Effect of antifluorite layer on the magnetic order in Eu-based 1111 compounds, EuTAsF (T = Zn, Mn, and Fe)

The 1111 compounds with an alternating sequence of fluorite and antifluorite layers serve as structural hosts for the vast family of Fe-based superconductors. Here, we use neutron powder diffraction and density-functional-theory (DFT) band-structure calculations to study magnetic order of Eu 2+ in the [EuF] + fluorite layers depending on the nature of the [TAs] − antifluorite layer that can be non-magnetic semiconducting (T = Zn), magnetic semiconducting (T = Mn), or magnetic metallic (T = Fe). Antiferromagnetic transitions at T N ∼ 2.4-3 K due to an ordering of the Eu 2+ magnetic moments were confirmed in all three EuTAsF compounds. Whereas in EuTAsF (T = Zn and Mn), the commensurate k 1 = (½ ½ 0) stripe order pattern with magnetic moments within the a - b plane is observed, the order in EuFeAsF is incommensurate with k = (0 0.961(1) ½) and represents a cycloid of Eu 2+ magnetic moments confined within the bc -plane. Additionally, the Mn 2+ sublattice in EuMnAsF features a robust G-type antiferromagnetic order that persists at least up to room temperature, with magnetic moments along the c -direction. Although DFT calculations suggest stripe antiferromagnetic order in the Fe-sublattice of EuFeAsF as the ground state, neutron diffraction reveals no evidence of long-range magnetic order associated with Fe. We show that the frustrating interplane interaction J 3 between the adjacent [EuF] + layers is comparable with in-plane J 1 - J 2 interactions already in the case of semiconducting fluorite layers [TAs] − (T = Zn and Mn) and becomes dominant in the case of the metallic [FeAs] − ones. The latter, along with a slight orthorhombic distortion, is proposed to be the origin of the incommensurate magnetic structure observed in EuFeAsF. Neutron powder diffraction and DFT calculations explain the difference between magnetic structures in layered 1111-type compounds EuTAsF (T = Zn, Mn and Fe) depending on the properties (magnetism, metallicity) of the T-containing layer.