Theory of roughness-induced anisotropy in ferromagnetic films: The dipolar mechanism

When ferromagnetic films are grown on stepped surfaces, or rough surfaces upon which there is a preferred direction, additional magnetic anisotropy associated with the presence of the roughness is found in experiments. This paper presents the theory of the contribution of one mechanism to this anisotropy, that is associated with the roughness-induced increase in magnetic dipolar energy. When the film surface profiles are modulated, the magnetization of the film fluctuates in direction, thus generating stray dipolar fields. The energy stored in such fields depends on the angle between the mean magnetization, and the preferred axis of the modulated surface profile. We present explicit calculations for various models of films on stepped surfaces. [S0163-1829(99)00218-0].