Metamagnetic domains in antiferromagnetically coupled multilayers with perpendicular anisotropy

In antiferromagnetically coupled superlattices with perpendicular anisotropy an applied magnetic-bias field stabilizes specific multidomain states, so-called metamagnetic domains. A phenomenological theory developed in this paper allows to derive the equilibrium sizes of metamagnetic stripe and bubble domains as functions of the antiferromagnetic exchange, the magnetic-bias field, and the geometrical parameters of the multilayer. The magnetic-phase diagram includes three different types of metamagnetic domain states, namely, multidomains in the surface layer and in internal layers, also mixed multidomain states may arise. Experimental investigations have been carried out for a [Co/Pt]/Ru superlattice consisting of $N=18$ antiferromagnetically coupled ferromagnetic blocks with $X=7,8,9$ Co/Pt bilayers, each, and in another system with $N=10$ and $X=5$. Magnetization curves and magnetic-force-microscopy images for [Co/Pt]/Ru superlattices provide detailed information on the magnetization reversal during the metamagnetic reorientation.