Investigation of Magnetotransport Phenomena in Half Metallic CrO2

(1)用CVD方法对玻璃衬底上的钛膜进行热氧化处理，发现CrO_2膜选择性地沉积在图案化的TiO_2膜上。利用该技术制作了隧道结。虽然隧道电阻值是足够的，但TMR特性并没有显示出良好的数据。(2)在较宽的温度范围内，测量了只有(100)织构的CrO_2薄膜的电阻率和磁阻。用半金属的描述和T^2相关系数与电学比热的关系可以解释电阻率随温度变化的形状，表明CrO_2属于重费米子群。通过分析磁阻数据获得的参数值包含关于平均自由程和它们的…的信息(3)(110)取向的(100)CrO_2薄膜的负磁电阻的大小大于(100)薄膜在ZrO_2衬底上的负磁电阻的大小。(4)经473K的退火后，在约20K以上，TiO_2/玻璃上的CrO_2薄膜的负磁电阻(MR)变大。经473K的退火后，a轴的晶格间距变大。能带计算和WKB近似表明，磁电阻的大小随退火温度的增加而变大。(5)磁阻随磁场的变化有阶梯分布。楼梯的阶梯高度在恒定电流下是恒定的，并且与电流成反比，这意味着阶梯在每个恒定电压区间都会发生变化。这些现象可以用薄膜中包含的多隧道结的共隧道效应来解释。较少

(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