Giacomo Prando

Correlated trends of coexisting magnetism and superconductivity in optimally electron-doped oxypnictides.

We report on the recovery of the short-range static magnetic order and on the concomitant degradation of the superconducting state in optimally F-doped SmFe(1-x)Ru(x)AsO(0.85)F(0.15) for 0.1≤x≲0.5. The two reduced order parameters coexist within nanometer-size domains in the FeAs layers and eventually disappear around a common critical threshold x(c)~0.6. Superconductivity and magnetism are shown to be closely related to two distinct well-defined local electronic environments of the FeAs layers. The two transition temperatures, controlled by the isoelectronic and diamagnetic Ru substitution, scale with the volume fraction of the corresponding environments. This fact indicates that superconductivity is assisted by magnetic fluctuations, which are frozen whenever a short-range static order appears, and totally vanish above the magnetic dilution threshold x(c).

Effect of external pressure on the magnetic properties of LnFeAsO (Ln = La, Ce, Pr, Sm)

We investigate the effect of external pressure on magnetic order in undoped LnFeAsO (Ln =La, Ce, Pr, Sm) by using muon spin relaxation measurements and ab initio calculations. Both the magnetic transition temperature Tm and the Fe magnetic moment decrease with external pressure. The effect is observed to be lanthanide dependent, with the strongest response for Ln = La and the weakest for Ln = Sm. The trend is qualitatively in agreement with our density functional theory calculations. The same calculations allow us to assign a value of 0.68(2) μB to the Fe moment, obtained from an accurate determination of the muon sites. Our data further show that the magnetic lanthanide order transitions do not follow the simple trend of Fe, possibly as a consequence of the different f-electron overlap.

Vortex dynamics and irreversibility line in optimally doped SmFeAsO0.8F0.2from ac susceptibility and magnetization measurements

Ac susceptibility and static magnetization measurements were performed in the optimally doped SmFeAsO

Long- to short-range magnetic order in fluorine-doped CeFeAsO

{}_{0.8}

Poisoning effect of Mn in LaFe1-xMnxAsO0.89F0.11: Unveiling a quantum critical point in the phase diagram of iron-based superconductors

F

Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor.

{}_{0.2}

Common effect of chemical and external pressures on the magnetic properties of RCoPO (R = La, Pr, Nd, Sm). II.

superconductor. The field-temperature phase diagram of the superconducting state was drawn, and, in particular, the features of the flux lines were derived. The dependence of the intragrain depinning energy on the magnetic field intensity was derived in the thermally activated flux-creep framework, enlightening a typical

Nanoscopic coexistence of magnetic and superconducting states within the FeAs layers of CeFeAsO 1 − x F x

1/H

ac susceptibility investigation of vortex dynamics in nearly optimally doped RFeAsO1-xFx superconductors (R = La, Ce, Sm)

dependence in the high-field regime. The intragrain critical current density was extrapolated in the zero-temperature and zero-magnetic-field limit, showing a remarkably high value

Mutual Independence of Critical Temperature and Superfluid Density under Pressure in Optimally Electron-Doped Superconducting LaFeAsO 1 − x F x

{J}_{c0}(0)~2\ifmmode\times\else\texttimes\fi{}{10}^{7}