Ultrasonic investigation of nicl2-4sc(nh2) 2 in the vicinity of the quantum critical points

Abstract

We report results of sound-velocity and sound-attenuation measurements in the quantum S = 1 spin-chain magnet NiCl2-4SC(NH2)2 that shows a field-induced antiferromagnetic (AF) ordering and two corresponding quantum critical points at Hc ∼ 2.1 T and Hs ∼ 12.6 T. The longitudinal acoustic c33 mode modulates the in-chain exchange interaction and shows a softening in the vicinity of the quantum critical points, accompanied by energy dissipation in the acoustic wave. We discuss our results with a model where the main contribution to the spin-lattice interaction arises from the exchange-striction coupling within one-dimensional spin-chains. © 2009 IOP Publishing Ltd.