Phase behavior in the system LaxSr1-xMnO(5+x)/2 (x=0.8-1.0) with trivalent state of manganese ion

The oxygen defect perovskite LaxSr1-xMnO(5+x)/2 phases (x=0.8-1.0) with valence state adjusted to trivalent manganese ion have been prepared by reducing oxygen content from the series of LaxSr1-xMnO3 solid solutions. These phases have been characterized by powder X-ray diffractometry and magnetization measurement. The crystal systems of LaxSr1xMnO(5+x)/2 are orthorhombic (x=1.0-0.9) and rhombohedral (x=0.8). The phase of LaxSr1-xMnO3+delta for x=0.9 shows structural change from rhombohedral to orthorhombic symmetry by degree of oxygen nonstoichiometry, while the compounds for x=1.0 and 0.8 do not show structural change by oxygen nonstoichiometry. The random distribution of the oxygen vacancies are assumed in each structure. For x=0.8, the behavior of the temperature dependence of gram magnetization is quite different for finite-field cooling and for zero-field cooling, whereas the magnetic transition temperature exists at around 138 K for both cases. It seems that the magnetic ordered state of this sample is weak ferromagnetic.