Magnetism in Eu(Fe1-xIrx)2As2 iron pnictides studied by complementary scattering methods

Abstract

Abstract: Doped EuFe2As2 is a unique representative of the 122 type family of iron based superconductors due to the two magnetic sublattices and the strong coupling between spin-, lattice- and charge degrees of freedom. In present work, the magnetic ground states of the localized Eu2+ spins in underdoped, nonsuperconducting Eu(Fe0.94Ir0.06)2As2 and optimally doped, superconducting Eu(Fe0.88Ir0.12)2As2 (TSC = 22 K) were investigated by polarized and unpolarized single-crystal neutron diffraction measurements, respectively. The Eu2+ spins in the underdoped (x = 0.06) crystal were found to order within the ab plane in the A-type antiferromagnetic (AFM) structure. However, the Eu2+ spins in the optimally doped (x = 0.12) crystal were found to be ferromagnetically aligned along the c direction with an ordered moment of 7.0(1) μB at 2.5 K, coexisting with the bulk superconductivity. In addition, compared with the parent compound EuFe2As2, which shows the AFM order of the Fe2+ moments below TN,Fe = 190 K, TN,Fe was significantly suppressed to 85(2) K and completely suppressed, by 6% and 12% Ir doping, respectively. Most strikingly, the x-ray resonant magnetic scattering measurements on the underdoped (x = 0.06) crystal revealed the magnetic polarization of the 5d Ir dopant atoms and suggested a possible interplay between the localized Eu2+ moments and the conduction d electrons on the FeAs layers