Heat capacity of Cu-2(C5H12N2)(2)Cl-4 in a magnetic field

Heat capacity measurements down to 0.5 K in a magnetic field up to 12 T hav e been performed on a single-crystal sample of a spin-ladder-like compound Cu-2(C5H12N2)(2)Cl-4 The singlet ground state with an energy gap becomes ma gnetic and gapless between 7 T (H-c1) and 13 T (H-c2). In the temperature d ependence of the heat capacity of this compound, we have observed a sharp a nd a round peak in the gapless region between H-c1 and H-c2. The former pea k most likely arises from the long-range order and the latter one is probab ly attributable to the low-energy excitation structure in a gapless spin-li quid system, (C) 2000 Elsevier Science B.V. All rights reserved.