Explanation on Exotic Magnetic Field Dependence of Staircase Pattern in Magneto-resistance of CrO2 Films

在CrO_2薄膜的低温磁阻中发现了奇特的阶梯图案。电阻的温度依赖性随温度的降低而减小，在120K附近达到最小。在两个温度范围内(高范围：50K-90K；低温度范围：30K-50K)，电阻的自然对数值与温度的倒数成正比，比例系数在高温范围内约为9.5K，相当于0.819 meV。低温范围内的温度范围约为3.6-4.1K，Do为2.9-4.1 meV。在低磁场下，阶梯图形中的台阶高度约为800μV，相当于0.8 meV。在强磁场下，磁化强度约为360-390μV，磁化强度为0.36-0.39 meV。因此，在高温区，比例系数的值在低场接近台阶高度的值，在低温下，在高场中，比例系数的值接近台阶高度的值。可能存在不连续…由于CrO_2具有半金属能带结构，并且MFM图像显示了颗粒中的多磁畴结构，所以在存在磁畴的过程中，颗粒中的OU态更多。扫描探针显微镜测量表明，所制备的样品为颗粒膜，即颗粒间存在不连续状态。考虑到电子系数的大小和电子的平均自由程，高、低温区的活化能必然分别是由薄膜颗粒内和颗粒间的不连续态引起的。虽然在高温范围内系数的大小取决于磁场，但在低温范围内系数的大小几乎不取决于磁场，这支持上述模型。因此，磁阻中的奇异阶梯图案既与薄膜中的不连续态有关，也与半金属性质有关。较少

The exotic staircase patterns have been found in the magenetoresistance of CrO_2 films in low temperature ranges. The temperature dependence of resistance decreased with decreasing temperature and had the minimum near about 120K. The natural logarithmic values of resistance were proportional to the inverse of temperature in two temperature ranges (high range : 50K-90K ; low range : 30K-50K).The value of the proportional coefficient was about 9.5K in the high temperature range and corresponds to 0.819meV. The value in the low temperature range was about 3.6-4.1K and does to 2.9-4.1meV. On the other hand, the value of step height in the staircase pattern was about 800μV in low magnetic field and corresponds to 0.8meV. The value in high magnetic field was about 360-390μV and does to 0.36-0.39meV. Therefore, the value of the proportional coefficient in high temperature range is close to one of step height in low field, and in low temperature, in high field.There are probably the discontinu … More ous states in grains during the existence of the magnetic domains because The CrO_2 has the half metallic band structure and the MFM images showed the polymagnetic domain structure in a grain. The scanning probe microscopic measurements showed that the present samples were granular films, which means that there are the discontinuous states between grains. These discontinuous states give rises to the temperature dependence in the resistance of the type of the activative energy.The activation energies in high and low temperature ranges must result from the discontinuous states in and between grains of films, respectively, by taking the magnitute of the coefficient and the mean free path of electrons into account. Although the value of coefficient in high temperature range depended on the magnetic field, one in low temperature range almost did not depend on the magnetic field, which supports the above model. Therefore, the exotic staircase patterns in the magnetoresitance are related to both the discontinuous states in the films and the half metallic properties. Less