Change of wall topography in soft Ferrites by isotropic and anisotropic external pressures

Polycrystalline toroidal samples of soft ferrites have been submitted successively to hydrostatic and uniaxial pressures. The influence of these stresses on the initial susceptibility and the frequency spectrum is studied. Uniaxial pressures applied along the director circles of the toroid produce no effect on these parameters whereas uniaxial pressures directed along the generating lines and hydrostatic pressures involve a decrease of the initial susceptibility and an increase of the frequency relaxation. An interpretation of these phenomena is given, considering that these materials have four easy axis and negative magnetostriction. The domain walls prealigned along the director circles after thermal demagnetization align themselves along the easy axis the nearest to that of the local stress, changing the initial wall topography.