ペロブスカイト型強磁性体La_<n-nx>Ca_<1+nx>Mn_nO_<3n+1>の磁気・伝導物性

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This paper reports on the magnetic and electrical properties of colossal magnetoresistance (CMR) ferromagnets La_<n-nx>Ca_<1+nx>Mn_nO_<3n+1> (n=2, 3, and ∞). The magnetic phase diagram of double perovskite La_<2-2x>Ca_<1+2x>Mn_2O_7 was deduced from data on polycrystalline samples. The system becomes a metallic ferromagnet for doping concentrations of 0.22≦x≦0.5. In the doping region, the results for bulk samples as well as for thin films clearly show that there are two types of ferromagnetic ordering, originating from an anisotropic exchange interaction. Results on the properties of epitaxial thin-film samples (x=0.3, n=2, 3, and ∞) indicate that a reduction in the number of layers results in systematic changes in various features. These include an increase in resistivity, a decrease in the transition temperature T_c, an enhancement of the maximum MR near T_c, and an increase in the low-temperature intrinsic MR. To explain the variation in these features with the number of MnO_2 layers, it is necessary to take account of both c-axis transfer interaction and two-dimensional spin fluctuation.
社団法人日本磁気学会の論文
1998-03-01