) and Sm(0.50)(Sr(0.50)Ca(0.50))(0.50)MnO(3). The parent compound (Sm(0.50)Sr(0.50)MnO(3)) lies close to the ferromagnetic-antiferromagnetic (FM-AFM) phase boundary and the consequent effects of the dopants are explained in terms of the changes in the one electron bandwidth and the cation size variation and disorder. Below 130 K the ground state for Sm(0.50)Sr(0.50)MnO(3) composition is seen to be a mixture of ferromagnetic and A-type antiferromagnetic phases. Partial substitution of a larger size cation (Nd) in place of Sm raises the ferromagnetic transition temperature while at the same time stabilizing the AFM phase. This latter trend is inferred from the differences in the hysteresis behaviour of the two systems and is explained in terms of the decrease of the size mismatch factor between cations. However, partial substitution of the smaller size cation (Ca) in place of Sr almost eliminates the ferromagnetic phase, leaving the system in a charge ordered state, which appears to be accompanied by the CE type of charge-orbital ordering, exhibiting extremely large values of resistivity.