Abstract
We present the results of a study of electron-doped Sm 1− x Sr x MnO 3 ( x>0.5) perovskite manganites by combining high-resolution neutron powder diffraction with measurements of resistivity, magnetization and magnetic susceptibility. Although investigated Sm 0.45Sr 0.55MnO 3 and Sm 0.37Sr 0.63MnO 3 compounds belonging to the same phase diagram area differ significantly in the strontium content, they are homogeneous antiferromagnetic (AF) insulators and do not exhibit CMR. They have different crystallographic symmetries (orthorhombic Pbnm and tetragonal I4 /mcm, respectively) in the entire temperature range under study (1.5–288 K), differ in the type of spin ordering at low temperatures (AF -A and AF -C), are characterized by different orbital polarizations ( d x 2 − y 2 and d 3 z 2 − r 2), and possess two- and one-dimensional magnetic properties, respectively. The lack of magnetoresistance for these compositions is explained by the lack of coexisting magnetic phases involving double exchange ferromagnetism, in contrast to what is observed for the magnetoresistive Sm 1− x Sr x MnO 3 compounds, that is with x⩽0.52.
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