Tuning the magnetic and structural phase transitions of PrFeAsO via Fe/Ru spin dilution

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 effectively 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 reflecting a significant magnetoelastic 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.