NQR Studies on Magnetism and Superconductivity of Oxides Superconductors

本文<139>研究了空穴掺杂La_M_xCuO_4（M=Sr，Ba）中^ La和^&lt;63，65&gt;Cu在宽x范围<2-x>内的核四极共振（NQR）。在Tc ~*-10K时，^ La的核弛豫率的发散<139>表明在3D反铁磁相与超导相之间存在着特殊的阻挫磁相。在零外场条件下，在30- 50 KHz范围内观察到^&lt;63，65&gt;Cu的自旋回波信号。当x&lt;0.4时，谱线由Cu-NQR谱线的两个分量组成，其来源尚不清楚。随着x的减小，弛豫速率1/T_1和1/T_2明显增大。当x&gt;0.4时，1/T_1的温度关系服从Korringa关系，T_1T=常数，确定了电子掺杂Ln_<2-x>Ce_xCuO_4（Ln =Nd，Pr，Sm）中Cu磁矩的反铁磁序。在Ce掺杂的样品中意外地观察到具有消失的小四极相互作用的核磁共振（NMR）表明，在电子掺杂的氧化物中的Cu位点处的局部电子性质不同于空穴掺杂的氧化物。

Nuclear quadrupole resonances (NQR) of ^<139>La and ^<63,65>Cu have been investigated in the wide range of x in hole-doped La_<2-x>M_xCuO_4 (M=Sr, Ba). The divergence of the nuclear relaxation rate of ^<139>La at T_c*-10K indicates the existence of the peculiar frustrated magnetic phase between the 3D-antiferro- magnetic and superconducting phases. The spin echo signals of ^<63,65>Cu are observed between 30-50KHz in zero external field. The spectra consist of the two component of the Cu-NQR lines for x<0.4, of which origin is still unclear. Relaxation rates, 1/T_1 and 1/T_2 are much enhanced with decreasing x. The temperature dependence of 1/T_1 for x>0.4 obeys the Korringa relation, T_1T=const., below 200K.We have confirmed the antiferromagntic order of Cu moments in the electron-doped Ln_<2-x>Ce_xCuO_4 (Ln =Nd, Pr, Sm). Unexpected observation of nuclear magnetic resonance (NMR) with vanishingly small quadrupole interactions in the Ce-doped samples suggests that the local electronic properties at Cu site in the electron-doped oxides differ from the hole-doped ones.