Technical Report of ISSP Ser. A: Number 2921

Abstract

Magnetic susceptibility (chi) and Nuclear Magnetic Resonance (NMR) / Nuclear Quadrupole Resonance (NQR) measurements were performed on La2Cu(x)Li(1-x)O4 (where x is greater than 0 and less than 0.5) and La(1.85)Sr(0.15)Cu(1-x)Li(x)O4 (where x is greater than or equal to 0 and less than or equal to 0.425). The narrow Cu-63 NQR line at nu(sub Q) = 46.3 MHz (1.3 K) is detected in La2Cu(0.5)Li(0.5)O4. This frequency is higher than all Cu-63 NQR frequencies found so far in all the cuprates. Moreover, a further increase of nu(sub Q) is observed in the solid solutions La2Cu(x)Li(1-x)O4 with decreasing x. Corresponding Electric Field Gradients (EFG's) are considered in terms of ionic and cluster models. The 3d hole density (n sub(x(exp 2)-y(exp 2)) which is approximately equal 1 and the radial average (r(exp (-3)) which is approximately equal 9.5 a.u. are derived from the EFG's, suggesting the d(exp 9)L state of the formally trivalent copper. The antiferromagnetic ordering is rapidly suppressed as a function of x in La2Cu(x)Li(1-x)O4, and for x being greater than 0.03, T(sub N) is found to be approximately equal 0. The evolution of chi vs. x shows a gradual decrease of Cu spin susceptibility and its disappearance in the diamagnetic La2Cu(0.5)Li(0.5)O4, in which chi = -6.7 x 10(exp -5) cc/mole is composed of Van Vleck and core terms. The electronic state is implied to be a local singlet A-1(sup 1g) of primarily d(exp 9)L character. The quandrupole signature of the local singlet in the range of which (63)nu(sub Q) is greater than 46.3 and less than 47.0 MHz is observed for x being greater than 0.15 in both systems La2Cu(x)Li(1-x)O4 and La(1.85)Sr(0.15)Cu(1-x)Li(x)O4. The differentiation of charge between local singlet and conductivity band states is discussed.

La2Cu(1-x)Li(x)O4とLa(1.85)Sr(0.15)Cu(1-x)Li(x)O4の磁化率とNMR･NQRを測定した。La2Cu(0.5)Li(0.5)O4では周波数46.3MHz(1.3K)で狭いCu-63NQR線を検出した。この周波数はこれまですべてのキュプラートで見付かったあらゆるCu-63NQR周波数よりも高い。その上、固溶体La2Cu(1-x)Li(x)O4でxが減少すると周波数が増加することを観測した。対応する電場勾配をイオンおよびクラスタの模型によって考察した。電場勾配から3d空孔密度とその動径平均を導き出したが、これは正規には3価の銅のd{9}配位子空孔状態を示唆している。反強磁性配列はLa2Cu(1-x)Li(x)O4 におけるxの関数として急速に抑制され、xが0.03以上になるとネール温度が0になることが分かった。磁化率対xの変化からCuスピン磁化率は漸次減少して、磁化率がバン･ブレック項と核項から構成された-6.7×10{-5}立方センチメートル/モルになる反磁性La2Cu(0.5)Li(0.5)O4ではCuスピン磁化率が消滅することが分かった。この電子状態は主としてd{9}配位子空孔特性をもつ局所1重項であることを示している。xが0.15より大きい場合には両方の系La2Cu(1-x)Li(x)O4とLa(1.85)Sr(0.15)Cu(1-x)Li(x)O4でCu-63FNQR周波数が46.3-47.0MHzの範囲の局所1重項の4重極シグナチャーを観測した。局所1重項と伝導帯状態との間の電荷の違いを議論した。