Crystal and magnetic structure of the SM0.55Sr0.45MnO3 and (Nd0.545Tb0.455)0.55Sr0.45MnO3 manganites

Neutron diffraction data are presented for the (Sm0.55Sr0.45MnO3)-Sm-152 (SSM) and (Nd0.545Tb0.455)(0.55)Sr0.45MnO3 (NTSM) manganites. The Nd and Tb contents in the latter composition are such that the average radius of the A cation [r(A)] in these two compounds is the same. The difference in local tolerance factor fluctuations was about 10%. It was found that replacement of a rare-earth cation with leaving [r(A)] unchanged has practically no effect on the structural and transport properties; indeed, both compounds are metals at low temperatures, have the same crystal structure from liquid-helium to room temperature, and exhibit the same pattern of structural distortions at the onset of magnetic ordering. Magnetic moments of Mn ions in both compositions are ferromagnetically ordered at low temperatures, with T-C = 122 and 90 K for the SSM and NTSM, respectively. Below 80 K, the rare-earth cation moments in NTSM undergo additional ordering. In contrast to compositions that are close in Sr concentration (x(Sr) = 0.4, 0.5), which feature a phase-separated state with a mixture of the ferromagnetic metallic and antiferromagnetic insulator phases, the ground state of both studied compositions with x(Sr) = 0.45 is uniformly ferromagnetic and metallic. (C) 2004 MAIK "Nauka/Interperiodica".