Magnetic behavior of the NixFe1-xNb2O6 quasi-one-dimensional system: Isolation of Ising chains by frustration

International audiencePhysical properties of the NixFe1-xNb2O6 compounds are investigated combining x-ray and neutron powder diffraction with magnetic and calorimetry measurements as well as 57Fe Mössbauer spectroscopy. This system is known to present quasi-one-dimensional magnetism with the magnetic moments arranged along weakly interacting Ising chains. Partial substitution of the magnetic ion tends to suppress the magnetic ordering observed in the end members of the series. When this happens, the low-temperature magnetic specific heat agrees well with what is expected for isolated Ising chains. The lowest temperature powder neutron-diffraction patterns exhibit evidence for the occurrence of short-range order, and analysis of these diffuse neutron-scattering patterns allow us to obtain information on the magnetic correlations. The suppression of magnetism is consistently interpreted as resulting from the magnetic-cation disorder induced by substitution, which enhances the system's tendency for frustration of geometrical origin

Suppression of magnetic ordering in quasi-one-dimensional FexCo1-xNb2O6 compounds

International audienceWe present a systematic investigation of the series of compounds FexCo1-xNb2O6 by means of x-ray and neutron powder diffraction combined with magnetic measurements, carried out in the paramagnetic as well as in the ordered state, to probe the stability of the magnetic ordering against the composition changes in this model Ising system. Fe for Co substitution induces a continuous lattice volume increase, preserving the orthorhombic crystal structure. The unit-cell expansion is anisotropic and occurs mainly in the ab plane. The observed magnetic structures for x=0,0.8, and 1 are described by the propagation vectors (0,1/2,0) and (1/2,1/2,0), and are consistent with the picture of ferromagnetic Ising-type chains of Fe/Co spins antiferromagnetically coupled by weak interchain interactions. We find out that for

New investigation of the magnetic structure of CoNb2O6 columbite

International audienceThe structural and magnetic properties of the CoNb2O6 compound have been investigated with a particular interest in their low-dimensional magnetic behavior which is characterized by the presence of weakly interacting ferromagnetic chains. We investigate this cobalt niobate by combining magnetic measurements; x-ray and neutron diffraction (ND). The ND was carried out on powder samples at different temperatures above (20 K) and below the ordering temperature (2.4, 1.8, and 1.4 K). The compound exhibits an orthorhombic crystal structure of Pbcn symmetry, typical of a columbite structure. Magnetic ordering at 2.5 K is found with the propagation vector (0, 0.4, 0), in agreement with earlier studies. However, at lower temperatures the present investigation shows the coexistence of two different magnetic phases: the propagation vector (0.5, 0.5, 0) is found to be necessary to refine the ND measurements at both 1.8 and 1.4 K, in addition to (0, 0.5, 0) which was the only one reported in earlier works

Deformation-induced martensitic transformation in Co-28Cr-6Mo alloy produced by laser powder bed fusion: Comparison surface vs. bulk

The wear resistance of the biomedical low-carbon Co-28Cr-6Mo (wt.-%) alloy is primarily determined by theonset and magnitude of the face-centered cubic to hexagonal close-packed deformation-induced martensiticphase transformation. In metal-on-metal joint bearings, local plastic deformation occurs on the surface and in thesubsurface regions. This can cause deformation-assisted structural changes in the material, such as mechanicaltwinning and/or martensitic transformation. In the present work, we report the structural transition on thesurface and bulk of a laser powder bed fusion additively manufactured Co-28Cr-6Mo alloy in response to anexternally imposed load. This study was possible using in-situ synchrotron X-ray diffraction at two differentenergy levels. Our results revealed that from tensile deformation to fracture, the phase transformation kineticsand magnitude were marginally higher on the surface. During transformation, {200}$_{FCC}$ peak broadening wasobserved in the bulk and this was attributed to stacking fault accumulation