Thickness dependent magnetic reversal process and hysteresis loops in exchange-coupled hard-soft trilayers

Abstract

The demagnetization process of a hard/soft/hard sandwich has been investigated systematically within a self-contained micromagnetic model, with particular attention on the cases with small hard layer thickness. The microscopic and macroscopic hysteresis loops, as well as the angular distributions of the magnetization between nucleation and pinning have been obtained numerically, with the formula for the nucleation field derived. It is found that both nucleation and pinning fields, as well as the gap in between decrease as the hard layer thickness reduces. The hard layer thickness has great effect on the hysteresis loops only when the thickness is very small, where the hysteresis loop is nearly square and the dominant coercivity mechanism is the nucleation. The thickness regions at which the theoretical and practical giant energy products can be achieved have been discussed. In most cases, the hard layer can be taken as sufficiently thick so that the magnetization at its surface obeys a simple coherent rotation model. In these cases, the calculation can be simplified significantly, with only the influence of the soft layer thickness accounted.

3D and 1D micromagnetic calculation for hard/soft bilayers with in-plane easy axes

“…4, suggesting that the angle near the surface of the hard layer obeys the Stoner-Wohfarth (SW) model [25] very well. This phenomenon justifies the simplifications used in our previous 1D calculation [12,13,16,18], that for large L h , the angle at the surface of the hard layer could be assumed to obey the SW model.…”

“…Similar model has been intensively used in the past two decades, by Leineweber and Kronmüller from Germany [6], by Fullerton and Jiang from USA [7,8], by Asti and Pellicelli et al from Italy [11,14,19] and by Zhao et al from China [12,13,16,18,21]. Such a simple model can reveal some important underlying physics with the derived analytical formula.…”

“…The above 3D energy could be simplified to a one dimensional (1D) expression if we ignore the magnetostatic interactions, which are small for an infinitely large thin film. In one dimension, the energy density per area in the film plane is [11,18] n ¼…”

“…Such a material has drawn much attention in the past two decades [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] due to its expected giant energy product, with the large coercivity provided by the hard phase and the large remanence coming from the soft phase. Nevertheless, the giant energy product as large as 1 MJ/m 3 predicted by Skomski and Coey [2] has never been achieved.…”

Model of hybrid interfacial domain wall in ferromagnetic/antiferromagnetic bilayers

“…The model describes a general interfacial spin structure in practical exchange-biased bilayers, containing a partial AFDW, a partial FMDW, and an abrupt spin flop across the interface, which may be a good candidate for the understanding of all kinds of exchange-coupled interfaces and may coexist with any other existing interfacial mechanism. [44][45][46] Previous models of the interfacial domain wall existing only 047502-4 on one side of the interface [10,11] can be regarded as particular cases of HIDWs. The simulation of the hysteresis loops in typical exchange-biased bilayers demonstrates the validity of our model, from which several important insights could be provided.…”