Remanence changes of magnetic tapes and disks stressed in zero and reverse fields

To estimate the extent to which a recording tape signal can be reduced during replay we have devised a rapid, sensitive, and simple testing technique. The method uses a Hall probe to measure the field profile after applying a localized stress to the center of a uniformly magnetized sample. We believe that this loss occurs when the pigment anisotropy is lowered by stressing particles, which have nonzero magnetostriction, in the presence of a demagnetizing field. The latter originates from particle interaction fields (H
I
), self-demagnetizing fields from short magnetized segments, and fields from oppositely magnetized adjacent regions. The first effect is observed by stressing a uniformly magnetized sample in its remanent state; the second two are associated with frequency-dependent losses and can be simulated by applying stress with the sample located in a reverse field after initial saturation. Results indicate that H
I
is anisotropic and depends on the average angle between the magnetizing field and the long particle axis. When a reverse field is applied during stress, the maximum loss occurs at the coercive field where the loss is greater than the interaction field loss. All stress-induced losses vary logarithmically with the number of stress cycles, and scale with the magnitude of the applied stress and the absolute value of the saturation magnetostriction.