Magnetization reversal processes in exchange-biased systems

The magnetization reversal mechanism in sputtered bilayer films of NiFe cou pled to a range of antiferromagnets has been studied using Lorentz microsco py and magnetic measurements. The reversal mechanism on the forward and rec oil loops appears different and the results have been interpreted in terms of a recently published seven-point model. Reversal is controlled by the ma gnetic domain structure in the antiferromagnet. Time-dependent studies show that the reversal field for the NiFe layer decreases for both the forward and recoil loops, as the time for which the film is held above the saturati on field of the NiFe layer increases. This can be explained by viscous rota tion of the magnetization in thermally activated domains in the antiferroma gnetic layer. (C) 2000 American Institute of Physics. [S0021-8979(00)85508- 5].