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 Pr(Fe,Ru)AsO. The isoelectronic substitution of Ru for Fe acts effectively as spin dilution, suppressing both the structural and magnetic phase transitions. The temperature of the tetragonal-orthorhombic structural phase transition decreases gradually as a function of x. Slightly below the transition temperature coherent precessions of the muon spin are observed corresponding to static magnetism, possibly reflecting a significant 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. 
Yuen Yiu, Pietro Bonf\`a, Samuele Sanna, Roberto De Renzi, Pietro   Carretta, Michael A. McGuire, Ashfia Huq, Stephen E. Nagler
cond-mat.supr-con