Neutron diffraction study of exotic magnetic order in the novel superconductor RbEuFe4As4

We propose to study magnetic structure of the novel iron-based superconductor RbEuFe4As4. This peculiar material exhibit superconductivity with a rather high Tc~36K and without any antiferromagnetic ordering of Fe magnetic moments unlike in the most common and well studied ”122” compounds. Surprisingly, bulk magnetisation measurements have provided the evidence of ferromagnetic ordering of the Eu2+ spins below Tm~15K. The first neutron diffraction measurement claims that magnetic Eu2+ sublattice has three-dimensional helical antiferromagnetic order. Moreover, recent theoretical work suggests that this helical magnetic structure appears due to the presence of the superconductivity. In order to check this theoretical prediction, we propose to perform a systematic temperature-dependent study of the magnetic structure in this material using single-crystal neutron diffraction at SXD.