Enhanced nuclear acoustic resonance in HoVO 4

Abstract

A strong resonant absorption is observed for longitudinal acoustic waves at 800 MHz, propagated along the [100] axis of a single crystal of the enhanced nuclear paramagnet HoVO 4 , in the presence of a magnetic field in the (001) plane. The strength of the resonant absorption is inversely proportional to the absolute temperature T , with a power attenuation coefficient of 4.5(2) x 10 2 T -1 m -1 . From this and the measured velocity of 6.52(6) x 10 3 ms -1 , a rate of 10 -3 T s -1 is deduced for the intrinsic direct spin—lattice relaxation process. This is orders of magnitude smaller than the Orbach rate (10 +4 to 10 +5 s -1 at T = 3 K), and slower than the measured rate at 0.2 K, that must therefore be attributed to the presence of paramagnetic impurities.