μSRand neutron diffraction investigations on the reentrant ferromagnetic superconductorEu(Fe0.86Ir0.14<

Abstract

Results of muon spin relaxation (µSR) and neutron powder diffraction measurements on a reentrant superconductor Eu(Fe0.86Ir0.14)2As2 are presented. Eu(Fe0.86Ir0.14)2As2 exhibits superconductivity at Tc on ≈ 22.5 K competing with long range ordered Eu +2 moments below ≈ 18 K. A reentrant behavior (manifested by nonzero resistivity in the temperature range 10-17.5 K) results from an exquisite competition between the superconductivity and magnetic order. The zero field µSR data confirm the long range magnetic ordering below TEu = 18.7(2) K. The transition temperature is found to increase with increasing magnetic field in longitudinal field µSR which along with the neutron diffraction results, suggests the transition to be ferromagnetic. The neutron diffraction data reveal a clear presence of magnetic Bragg peaks below TEu which could be indexed with propagation vector k = (0, 0, 0), confirming a long range magnetic ordering in agreement with µSR data. Our analysis of the magnetic structure reveals an ordered magnetic moment of 6.29(5) µB (at 1.8 K) on the Eu atoms and they form a ferromagnetic structure with moments aligned along the c-axis. No change in the magnetic structure is observed in the reentrant or superconducting phases and the magnetic structure remains same for 1.8 K ≤ T ≤ TEu. No clear evidence of structural transition or Fe moment ordering was found.

Reentrant phases in electron-dopedEuFe2As2: Spin glass and superconductivity

“…The origin of this feature could be either due to vortex dynamics or attributed to a ferromagnetic transition regarding to the results obtained in Ru-doped samples [15]. This would be consistent with recent publications of neutron diffraction measurements report indications of a ferromagnetic state in c-direction for Co- [16], Ir- [17,18] and P-doped [19] samples; however they cannot rule out a small canting of the spins which is enough to form a spin glass in the ab-plane. Hence it is reasonable to have a closer look at all features from the results out of the magnetization measurements.…”

Hydrostatic pressure effects on the static magnetism in Eu(Fe0.925Co0.075)2As2

“…The magnetic ground state of the Eu 2+ moments displays a systematic change with increasing doping concentration, from the A-type AFM structure (with the spins lying in the ab planes) at low doping levels to the pure ferromagnetic structure (with the spins aligning along the c axis) at high doping levels 24 . Interestingly, the strong ferromagnetic (FM) order of the localized Eu 2+ spins, with a huge moment close to 7  μ B per Eu, was confirmed to be compatible with the SC 13–15, 33–37 .…”

Magnetic phase diagram of Ca-substituted EuFe2As2

“…19 The magnetic ground state of the Eu-subsystem, however, changes from an A-type antiferromagnet, via a canted antiferromagnet, to a ferromagnet upon doping the FeAssublattice. [19][20][21] A rather different behavior is observed for isovalent substitution of europium. On one hand, the Ca-doping does not lead to superconductivity under ambient pressure since the Fe-related SDW remains nearly unchanged, i.e., the substitution does not modify significantly neither the shape of SDW, nor its ordering temperature.…”

“…It is worth noting that the µSR spectroscopy has been successfully used to investigate other EuFe 2 As 2 -based compounds, for which it could reveal the nature of magnetic order, the magnetic phase diagram, and the internal field values. 20,26,27 Unlike previous studies, where only the effects of Fe magnetic lattice dilution or As isoelectronic replacement were considered, here we investigate the microscopic consequences of the Eu magnetic lattice dilution via on-site substitution with nonmagnetic Ca 2+ ions. To date no microscopic studies of the Ca-doped EuFe 2 As 2 system exist.…”