Amorphous Exchange-Spring Magnets With Crossed Perpendicular And In-Plane Anisotropies

We study the magnetic coupling in a thin film bilayer exchange-spring magnet composed of an amorphous Tb10Co90 layer with a large perpendicular anisotropy and an amorphous Co-85(Al70Zr30)(15) layer with uniaxial inplane anisotropy. The CoAlZr is directly exchange coupled to the TbCo with an interface region of at least 7.5 nm within which the CoAlZr magnetization is perpendicular to the plane and switches with the underlying TbCo. The influence of the coupling extends up to 30 nm into the CoAlZr resulting in an effective tilted anisotropy. The coercivity of the CoAlZr is greatly enhanced due to the coupling and is tuneable over a large range by varying its thickness.