Ultrasonic Investigation on the Distorted Diamond Chain Compound Azurite
Ultrasonic Investigation on the Distorted Diamond Chain Compound Azurite P T Cong1, B Wolf1, U Tutsch1, K Remović-Langer1, J Schreuer2, S Süllow3, and M Lang1 1 Physikalisches Institut, Universität Frankfurt, SFB/TR49, 60438 Frankfurt(M) 2 Institut für Mineralogie, Ruhr- Universität, 44780 Bochum 3 Institut für Physik der Kondensierten Materie, TU Braunschweig, 38106 Braunschweig
E-mail: cong@physik.uni-frankfurt.de
Abstract. The natural mineral Azurite [Cu3(CO3)2(OH)2] has been considered as a model substance for the 1D distorted antiferromagnetic diamond chain, the microscopic couplings of which, however, are still under discussion. Here we present results of the longitudinal elastic constant c22 down to 80 mK and magnetic fields up to 12 T. c22 reveals clear signatures of the magnetic energy scales involved and discloses distinct anomalies at the Néel ordering TN = 1.88 K. Based on measurement as a function of temperature and magnetic field, a detailed B-T phase diagram is mapped out which includes an additional phase boundary of unknown origin at low temperature (T < 0.5 K). Entering the new phase is accompanied by a pronounced softening of the c22 elastic constant. These observations, together with results obtained by spectroscopic investigations reported in the literature, reflect an unusual long-range magnetically ordered state at very low temperatures.
Introduction Low-dimensional (low-D) quantum spin systems are of great interest in solid state physics due to the wealth of exciting phenomena originating from the interplay of reduced dimensionality, competing interactions and strong quantum fluctuations. Recently, great interest and controversy has surrounded the proposal that the spin S = 1/2 moments of the Cu2+ ions in azurite [Cu3(CO3)2(OH)2] form a frustrated 1D distorted diamond chain [1-3]. The magnetic structure of azurite and the relevant microscopic couplings,
E-mail: cong@physik.uni-frankfurt.de
Abstract. The natural mineral Azurite [Cu3(CO3)2(OH)2] has been considered as a model substance for the 1D distorted antiferromagnetic diamond chain, the microscopic couplings of which, however, are still under discussion. Here we present results of the longitudinal elastic constant c22 down to 80 mK and magnetic fields up to 12 T. c22 reveals clear signatures of the magnetic energy scales involved and discloses distinct anomalies at the Néel ordering TN = 1.88 K. Based on measurement as a function of temperature and magnetic field, a detailed B-T phase diagram is mapped out which includes an additional phase boundary of unknown origin at low temperature (T < 0.5 K). Entering the new phase is accompanied by a pronounced softening of the c22 elastic constant. These observations, together with results obtained by spectroscopic investigations reported in the literature, reflect an unusual long-range magnetically ordered state at very low temperatures.
Introduction Low-dimensional (low-D) quantum spin systems are of great interest in solid state physics due to the wealth of exciting phenomena originating from the interplay of reduced dimensionality, competing interactions and strong quantum fluctuations. Recently, great interest and controversy has surrounded the proposal that the spin S = 1/2 moments of the Cu2+ ions in azurite [Cu3(CO3)2(OH)2] form a frustrated 1D distorted diamond chain [1-3]. The magnetic structure of azurite and the relevant microscopic couplings,