Nanostructure and low-dimensional properties of CMR materials

The colossal magnetoresistance(CMR)ferromagnets of perovskite series La i D2n-nx文件D2Ca锡D21+nx文件D2Mn锡D2n锡D2锡D23+1 ii D2(n=2，3，and∞)have been examined with respected to their electrical and magnetic properties.Results on the transport properties of epitaxial a-axis thin film samples with a fixed carrier concentration(x=0.3)have indicated that a reduction in the number of layers results in systematic changes in the various features.These include an increase in resistivity，a decrease in resistivity peak temperature Tc i D1p文件D1 corresponding to the metal-insulator transition，an enhancement of the maximum MR near Tc I D 1 p文件D1，and an increase in low temperature intrinsic MR.In order to explain the variation in these features with the number of MnO I D12文件D1 layers，it is necessary to take both c-axis transfer interaction two features with the number of MnO I D12文件D1 layers，it is necessary to take both c-axis transfer interaction two features with the number of Mno D12文件D1 layers。These insights are important from the view points of basic understanding of the CMR mechanism and their practical applications.The lattice effect of La y D2n-nx文件D2Ca锡D21+nx文件D2Mn锡D2n锡D2O锡D23n+1锡D2have been investigated using thin films(n=2 and∞)grown on various substrates with the lattice mismatch in the range of-4~1%.For the n=2thin films，the curie temperature decreased very sharply with a decrease of the out-of plane lattice parameters，which results in the enhancement of the MR effect.These results are interpreted in terms of the strain effect induced by the lattice mismatch.The junctions are fabricated using the perovskite manganite(n=∞)and Fe(Or Co)。These results suggest that the spin polarization of tunneling electrons in these junctions is highly dependent on the electronic structure of the barrier/Fe(Or Co)interface。

The colossal magnetoresistance (CMR) ferromagnets of perovskite series LaィイD2n-nxィエD2CaィイD21+nxィエD2MnィイD2nィエD2ィイD23+1ィエD2 (n=2,3, and ∞) have been examined with respected to their electrical and magnetic properties. Results on the transport properties of epitaxial a-axis thin film samples with a fixed carrier concentration (x=0.3) have indicated that a reduction in the number of layers results in systematic changes in the various features. These include an increase in resistivity, a decrease in resistivity peak temperature TcィイD1pィエD1 corresponding to the metal-insulator transition, an enhancement of the maximum MR near TcィイD1pィエD1, and an increase in low temperature intrinsic MR. In order to explain the variation in these features with the number of MnOィイD12ィエD1 layers, it is necessary to take both c-axis transfer interaction an two dimensional spin fluctuation into account. These insights are important from the view points of basic understanding of the CMR mechanism and their practical applications.The lattice effect of LaィイD2n-nxィエD2CaィイD21+nxィエD2MnィイD2nィエD2OィイD23n+1ィエD2 have been investigated using thin films (n=2 and ∞) grown on various substrates with the lattice mismatch in the range of -4 〜1%. For the n=2 thin films, the curie temperature decreased very sharply with a decrease of the out-of plane lattice parameters, which results in the enhancement of the MR effect. These results are interpreted in terms of the strain effect induced by the lattice mismatch.The junctions are fabricated using the perovskite manganite (n=∞) and Fe (or Co). These results suggest that the spin polarization of tunneling electrons in these junctions is highly dependent on the electronic structure of the barrier/Fe (or Co) interface.