title: Structural properties and phase diagram of the La(Fe₁-xRux)AsO system.
abstract: Structural refinement, lattice micro-strain and spontaneous strain analyses have been carried out on selected members of the La(Fe1-xRux)AsO system using high-resolution neutron and synchrotron powder diffraction data. The obtained results indicate that the character of the tetragonal to orthorhombic structural transition changes from first order for x = 0.10, possibly to tricritical for x = 0.20, up to second order for x = 0.30; for x ≥ 0.40 symmetry breaking is suppressed, even though a notable increase of the lattice micro-strain develops at low temperature. By combining structural findings with previous muon spin rotation data, a phase diagram of the La(Fe1-xRux)AsO system has been drawn. Long-range ordered magnetism occurs within the orthorhombic phase (x ≤ 0.30), whereas short-range magnetism appears to be confined within the lattice strained region of the tetragonal phase up to x < 0.60. Direct comparison between the magnetic and structural properties indicates that the magnetic transition is always associated with structural symmetry breaking, although confined to a local scale at high Ru contents.
authors.affiliation: SPIN-CNR, C.so Perrone 24, I-16152 Genova, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Martinelli
authors.forename: A
authors.initials: A
authors.lastname: Palenzona
authors.forename: I
authors.initials: I
authors.lastname: Pallecchi
authors.forename: C
authors.initials: C
authors.lastname: Ferdeghini
authors.forename: M
authors.initials: M
authors.lastname: Putti
authors.forename: S
authors.initials: S
authors.lastname: Sanna
authors.forename: C
authors.initials: C
authors.lastname: Curfs
authors.forename: C
authors.initials: C
authors.lastname: Ritter