Giant Negative Magnetoresistance Reflecting Molecular Symmetry in Dicyano(phthalocyaninato)iron Compounds

Abstract

Materials containing Fe(Pc)(CN) 2 dicyano(phthalocyaninato)iron molecules show a giant negative magnetoresistance from the interaction between the conduction and the local moment. Under a magnetic field, the resistance becomes two orders of magnitude smaller than the zero-field resistance. The magnetic-field-angle dependence of the magnetoresistance reflects the symmetry of the Fe(Pc)(CN) 2 molecule. We discuss, according to the scaling relation, the correlation between the magnetoresistance and the molecular spin fluctuation. The giant response of spin-dependent transport has made many important contributions to physics and has been applied to magnetic storage and sensors, such as gigantic magnetoresistance.1) For molecular application, giant magnetoresistance in molecular materials is a key phenomenon. The intermolecular or intramolecular interaction between the conduction and the local moments is indispensable. Several studies have focused on molecular conductors having an interaction (-d interaction) between the molecules contributing to the conduction of the electron and the other molecules contributing to the magnetism of the d electron.2,3) In these conductors, it is important to control the molecular arrangement in the crystal. 4) If a single molecule contributes to both the electron conduction and the local moments, one can expect the possibility of an intramolecular -d interaction independent of the molecular arrangement. The physical properties resulting from the intramoleculard interaction can be realized not only in the crystal but in other various forms, such as film. The metal-phthalocyanine molecule is advantageous, since it provides the -d interaction between the electron conduction of the phthalocyanine molecular orbitals and the local moment of the central transition metal. 9) In this letter, we report the magnetoresistance and its dependence on the magnetic field angle in the Fe(Pc)(CN) 2 molecular complexes. The various Fe(Pc)(CN) 2 complexes show a giant negative magnetoresistance reflecting the molecular symmetry. The -d interaction causes a giant negative magnetoresistance in various compounds, in spite of the different molecular arrangements. Because the CN ligands of the Fe(Pc)(CN) 2 molecule markedly improve its solubility, the CN-ligands enable not only the growth of the molecular crystal but also the fabrication of a molecular thin film by a wet process. The needlelike single crystal is synthesized by the electrochemical method.9,11) The proportions of iron and cobalt atoms in the alloy TPP[Fe x Co 1Àx (Pc)(CN) 2 ] 2 are investigated by electron probe micro analysis (EPMA). Gold wires were glued with gold paint to the sample surface, and dc resistance was measured. A constant current (or voltage) was applied along the c axis, and sample voltage (or current) was measured. The experiments were performed with an 18 T superconducting magnet and a pulse magnet.

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.…”

Theoretical Studies on Phase Transitions in Quasi-One-Dimensional Molecular Conductors

“…A typical example is found in phthalocyanine (Pc) compounds such as TPP[Fe(Pc)(CN) 2 ] 2 [67], where observations of a giant magnetoresistance [68] has attracted much interest. In the latter material, π-electrons in the HOMO of Pc forms a 1D conduction band, whereas d-electrons in the center Fe atom are considered to be localized spins with strong anisotropy, namely Ising spins [68]. Since these two types of electron exist in one molecule, we expect strong π-d interaction between them.…”

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

“…7 In the case of TPP͓Fe͑Pc͒͑CN͒ 2 ͔ 2 , the resistance ratio R͑H͒ / R͑0͒ is less than 0.01 at T = 20 K and H = 350 kOe. 8 It is not caused by a phase transition such as the field-induced metal-insulator transition observed in the manganese oxides 9 and -͑BETS͒ 2 FeCl 4 . 10 It is highly anisotropic in regard to the magnetic-field direction reflecting the molecular orientations of ͓Fe͑Pc͒͑CN͒ 2 ͔.…”