Mixed valency of Cu, electron-mass enhancement, and three-dimensional arrangement of magnetic sites in the organic conductors (R1,R2-N,N'-dicyanoquinonediimine)2Cu (where R1,R2=CH3,CH3O,Cl,Br)

H. Kobayashi, A. Miyamoto, R. Kato, F. Sakai, A. Kobayashi, Y. Yamakita, Yukio Furukawa, M. Tasumi, T. Watanabe

Research output: Contribution to journalArticle

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Abstract

The unique molecular conductors with pπ-d mixing band structures (R1,R2-N,N'-dicyanoquinonediimine)2Cu [(R1,R2-DCNQI)2Cu] (R1,R2=CH3,CH3O,Cl,Br) were examined. General features of the phase diagram of the DCNQI-Cu system were depicted. A region that is related to the existence of anomalously heavy-metal electrons has been found. The T2 dependence of the low-temperature resistivity of the alloyed system (DMe1-xMeBrx-DCNQI)2Cu (where Me=CH3) suggests a large enhancement of the electron mass at the critical situation where the system begins to exhibit a characteristic metal instability. The mixed valency of Cu (Cu+1.3) in (DMe-DCNQI)2Cu was confirmed by ir experiments performed on neutral DMe-DCNQI crystals and (DMe-DCNQI)2M (M=Li, Ba, Cu). The same conclusion was also derived from a low-temperature x-ray-diffraction experiment. The gradual temperature dependences of the ir absorption intensities of totally symmetric modes of (DBr-DCNQI)2Cu observed below the metal-insulator transition temperature (TMI) are in contrast with the discontinuous resistivity and susceptibility changes at TMI. This may be attributable to the existence of two driving forces characterizing the M-I transition. One is the sharp charge ordering in Cu sites and the other is the continuous development of charge-density waves on DCNQI stacks. The arrangement of Cu2+ and Cu+ below TMI was determined by an x-ray crystal-structure analysis of the threefold insulating phase of (MeBr-DCNQI)2Cu at 110 K. The nearest-neighbor Cu2+ ions interact with each other via two DCNQI molecules. A plausible spin structure of the antiferromagnetic ground state was proposed. According to this spin-structure model, the magnetic moments of Cu2+ along the crystallographic c axis will be arranged ferromagnetically.

Original languageEnglish
Pages (from-to)3500-3510
Number of pages11
JournalPhysical Review B
Volume47
Issue number7
DOIs
Publication statusPublished - 1993
Externally publishedYes

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Organic conductors
electron mass
conductors
electrical resistivity
Electrons
augmentation
heavy metals
metals
Charge density waves
X rays
Metal insulator transition
x ray diffraction
magnetic moments
transition temperature
phase diagrams
insulators
Heavy Metals
Model structures
Magnetic moments
magnetic permeability

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Mixed valency of Cu, electron-mass enhancement, and three-dimensional arrangement of magnetic sites in the organic conductors (R1,R2-N,N'-dicyanoquinonediimine)2Cu (where R1,R2=CH3,CH3O,Cl,Br). / Kobayashi, H.; Miyamoto, A.; Kato, R.; Sakai, F.; Kobayashi, A.; Yamakita, Y.; Furukawa, Yukio; Tasumi, M.; Watanabe, T.

In: Physical Review B, Vol. 47, No. 7, 1993, p. 3500-3510.

Research output: Contribution to journalArticle

Kobayashi, H. ; Miyamoto, A. ; Kato, R. ; Sakai, F. ; Kobayashi, A. ; Yamakita, Y. ; Furukawa, Yukio ; Tasumi, M. ; Watanabe, T. / Mixed valency of Cu, electron-mass enhancement, and three-dimensional arrangement of magnetic sites in the organic conductors (R1,R2-N,N'-dicyanoquinonediimine)2Cu (where R1,R2=CH3,CH3O,Cl,Br). In: Physical Review B. 1993 ; Vol. 47, No. 7. pp. 3500-3510.
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abstract = "The unique molecular conductors with pπ-d mixing band structures (R1,R2-N,N'-dicyanoquinonediimine)2Cu [(R1,R2-DCNQI)2Cu] (R1,R2=CH3,CH3O,Cl,Br) were examined. General features of the phase diagram of the DCNQI-Cu system were depicted. A region that is related to the existence of anomalously heavy-metal electrons has been found. The T2 dependence of the low-temperature resistivity of the alloyed system (DMe1-xMeBrx-DCNQI)2Cu (where Me=CH3) suggests a large enhancement of the electron mass at the critical situation where the system begins to exhibit a characteristic metal instability. The mixed valency of Cu (Cu+1.3) in (DMe-DCNQI)2Cu was confirmed by ir experiments performed on neutral DMe-DCNQI crystals and (DMe-DCNQI)2M (M=Li, Ba, Cu). The same conclusion was also derived from a low-temperature x-ray-diffraction experiment. The gradual temperature dependences of the ir absorption intensities of totally symmetric modes of (DBr-DCNQI)2Cu observed below the metal-insulator transition temperature (TMI) are in contrast with the discontinuous resistivity and susceptibility changes at TMI. This may be attributable to the existence of two driving forces characterizing the M-I transition. One is the sharp charge ordering in Cu sites and the other is the continuous development of charge-density waves on DCNQI stacks. The arrangement of Cu2+ and Cu+ below TMI was determined by an x-ray crystal-structure analysis of the threefold insulating phase of (MeBr-DCNQI)2Cu at 110 K. The nearest-neighbor Cu2+ ions interact with each other via two DCNQI molecules. A plausible spin structure of the antiferromagnetic ground state was proposed. According to this spin-structure model, the magnetic moments of Cu2+ along the crystallographic c axis will be arranged ferromagnetically.",
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T1 - Mixed valency of Cu, electron-mass enhancement, and three-dimensional arrangement of magnetic sites in the organic conductors (R1,R2-N,N'-dicyanoquinonediimine)2Cu (where R1,R2=CH3,CH3O,Cl,Br)

