AVS 46th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Friday Sessions
       Session MI-FrM

Invited Paper MI-FrM5
Magnetization Reversal in Ultrashort Magnetic Field Pulses

Friday, October 29, 1999, 9:40 am, Room 618/619

Session: Magnetic Thin Films
Presenter: H.C. Siegmann, Swiss Federal Institute of Technology, Switzerland
Authors: H.C. Siegmann, Swiss Federal Institute of Technology, Switzerland
C.H. Back, Swiss Federal Institute of Technology, Switzerland
R. Allenspach, IBM Zurich Research Laboratory, Switzerland
Correspondent: Click to Email
Ultrashort magnetic field pulses with amplitudes of up to 20 Tesla at picosecond duration are generated in the final focus test beam facility of the Stanford Linear Accelerator. These unique magnetic field pulses have been used to study magnetization reversal in a variety of thin ferromagnetic films. High resolution magnetic contrast images reveal the magnetization patterns generated by one or several field pulses from which we deduce the elementary processes responsible for the magnetization reversal. For perpendicular magnetized samples we observe ring domains which are reminiscent of the field contour lines during exposure. Their radii represent switching fields which are in quantitative agreement with the coherent rotation model. The broadening of the transition region between oppositely magnetized domains is due to static and dynamic fluctuations of the magnetic anisotropy. For films with uniaxial anisotropy in the plane of the film we observe "figure 8" magnetic patterns due to the necessity to conserve angular momentum while generally much smaller fields compared to the perpendicular samples are sufficient for the ultrafast reversal. We show that the demagnetizing field produced by the precession of the magnetization out of the plane of the film completes the reversal after the external field ceases to exist. The material property of primary importance in ultrafast reversal is the damping of the precession of the magnetization around the direction of the external field. We show that it is strongly influenced by the degree of crystallinity of the sample.