RbEuFe₄As₄ exhibits both superconducting order in the FeAs layers and ferromagnetic order in the Eu layers, providing a good platform to study the interaction and microscopic coexistence of these two traditionally incompatible orders. Growing high-quality RbEuFe₄As₄ single crystals is essential to investigate these phenomena at a deeper level. Here we report the successful growth of the RbEuFe₄As₄ single crystals with millimeter-size dimensions using a RbAs flux. The high-quality crystals were characterized via resistivity, magnetization, and heat capacity measurements. Single crystal X-ray diffraction data refinements reveal almost regular FeAs₄ tetrahedra (As1–Fe–As1 = 108.60(7)°, As2–Fe–As2 = 109.01(8)°, and As1–Fe–As2 = 109.81(2)°) in RbEuFe₄As₄, providing structural support for the highest superconducting transition temperature (T_c = 36.8 K) among all known AAeFe₄As₄ (A = K, Rb, Cs; Ae = Ca, Sr, Eu) compounds. Our flux method using RbAs can also be employed to grow other desired transition metal compounds targeting the same crystal structure.

中文翻译：

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铁磁超导体RbEuFe ₄ As _4的单晶生长及其研究

RbEuFe ₄ As ₄在FeAs层和Eu层均表现出超导顺序，为研究这两个传统不相容顺序的相互作用和微观共存提供了一个良好的平台。生长高质量的RbEuFe ₄ As ₄单晶对于更深入地研究这些现象至关重要。在这里，我们报告了使用RbAs助熔剂成功地生长了毫米尺寸的RbEuFe ₄ As ₄单晶。通过电阻率，磁化强度和热容量测量来表征高质量的晶体。单晶X射线衍射数据的精炼显示出几乎规则的FeAs ₄RbEuFe ₄ As _4中的四面体（As1-Fe-As1 = 108.60（7）°，As2-Fe-As2 = 109.01（8）°，As1-Fe-As2 = 109.81（2）°）为结构提供了支撑在所有已知的AAe Fe ₄ As ₄（A = K，Rb，Cs；Ae = Ca，Sr，Eu）化合物中，超导转变温度最高（T _c = 36.8 K）。我们使用RbAs的助熔剂方法也可以用于生长靶向相同晶体结构的其他所需过渡金属化合物。