Reversal modes and reversal times in submicron sized elements for MRAM applications

The switching behavior of submicron sized NiFe nanoelements was calculated using a hybrid finite element/boundary element method. The numerical integration of the Gilbert equation of motion reveals the transient states during magnetization reversal under the influence of a constant applied field. The reversal mode and the reversal time sensitively depend on the size and the shape of the elements. The 200 × 100 × 10 nm3 elements switch well below 1 ns for an applied field of 80 kA/m and a Gilbert damping constant α=0.1. The elements reverse by non-uniform rotation. If an external field is applied the magnetization starts to rotate near the ends, followed by the reversal of the center. This process requires only about 0.1 ns. In what follows, the magnetization component parallel to the field direction shows oscillations, which decay within a time of 0.4 ns. The excitation of spin waves is caused by the precession of the magnetization around the local effective field. A rapid decay of the oscillations is obtained in elements with slanted ends, where surface charges cause a transverse demagnetizing field.