  We present a 31P NMR study of the coupled spin 1/2 ladder compound BiCu2PO6.
In the pure material, intrinsic susceptibility and dynamics show a spin gap of
about . Substitution of non magnetic Zn or magnetic Ni impurity at Cu site
induces a staggered magnetization which results in a broadening of the 31P NMR
line, while susceptibility far from the defects is unaffected. The effect of Ni
on the NMR line broadening is twice that of Zn, which is consistent with
Quantum Monte Carlo (QMC) calculations assuming that Ni couples
ferromagnetically to its adjacent Cu. The induced moment follows a 1/T
temperature dependence due to the Curie-like development of the moment
amplitude while its extension saturates and does not depend on impurity content
or nature. This allow us to verify the generically expected scenario for
impurity doping and to extend it to magnetic impurity case: in an
antiferromagnetically correlated low dimensional spin system with
antiferromagnetic correlations, any type of impurity induces a staggered moment
at low temperature, whose extension is not linked to the impurity nature but to
the intrinsic physics at play in the undoped pure system, from 1D to 2D
systems.
