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

本文测量了掺氢四元化合物YBa_2Cu_3O_（6+X）H_y的反铁磁相（T_N = 410 K）的质子NMR和Cu（1）和C（2）位的Cu NQR。质子核磁共振研究发现，氢原子占据在缺氧层Cu（1）位附近。~ 1H NMR谱线宽度Δ ω在20 K以下突然增加。~ <-1><-1>1Cu<63>（1）NQR的T_2^和T_1^分别在20 K和40 K附近增强。在80 K以下，核磁不能以简单的指数方式恢复。在80 K以下，控制T_1的主要机制是空穴掺杂效应引起的涨落磁场。这些增强和Δ ω的突然增加归因于这种起伏的磁场。然而，在80 K以上，核磁以简单的指数方式恢复。在80 K以上，涨落磁场对T_1的贡献迅速减小，其它T_1弛豫机制取代了涨落磁场。为了研究80 K以上的弛豫机制，我们测量了Cu（1）中的T_1、T_2、共振频率和^ NQR谱线宽度随温度的变化<63>。在80 K以上的高温区测量了YBCO的Cu（2）位的NQR，并对Cu（2）位的NQR进行了测量，研究了YBCO的反铁磁相。

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.