Metal-Insulator Transition in Bi_xV_8O_<16> : ^<51>V NMR Study(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

概要

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The ^<51>V nuclear magnetic resonance and relaxation (NMR) are measured for Bi_xV_8O_<16> in the temperature range from 4.2K to 280K. The Bi_xV_8O_<16> system with 1.60 ≤ x ≤ 1.80 is known to crystallize in the Hollandite structure with a [V_8O_<16>] framework which is composed of double chains formed by edge-shared VO_6, octahedra. In this system, we observed temperature-induced Metal-Insulator transition (MIT) in the composition range of 1.72 ≤ x ≤ 1.80. In order to reveal the mechanism of MIT in this system, ^<51>V NMR measurements have been performed on Bi_<1.77>V_8O_<16> as well as on the simple Pauli paramagnetic compound Bi_<1.60>V_8O_<16> for a comparative study: the Knight shift K and the spin-lattice relaxation rate 1/T_1 of ^<51>V NMR have been measured to investigate the magnetic and electric properties. By applying the random phase approximation (RPA) method the absolute values of 1/T_1T are analyzed in the Pauli paramagnetic regime of Bi_<1.77>V_8O_<16> above T_<MIT> and Bi_<1.60>V_8O_<16> for whole temperature region. As a result, the modification factor K(a) for applying the RPA theory to the interacting system has been found to be 0.9 (nearly non-interacting) for the case of x = 1.60 and 1.7 (antiferromagnetic) for x = 1.77, implying that the antiferromagnetic spin correlation and frustration may cause the occurrence of MIT in Bi_<1.77>V_8O_<16>
社団法人日本物理学会の論文
2004-01-15