Quantitative approach to the effect of parallel stresses on soft ferrimagnetic polycrystals

When mechanical compression is applied parallel to the direction of magnetic induction in materials with negative magnetostriction constant, a simple theoretical analysis shows that, in most cases, the magnetization increases in magnitude because spins rotate into the stress direction. Experiment shows that this is true for materials in which the domain-wall configuration is initially dispersed at random. However, it is demonstrated in the present work that the results are quite different when the domain-wall configuration is already oriented along the stress direction. In this case, it is believed that compression directly acts on the pinning strengths binding the 180° domain walls together through the grain boundaries. A measurement of this pinning effect is made on the basis of a well-tested model. Experiments on toroids of polycrystalline soft magnetic materials, YIG and Ni-Zn ferrites, are reported and the results are discussed