Behaviors of Magnetizations in Nanostructured Systems

利用电子束光刻技术结合剥离法制备了纳米铁磁材料（坡莫合金）点和线。通过磁力显微镜（MFM）观察，证实了坡莫合金圆点中心处存在关闭磁化斑。在直径为0.2 ~ 5 μm的量子点中，实现了具有关闭核的涡旋自旋结构。如果沿薄膜法线沿着施加一个外场，则在约0.4T处，点磁化已被反转。对于面内场，在0.1T附近，涡旋结构消失。因此，逆转的机制是不同的。对于正方形或椭圆形点，闭合磁畴结构被观察到，并确定了环流模式。然而，实验证实，关闭磁化的方向和涡旋环流的模式没有相关性。即手性规则不存在。在纳米尺度的矩形坡莫合金板的交叉结壁也得到了MFM图像，并确认在每个交叉点的域的垂直磁化斑点的存在。通过对直径为5 μm的单点的电磁共振测量，研究了外场作用下的磁化旋转。我们已经准备了坡莫合金线系统，包括纳米级接触。虽然畴壁被限制在接触处，但磁电阻的变化不大，但可以解释为AMR效应。

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.