ACTA

Experimental Studies of S=1 Heisenberg Planar Antiferromagnetic Chain Ni(C₁₁H₁₀N₂O)₂Ni(CN)₄

E. Čizmár^a, J. Černák^a, M. Orendáč^a, T. Herrmannsdörfer^b and A. Feher^a
^a Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 04154 Košice, Slovakia
^b Physikalisches Institut, Universität Bayreuth, 95440 Bayreuth, Germany

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In this paper we discuss the results of experimental studies of specific heat and magnetic susceptibility of chain compound Ni(C₁₁H₁₀N₂O)₂Ni(CN)₄. We have observed a Schottky type anomaly at T=2.2 K in a temperature dependence of specific heat and the compound was identified as a S=1 Heisenberg 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 Heisenberg chains with the strong planar anisotropy. The analysis suggests that the in-plane anisotropy should be considered in any attempt to find a compound potentially located in the boundary of Haldane and "large-D" phases.

DOI: 10.12693/APhysPolA.97.579
PACS numbers: 75.40.Cx, 71.20.Be, 75.50.Ee