Characteristics of 360°-domain walls observed by magnetic force microscope in exchange-biased NiFe films

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Abstract
The characteristics of 360° domain walls have been investigated by magnetic force microscopy(MFM) in glass/Ta(10 nm)/NiFe(7.2 nm)/FeMn(8.0 nm)Ta(5 nm). The sample was prepared by radio-frequency-magnetron sputtering and characterized with a vibrating sample magnetometer. Both closed and line types of 360° domain walls were observed. The closed type (loop) walls include circular, ellipsoidal, and irregular shapes of domain wall, the long axis of which is generally perpendicular to the overall easy direction (pinned direction) of the exchange biased NiFe film. 360° wall loops were also classified by their chirality. Many 360° domain walls were observed near defects and the measured wall thickness ranged from 1.5 to 3 μm. The magnetic structure of the 360° loop was verified by simulations using a simplified model of the MFM imaging process. The formation of a 360° wall loops appears to originate from the rotational nature of the magnetization in the exchange-biased film, which comes from the distribution of the unidirectional anisotropy.

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