Spin-Peierls transitions in magnetic donor-acceptor compounds of tetrathiafulvalene (TTF) with bisdithiolene metal complexes

Abstract

The spin-Peierls transition is considered as a progressive spin-lattice dimerization occurring below a transition temperature in a system of one-dimensional antiferromagnetic Heisenberg chains. In the simplest theories, the transition is second order and the ground state is a singlet with a magnetic gap. The historical origins and theoretical development of the concept are examined. Magnetic susceptibility and EPR measurements on the 7T-donor-acceptor compounds TTF· MS4C.(CF3) 4 (M =Cu, Au; TTF is tetrathiafulvalene) are reported. These compounds exhibit clearly the characteristics of the spin-Peierls transition in reasonably good agreement with a mean-field theory. The susceptibility of each compound has a broad maximum near 50 K, while the transitions occur at 12 and 2.1 K for M =Cu and Au, respectively. EPR linewidth observations over a broad temperature range are examined. Areas for further experimental and theoretical work are indicated, and a critical comparison is made of related observations on other materials.

Two-gap magnetic structure of the two-stack anion-radical salt (N-Me-3,5-Di-Me-Py)(TCNQ)2 (Py is pyridine)

“…This transition was experimentally observed for the first time in charge-transfer complexes (TTF)[M{S 2 C 2 (CF 3 ) 2 }] (TTF = tetrathiafulvalene) (M = Cu, Au) [6,7] and MEM-(TCNQ) 2 (MEM = methyl-ethylmorpholinium) [8]. Decades later, the spin-Peierls transition was observed also in inorganic compounds, firstly in CuGeO 3 [9], which is a main representant of spinPeierls inorganic systems, and later also in (VO) 2 P 2 O 7 [10], which is a model system of interacting chains.…”

Another dimension: investigations of molecular magnetism using muon–spin relaxation

“…These results have now been extended to the related material DEM(TCNQ) 2 [49]. Other examples of spin-Peierls systems include other organic systems such as TTF-CuS 4 C 4 (CF 3 ) 4 (T sP = 12 K) [50] and TTF-AuS 4 C 4 (CF 3 ) 4 (T sP = 2 K) [50,51]. A common feature of such materials is flat organic molecules in columnar stacks.…”

Low-temperature heat transport of spin-gapped quantum magnets

“…The SP transition was originally observed in some organic compounds [19], and was found in an inorganic compound, CuGeO 3 , for the first time by Hase et al in 1993 [20]. For the occurrence of a SP transition, several preconditions are necessary: firstly, a crystal must contain (quasi-) 1D AFM chains of half-integer spin; secondly, the spin-phonon coupling is strong.…”