MAGNETIZATION REVERSAL IN A THIN FERROMAGNETIC FILM WEAKLY EXCHANGE-COUPLED TO A BULK FERROMAGNET

The static magnetization distribution in a thin film and in a bulk mag net has been calculated using a simplified model in which the ferromag netic thin film is coupled to the bulk magnet through a contact exchan ge interaction. The lowest lying frequencies of oscillation of the mag netization around this equilibrium configuration have also been calcul ated. It has been shown that for weak antiferromagnetic coupling, and assuming that the system adopts a configuration corresponding to a sta te of lowest free energy, there exists a range of applied magnetic fie ld strengths for which the magnetization orientation in the thin film deviates from the applied field direction. In the state characterized by this non-parallel thin film magnetization, the magnetization orient ations both in the thin film and in the bulk magnet become position de pendent. For a 20 monolayer iron Nm the twist in magnetization orienta tion is similar to 1-3 degrees for exchange coupling strengths ranging from 0.5-1.5 erg/cm(2). The magnetization in the bulk is twisted a fe w degrees from the applied field direction at the bulk surface, and th e angle through which the magnetization is turned decays towards zero for distances progressively deeper into the bulk magnet. The decay len gth is similar to 100 Angstrom for iron. Calculated magnetic field dep endencies for the thin film frequency are found to be in reasonable ag reement with data reported for 20 ML Fe(001) films exchange coupled th rough Cr(001) to a Fe(001) whisker.