Multiple scattering theory for a magnetic impurity coupled to quantum antiferromagnets in quasi-two dimensions

We study a magnetic impurity coupled to quantum antiferromagnets in quasi-two dimensions on the basis of the pseudofermion representation for the impurity spin. The dynamical impurity spin-correlation function and the impurity susceptibility are calculated. In the Neel phase, we use the self-consistent Born approximation in addition to the spin-wave expansion for the spins in the plane. In the paramagnetic phase, we consider the leading order in the 1/N expansion (the self-consistent ladder approximation) in addition to the Schwinger-boson-mean-field theory for the spins in the plane. It is shown that the impurity susceptibility obeys the Curie law at high temperatures and converges to a finite value as T --> 0. Relations to the experiments on Nd2-xCexCuO4 are discussed.