Abstract
In this paper we study an organic system of geometrical spin frustration. m-N-methylpyridinium α-nitronyl nitroxide (m-) is a spin-1/2 organic radical. The simple salt, m-⋅⋅1/3 (acetone), crystallizes in a trigonal P3c1 space group, where the m- molecules exist as a dimer and the dimer units form a two-dimensional (2D) triangular lattice. One-third of the ions are in the organic layer, joining the m- molecules, and the remainder is between the layers, compensating the excess of positive charge in the organic layers. The single-crystal EPR measurements clearly indicate a 2D Heisenberg character of the magnetic system in it. m- makes a crystalline solid-solution system, m-⋅(⋅⋅1/3 (acetone) (0≤x≤1), which also belongs to the trigonal system. Both the a and c axes are slightly lengthened with increasing the ratio of the ion, x, in the solid solution: The unit-cell volume is increased by 3.2% when x runs from 0 to 1. The temperature dependence of the magnetic susceptibilities of the solid solutions can be well interpreted in terms of a strong ferromagnetic intradimer interaction forming a triplet state and a weak antiferromagnetic interdimer interaction which is expected to give rise to spin frustration among the triplet spin species on each side of the triangles. It is found that quickly weakens with an increase in x, while shows little dependence. There is a possibility that this organic system can be characterized as a spin-1 kagomé antiferromagnet at very low temperatures.
- Received 16 August 1993
DOI:https://doi.org/10.1103/PhysRevB.49.3975
©1994 American Physical Society