PHENOMENOLOGY OF ANISOTROPY IN THE FERROMAGNETISM OF ULTRATHIN FILMS

The role of anisotropy in the micromagnetics and in the dynamic response of the magnetization of ultrathin films is explained for a nonspecialist audience. The energetics of domain walls are used to introduce the parameters of micromagnetism. The arguments why demagnetizing fields do not cause domains in ultrathin films are restated. It is shown that in the absence of anisotropy large nonlinear fluctuations would destroy the magnetic order. Brown's paradox is discussed. Particular emphasis is placed on the effects of pinning sites on the static magnetic response. It is shown how pinning sites can cause the surface to show a magnetic response that differs from that a few nanometers away from the surface. The creation of a freely moving domain wall from the interaction of a pair of pinning sites is demonstrated. The temperature dependence of the magnetization from spin wave excitation is calculated for ultrathin films. In each case the mathematics is provided.