Propagation of Ultrasound in Ferromagnetic Metals at Low Temperatures

Abstract

The theory of cyclotron resonance absorption of microwaves and of ultrasonic waves in ordinary metals is extended to ferromagnetic metals. First some arguments are given about the value of the force on the conduction electrons in a ferromagnet. If this force is known, the calculation of the current can be carried out in the same way as in ordinary metals. The elastic waves are coupled to the ferromagnetic resonance through the magnetostriction (magnetoacoustic resonance), and the absorption of elastic waves arises from two entirely different sources but depends in both cases essentially on the conductivity, that is, eddy currents are created by the motion of the magnetization in addition to the effects as in ordinary metals (viscosity of the electron gas, etc.). Formulas for velocity and attenuation of elastic waves are derived. For the case of microwave absorption, the surface impedance in the anomalous skin-effect region, including ferromagnetic resonance, is calculated.