Next, here are the expressions for the various fields in a magnetic medium. Magnetic tapes consist of narrow bands of a magnetic medium bonded in paper or plastic. The material of the main "magnetic medium" layer is usually a cobalt-based alloy. This difference suggested that an isotropic magnetic medium would be desirable. A multielement tunable magnetic medium was reported by Zhao et al. The magnetic medium passes across a semi-fixed head which reads or writes data. Magnetic disks and drums include a rotating magnetic medium combined with a movable read/write head. The magnetic medium are typically amorphous R-Fe-Co thin film (R being a rare earth element).