Investigation of Magnetotransport Phenomena in Half Metallic CrO2

(1)利用CVD法对玻璃基板上的Ti膜进行热氧化，发现CrO2膜选择性沉积在图案化的TiO2膜上。隧道连接处采用该技术制造。虽然隧道电阻值足够，但TMR性能没有显示出良好的数据。通过使CrO2薄膜与绝缘体之间的界面光滑，可以改善其性能。(2)测量了ZrO2衬底上仅（100）织构的CrO2薄膜在10T宽温度范围内的电阻率和磁阻。电阻率的温度依赖性可以通过半金属的描述来解释，而T^2依赖性系数值与电子比热的关系表明，CrO2属于重费米子族。通过对磁阻数据的分析得到的参数值包含了平均自由程的信息，且在5K以下突然增大，说明由于半金属的存在，缺少了磁振子激发的自旋翻转散射过程。(3) (100) CrO2薄膜在（110）取向的TiO2/Si（111）上的负磁阻幅度大于（100）薄膜在ZrO2衬底上的负磁阻幅度。(4) 473K退火后，TiO2/玻璃上的CrO2膜的负磁电阻（MR）在20K左右以上变大，在20K左右以下变小。473K退火使a轴晶格间距增大。波段计算和WKB近似表明，MR的大小是由这种扩展。(5)发现磁场对磁阻的依赖呈阶梯状。楼梯的台阶高度在恒定电流下是恒定的，并且与电流成倒数，这意味着台阶在每个恒定电压区间内都会发生变化。这些现象可以用薄膜中包含的多隧道结的共隧道来解释。少

(1) It was found that the CrO2 film is selectively deposited onto the patterned TiO2 film by the thermal oxidation of the Ti film on the glass substrates in terms of CVD method. The tunnel junction was made using the technique. Although the value of tunnel resistance was adequate, the TMR properties did not show the good data. The properties may be improved by making the interface between the CrO2 film and insulator smooth.(2) The resistivity and magnetoresistance of the CrO2 film with only (100) texture on the ZrO2 substrate were measured in the wide temperature range up to 10T.The shape of the temperature dependence of resistivity can be interpreted by the description of the half metal and the relation of the values of the coefficient of T^2 dependence and electronic specific heat suggested the CrO2 belongs to the group of the heavy fermion. The value of the parameters obtained by the analysis of the data of the magnetoresistance contain the information on the mean free path and they … More suddenly increased below about 5K, which shows the lack of spin flip scattering process by magnon excitation because of the half metal.(3) The magnitude of the negative magnetoresistance of (100) CrO2 film on TiO2/Si (111) with (110) orientation was larger than that of (100) film on ZrO2 substrate.(4) By the annealing at 473K, the magnitude of the negative magnetoresistance (MR) of the CrO2 film on TiO2/glass became large above about 20K, while the magnitude small below about 20K.The lattice spacing of a-axis was extented by the annealing at 473K.The band calculation and WKB approximation suggest that the magnitude of MR becomes by this extension.(5) The staircase pattern in magnetic field dependence in magnetoresistance was found. The step height of the staircase was constant under a constant current and reciprocal to the current, which means that the steps change at each the constant voltage interval. These phenomena can be interpreted by co-tunneling of the multi-tunnel junctions contained in the films. Less