Structural and magnetic investigations for the doping effect of nonmagnetic impurity on the spin-Peierls-like transition in a quasi-one-dimensional magnet: 1-(4′-nitrobenzyl)pyridinium bis(maleonitriledithiolato)nickelate

A nonmagnetic compound, [NO₂BzPy][Au(mnt)₂] (NO ₂BzPy⁺ = 1-(4′-nitrobenzyl)pyridinium; mnt ² = maleonitriledithiolate), was synthesized and characterized structurally, which is isostructural with [NO₂BzPy][Ni(mnt) ₂] that is a quasi-one-dimensional magnet and possesses a spin-Peierls-like transition with J = 192 K in the gapless state and spin energy gap = 738 K in the dimerization state, respectively. Further, ten nonmagnetic impurity doped compounds with a formula [NO₂BzPy][Au _xNi_1-x(mnth)₂ (x = 0.01-0.73) were prepared and investigated by crystal structural determinations and magnetic susceptibility measurements. The nonmagnetic doping causes the suppression of the spin transition with an average rate of 221(12) K/percentage of dopant concentration. From the plots of χ_m-T, the transition collapse (the characteristic of the transition is the sudden drop of χ_m upon cooling, and the disappearance of this characteristic is considered as the criterion for the transition collapse) is estimated at around x> 0.27. In heavier doped system x = 0.49, the spin gap vanishes and a gapless phase is achieved again.