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L. Lederová, A. Orendáčová, R. Tarasenko, M. Bartosik, V. Tkáč, P.H. Mayrhofer, M. Orendáč, V. Sechovský, A. Feher:
"Thermodynamic properties of the two-dimensional quantum magnet Cu(tn)Cl2";
Talk: The 21st International Conference on Solid Compound of Transition Elements, Vienna; 2018-03-25 - 2018-03-29.

Previous studies of polycrystalline Cu(tn)Cl2, (tn = C3H10N2) identified the compound as an excellent realization of a two-dimensional (2d) quantum magnet. While the phase transition to magnetic long-range order was not observed down to 50 mK, the response of the material to the applied magnetic field mimics a field-induced Berezinskii-Kosterlitz-Thouless transition theoretically predicted for the Heisenberg antiferromagnet (HAF) on a square lattice+. While such behavior indicates an extreme weakness of interlayer magnetic correlations, the character of the 2d magnetic lattice is not known+.
Present work is focused on the determination of the intra-layer exchange interactions. For that purpose, specific heat, magnetic susceptibility and elastic properties of a single crystal were experimentally investigated nominally at temperatures from 0.3 to 300 K. Since the quantitative analysis of the magnetic specific heat is highly sensitive to the estimation of the phonon contribution, various approaches were applied for its determination as the use of diamagnetic isomorph Zn(tn)Cl2 and elastic constants. The resulting magnetic contribution was analyzed within a model of the spin ½ HAF on the spatially anisotropic square lattice with nearest-neigbour coupling J and J´. The best agreement was obtained for J´/J = 0.3 and J/kB = 4.4 K. However, susceptibility data suggest the co-existence of ferro and antiferromagnetic interactions within the magnetic layer, namely J´/J = -0.5 and J/kB = 4.4 K. Additional steps including first-principle study are discussed.