Multiple transition phenomena in divalent Eu compound EuAl₄ with the tetragonal structure were investigated via the single-crystal time-of-flight neutron Laue technique. At 30.0 K below a charge-density-wave (CDW) transition temperature of T_CDW = 140 K, superlattice peaks emerge near nuclear Bragg peaks described by an ordering vector \(\boldsymbol{q}_{\text{CDW}} = (0,0,\delta _{c})\) with δ_c ∼ 0.19. In contrast, magnetic peaks appear at \(\boldsymbol{q}_{2} = (\delta _{2},\delta _{2},0)\) with δ₂ = 0.085 in a magnetic-ordered phase at 13.5 K below T_N1 = 15.4 K. By further cooling to below T_N3 = 12.2 K, the magnetic ordering vector changes into \(\boldsymbol{q}_{1} = (\delta _{1},0,0)\) with δ₁ = 0.17 at 11.5 K and slightly shifts to δ₁ = 0.194 at 4.3 K. No distinct change in the magnetic Bragg peak was detected at T_N2 = 13.2 K and T_N4 = 10.0 K. The structural modulation below T_CDW with q_CDW is characterized by the absence of the superlattice peak in the (0 0 l) axis. As a similar CDW transition was observed in SrAl₄, the structural modulation with q_CDW could be mainly ascribed to the displacement of Al ions within the tetragonal ab-plane. Complex magnetic transitions are in stark contrast to a simple collinear magnetic structure in isovalent EuGa₄. This could stem from different electronic structures with the CDW transition between two compounds.

中文翻译：

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二价Euro化合物EuAl4中的电荷密度波阶和多重磁跃迁

通过单晶飞行时间中子Laue技术研究了具有四方结构的二价Eu化合物EuAl _4的多重跃迁现象。在T _CDW = 140 K的电荷密度波（CDW）转变温度以下30.0 K处，超晶格峰出现在有序矢量描述的核布拉格峰附近\（\ boldsymbol {q} _ {\ text {CDW}} =（0,0，\ delta _ {c}）\）用δ _Ç〜0.19。相反，磁峰出现在\（\ boldsymbol {q} _ {2} =（\ delta _ {2}，\ delta _ {2}，0）\）与δ ₂在磁性有序相= 0.085在低于13.5ķ Ť _N1 = 15.4 K.通过进一步冷却至低于Ť _N3 = 12.2 K，所述磁有序向量变为\（\ boldsymbol {q} _ {1} =（\ delta _ {1}，0,0）\）用δ ₁ = 0.17 11.5 K和略微移向δ ₁ = 0.194 4.3在磁布拉格峰K.没有明显的变化，在检测到Ť _N2 = 13.2 K和Ť _N4 = 10.0 K.下面的结构调制Ť _CDW与q _CDW的特征是在（0 0 l）轴上不存在超晶格峰。由于在SrAl ₄中观察到了类似的CDW跃迁，因此q _CDW的结构调节可能主要归因于四方晶胞内Al离子的位移。-飞机。复杂的磁跃迁与等价EuGa _4中的简单共线磁结构形成鲜明对比。这可能源于两种化合物之间CDW跃迁的不同电子结构。