Physical Structure and Magnetic Anisotropy of Alnico 5. Part II

Abstract

As a result of measurements of magnetic anisotropy and coercive force on single crystals of Alnico 5 and the electron metallography of Part I, the following conclusions were obtained. When the crystals are heat treated in a field in the principal crystallographic directions, the easy direction of magnetization is the field direction, and magnetically the crystals have twofold symmetry. However, there is a strong tendency because of crystal forces for the precipitate to grow in 〈100〉 directions; and, therefore, the crystal has the highest anisotropy when the heat‐treating field and a 〈100〉 direction are parallel. The large increase in residual induction of Alnico 5 which results from the magnetic field heat treatment is caused by the easy directions of the crystal changing from the 〈111〉 directions to a single easy direction approximately parallel to the field. Domain rotations rather than boundary movements account for the coercive force of the alloy, since the dimensions of the individual particles are approximately 200 angstroms. The present physical picture of the alloy is one of single domains of precipitate material in parallel with single domains of matrix material, the observed coercive force being the resultant of this parallel combination.