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

在反铁磁相（T_N = ca.410 K）上测定了氢掺杂YBa_2Cu_3O_<6+X>H_y粉末样品的Cu(1)和C(2)位的质子核磁共振和Cu(1)位的Cu NQR。质子核磁共振研究发现，在缺氧层的Cu(1)位点附近有氢原子占据。谱线宽度δ δ在20k以下突然增大。^<63>Cu (1) NQR的T_1^<-1>和T_1^<-1>的增强分别发生在20 K和40 K左右。在80k以下，核磁化强度不会以简单的指数方式恢复。在80k以下，控制T_1的主要机制是由空穴掺杂效应引起的波动磁场。这些增强和δ的突然增加归因于这个波动的磁场。然而，在80k以上，核磁化以简单的指数方式恢复。在80k以上，波动磁场对T_1的贡献迅速减小。在80k以上，其他T_1弛豫机制取代了波动场。为了研究80 K以上的弛豫机制，在80 K以上的高温区域测量了Cu(1)位点T_1、T_2、共振频率和^<63>NQR线宽的温度依赖性。为了研究YBCO的反铁磁相，还对Cu(2)位的Cu NQR进行了测量。

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.