Hyperfine Nuclear Interaction at Copper Lattice Sites of High-Temperature Superconductors Studied by ~(61)Cu(~(61)Ni) Mossbauer Emission Spectroscopy

摘要

Mossbauer emission spectroscopy on the ~(61)Cu(~(61)Ni) isotope has been used to determine the quadrupole coupling constant C(Ni) and magnetic induction B(Ni) for the ~(61)Ni~(2+) probe at copper sites in Cu_2O, CuO, La_(2-x)Ba_xCuO_4, Nd_(2–x)Ce_xCuO_4, RBa_2Cu_3O_6, and RBa_2Cu_3O_7 (R = Y, Nd, Gd, Yb). The compounds containing divalent copper were found to exhibit linear C(Ni) vs. C(Cu) and B(Ni) vs. B(Cu) relations [C(Cu) and B(Cu) are the quadrupole coupling constant and magnetic induction for the ~(63)Cu probe, respectively, found by NMR], which is interpreted as an argument for the copper being in divalent state. The deviation of the data points corresponding to the Cu(1) sites in RBa_2Cu_3O_6 and RBa_2Cu_3O_7 from the C(Ni) vs. C(Cu) straight line may be due either to the copper valence being other than 2+ (in the RBa_2Cu_3O_6 compounds) or to the principal axes of the total and valence electric field gradient being differently oriented (in the RBa_2Cu_3O_7 compounds).