Experimental studies of S=1 Heisenberg planar antiferromagnetic chain Ni(C11H10N2O)(2)Ni(CN)(4)

In this paper we discuss the results of experimental studies of specific he at and magnetic susceptibility of chain compound Ni(C11H10N2O)(2)Ni(CN)(4). We have observed a Schottky type anomaly at T = 2.2 K in a temperature dep endence of specific heat and the compound was identified as a S = 1 Heisenb erg antiferromagnetic chain with the subcritical exchange coupling D/k(B) = 5 K, D/\J\ = 5.2 and the strong in-plane anisotropy E/k(B) = 2.8 K. It has been found that the in-plane anisotropy affects the region of validity of a diluted exciton model [1] and a strong coupling model [2] for S = 1 Heise nberg chains with the strong planar anisotropy. The analysis suggests that the in-plane anisotropy should be considered in any attempt to find a compo und potentially located in the boundary of Haldane and "large-D" phases.