Microscopic Evidence for Significant Ionic Disorder in the Yb^<3+>-Chain in Yb_4(As_<1_x>P_x)_3: ^<31>P NMR Studies (Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

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We report unambiguous microscopic evidence from ^<31>P NMR under H_<ext> ≅ 7.3 T for significant ionic disorder in the Yb^<3+> chain in Yb_4(As_<1-x>P_x)_3 (x = 0.05 and 0.40), which have similar characteristic _x(T) and C_p(T,H_<ext>) behavior to the antiferromagnetic quantum spin chain (AFQSC) system Yb_4As_3. Our conclusion is based on the observations only below the charge-ordering transition at T_0 ≅ 292 K of clear structures in the spectrum, which can be fitted well by the superpositions of almost equally spaced five Gaussian components. Since perfect ordering of Yb^<3+> in the chain sites would lead to a single-line spectrum also below T_0, the structures should be ascribed to significant ionic disorder in the Yb^<3+> chain and resulting distribution of local configurations of Yb^<3+> in the eight nearest-neighboring Yb sites around ^<31>P. Quantitative comparisons with a simple model show that about 1/3 and at least 10% of the chain sites are disordered, namely occupied by Yb^<2+>, for x = 0.40 and 0.05, respectively. Combining with previous other experimental results, extreme robustness against the disorder in the Yb^<3+> chain is deduced for the characteristic _x(T) and C_p(T,H_<ext>) behavior normally attributed to the AFQSC.
社団法人日本物理学会の論文
2003-05-15