Non-linear reversible demagnetization phenomena in magnetic tape

Non-linear reversible demagnetization effects in magnetic tape are analyzed using the Wohlfarth model of perfectly aligned particles. The non-linear reversible susceptibility tensor components are evaluated and used for calculation of third-harmonic distortion of an initially undistorted magnetization pattern. The inherent tape distortion is entirely different from the distortion occurring in the anhysteretic recording process itself. The two non-linear processes are both involved and determine the overall distortion in analog recorded signals. A computer program was written to analyze the distortion for uniform, triangular, and parabolic cross-sectional distributions of the initial magnetization. The results show that the inherent tape distortion is the dominant non-linear effect in the intermediate and high frequency end of the frequency band, from ka = 0.5 and upwards. For five percent constant distortion, all the three analyzed distributions have the same output at the high frequency end to within one decibel. Moreover, the output is proportional to the tape coercivity Hcand is independent of saturation magnetization Msor other tape parameters. These theoretical predictions agree with experimental results which are presented for a number of well-oriented modern tapes with coercivity between 350 and 1030 Oersted.