  The local response to a uniform field around vacancies in the two-dimensional
(2D) spin-1/2 Heisenberg antiferromagnet is determined by numerical quantum
Monte Carlo simulations as a function of temperature. It is possible to
separate the Knight shifts into uniform and staggered contributions on the
lattice which are analyzed and understood in detail. The contributions show
interesting long and short range behavior that may be of relevance in NMR and
susceptibility measurements. For more than one impurity remarkable non-linear
enhancement and cancellation effects take place. We predict that the Curie
impurity susceptibility will be observable for a random impurity concentration
even in the thermodynamic limit.
