Magnetic phase diagrams for models of synthetic antiferromagnets

Abstract

Phenomenological macrospin models have been studied to elucidate the field-driven reorientation transitions in antiferromagnetically coupled magnetic thin-film elements with uniaxial anisotropy. For planar bilayer systems, there are four topologically different phase diagrams depending on the ratio of anisotropy to exchange energy. Only for weak anisotropies, the usual phase diagram of antiferromagnets with a spin flop is realized. Analytic and numeric results are presented for a model of a synthetic antiferromagnet composed of four layers, where two ferromagnetically coupled bilayers are coupled antiferromagnetically. Applied fields may stabilize collinear ferrimagnetic and canted phases in these four-layer systems for certain ranges of the ratio between ferromagnetic exchange and antiferromagnetic exchange.