Magnetization reversal and coercive force in ultrathin films with perpendicular surface anisotropy: Micromagnetic theory

Quasistatic magnetization reversal in ultrathin magnetic films with perpendicular surface anisotropy is discussed. In order to focus on the role of the surface anisotropy, magnetization is presumed uniform across the film plane, and its variation along the film normal is subject to micromagnetic analysis of a functional including the shape anisotropy energy from dipolar interactions. Different reversal processes-such as nucleations, coherent and incoherent rotations, domain-wall motion, and abrupt jumps-are found in films, depending on the values of shape anisotropy, surface anisotropy, exchange stiffness, and film thickness. The coercivity of ultrathin magnetic films in fields perpendicular to the film plane decreases with the square of the reciprocal of the Nm thickness. which coincides very well with experimental observations. Magnetization reversal processes resulting from applying in-plane external fields are also described.