| Research Abstract |
Organic dilute magnetic alloy Co_<0.01>Ni_<0.99>Pc(AsF_6)_<0.5> involves localized spins on Co sites and itinerant π electrons along the one-dimensional Pc chain. From the angular dependence of the ESR properties, we identified that CoPc is relevantly substituted in this alloy. Based on the analysis of the anisotropic hyperfine structure, we determined the atomic orbital as 3d_<Z^2>, in which an unpaired electron is occupied. Analyzing the temperature dependence of g value and linewidth, we succeed to determine the π-d exchange energy between the localized spin on Co and itinerant electrons on Pc chain as |J_<πd>|=0.013 eV.The density of state at the Fermi level is determined as D_F=3.5 eV^<-1> per a spin through the analysis of the temperature dependence of the g value. Using these parameters, we estimate the Kondo temperature as T_K=2×10^<-5> K.The small value of the exchange energy comes from the characteristic electronic structure and molecular arrangement. HOMO and 3d_<Z^2> orbita
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l are separately distributed from each other in the CoPc molecule, which causes the small intra-molecular exchange energy. The phthalocyanine molecules are stacked in a fashion of metal-over-metal overlap. This overlap makes the overlap integral between HOMO and 3d_<Z^2> of adjacent molecule negligibly small, and thus causes the small inter-molecular exchange energy.
θ-(BDT-TTP)_2Cu(NCS)_2 is regarded as a quasi-two-dimensional conductor according to the band calculation. This compound shows a second-order phase transition in resistivity around 250 K.Below the phase transition temperature, we found a drastic change in optical conductivity spectrum, in which the lowest electronic transition shifted to high-energy side opening a wide gap. The temperature and excitation light dependence of polaized Raman spectrum indicated that a charge disproportionation such as 2B^<+0.5>→B^0+B^<+1> occurred below the phase transition temperature. The magnetic susceptibility and ESR experiment suggest that the separated charge is vertically ordered along the molecular stack. Less
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