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

CrO2 薄膜磁阻阶梯图案与外来磁场依赖性的解释

• 批准号: 13650034
• 负责人: SUZUKI Katsuhiko
• 金额: $ 2.24万
• 依托单位: Miyagi National College of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650034/
• 关键词: CrO_2; Half Metal; Magneto-resistance; MFM; Temperature Dependence of Resistance; Staircase Pattern; Thermal Activation Tunneling; トンネリング; ハーフメタル; 走査型プローブ顕微鏡

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

在低温范围内，CrO_2 薄膜的磁电阻出现了奇异的阶梯图案，电阻的温度依赖性随着温度的降低而降低，并在 120K 左右达到最小值，电阻的自然对数值与温度成反比。两个温度范围（高温范围：50K-90K；低温范围：30K-50K）。高温范围内比例系数值约为9.5K，低温范围内的值约为3.6-4.1K，对应于2.9-4.1meV。另一方面，阶梯图案中的阶梯高度值在低磁场下约为800μV。 0.8meV，在高磁场下约为360-390μV，达到0.36-0.39meV。高温范围内的比例系数值接近于低场中的阶梯高度之一，而在低温、高场中。在磁畴存在期间，晶粒中可能存在不连续状态，因为CrO_2具有半金属能带结构，MFM图像显示晶粒中的多磁畴结构，扫描探针显微测量表明，本样品是粒状薄膜，这意味着晶粒之间存在不连续状态。不连续状态导致活化能类型的电阻与温度相关。高温和低温范围内的活化能必须分别由薄膜晶粒内和晶粒之间的不连续状态产生，通过取系数的大小并考虑了电子的平均自由程，虽然高温范围内的系数值取决于磁场，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。中的模式磁阻与薄膜的不连续态和半金属特性有关。