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Magnetic anisotropy is the directional dependence of a material's magnetic properties. The magnetic moment of magnetically anisotropic materials will tend to align with an "easy axis", which is an energetically favorable direction of spontaneous magnetization. The two opposite directions along an easy axis are usually equivalent, and the actual direction of magnetization can be along either of them (see spontaneous symmetry breaking). In contrast, a magnetically isotropic material has no preferential direction for its magnetic moment unless there is an applied magnetic field. Magnetic anisotropy is a prerequisite for hysteresis in ferromagnets: without it, a ferromagnet is superparamagnetic. ==Sources== There are several sources of magnetic anisotropy: * Magnetocrystalline anisotropy: the atomic structure of a crystal introduces preferential directions for the magnetization. * Shape anisotropy: when a particle is not perfectly spherical, the demagnetizing field will not be equal for all directions, creating one or more easy axes. * Magnetoelastic anisotropy: tension may alter magnetic behaviour, leading to magnetic anisotropy. * Exchange anisotropy: occurs when antiferromagnetic and ferromagnetic materials interact. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「magnetic anisotropy」の詳細全文を読む スポンサード リンク
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