Open-Orbit Resonances and Magnetic Field Dependence of the Ultrasonic Attenuation of Shear Waves in Magnesium

The open-orbit resonances in the ultrasonic attenuation of shear waves in magnesium have been studied. The ultrasonic open-orbit resonances have been observed for magnetic fields applied in the basal plane for fields as high as 1100 G. The existence of the open-orbit resonance provides direct evidence for the presence of a spin-orbit-induced energy gap in the $\mathrm{AHL}$ Brillouin-zone plane. The period of the open orbit is in excellent agreement with the Brillouin-zone dimension in the [0001] direction. The effects of magnetic breakdown are observed to be of importance in fields of about 1 kG.