$\hat{I}¼$SR and Neutron Diffraction Investigations on Reentrant Ferromagnetic Superconductor Eu(Fe{0.86}Ir{0.14})2As2

Abstract

Results of muon spin relaxation ($\hat{I}¼$SR) and neutron powder diffraction measurements on a reentrant superconductor Eu(Fe${}_{0.86}$Ir${}_{0.14}$)${}_2$As${}_2$ are presented. Eu(Fe${}_{0.86}$Ir${}_{0.14}$)${}_2$As${}_2$ exhibits superconductivity at $T_{\mathrm{c}\mathrm{on}}\approx 22.5$~K competing with long range ordered Eu${}^{+2}$ moments below $\approx 18$ 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 $\hat{I}¼$SR data confirm the long range magnetic ordering below $T_{\mathrm{Eu}}=18.7(2)$ K. The transition temperature is found to increase with increasing magnetic field in longitudinal field $\hat{I}¼$SR 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 $T_{\mathrm{Eu}}$ which could be indexed with propagation vector k = (0, 0, 0), confirming a long range magnetic ordering in agreement with $\hat{I}¼$SR data. Our analysis of the magnetic structure reveals an ordered magnetic moment of $6.29(5)\hat{I}{¼}_{\mathrm{B}}$ (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 $\le T\le T_{\mathrm{Eu}}$. No clear evidence of structural transition or Fe moment ordering was found.

9 pages, 7 figures, to appear in Phys. Rev. B