EFFECTS OF OXYGEN AND MAGNETIC IMPURITIES ON NUCLEAR RELAXATION ANOMALIES IN La-M-Cu-O (M = Ba, Sr) SYSTEMS

Nuclear quadrupole resonance (NQR) of 139La in La2-xMxCuO4 (M = Ba, Sr) have revealed unexpected enhancement of nuclear relaxation rate, 1 / T1 at T*c 10 K, suggesting the occurrence of magnetic instability in the low temperature region. In the undoped La2CuO4, oxygen deficiencies affect strongly the nuclear relaxation rate. Magnetic impurities (Fe etc.) suppress the enhancement of 1 / T1, but non-magnetic Zn does not. In the superconducting region, fluctuations of Cu moments at low temperatures seem to remain extremely fast as same as that at high temperatures