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.

我们拟对新型铁基超导体RbEuFe4As4的磁结构开展研究。该独特材料展现出约36K的较高超导临界转变温度Tc，且与目前最常见、研究最为充分的“122”型化合物不同，其铁磁矩未呈现任何反铁磁有序。令人意外的是，块体磁化测量结果证实，在约15K的Tm以下，Eu²+自旋存在铁磁有序。首次中子衍射测量结果显示，磁性Eu²+子晶格具有三维螺旋反铁磁有序结构。此外，近期的理论研究表明，该螺旋磁结构的出现与超导性的存在密切相关。为验证这一理论预言，我们提议在SXD装置上利用单晶中子衍射，对该材料的磁结构开展系统性的温度依赖研究。