NMR Studies of the magnetic order in the Oxide High-Tc Superconductor

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Cu (1) NQR,Cu (2) zero field NMR,and Proton NMR have been measured in the antiferromagnetic phase of powdered samples of hydrogen-doped tetragonal YBa_2Cu_3O_<6+x>H_y from 4.2 to 300 K.Four samples with different concentration types of oxygen and hydrogen atoms (x, y), which are (0.07,0.118), , (0.1,0.14), (0.11,0.078), and (0.17,0.01), were used. The line width of ^1H NMR increases abruptly below 20 K.The enhancements of T_2^<-1> and T_1^<-1> of ^<63>Cu (1) NQR occur around 20 and 40 K,respectively. The relaxation mechanism of T_1 of ^<63>Cu (1) NQR changes at T_m=about 80 K and the time dependence of its magnetization recovery shows a nonexponential type for T < T_m and an exponential one for T > T_m. The predominant origin for T_1 below T_m is found to be the fluctuating magnetic fields due to the staggered Cu^<2+> moments on the Cu (1) or Cu (2) site induced by the hole doping effect. Above T_m, T_1^<-1> of ^<63>Cu (1) NQR increases gradually with temperature but it is almost temperature independent above 150 K,what can not be explained by the effect of the ordered AF Cu^<2+> moments in the Cu (2) O_2 plane and also by the Raman process of the lattice vibrations.