Anisotropic erasure and demagnetization characteristics of recording tapes comprising particles with uniaxial magnetocrystalline anisotropy

Ten magnetic recording tapes were tested for anisotropic erasure and demagnetization characteristics to determine if the four experimental recording tapes made with barium ferrite (with high uniaxial-magnetocrystalline-anisotropy) were significantly more anisotropic than conventional recording materials. The barium ferrite tapes had easy-axis coercive(Hmin{c}max{e})values of 715, 960, 1160, and 1560 Oe, respectively. The conventional materials include γ-Fe2O3, Co-γ-Fe2O3, CrO2, Fe3O4, and Fe in anHmin{c}max{e}range from 290 to 1080 Oe. A set of four curves was obtained for each tape sample; digital signal output vs. easy-axis AC(60 Hz, sinusoidally-varying) erase field, and vs. hard-axis AC erase field; and residual magnetic moment vs. easy-axis AC demagnetizing field, and vs. hard-axis AC demagnetizing field. The barium ferrite tapes were found to be much more resistant to erasure and demagnetization by hard-axis AC fields than conventional recording materials of the sameHmin{c}max{e}(e.g. retaining 76-78% of a recorded digital signal after being exposed to a2Hmin{c}max{e}(peak) hard-axis AC field (conventional materials retained less than 10%).