J. Soh | Searcharxiv

arXiv2013

Spin polarization of Ru in superconducting Ba(Fe$_{0.795}$Ru$_{0.205}$)$_2$As$_2$ studied by x-ray resonant magnetic scattering

We have employed the x-ray resonant magnetic scattering (XRMS) technique at the Ru $L_2$ edge of the Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ ($x = 0.205$) superconductor. We show that pronounced resonance enhancements at the Ru $L_2$ edge are observed at the wave vector which is consistent with the antiferromagnetic propagation vector of the Fe in the undoped BaFe$_2$As$_2$. We also demonstrate that the XRMS signals at the Ru $L_2$ edge follow the magnetic ordering of the Fe with a long correlation length, $ξ_{ab} > 2850\pm400$ Å. Our experimental observation shows that the Ru is spin-polarized in Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ compounds.

cond-mat.str-el↗

arXiv2012

Control of magnetic, non-magnetic and superconducting states in annealed Ca(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$

We have grown single crystal samples of Co substituted CaFe2As2 using an FeAs flux and systematically studied the effects of annealing/quenching temperature on the physical properties of these samples. Whereas the as-grown samples (quenched from 960C) all enter the collapsed tetragonal phase upon cooling, annealing/quenching temperatures between 350C and 800C can be used to tune the system to low temperature antiferromagnetic/orthorhomic or superconducting states as well. The progression of the transition temperature versus annealing/quenching temperature (T-T$_{anneal}$) phase diagrams with increasing Co concentration shows that, by substituting Co, the antiferromagnetic/orthorhombic and the collapsed tetragonal phase lines are separated and bulk superconductivity is revealed. We established a 3D phase diagram with Co concentration and annealing/quenching temperature as two independent control parameters. At ambient pressure, for modest x and T$_{anneal}$ values, the Ca(Fe1-xCox)2As2 system offers ready access to the salient low temperature states associated with Fe-based superconductors: antiferromagnetic/orthorhombic, superconducting, and non-magnetic/collapsed tetragonal.

cond-mat.supr-con↗