Charge density wave in BaFe₂Al₉

Charge density waves (CDW) are modulations of the crystal lattice that develop in crystalline materials on cooling. Generally, CDW compounds have strongly 1-d or 2-d character. In contrast, BaFe₂Al₉ is a hexagonal intermetallic compound with a distinctly 3-d electronic structure. Despite this, a hysteretic phase transition is observed in single crystals centered around 100K in magnetic susceptibility and resistance measurements. Diffraction and Mössbauer experiments reveal this transition is due to the formation of a CDW via a first order phase transition with a large lattice strain (-1.5% along the c-axis). Details of this modulated phase will be discussed as well as why charge order is favored over magnetic order in this metallic, iron-containing compound.