S=1/2 Ferromagnetic Heisenberg Chain In A Verdazyl-Based Complex

We present a model compound for the S = 1/2 ferromagnetic Heisenberg chain composed of the verdazyl-based complex [Zn(hfac)(2)][4-Cl-o-Py-V-(4-F)(2)]. Ab initio MO calculations indicate a predominant ferromagnetic interaction forming an S = 1/2 ferromagnetic chain. The magnetic susceptibility and specific heat indicate a phase transition to an antiferromagnetic (AF) order due to the finite interchain couplings. We explain the magnetic susceptibility and magnetization curve above the phase-transition temperature based on the S = 1/2 ferromagnetic Heisenberg chain. The magnetization curve in the ordered phase is described by a conventional AF two-sublattice model. Furthermore, the obtained magnetic specific heat reproduces the almost temperature-independent behavior of the S = 1/2 ferromagnetic Heisenberg chain. In the low-temperature region, the magnetic specific heat exhibits a root T dependence, which is attributed to the energy dispersion in the ferromagnetic chain.