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2~ in Tl2Ba2Can_lCunOs_ 6 for different n and 6 is reviewed. For n = 2,3 the 2~ spectra consist of two lines. The main line arises from TI(l) in the TlO-layer whereas the defect line belongs to Tl(2) in the Ca-layers between the CuO2-1ayers. The temperature dependent Knight shift of the TI(2) (defect) line is caused by the hyperfine interaction with the CuOz-layer and is strongly related to the oxygen content of the sample. We find quasiparticle behavior for the TI(2) line similar to the 89y Knight shift in the YBa2Cu306+ £ system. In contrast the TI(l) line shows strong antiferromagnetic correlations with indication of pseudo spin gap opening above the superconducting transition temperature T c.

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