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${}_2$ ($x$ = 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 $T_S$ = 111 (2) K and $T_{N,Fe}$= 85 (2) K by 6% Ir doping, respectively. In addition, the Eu${}^{2+}$ spins order within the $ab$ plane in the A-type antiferromagnetic structure similar to the parent compound. However, the order temperature is evidently suppressed to $T_{N,Eu}$= 16.0 (5) K by Ir doping. Most strikingly, the XRMS measurements at the Ir $L_3$ edge demonstrates that the Ir 5$d$ states are also magnetically polarized, with the same propagation vector as the magnetic order of Fe. With $T_{N,Ir}$ = 12.0 (5) K, they feature a much lower onset temperature compared with $T_{N,Fe}$. Our observation suggests that the magnetism of the Eu sublattice has a considerable effect on the magnetic nature of the 5$d$ Ir dopant atoms and there exists a possible interplay between the localized Eu${}^{2+}$ moments and the conduction $d$-electrons on the FeAs layers.

7 pages, 5 figures