AU - Kobayashi, H.

AU - Miyamoto, A.

AU - Kato, R.

AU - Sakai, F.

AU - Kobayashi, A.

AU - Yamakita, Y.

AU - Furukawa, Yukio

AU - Tasumi, M.

AU - Watanabe, T.

PY - 1993

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N2 - The unique molecular conductors with pπ-d mixing band structures (R1,R2-N,N'-dicyanoquinonediimine)2Cu [(R1,R2-DCNQI)2Cu] (R1,R2=CH3,CH3O,Cl,Br) were examined. General features of the phase diagram of the DCNQI-Cu system were depicted. A region that is related to the existence of anomalously heavy-metal electrons has been found. The T2 dependence of the low-temperature resistivity of the alloyed system (DMe1-xMeBrx-DCNQI)2Cu (where Me=CH3) suggests a large enhancement of the electron mass at the critical situation where the system begins to exhibit a characteristic metal instability. The mixed valency of Cu (Cu+1.3) in (DMe-DCNQI)2Cu was confirmed by ir experiments performed on neutral DMe-DCNQI crystals and (DMe-DCNQI)2M (M=Li, Ba, Cu). The same conclusion was also derived from a low-temperature x-ray-diffraction experiment. The gradual temperature dependences of the ir absorption intensities of totally symmetric modes of (DBr-DCNQI)2Cu observed below the metal-insulator transition temperature (TMI) are in contrast with the discontinuous resistivity and susceptibility changes at TMI. This may be attributable to the existence of two driving forces characterizing the M-I transition. One is the sharp charge ordering in Cu sites and the other is the continuous development of charge-density waves on DCNQI stacks. The arrangement of Cu2+ and Cu+ below TMI was determined by an x-ray crystal-structure analysis of the threefold insulating phase of (MeBr-DCNQI)2Cu at 110 K. The nearest-neighbor Cu2+ ions interact with each other via two DCNQI molecules. A plausible spin structure of the antiferromagnetic ground state was proposed. According to this spin-structure model, the magnetic moments of Cu2+ along the crystallographic c axis will be arranged ferromagnetically.

AB - The unique molecular conductors with pπ-d mixing band structures (R1,R2-N,N'-dicyanoquinonediimine)2Cu [(R1,R2-DCNQI)2Cu] (R1,R2=CH3,CH3O,Cl,Br) were examined. General features of the phase diagram of the DCNQI-Cu system were depicted. A region that is related to the existence of anomalously heavy-metal electrons has been found. The T2 dependence of the low-temperature resistivity of the alloyed system (DMe1-xMeBrx-DCNQI)2Cu (where Me=CH3) suggests a large enhancement of the electron mass at the critical situation where the system begins to exhibit a characteristic metal instability. The mixed valency of Cu (Cu+1.3) in (DMe-DCNQI)2Cu was confirmed by ir experiments performed on neutral DMe-DCNQI crystals and (DMe-DCNQI)2M (M=Li, Ba, Cu). The same conclusion was also derived from a low-temperature x-ray-diffraction experiment. The gradual temperature dependences of the ir absorption intensities of totally symmetric modes of (DBr-DCNQI)2Cu observed below the metal-insulator transition temperature (TMI) are in contrast with the discontinuous resistivity and susceptibility changes at TMI. This may be attributable to the existence of two driving forces characterizing the M-I transition. One is the sharp charge ordering in Cu sites and the other is the continuous development of charge-density waves on DCNQI stacks. The arrangement of Cu2+ and Cu+ below TMI was determined by an x-ray crystal-structure analysis of the threefold insulating phase of (MeBr-DCNQI)2Cu at 110 K. The nearest-neighbor Cu2+ ions interact with each other via two DCNQI molecules. A plausible spin structure of the antiferromagnetic ground state was proposed. According to this spin-structure model, the magnetic moments of Cu2+ along the crystallographic c axis will be arranged ferromagnetically.

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