Magnetomechanical Damping and Magnetic Properties of Iron Alloys

Abstract

This work investigates experimentally a recent model of magnetomechanical damping based on a distribution of internal stresses, verifies some predictions and extends the model. Damping results are reported for cast irons and iron alloyed with silicon or germanium. As predicted, the maximum magnetomechanical damping ψmax is inversely proportional to the strain amplitude which produces ψmax. To explain the relatively slow decrease of ψmax with superimposed static shear stress or external magnetic field, the model must be modified to account for stress components or demagnetizing fields. By considering stress components along magnetization directions on opposite sides of a domain wall, we introduce a technique for describing the effect of single-crystal and grain orientations. This description qualitatively explains why bars with random grain orientations have larger damping in bending than in torsion. Although models relating damping to magnetic properties are in-exact, damping correlates experimentally with permeability and magnetic energy loss. These correlations are qualitatively explained by arguing that the 90° walls governing damping are less mobile than the 180° walls governing magnetic properties.