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6.2 Spin-Peierls material CuGeO3

The first spin Peierls materials were all organic. This may be attributed to the characteristics of organic materials that (1) the lattice is soft and its deformation is relatively easy and (2) the distance between the spin-chains is relatively large, so that they are magnetically well isolated from each other. As an inorganic material, CuGeO3 was the first material identified to exhibit a spin Peierls transition [141].


  
Figure: Crystal structure of CuGeO3. In the c-axis direction, CuO2 chains are present. The lattice parameters are cited from Ref. [142]; the in-chain magnetic coupling parameters are from Ref. [143].
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The crystal structure of CuGeO3 is shown in Fig.52. A Cu2+ ion (S=1/2) is surrounded by six O2- ions, which form a distorted CuO6 octahedron. Cu2+ ions are bridged with four closer O2- ions, making a CuO2 chain (ribbon) in the c-axis direction. These chains are supported with Ge4+ ions, which locate at the tetrahedral site surrounded by four O2- ions. Reflectivity and photoemission measurements [144] have shown that the $p\!-\!d$ hybridization of the CuO2 chain is small. Hence the localized-moment picture of the Cu2+ spins should be good in CuGeO3.

In the first report, Hase et al. [141] presented (1) an isotropic drop of susceptibility at $T_{\rm SP}$=14 K and (2) the field dependence of $T_{\rm
SP}(H)\propto H^2$, as signatures of the spin Peierls transition in CuGeO3. Since then, there have been many experiments performed on this material, and some of them report typical signatures of spin Peierls transition, as reviewed in the following.



 
next up previous contents
Next: 6.2.1 Previous measurements Up: 6 Spin-Peierls system Previous: .