Magnetic recording theories: Accomplishments and unresolved problems

The published theoretical treatments on the magnetic recording process are reviewed with particular emphasis on the validity of the models and the assumptions on which they are based. It is concluded that the existing theories fairly well describe the geometrical aspects of recording-transducer to medium spacing and gap lengths-but are deficient in describing analytically the magnetic state of the recording medium before and after demagnetization. Calculated magnetization distributions by harmonic analysis for different recording media are in support of the fact that the usually assumed linear and arctangent magnetization transitions are only rough approximations of the magnetic state of a recording medium between regions of opposite magnetization. Additional shortcomings of our theoretical understanding are indicated by the assumptions of uniform magnetization through the recording medium thickness, neglecting the perpendicular component of the magnetization, and not taking into account finite track widths and magnetostatic interactions between adjacent transitions.