Soft spin waves and magnetization reversal in elliptical permalloy nanodots: Experiments and dynamical matrix results

We present an experimental and theoretical investigation of magnetization reversal in Permalloy elliptical nanodots under the application of a varying (quasistatic) magnetic field directed along the hard (short) and easy (long) axes of the ellipses. The magnetic response of the particles is investigated with the magneto-optic Kerr effect (MOKE) and Brillouin scattering (BLS). Experimental MOKE results are reproduced by micromagnetic simulations. The spectrum of the normal modes, calculated with the dynamical matrix method, reproduces the BLS results. We find that when an abrupt magnetization switching occurs it is accompanied by a soft magnetic mode (different in the two cases), the symmetry of which determines the initial steps (onset) of the microscopic reversal path.