Nonuniform magnetization structures in thin soft type ferromagnetic elements of elliptical shape

Stable micromagnetic configurations are investigated numerically in thin soft type ferromagnetic elements of elliptical shape with typical thickness of L-z = 30 nm and with aspect ratios 1 less than or equal to L-x/L-y less than or equal to 3.5. In this range of aspect ratios, a complete description of stable magnetization patterns is obtained including the critical sizes for stability of one-vortex and quasiuniform micromagnetic configurations. Due to the absence of sharp corners, the behavior of the quasiuniform state in an external magnetic field resembles that of a single-domain ellipsoidal particle of similar shape. Nevertheless, the calculated hysteresis loops of elliptical elements show a considerable reduction of the switching fields in comparison with the Stoner-Wohlfarth model due to the development of a new mode of instability. The magnetization curves for elliptical elements, initially in one-, two- or three- vortex states, show significant dependence on the direction of external magnetic field with respect to the longest particle's axis. (C) 2001 American Institute of Physics.