Abstract
Abstract We have performed 17O and 63Cu NMR measurements in YBa2Cu3O7-δ (δ ≈ 0.15) oriented powder samples at CuO2 plane sites Cu(2) and 0(2, 3) in the temperature range 10-300 K. The temperature dependent Knight shift K(T) and spin lattice relaxation rate T1 -1-(T) of O(2, 3) yield K2T1T = const in accordance with the presence of free carriers at plane oxygen sites. A sharp decrease of T1 -1 of Cu(2) below 120 K is associated with the opening of a gap in the spectrum of antiferromagnetic spin fluctuations of localized copper 3 d9 electrons. The comparison of different temperature dependences of spin densities at the Cu and O sites shows the presence of two nearly independent spin systems. A close similarity of YBa2Cu3O7-δ a with heavy fermion superconductors is discussed.
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