NMR Studies of the magnetic order at low temperatures in the Antiferromagnetic Phase of Oxide High-T_c Superconductor

点击翻译按钮获取中文摘要

Proton NMR and Cu NQR of Cu (1) and C (2) sites have been measured on the antiferromagnetic phase (T_N = ca.410 K) of a powdered sample of hydrogen-doped tetragonal YBa_2Cu_3O_<6+X>H_y. It was found by proton NMR studies that hydrogen atoms are occupied in the vicinity of Cu(1) site in the oxygen deficient layr. The line width, DELTAomega, 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 K and 40 K,respectively. The nuclear magnetization does not recover in a simple exponential manner below 80 K.The predominant mechanism governing T_1 below 80 K was found to be the fluctuating magnetic fields induced by the hole doping effect. These enhancements and the abrupt increase in DELTAomega are attributed to this fluctuating magnetic field.Above 80 K,however, the nuclear magnetization recover in a simple exponential manner. The contribution of the fluctuating magnetic field to T_1 decreases rapidly above 80 K.Taking the place of the fluctuating field, other T_1 relaxation mechanismsm dominate above 80 K.In order to investigate the relaxation mechanism above 80 K,the temperature dependence of T_1, T_2, the resonance frequencies, and the line width of ^<63>NQR in the Cu (1) site has been measured in the high temperature region above 80 K.The measurement of Cu NQR in the Cu (2) site has also carried out to investigate the antiferromagnetic phase of YBCO.