Charge ordering in Eu₄As₃

The one-dimensional magnetic chain model clarified the unusual properties of Yb₄As₃. However, there are still unexplained problems. The Madelung energy calculation pointed out that the actual arrangement of Yb³⁺ and Yb²⁺ in the charge-ordered state, which forms the one-dimensional Yb³⁺ chains, is not a lowest energy state. To examine the role of the orbital moment and the exchange interaction, which are candidates dominating the charge ordering, we prepared a single crystal of Eu₄As₃, in which only spin moment is dominant. The measurements of X-ray diffraction, transport properties and susceptibility revealed that the charge ordering in Eu₄As₃ is very similar to that in Yb₄As₃, however, an appearance of ferromagnetism in Eu₄As₃ is a striking contrast to Yb₄As₃. These results may indicate that the charge-ordering formation is subject to neither orbital moment nor exchange interaction.