Micromagnetic calculation of hysteresis loops in exchange-coupled nanolayers

In this study, hysteresis loops have been investigated based on a self-contained micromagnetic model for various exchange-coupled layer systems, including oriented hard/soft multilayers and double-layer systems with perpendicular easy axes. In the former case, the soft layer acts as the nucleation center while the hard layer plays the role of pinning. Both the nucleation field and coercivity decrease with the thickness of the soft layer L s while they are not sensitive to that of the hard one, L h . The reduction of the remanence due to the deterioration of the squareness of the hysteresis loop accompanying the increase of L s could be compensated by the improvement of the saturation magnetization contributed by the soft layer. The optimum thickness at which the largest energy product could be achieved is given. In the latter case, the misaligned layer acts in a similar role to that of the soft layer in hard/soft multilayers considering that it nucleates the reversed domain walls and decreases the coercivity significantly. As the thickness of the misaligned layer increases, both the remanence and the coercivity decrease and the loop loses its rectangularity. As a result, the energy product shrinks, suggesting that the misaligned grains affect the energy product greatly. In the case where the thicknesses of the aligned and misaligned layers are equal and increase simultaneously, the coercivity increases while the remanence decreases. Thus an optimum thickness for largest energy product also exists.