Charge Disproportionation in Highly One-Dimensional Molecular Conductor TPP[Co(Pc)(CN)₂]₂

Abstract

We investigated the ground state of a highly one-dimensional conductor, TPP[Co(Pc)(CN) 2 ] 2 (TPP = tetraphenylphosphonium and Pc = phthalocyanine), by the measurement of the X-ray diffraction, electron spin resonance, nuclear quadrupole resonance, and magnetoresistance. An increase of the magnetic fluctuations was observed below 20 K, where no structural deformation was detected. In the 59 Co nuclear quadrupole resonance, we found an asymmetric broadening of the spectra owing to the intrinsic inhomogeneity of the molecular charge. We propose that the ground state is characterized by a weak charge disproportionation with antiferromagnetic fluctuations due to the high one dimensionality. A large magnetoresistance was observed under a high magnetic field. Spin effects are dominant at low fields. The anisotropic magnetoresistance suggests a change in the ground-state nature above 10 T.

Interplay of strongly correlated electrons and localized Ising moments in one dimension

“…Therefore, J does not seem to favor the suppression of charge order by the magnetic field. While, the Co-salt shows a small but positive MR 19 , which is incompatible with our results. Also the present model which focuses on the particular density of d-spins cannot cope with the issue (7).…”

“…even when the degree of replacement is as large as Fe 0.07 Co 0.93 , the MR amounts to ρ(H)/ρ(0) ∼ 0.5 20 , (8) the magnetization of electrons gradually increases with H, and that of the Fe-moments starts at H c ∼ 15T 21 . (9) the ground state of the electronic chain is weakly charge ordered which is observed by the NQR study 19 .…”

“…(4) Residual magnetization is observed at T < 12K, which is attributed to the ferrimagnetism of π-electrons by the torque experiment 18 . (5) The MR is not scaled by the magnetization and shows large Tdependence 19 . (6) Phase transition is absent (in contrast to DEX), namely the scenario of the competition of two different orders are not applicable.…”

Local Lattice Distortion Caused by Short-Range Charge Ordering in Transition Metal Oxides

“…[1][2][3] However, in several materials including the transition metal ions with non-integer valences and non-metallic conductivities, superlattice reflection and/or structural phase transition showing charge ordering are not observed. [4,5] It is expected that because the electrons are localized only with a short-range ordering in such materials, the arrangement of the inequivalent sites with the different valences also has shortrange correlation, resulting in the absence of superlattice Bragg reflection. Because the atomic pair distribution function (PDF) can determine the atomic arrangement without the long-range ordering, it is appropriate to reveal the local lattice distortion caused by such a short-range charge ordering.…”

Magnetic torque and ac and dc magnetic susceptibility measurements onPTMA0.5[Fe(Pc)(CNTajima1, Yoshida2, Matsuda3 et al. 2009Phys. Rev. B13050View full textAdd to dashboardCite

“…18,19 This phenomenon was experimentally suggested in TPP͓Co͑Pc͒͑CN͒ 2 ͔ 2 , which is isostructural with TPP͓Fe͑Pc͒͑CN͒ 2 ͔ 2 but does not have a local magnetic moment. 20 Since TPP͓Fe͑Pc͒͑CN͒ 2 ͔ 2 has a local magnetic moment associated with d electrons, the situation is not completely the same as those described above. However, a 4k F diffuse streak was recently found in TPP͓Fe͑Pc͒͑CN͒ 2 ͔ 2 at low temperatures below 80 K. 21 This finding provides some basis for assumption ͑iv͒.…”