μSRand neutron diffraction investigations on the reentrant ferromagnetic superconductorEu(Fe0.86Ir0.14)2As2

Abstract

Results of muon spin relaxation $(\ensuremath{\mu}\mathrm{SR})$ and neutron powder diffraction measurements on a reentrant superconductor $\mathrm{Eu}({\mathrm{Fe}}_{0.86}{\mathrm{Ir}}_{0.14}){}_{2}{\mathrm{As}}_{2}$ are presented. $\mathrm{Eu}({\mathrm{Fe}}_{0.86}{\mathrm{Ir}}_{0.14}){}_{2}{\mathrm{As}}_{2}$ exhibits superconductivity at ${T}_{\mathrm{c}\phantom{\rule{0.16em}{0ex}}\mathrm{on}}\ensuremath{\approx}22.5$ K competing with long range ordered ${\mathrm{Eu}}^{+2}$ moments below $\ensuremath{\approx}18$ 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 $\ensuremath{\mu}\mathrm{SR}$ 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 $\ensuremath{\mu}\mathrm{SR}$ 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 $\mathbf{k}=(0,\phantom{\rule{0.16em}{0ex}}0,\phantom{\rule{0.16em}{0ex}}0)$, confirming a long range magnetic ordering in agreement with $\ensuremath{\mu}\mathrm{SR}$ data. Our analysis of the magnetic structure reveals an ordered magnetic moment of $6.29(5)\phantom{\rule{0.222222em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ (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 $1.8\phantom{\rule{0.222222em}{0ex}}\text{K}\ensuremath{\le}T\ensuremath{\le}{T}_{\mathrm{Eu}}$. No clear evidence of structural transition or Fe moment ordering was found.