硬磁/软磁多层膜的成核场、磁滞回线、磁相图和临界厚度

本文通过微磁学方法,较为系统地研究了同组合的硬磁/软磁多层膜的磁矩分和磁滞回,并出了成核场以及成核场和钉扎场分离的软磁厚度（临界厚度）的解析公.研究发现,当软磁厚度Ls较小时,钉扎场与成核场一致,磁滞回为矩形,对应的磁为刚性磁体;随着Ls增大,钉扎场与成核场发生分离,磁滞回在第二开发生倾斜,磁由刚性磁体变为交换弹簧磁体;随着软磁厚度进一增大,硬磁和软磁的磁矩反转对独立,磁由交换弹簧磁体变为退耦合磁体.解析推导表明,临界厚度和硬磁的磁晶异性的平方成反比,这一点与Kneller的估算公一致.据临界厚度的解析公,我们计算了同材料的临界厚度,并与实验值和Kneller等人的估算值进行了比较,探讨了差别产生的原因.

Nucleation fields, hysteresis loops, magnetic phase diagrams and critical thickness in hard/soft multilayers

Magnetization distribution and hysteresis loops have been systematically investigated for various hard/soft multilayers in this paper, with the formulae for the nucleation fields and the critical thickness （where the nucleation and pinning fields detached） analytically derived. It is found that the nucleation fields equal to the pinning ones when the soft layer thickness L~ is small, accompanied by the square hysteresis loops and corresponding to the rigid magnets. As L~ increases, the pinning field detaches from the nucleation one and the hysteresis loops in the second quadrant are slant, corresponding to the exchange spring magnets. Further increase of Ls will lead to independent reversal of the magnetizations in the soft and hard layers, signifying the decoupled magnets. The critical thickness is inversely proportional to the crystalline anisotropy of the hard phase according to our analytical derivation, which is consistent with the approximate formula by Kneller. Finally, the critical thicknesses have been calculated for various hard/soft multilayers and compared with Krleller＇s formula as well as the experimental results, with the possible reason for the differences discussed.