Magnetization and domain structure of bcc ${\mathrm{Fe}}_{81}{\mathrm{Ni}}_{19}/\mathrm{Co}$ (001) superlattices

Dense stripe domains were observed for a ${\mathrm{Fe}}_{81}{\mathrm{Ni}}_{19}/\mathrm{Co}$ superlattice grown on a MgO(100) single crystal substrate using dc magnetron sputtering. The stripe domain period exhibits nonreversible changes with the magnetic field, as determined by magnetic force microscopy. We present a simple theoretical model for this system and calculate the magnetization and domain period as functions of the applied field by minimizing the total energy. For this purpose, an expression for the domain wall energy and wall width for arbitrary angles and one for the magnetostatic energy are derived. The model correctly predicts a decreasing domain period with the increasing applied field. At larger magnetic fields a transition to “chaotic” two-dimensional stripe patterns is observed and a qualitative discussion of this phenomenon is given.