Dynamic configurational anisotropy in nanomagnets

The angular dependence of ultrafast magnetization dynamics in nanomagnets of square shape was studied by magneto-optical pump-probe measurements. In agreement with micromagnetic simulations, both the number of precessional modes and the values of their frequencies were observed to vary as the orientation of the external magnetic field was rotated in the element plane. We show that the observed behavior cannot be explained by the angular variation of the static effective magnetic field. Instead, it is found to originate from a new type of magnetic anisotropy---a dynamic configurational anisotropy, which is due to the variation of the dynamic effective magnetic field. Although always present, the dynamical anisotropy may dominate in nanoscale magnetic elements in which the static configurational anisotropy is suppressed.