Orientational variation of hysteretic properties in particulate recording media

The angular variation of the coercivity and the squareness in three mutually perpendicular planes was measured in unoriented and longitudinally oriented magnetic recording tapes. Because of the strong contribution of the crystalline anisotropy to the coercivity in the unoriented medium, the measurements for this material were made over a temperature range extending from -1.5° C to 81.3° C; measurements on the oriented medium were made at room temperature. The orientational behavior of the coercivity in the two planes perpendicular to the coating surface is qualitatively similar for both materials in that as the measurement direction leaves the plane of the tape, the coercivity steadily increases to a maximum at
\approx 60\deg
and then decreases to a minimum in the perpendicular direction. A demagnetizing field, which adds vectorially to the applied field and which varies in magnitude in a complicated fashion, contributes to this behavior. Support for this conclusion comes from measurements on both materials of the angular, distribution of the remanence for different saturation directions in the two planes perpendicular to the coating surface.