Significant Structure Modulation in Polar Antiferromagnet FeCoMo3O8

The discovery of giant magnetoelectric effect in Fe2Mo3O8 has sparked considerable interest in investigating the novel effects of M2Mo3O8 (M = Zn, Mn, Fe, Co, Ni) family, in particular the emergent physics driven by the M‐site ions. Herein, the structural evolution due to M‐site mixing is studied in the compound FeCoMo3O8 whose unit cell volume and lattice constant are slightly tuned compared with those of Fe2Mo3O8 and Co2Mo3O8. However, significant structure distortion occurs on the octahedron and tetrahedron as a result of the relaxation of the unbalanced force, caused by the distinction of the M ion radius in the mixing case. The octahedron and tetrahedron are shifted toward each other along the c‐axis which increases the coplanarity of the Fe and Co ions. The octahedron is compressed along the D3d‐symmetry axis and its bonds are elongated significantly. A complex tension‐like distortion is induced for the tetrahedron. Its bond along the C3v‐symmetry axis is elongated and other three bonds are shortened. The study demonstrates that ions mixing at the M sites would introduce intrigue structure modulation in the M2Mo3O8 family, which would tune the electronic orbit structure. This may shed new light on understanding the emergent behaviors of the material family. The M2Mo3O8 (M = Zn, Mn, Fe, Co, Ni) family hosts giant magnetoelectric effect modulated by crystallographic structures. Herein, the structure modulation during the M sites doping is investigated, taking the Co doping at Fe sites as an example, which demonstrates that the ions mixing at the M sites causes significant distortions of the local octahedral MO6 and tetrahedral MO4.