S=1/2 Heisenberg antiferromagnetic spin chain [Cu(dmbpy)(H2O)(2)SO4] (dmbpy=4,4 '-dimethyl-2,2 '-bipyridine): Synthesis, crystal structure and enhanced magnetocaloric effect
Abstract
[Cu(dmbpy)(H2O)(2)SO4] in the form of small blue crystals was prepared from the aqueous-ethanolic reaction mixture formed of CuSO4 and dmbpy (dmbpy = 4,4'-dimethyl-2,2'-bipyridine). Its crystal structure consists of chains in which hexacoordinated Cu(II) atoms are linked by (mu(2)-SO4)(2-) anions.
The Cu(II) atom exhibits elongated tetragonal bipyramidal coordination with one chelate bonded dmbpy and two aqua ligands placed in the equatorial plane while the axial positions are occupied by bridging sulfato ligands. The study of electron spin resonance and specific heat enabled to identify the studied material as an S = 1/2 Heisenberg antiferromagnetic chain with weak intrachain exchange interaction, 2J/k(B) = -1.12 K and a small anisotropy of g - factor, Delta g/g approximate to 0.1.
The analysis of the magnetic entropy revealed pronounced release of the entropy at the saturation magnetic field, which for spin chains induces quantum phase transition, namely B-sat = 1.56 T. The maximum isothermal change of the entropy Delta S-M = 2.86 J/Kmol is comparable to that released in a critical region for materials with magnetic phase transitions.
The obtained results suggest that the existence of a quantum critical point significantly influences finite-temperature properties. (C) 2013 Elsevier Masson SAS. All rights reserved.