Characterization and application of La0.7A0.3MnO3/ Ni0.5Zn0.5Fe2O4 (A=Ba, Sr) granular film

• Main Authors: Han-Wei Wu, 吳漢威
• Other Authors: 郭博成
• Format: Others
• Language: en_US
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/69789841836791089235

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 91 === We include two parts of work in our study. In first part, the polycrystalline samples of La1-xBaxMnO3 (x=0.2~0.4) and Ni0.5Zn0.5Fe2O4 were prepared by the standard solid-state reaction ; while the thin films of La0.7Ba0.3MnO3 (La0.7Sr0.3MnO3)and Ni0.5Zn0.5Fe2O4 , were grown epitaxially on LaAlO3 and Si substrates by RF magnetron sputtering. The structure, transport and magnetoresistance properties of these samples have been studied and physical property measurement system (PPMS) have been performed on the bulk samples of the series La1-xBaxMnO3 (x=0.2~0.4) and thin films for La0.7Ba0.3MnO3 (La0.7Sr0.3MnO3). The results of bulk samples indicate that La0.7Ba0.3MnO3 has optimal condition for larger MR ratio and lower resistivity, and Ni0.5Zn0.5Fe2O4 has soft magnetic property. The heterostructure La0.7Ba0.3MnO3/ Ni0.5Zn0.5Fe2O4 and La0.7Ba0.3MnO3 /Ni0.5Zn0.5Fe2O4was fabricated by RF magnetron sputtering. First, the LBMO layers were grown on top of 100nm NZFO layers which were annealed at 600 ℃and 700℃. It show that no metallic condiction are observed . The MR ratio is positive for heterostructure LSMO/NZFO when NZFO layer annealed at 600℃. And when NZFO layer annealed at 700℃, the MR ratio for heterostructure LSMO/NZFO is negative below a particular temperature. In the second route, 150nm LSMO layers were grown on top of different thickness and annealing temperature of NZFO layers. The LSMO layers show insulating behavior when LSMO layer was annealed at 600℃. And LSMO layer have metal-insulate transition temperature, when LSMO layer was annealed at 700℃. If NZFO annealed at 600℃, we observed that the MR ratio keeps positive for heterostructure LSMO/NZFO when the thickness of NZFO layer is longer than 40nm. And when the thickness of NZFO layer is thinner than 40nm, the MR ratio is negative below a particular temperature.The MR ratio for all samples at the room temperature is 15.4%, 4.4%, 8.7%, 0.8%, 1.1%, 3.7%. If NZFO annealed at 700℃, we observe that the MR ratio keeps positive over a particular temperature when the thickness of NZFO layer increases from 70nm to 100nm. And when the thickness of NZFO layer is thinner than 40nm, the MR ratio keeps negative. The MR ratio for all samples at the room temperature is 12.4%, 2.3%, and -0.6%. From the results of experiments, it is concluded that the electric properties in the heterostructure is depended on the density of NZFO grains and the mismatch between LSMO and NZFO layer. In sumarry, the MR ratio of heterostructures LBMO/NZFO and LSMO/NZFO is higher than those of single laryer LBMO and LSMO. We also observed, for the first time, that a very large positive MR ratio occur in LSMO/NZFO haterostructure.