斯托纳粒子的磁矩翻转

文章根据朗道-利夫席茨-吉尔伯特（Landau-Lifshitz-Gilbert）理论,介绍了斯托纳（Stoner）粒子（单个磁畴的磁性颗粒）磁矩翻转的相关理论.其中指出了有关磁矩翻转的斯托纳-沃尔法特（Wohlfarth）极限（SW极限）只有在阻尼系数无穷大时才是真正准确的.在此极限下,磁矩是沿着能量下降最快的路径翻转.最小的翻转磁场出现在当系统能量曲面中只有一个稳定的不动点的情形.文中还指出了对于一个给定的各向异性的磁体,阻尼系数存在一个临界值,超过它时,最小翻转磁场与SW极限是相同的.低于此临界值,最小翻转磁场可以小于SW极限.对于在有阻尼情况下的弹道式磁矩翻转,文中指出,施加的磁场方向应该处在一特定的方向内.这个方向窗口的宽度与阻尼系数和磁内能有关.对于一给定的磁内能,窗口的上下边界随着阻尼系数的增加而增加,窗口的宽度则随着阻尼系数的增加而呈振荡的变化.在没有阻尼和阻尼无穷大的极限下,窗口宽度变为零。

Magnetization reversal of Stoner particles

Based on the Landau-Lifshitz-Gilbert formulation, we show that the so-called Stoner-Wohlfarth (SW) limit is exact when the damping constant is infinitely large. Under this limit, the magnetization moves along the steepest energy descent path. The minimal switching field is that at which there is only one stable fixed point in the system. We show that there is a critical value for the damping constant, above which the minimal switching field is the same as that of the SW-limit, for a given magnetic anisotropy. The field of a ballistic magnetization reversal should be along a certain direction window in the presence of energy dissipation. The width of the window depends on both the damping constant and the magnetic anisotropy. The upper and lower bounds of the direction window increase with the damping constant. The window width oscillates with the damping constant for a given magnetic anisotropy, and is zero for both zero and infinite damping.