Cu NQR study of host and guest spin dynamics in impurity-doped YBa 2Cu 4O 8

Abstract

We present the planar 63 Cu nuclear spin–lattice relaxation study of impurity-doped YBa 2(Cu 1− x M x ) 4O 8 (M=Ni, Zn) at T=4.2–300 K with Cu nuclear quadrupole resonance (NQR) spin-echo technique. In the light of an impurity-induced NQR relaxation theory, we estimated the host Cu nuclear spin–lattice relaxation time ( T 1) HOST, the impurity-induced Cu nuclear spin–lattice relaxation time ( τ 1), and the wipeout region around the impurity in the superconducting state. The pseudo spin-gap behavior of the host Cu antiferromagnetic spin fluctuation above T c is not readily removed by a small amount of the impurity. The Zn-induced non-Korringa behavior of ( T 1) HOST below T c is in sharp contrast to the doping effect of the magnetic impurity Ni.