The existence of local moments in both Zn- and Ni-doped YBa2Cu4O8 (Y1248) is confirmed by a Curie-law T-dependence of NMR linewidth and the Cu relaxation at low T. The reduction of Cu-NQR signal intensity in Ni-doped Y1248 suggests that, in contrast to the case of Ni-doped YBa2Cu3O7 (Y1237), the Cu spin correlation around Ni is destroyed. This effect may be responsible for the larger reduction of Tc by Ni-doping than in Y1237. For Cu sites which are away from an impurity by two lattice constants, 1/T1T continues to increase below T*, at which it has a maximum in the non-doped material. The effect in reducing T*, which is sometimes called the spin gap temperature, is much more pronounced in Zn-doped samples, suggesting that the reduction of T* is mainly due to the induction of magnetic moments in the dx2-y2 orbital, which may modify Cu spin fluctuation.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering