Spin-Peierls transition in N-methyl-N-ethyl-morpholinium-ditetracyanoquinodimethanide [MEM-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mn/><mml:mo>(</mml:mo><mml:mi mathvariant="normal">TCNQ</mml:mi><mml:mo>)</mml:mo><mml:mn/></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>]

Abstract

In this paper we reinterpret the magnetic-susceptibility data and present and discuss specificheat data on MEM-${(\mathrm{TCNQ})}_{2}$ in terms of a spin-Peierls transition theory. We find that the data can be described reasonably well by a mean-field spin-Peierls transition theory which suggests that at low temperatures the TCNQ chain should be tetramerized. The magnetic susceptibility above the transition temperature is shown to behave like a one-dimensional Heisenberg antiferromagnet. The consequences of this behavior on the relative magnitude of the on-site Coulomb interaction are discussed.