Effective field theory for layered quantum antiferromagnets with nonmagnetic impurities

We propose an effective two-dimensional quantum nonlinear sigma model combi ned with classical percolation theory to study the magnetic properties of s ite diluted layered quantum antiferromagnets such as La2Cu1-xMxO4 (M=Zn,Mg) . We calculate the staggered magnetization at zero temperature, M-s(x), the magnetic correlation length, xi(x,T), the NMR relaxation rate, 1/T-1(x, T) , and the Neel temperature, T-N(x),in the renormalized classical regime. Du e to quantum fluctuations we find a quantum critical point at x(c)approxima te to 0.305 at lower doping than the two-dimensional percolation threshold x(p)approximate to 0.41. We compare our results with the available experime ntal data.