Multilayer bispinel composites, in which one member is magnetite, ${\text{Fe}}_3{\text{O}}_4$, and the other is $X{\text{Fe}}_2{\text{O}}_4$ $(X=\text{Mg},\text{Mn},\text{Ni},\text{Co})$ are modeled using first-principles density-functional theory in a periodic supercell scheme. Effects of transition metal composition on charge distribution and magnetization are examined in detail in order to determine the range of variability attainable upon cation substitution and distribution. Magnetic measurement on bilayer ${\text{Fe}}_3{\text{O}}_4/{\text{MgFe}}_2{\text{O}}_4$ and ${\text{Fe}}_3{\text{O}}_4/{\text{CoFe}}_2{\text{O}}_4$ compositions are reported, showing a considerable increase in magnetization relative to the separate bulk compounds, in qualitative agreement with theory.

• Received 4 February 2010

DOI:https://doi.org/10.1103/PhysRevB.81.174422