Controlling the magnetocrystalline anisotropy of ε-Fe2O3.

The magnetocrystalline anisotropy of pristine and Co-substituted ε-Fe₂O₃ is investigated by density functional calculations. The epsilon-iron oxide is the only polymorph of Fe₂O₃ magnetoelectric in its antiferromagnetic ground states other crystalline forms being α-Fe₂O₃ (hematite), β-Fe₂O₃, and γ-Fe₂O₃ (maghemite). The magnetizations of the four iron sublattices are antiferromagnetically aligned with slightly different magnetic moments resulting in a ferrimagnetic structure. Compared to the naturally occurring hematite and maghemite, bulk ε-Fe₂O₃ is difficult to prepare, but ε-Fe₂O₃ nanomaterials of different geometries and feature sizes have been fabricated. A coercivity of 20 kOe [2 T] was reported in nanocomposites of ε-Fe₂O₃, and an upper bound for the magnetic anisotropy constant K at a low temperature of ε-Fe₂O₃ is previously measured to be 0.1 MJ/m³. In the Co-substituted oxides, one octahedral or tetrahedral Fe atom per unit cell has been replaced by Co. The cobalt substitution substantially enhances magnetization and anisotropy. [ABSTRACT FROM AUTHOR]