In this paper we study in a large-S expansion effects of substituting spins by non-magnetic impurities in two- and three- dimensional Heisenberg antiferromagnets in a weak magnetic field. In particular, we demonstrate a novel mechanism where magnetic moments are induced around non-magnetic impurities when magnetic field is present. As a result, Curie-type behaviour in magnetic susceptibility can be observed well below the Neel temperature, in agreement with what is being observed in $La_2Cu_{ 1-x}Zn_{ x}O_4$ and $Sr(Cu_{ 1-x}Zn_x)_2O_3$ compounds.
Categories: cond-mat