Further Studies of the Enhanced Nuclear Magnet HoVO_4 II. Experiments With Acoustic Waves

Acoustic measurements on single crystals of HoVO_4 at a frequency of 800 MHz (Bleaney et al., Proc. R. Soc. Lond. A 388, 479 (1983a)) revealed the presence of both non-resonant acoustic absorption at low applied-field strengths and resonant absorption at the enhanced nuclear magnetic resonance frequency. In a recent paper (Bleaney & Gregg Proc. R. Soc. Lond. A 413, 313 (1987)) the theory of such acoustic resonance in enhanced nuclear paramagnets has been extended to include other acoustic modes for ions at sites of tetragonal symmetry. In this paper the advantages of using acoustic waves rather than conventional nuclear magnetic resonance for the region 1-2 GHz is described, together with the preparation of transducers of ZnO and the experimental apparatus. Measurements of the acoustic velocities at 1 GHz in HoVO_4 are compared with those of (Goto et al., J. Phys. Soc. Japan 55, 1613 (1986)) at 10 MHz. Further measurements of the non-resonant and resonant attenuation will be presented in papers III and IV (Bleaney et al., Proc. R. Soc. Lond. A 416, 83; 93 (1988)), together with the appropriate theory.