Electromagnetic generation of ultrasonic waves in 3-<i>d</i> transition metals

Abstract

We investigated experimentally acoustic waves generated by electromagnetic means in the surface of 3-d transition metals. The signal amplitude was greatest when the static magnetic field was normal to the generating surface. The amplitude increased in proportion to the external field only up to 3 kOe in both polycrystalline and single crystals of Ni, while there was a tendency for the signal to decrease at high fields. Generation efficiency in Ni improved with increasing temperature at low fields, but the amplitude observed at high fields decreased at high temperatures. The experimental results in ferromagnetic nickel are explained in terms of dynamic magnetostriction. Above the Curie temperature, the magnitude of the amplitude was accounted for by the Lorentz force mechanism applicable to nonmagnetic metals. The same mechanism also accounted for the amplitude observed in Fe and Co at room temperature. The results in ferromagnetic nickel are unique because of the large magnetostriction and small crystal anisotropy.