MAGNETIC PERMEABILITY ANOMALY IN HEXAGONAL CLOSE PACKED METALS

Inductance measurements with polycrystalline Gd were found to exhibit an anomalous giant permeability well below the Curie temperature. This giant permeability is evidently related to the anomaly in the weak field magnetization curves of polycrystalline Gd observed by K. P. Belov, who suggested that the anomaly implies a helical spin structure for Gd. It is shown that such an anomaly should occur for a hexagonal, ferromagnetic, polycrystalline material with low basal plane anisotropy (such as Gd) when the direction of easy magnetization departs from the c-axis. If the basal plane anisotropy is neglected, the theoretical weak field permeability is approximately proportional to sin theta, where theta is the angle between the c-axis and the magnetization vector in a representative domain. Good agreement is obtained between the observed permeability and experimental values of sin theta based upon magnetic anisotropy or neutron diffraction measurements of others. (Author) Prepared in cooperation with California Univ., Los Angeles. School of Engineering and Applied Science.