Quantum model for magnetic multivalued recording in coupled multilayers
  In this paper, we discuss the possibilities of realizing the magnetic multi-valued (MMV) recording in a magnetic coupled multilayer. The hysteresis loop of a double-layer system is studied analytically, and the conditions for achieving the MMV recording are given. The conditions are studied from different respects, and the phase diagrams for the anisotropic parameters are given in the end. 
Lei Zhou, Ning Xie, Shengyu Jin and Ruibao Tao