Giant negative magnetoresistance in quasi-one-dimensional conductorTPP[Fe(Pc)(CN)2

Abstract

We have found giant negative magnetoresistance in the one-dimensional conductor TPP͓Fe(Pc)(CN) 2 ͔ 2 below 50 K. The reduction of the resistance is larger in the field perpendicular to the one-dimensional axis than parallel to the axis. The magnetic susceptibility shows anisotropic Curie-Weiss behavior. The experimental results suggest the interaction between the one-dimensional electron system and the local moments. The reduction of the spin scattering of the itinerant electrons by the local moments under the field is proposed as the origin of the giant negative magnetoresistance.The interplay between conduction electrons and local magnetic moments has provided a variety of interesting phenomena such as Kondo effect, Ruderman-Kittel-KasuyaYosida interaction, heavy fermion, giant magnetoresistance, and colossal magnetoresistance. 1-5 The giant negative magnetoresistance was reported in the manganese oxides 5 and -BETS 2 FeCl 4 , 6 and is accompanied or caused by the sharp metal-insulator transition.There have been very few reports on these phenomena in the one-dimensional system, although theoretical studies predict several attractive phenomena such as Kondo effects in a Luttinger liquid. 3,7,8 Quasi-one-dimensional molecular conductors are good candidates for this research. By introducing the local moments (d electron͒ into these conductors, the interaction (-d interaction͒ between the one-dimensional conduction electrons ( electron͒ and the local moments is expected to give different electronic states. In fact, interesting phenomena such as negative magnetoresistance were reported in the one-dimensional molecular conductor ͓Cu x Ni 1Ϫx (Pc)͔(I 3 ) 1/3 , 9,10 where electron in Pc ͑ϭphthalocyanine͒ forms the conduction band and d electron in Cu 2ϩ affords the local moment. However, owing to the experimental difficulty, the systematic studies on the anisotropy of this system have not been reported. The negative magnetoresistance was also reported in the one-dimensional Peierls compounds, 11 and the critical temperature of the negative magnetoresistance decreases on increasing the magnetic-field strength.The title compound TPP͓Fe(Pc)(CN) 2 ͔ 2 and the isostructural compound TPP͓Co(Pc)(CN) 2 ͔ 2 ͑TPPϭtetraphenyl-phosphonium͒ have a one-dimensional conduction band coming from the orbital of Pc, since the partially oxidized Pc units stack uniformly along the c axis. The Fe compound has Sϭ1/2 local moments of Fe 3ϩ in the conduction path, 12 while there are no local moments in the Co compound. 13 TPP molecules and CN ligands hold closed-shell orbitals. The striking difference in the resistance behavior of these compounds was reported. 12,13 This difference suggests the possibility of the interaction between the one-dimensional conduction electrons and the local moments.The Pc molecule has a structure with fourfold symmetry and one can expect the degeneracy in the molecular orbitals of Pc. It is of great interest how this degeneracy influences the physical properties.In order to obtain the clear-cut experimental evidenc...

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

“…Both salts have semi-conducting temperature dependence of resistivity. The Fe-salt shows a large negative magnetoresistance (MR) which amounts to ρ(H)/ρ(0) ∼ 10 −2 , where ρ(H) is the resistivity under the magnetic field H. The experimental findings are summarized as follows; (1) the activation energy derived from the resistivity data are ∆ a ∼ 10 −3 eV and ∼ 10 −2 eV for Co-and Fe-salts, respectively 9 . (2) The localized moment has anisotropic g-values, g ⊥ ∼ 3.6 and g ∼ 0.5 − 1 which are roughly perpendicular and parallel to the molecular-axis, respectively.…”

Photochemical modification of magnetic properties in organic low-dimensional conductors

“…Therefore the lower dimensionality involves a smaller number of intermolecular interactions, which are basically weak van der Waals interactions, dominating electrical and magnetic properties. Accordingly these structural situations peculiar to molecular charge transfer salts make the resultant electronic system far more sensitive to perturbations such as structural change [1][2][3], magnetic field [4][5][6][7][8][9][10][11], and lattice defects [12] than usual conductors having isotropic structures. This is one of the reasons the organic charge transfer salts are interesting in terms of sensors and devices.…”

Magnetic torque and heat capacity measurements onTPP[Fe(Pc)(CN)2Tajima1, Yoshida2, Matsuda3 et al. 2008Phys. Rev. B290130View full textAdd to dashboardCite

“…One piece of evidence to support this consideration is the magnetic torque for the field rotated within the ac plane. 1 Because of the anisotropic g factors, these data mainly reflect the contributions of d electrons rather than those of electrons. The data exhibit a smooth decrease in torque amplitude below 20 K and do not exhibit any anomaly associated with the abrupt increase in the susceptibility below 13 K. This implies that the abrupt increase in susceptibility is not associated with d electrons but with electrons.…”

“…Figure 2 shows the temperature dependence of the magnetic susceptibility for TPP͓Fe͑Pc͒͑CN͒ 2 ͔ 2 , reported elsewhere. 1,8 The susceptibility is highly anisotropic for the field direction. Since the z axis ͑ ʈ CN axis: the direction of the largest g factor͒ is almost perpendicular to the crystallographic c axis, the magnetic susceptibility for B Ќ c is much larger than that for B ʈ c. The B Ќ c susceptibility exhibits a peak around 25 K, gradually decreases down to 13 K, and then abruptly increases.…”

“…1,2 Here, Pc and TPP denote phthalocyanine and tetraphenylphosphonium, respectively. This GNMR is an interesting phenomenon both experimentally and theoretically, 3 since it is not caused by a sharp transition such as the field-induced metal-insulator transition observed in the manganese oxides 4 and -͑BETS͒ 2 FeCl 4 .…”