Magnetization reversal in thin magnetic films with perpendicular anisotropy

A one-dimensional theory of magnetization reversal in thin, perpendicularly anisotropic magnetic films is presented. It is postulated that the presence of a defective point creates an infinitely deep, infinitely narrow potential well which inhibits the rotation of local magnetization. The interval D between neighboring defects, the saturation magnetization M_s, the anisotropy constant K_u, and the exchange energy constant A are assumed to be finite and uniform across the film. Starting with an initial state where the film is uniformly magnetized to saturation in the easy direction, we show that a discontinuous change of state occurs when the reverse external field H reaches a critical value H_c. The domains thus nucleated at the critical field expand to cover the entire area of the film as H increases beyond H _c. Using the normalized values of H and D, defined, respectively, as h = H/(2K_u/M_s) and d = D/(4A/K_u)^1/2, we show that the critical field h_c is a function only of d and that its value decreases significantly as d increases.