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

在低温范围内，发现了奇特的阶梯状磁阻。电阻的温度依赖性随温度的降低而降低，在120K左右达到最小值。在两个温度范围内（高范围50K-90K，低范围30K-50K），电阻的自然对数值与温度成反比。比例系数在高温范围内约为9.5K，对应于0.819meV。低温范围为3.6 ~ 4.1 k，低温范围为2.9 ~ 4.1 mev。另一方面，在低磁场条件下，阶梯图的台阶高度约为800μV，对应于0.8meV。在强磁场下，该值约为360 ~ 390μ v，可达0.36 ~ 0.39 mev。因此，在高温范围内比例系数的值与低场阶跃高度接近，在低温范围内与高场阶跃高度接近。在磁畴存在期间，由于CrO_2具有半金属带结构，MFM图像显示晶粒具有多磁畴结构，晶粒中可能存在不连续态。扫描探针显微测量结果表明，样品为颗粒状膜，晶粒之间存在不连续状态。这些不连续状态引起了有功能类型电阻的温度依赖性。考虑系数的大小和电子的平均自由程，在高、低温范围内的活化能必须分别由薄膜颗粒内部和颗粒之间的不连续状态产生。虽然高温范围内的系数值依赖于磁场，但低温范围内的系数值几乎不依赖于磁场，这支持了上述模型。因此，磁阻中的奇异阶梯图案与薄膜的不连续状态和半金属性质有关。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