Abstract
Neutron diffraction and muon spin relaxation measurements are used to obtain a detailed phase
diagram of PrFe1{xRuxAsO. The isoelectronic substitution of Ru for Fe acts e ectively as spin dilution,
suppressing both the structural and magnetic phase transitions. The temperature, TS, of the
tetragonal-orthorhombic structural phase transition decreases gradually as a function of x. Slightly
below TS coherent precessions of the muon spin are observed corresponding to static magnetism,
possibly re
ecting a signi cant magneto-elastic coupling in the FeAs layers. Short range order in
both the Fe and Pr moments persists for higher levels of x. The static magnetic moments disappear
at a concentration coincident with that expected for percolation of the J1 - J2 square lattice model.
