Fingerprints of field-induced Berezinskii-Kosterlitz-Thouless transition in quasi-two-dimensional S=1/2 Heisenberg magnets Cu(en)(H2O)(2)SO4 and Cu(tn)Cl-2
Abstract
Organo-metallic compounds Cu(en)(H2O)(2)SO4 (en=C2H8N2) and Cu(tn)Cl-2 (tn=C3H10N2) representing S = 1/2 quasi-two-dimensional Heisenberg antiferromagnets with an effective intra-layer exchange coupling J/k(B) approximate to 3 K, have been examined by specific heat measurements at temperatures down to nominally 50 mK and magnetic fields up to 14 T. A comparative analysis of magnetic specific heat in zero magnetic field revealed nearly identical contribution of short-range magnetic correlations and significant differences were observed at lowest temperatures.
A phase transition to long-range order was observed in Cu(en)(H2O)(2)SO4 at T-c=0.9 K while hidden in Cu(tn)Cl-2. A response of both compounds to the application of magnetic field has rather universal features characteristic for a field-induced Berezinskii-Kosterlitz-Thouless transition theoretically predicted for ideal two-dimensional magnets.