63Cu and 17O Nuclei Spin-Lattice Relaxation in Y1−xCaxBa2Cu4O8

The temperature dependences of the 63Cu and 17O nuclei spin-lattice relaxation rate 63(1/T1) and 17(1/T1) in YBa2Cu4O8 have been measured by the nuclear quadrupole resonance(NQR) and nuclear magnetic resonance(NMR) techniques, respectively. The frequency spectra in Y1−xCaxBa2Cu4O8 (x=0, 0.025, 0.075) and 63(1/T1) in the case of x=0, 0.075 were also measured. From the frequency spectra, we conclude that the Ca ions substitute for Y sites rather than Ba sites. The antiferromagnetic correlation derived from the Ca concentration dependence of 63(1/T1) is reduced with increasing Ca content. The absolute value of 17T1/63T1 is located between that of YBa2Cu3O7 and YBa2Cu3O6.63. Therefore, it seems that the transition temperature Tc depends on the value of antiferromagnetic correlation length ξ that indicates a degree of breaking down of the correlation by introduction of itinerant carriers.