FERROMAGNETIC COERCIVITY AND APPLIED-FIELD ORIENTATION

We analyze the relationship between the coercive force of a ferromagne tic material and the angle of the applied magnetic field. The material is assumed to contain a ferromagnetic domain wall as well as a planar defect parallel to the wall and it is further assumed that the domina nt mechanism determing the coercivity is that of pinning of the wall b y the defect. Our formulation takes into account the spatial dependenc e of the direction of magnetization along the normal to the plane of t he defect. Numerical solutions are obtained for the resulting nonlinea r differential equations and analysis is done on the roles of the anis otropic, magnetostatic, and exchange energies in determining the behav ior of the coercivity as the direction of the applied magnetic field i s varied. Our results show that, in contradiction to previous thought, the inverse cosine of the applied field angle is not a good approxima tion to the coercivity dependence unless the coercivity is about two o rders of magnitude smaller than the anisotropy field. Also, there exis t ranges of parameter values for which the domain wall pinning coerciv ity decreases as the angle between the applied magnetic field and the anisotropy field increases - a behavior previously assumed to occur on ly when the coercivity is dominated by nucleation rather than pinning of domain walls. Thus, caution must be exercised when using the angula r dependence of the applied field to determine the mechanism of magnet ic reversal of a given material.