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Dresden 2011 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 44: Poster Session Correlated Electrons

TT 44.29: Poster

Thursday, March 17, 2011, 10:00–13:00, P1

Grüneisen ratios at the magnetic-field-induced quantum phase transition in NiCl2-4SC(NH2)2 — •Manuel Brando1, Robert Kuechler1, Luis Pedrero1, Alexander Steppke1, Armando Paduan-Filho2, Christian Batista3, Franziska Weickert3, Vivien Zapf3, Marcelo Jaime3, and Frank Steglich11Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187 Dresden, Germany — 2Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo, Brazil — 3Los Alamos National Laboratory, Los Alamos, USA

The tetragonal organic system NiCl2-4SC(NH2)2 (known as DTN) is a quantum paramagnet where the Ni atoms form S=1 dimers which are weakly coupled along the crystallographic c axis. The Ni2+ single ion anisotropy D = 8.9 K opens an energy gap between the Sz = 0 ground state and the Sz = ± 1 first excited state. When a magnetic field H is applied along c, it closes the gap and induces a transition into an XY-antiferromagnetic ordered state at low temperatures. For T=0 the critical field Hc1 ≈ 2 T. Such a quantum critical point belongs to the d=3 and z=2 universality class and the following theoretical laws are predicted: The magnetization MTd/z, the phase boundary line (HHc1)∝ Tcd/z, the thermal and magnetic Grüneisen ratios, Γ and ΓH, are expected to follow T−1. We present measurements of the magnetization, specific heat and thermal expansion in the temperature range 0.05 ≤ T ≤ 5 K across Hc1 and analyse the critical behavior of Γ and ΓH at Hc1.

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