Microstructure of mechanically alloyed Fe78Mo 10Sm12 magnets with the ThMn 12 structure

Abstract

The ThMn12-type Fe78Mo 10Sm12 magnet has been characterized by high-resolution electron microscopy, x-ray microanalysis, and microdiffraction. In general, the microstructure of the mechanically alloyed and annealed magnets consists of the tetragonal 1:12 matrix phase with an average matrix grain diameter of 200-300 nm and two rare-earth oxide phases, the SmO and the Sm2O3 phases. Microdiffraction data clearly verify the fcc structure of the single and polycrystalline SmO grains, while the Sm2O3 phase was found to exist only in a single-crystal hcp and monoclinic structure. In this material, no grain boundary phases at multigrain junctions were observed. The high defect concentration in the matrix grains seems to be responsible for the pinning of the domain walls and the good magnetic properties of the Fe78Mo10Sm12 magnets. However, it was not possible to resolve magnetic domains by Lorentz imaging methods.