The scaling exponent of 1.6 between anomalous Hall and longitudinal conductivity, characteristic of the universal Hall mechanism in dirty-metal ferromagnets, emerges from a series of CrO 2 films as we systematically increase structural disorder. Magnetic disorder in CrO 2 increases with temperature and this drives a separate topological Hall mechanism. We find that these terms are controlled discretely by structural and magnetic defect populations, and their coexistence leads to apparent divergence from exponent 1.6, suggesting that the universal term is more prevalent than previously realised.
The authors examine the electrical properties of ultrathin MgO barriers grown on ͑001͒ InAs epilayers and the dependence on InAs surface pretreatment and growth conditions. Pretreatment improves the yield of tunnel junctions and changes the roughness of the interface between oxide and semiconductor. Electrical characterization confirms that tunnel barriers with appropriate values of interface resistance for efficient spin injection/detection have been achieved. Using the Rowell criteria and various tunneling models, the authors show that single step tunneling occurs above 150 K. Incorporating a thermal smearing model suggests that tunneling is the dominant transport process down to 10 K.
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