Study of the Gr\"{u}neisen Parameters at a Field-induced Quantum Critical Point in NiCl2-SC(NH2)2*

NiCl$_{2}$-SC(NH$_{2})_{2}$, also known as DTN, is a quantum paramagnet, where the Ni$^{2+}$ single ion anisotropy $D$ = 8.9K opens an energy gap between the $S_{z}$ = 0 ground state and the $S_{z}=\pm $1 exited state. In this material an XY-antiferromagnetic ordered state is induced at low temperatures by applying magnetic fields between $H_{c1} \quad \approx $ 2T and $H_{c2}$ = 10.5T. At the phase boundaries critical exponents consistent with Bose-Einstein condensation of magnons are found. Here we present investigations of quantum criticality close to $H_{c1}$ by thermal expansion, magnetization and specific heat measurements. Our data reveal a divergency for T$\to $ 0 of the thermal and magnetic Gr\"{u}neisen parameters as expected for a quantum critical point of a diluted Bose gas.