Stress Sensitivity Coefficient In Polycrystalline and Amorphous Ferromagnetic Materials Below Room-temperature

The piezomagnetic coupling coefficient (the <>) is quantitatively investigated below room temperature and a comparison is made among polycrystalline samples and amorphous ones. The technique used is an original one. It experimentally consists in the measurement of the amplitude of magnetoelastic waves, their resonance frequency and differential susceptibility; theoretically, it consists in coupling Newton's law of force with the piezomagnetic state equations. The results clearly show different responses of polycrystalline samples with respect to the amorphous ones; in particular the nonmonotonic behaviour of the <> for metallic glasses is interesting for establishing their actual magnetic states at low temperature.