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TT: Fachverband Tiefe Temperaturen

TT 23: CE: Quantum-Critical Phenomena 2

TT 23.4: Vortrag

Dienstag, 15. März 2011, 11:15–11:30, HSZ 105

Thermodynamics of the spin-dimer NiCl₂-4SC(NH₂)₂ system at the magnetic-field-induced quantum phase transition — •Alexander Steppke¹, Robert Kuechler¹, Luis Pedrero¹, Manuel Brando¹, Armando Paduan-Filho², Christian Batista³, Franziska Weickert³, Vivien Zapf³, Marcelo Jaime³, and Frank Steglich¹ — ¹Max-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 concept of universality class in magnetic systems undergoing a quantum phase transition (QPT) can be tested in so-called quantum magnets, where the local spins are coupled forming ladders (TlCuCl₃), planes of dimers (BaCuSi₂O₆) or weakly coupled chains of S=1 Ni atoms, as in the organic system NiCl₂-4SC(NH₂)₂ (DTN). In DTN the Ni²⁺ single ion anisotropy D = 8.9 K opens an energy gap between the S_z = 0 ground state and the S_z = ± 1 first excited state. At a magnetic field Hc₁ ≈ 2 T the gap closes and a transition into an XY-antiferromagnetic ordered state is induced at low temperatures. Such a QPT belongs to the d=3 and z=2 universality class and the following theoretical laws are predicted: The magnetization M∝ T^d/z, the phase boundary line (H−Hc₁)∝ T_c^d/z, the thermal and magnetic Grüneisen ratios are expected to follow T⁻¹. We have investigated the temperature and field dependences of all these thermodynamic quantities in the temperature range 0.05 ≤ T ≤ 5 K.