ULTRASOUND INVESTIGATION OF THE MAGNETIC-STRUCTURE OF ER IN AN APPLIED MAGNETIC-FIELD

The magnetic structure of erbium has been studied by a wide variety of techniques including magnetic X-ray and neutron scattering. The intermediate phase, where a c-axis sinusoidally modulated structure is combined with a modulated moment in the basal plane, has been shown to contain high symmetry structures, which arise as a result of the competition between the long range exchange interaction, the magnetocrystalline anisotropy and the effects of the magnetostrictive energy. The occurrence of these high symmetry structures produces anomalies in the ultrasonic elastic moduli and associated ultrasonic attenuation. These anomalies become increasingly more dramatic in an increasing c-axis field, where it appears that the effect of the field is to render the high symmetry structures more stable causing a lock-in of the period of the modulation over wider temperature ranges than at zero field.