Use of the chemical potential for a limited number of fermions with a degenerate groundstate

A full analysis of domain structure using a micromagnetic model is developed in order to get a clear insight into the behaviour of transverse initial susceptibility as a function of dc applied field for thin films and bilayers exhibiting both in-plane and perpendicular anisotropy. The numerical simulations are in good agreement with available experimental results in case of single layers with the so-called stripe domain pattern while some predictions are done for bilayers. As the main result, it is shown that in low field, the transverse initial susceptible cannot be interpreted without the knowledge of the static domain pattern while, above saturation, it is only affected by the in-plane anisotropy. Received 10 October 2002 Published online 4 February 2003 RID="a" ID="a"e-mail: ml@lpmtm.univ-paris13.fr RID="b" ID="b"UMR CNRS 8634