Ultrasonic investigation of NiCl2-4SC(NH2)2

• Published in: Journal of physics. Conference series 2009-03, Vol.150 (4), p.042016
• Main Authors: Chiatti, O, Zherlitsyn, S, Sytcheva, A, Wosnitza, J, Zvyagin, A A, Zapf, V S, Jaime, M, Paduan-Filho, A
• Format: Article
• Language: English
• Subjects: Acoustic propagation; Anomalies; Antiferromagnetism; Chains; Critical point; Energy dissipation; Low temperature; Nickel chloride; Phase diagrams; Phase transitions; Physics; Propagation modes; Sound waves
• ISSN: 1742-6596; 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/150/4/042016

We report results of ultrasonic investigations of the quantum S 1 spin-chain magnet NiCl2-4SC(NH2)2, also known as DTN, in magnetic fields up to 18 T and temperatures down to 0.3 K. A field H along the [001] direction induces a transition into an antiferromagnetic phase with TNmax ≈ 1.2 K. Accordingly, at T 0 there are two quantum critical points at ∼2.1 T and at ∼12.6 T. The acoustic c33 mode, propagating along the spin chains, shows a pronounced softening close to the phase transition, accompanied by energy dissipation of the sound wave. The H-T phase diagram obtained from our measurements is compared with results from other experimental investigations and the low-temperature acoustic anomalies are traced up to T > TN. We also report frequency-dependent effects, which open the possibility to investigate the spin fluctuations in the critical regions. Our observations show an important role of the spin-phonon coupling in DTN. PACS numbers: 72.55.+s, 75.45.+j