Hierarchical Inverted/Normal Cobalt Ferrite Nano-Chessboard

Decomposing phases can arrange themselves in a regular pattern. This paper reports on a nano-sized hierarchical chessboard consisting of two isomers of cobalt ferrite, metastable normal Co 2+ tet [Fe 3+ oct ] 2 0 4 [nCFO] and tetragonal inverted Fe 3+ tet [Co 2 + Fe 3+ ] oct 0 4 [iCFO], which adapts to the cubic MgO substrate by twinning. This structure forms when CoFe2O4 (CFO) is epitaxially deposited on MgO at 800℃, driven by an average misfit of 1.7%. The magnetic characterization of the chessboard reveals the hitherto unknown properties of nCFO. We confirm that its saturation magnetization is more than twice that of iCFO, 0.93 MAm-1 as theoretically expected. In addition, using torque magnetometry, we find that the anisotropy density of nCFO equals −1.16∙104 Jm-3, about one fifth of that of pure iron. Strain stabilized nCFO thus represents an attractive magnetic oxide material; it possesses a very high saturation magnetization and is extremely soft.