Magnetic polarization of Ir in underdoped, non-superconducting Eu(Fe$_{0.94}$Ir$_{0.06}$)$_{2}$As$_{2}$

Abstract: Using polarized neutron diffraction and x-ray resonant magnetic scattering (XRMS) techniques, multiple phase transitions were revealed in an underdoped, non-superconducting Eu(Fe${1-x}$Ir${x}$)${2}$As${2}$ ($\mathit{x}$ = 0.06) single crystal. Compared with the parent compound EuFe${2}$As${2}$, the tetragonal-to-orthorhombic structural phase transition and the antiferromagnetic order of the Fe$^{2+}$ moments are significantly suppressed to $\mathit{T_{S}}$ = 111 (2) K and $\mathit{T_{N,Fe}}$= 85 (2) K by 6% Ir doping, respectively. In addition, the Eu$^{2+}$ spins order within the $\mathit{ab}$ plane in the A-type antiferromagnetic structure similar to the parent compound. However, the order temperature is evidently suppressed to $\mathit{T_{N,Eu}}$= 16.0 (5) K by Ir doping. Most strikingly, the XRMS measurements at the Ir $\mathit{L_{3}}$ edge demonstrates that the Ir 5$\mathit{d}$ states are also magnetically polarized, with the same propagation vector as the magnetic order of Fe. With $\mathit{T_{N,Ir}}$ = 12.0 (5) K, they feature a much lower onset temperature compared with $\mathit{T_{N,Fe}}$. Our observation suggests that the magnetism of the Eu sublattice has a considerable effect on the magnetic nature of the 5$\mathit{d}$ Ir dopant atoms and there exists a possible interplay between the localized Eu$^{2+}$ moments and the conduction $\mathit{d}$-electrons on the FeAs layers.