Magnetic Structure of Sr_2MnO_<3.5>(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

概要

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Magnetic behavior of Sr_2MnO_<3.5> has been studied by measuring the magnetic susceptibility X, highfield magnetization and specific heat C. The spin structure has also been studied by means of the powder neutron diffraction. The system has the two-dimensional linkage of corner-sharing MnO_5 pyramids derived by regularly reducing the oxygen atoms from the MnO_2 layers of Sr_2MnO_4. The oxygen shared by two neighboring pyramids belongs, in one case, to the basal planes of both pyramids, or in another case, to the basal plane of one pyramid and the apex of another one. Due to the existence of these two kinds of the bridging oxygens, it provides a quite characteristic example of moment systems with ferromagnetic (F) clusters of four Mn^<3+> moments, which are interacting with the neighboring clusters in the antiferromagnetic (AF) way. The results of the studies are as follows. The Neel temperature T_N is 126K. The exchange interactions corresponding to the two kinds of the bridging oxygens are estimated by the high temperature expansion method to be -50.9K (AF) and 18.7K (F), where the signs are in agreement with our expectation. The magnetic structure is consistent with the picture of interacting clusters, though the F-interaction is weaker than the AF one. It is collinear AF one with the moments along the b axis.
社団法人日本物理学会の論文
2005-03-15