Micromagnetism and high temperature coercivity of MnBi/Al multilayers

The micromagnetic properties of multilayered MnBi/Al films have been invest igated and compared to pure MnBi thin films. Pure MnBi films reveal an anom alous increase of the high temperature coercivity, which has been explained on the basis of a hybrid domain wall pinning model. The multilayer-type pr eparation of MnBi/Al thin films results in significantly reduced MnBi parti cle size of approximately 40 nm. The smaller particle size leads to a chang e of the dominant magnetization reversal process from one driven by domain wall movement toward coherent rotation. This was investigated via magnetic force microscopy imaging and micromagnetic calculations. The absence of dom ain walls during magnetization reversal results in a clear suppression of t he increase of the high temperature coercivity observed in pure MnBi films. (C) 2000 American Institute of Physics. [S0021-8979(00)01620-0].