Magnetic effects on the symmetry of CBED patterns of ferromagnetic PrCo₅

Abstract A high-energy permanent magnet, whose nonmagnetic structure belongs to the space group P6/m mm, has been used to study the magnetic effect on symmetry determination by convergent-beam electron diffraction (CBED) patterns. At the [0001] zone axis, along which the magnetization of the domains is aligned, the symmetry of CBED patterns remains 6mm as if the specimen were nonmagnetic. However, at the zone axis, the mirror planes contained by the c axis were absent in the zero-order disks even though the whole pattern appeared to have 2mm symmetry. By looking into the interaction between the electron beam and the magnetic field produced by the specimen, it was found that the magnetic effect of the specimen was zero in the first-order approximation when the electron beam was along the [0001] direction, and was maximized when the electron beam was parallel to the basal plane. The apparent 2mm symmetry in the whole pattern of zone axis indicates that diffraction is overwhelmed by the Coulombic potential in the specimen.