Nucleation field, hysteresis loop, coercivity mechanism and critical thickness in composite multilayers with perpendicular anisotropy

Analytical expression for the nucleation field has been derived for a hard/soft multilayer system with anisotropy perpendicular to the film plane, which depends on the soft thickness L s , the interface exchange coupling constant J i and the intrinsic material parameters. Both nucleation field and coercivity decrease as L s increases. For very small L s , the coercivity mechanism is pure nucleation and the hysteresis loops are square. As L s rises, the coercivity mechanism changes from nucleation to pinning gradually, where the hysteresis loops have to be calculated numerically. The critical thickness at which the mechanism varies has been discussed in detail on the basis of easy axis orientation and the interface exchange coupling constant.