STRESS-INDUCED PLAYBACK LOSS AND SWITCHING FIELD REDUCTION IN RECORDING MATERIALS

When a magnetized tape in an oppositely directed field is rubbed, the stress σ reduces the switching field by an amount ΔH σ so as to produce a partial reversal of the magnetization ΔMH,σ. This inverse magnetostrictive effect leads to the playback loss ΔL that is observed in a recorded tape. The loss depends on ΔHσ, the coercive force Hc, the demagnetizing field and the shape of the hysteresis loop. The parameter ΔH σ is proportional to σ and is related to the magnetostriction constants. It can exceed 300 Oe or greater than one half the coercive force in a 3.5% Co-doped γ-Fe2O3 sample when σ=500 kg/cm2. When Co is adsorbed on the surface of γ-Fe2O3 particles the saturation magnetostriction ∥γs∥, ΔHσ and ΔL are all smaller than for a Co-doped tape with an equivalent Hc. The small ΔL for CrO2 is due to its low λs whereas low stress related losses in Fe are due primarily to a high Hc.