The phenomenon of spin reorientations in ultrathin magnetic films is discussed. A micromagnetic theory is presented which reveals the competition between the in-plane shape anisotropy and the normal surface anisotropy through a finite exchange stiffness. For small surface anisotropy, two continuous transitions in spin orientation are derived as the film thickness is increased: first from the uniform, normal configuration to a nonuniform, canting configuration, and then to the uniform, in-plane configuration. This result is consistent with experimental observations. For large surface anisotropy, it is derived theoretically that only the first spin reorientation occurs and the canting configuration remains stable even at large thickness limit.
- Normal surface anisotropy
- Spin-reorientation transition
- Ultrathin magnetic film