Effect of soft-phase anisotropy on reversal behavior in two-phase exchange-coupled bilayer ferromagnetic thin films

A two-dimensional micromagnetic simulation has been used to study a thin-film bilayer consisting of two ferromagnetic phases with different magnitudes of magnetocrystalline anisotropy. The aim was to investigate the effect the magnitude of magnetocrystalline anisotropy of the soft-phase has upon the resulting hysteresis properties. For low soft-phase anisotropy, reversal of the soft phase occurs in low fields while the hard phase remains unreversed until higher fields, whereupon the domain wall becomes unpinned from the interface. For higher values of the soft-phase anisotropy, the soft phase is more resistant to change in magnetization, but once reversal begins the domain wall propagates more easily into the hard phase. The result is that the coercivity of the hard phase decreases with increasing soft-phase anisotropy. The ultimate point is reached when the nucleation field of the soft phase is larger than the pinning field of the interface anisotropy mismatch and an almost single-phase reversal process results. This is explained in terms of previous analytic theories of domain-wall pinning developed for two-section nanowires and planar defects. (C) 2002 American Institute of Physics.