Behaviors of Magnetizations in Nanostructured Systems

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Using electron-beam lithography with lift-off method, nanoscale dots and wires of ferromagnetic materials (Permalloy) has been prepared. By MFM (Magnetic Force Microscopy) observation, the existence of turned-off magnetization spot at the center of circular permalloy dot has been confirmed. The vortex spin structure with a turned-off core is realized in the dots of 0.2〜5 μm diameter. It an external field is applied along the film normal, the spot magnetization has been reversed at about 0.4T. For in-plane field, the vortex structure is annihilated at about 0.1T. The mechanisms for the reversal are therefore different. For square or ellipsoidal dots, the closure magnetic domain structures are observed and the mode of circulation is identified. However, it is experimentally confirmed that the direction of turned-off magnetization and the mode of vortex circulation have no correlation. Namely the chirality rule does not exist. MFM images were also obtained for cross-tie walls in nanoscal rectangular permalloy plates and the existence of perpendicular magnetization spots are confirmed at each cross point of domains. By electric resistively measurements for a single dot with 5 μm diameter, the rotation of magnetization by external field is studied.Recently there have been two reports for extremely large MR effect happened at point-contact systems. We have prepared permalloy wire systems including nanoscale contact. Although the domain wall is confined at the contact place, the resistively change is not large but can be accounted for as the AMR effect.