Magnetic property modulation of sputter-grown BiFeO3CoFe2O4 nanocomposite thin films

Self-assembled nanocomposite thin films in which ferromagnetic CoFe2O4 nanopillars grow in a ferroelectric BiFeO3 matrix have attracted tremendous interest for use as next-generation multiple state memory devices. To take advantage of the various magnetic properties of nanocomposites, it is necessary to control the strain state and shape of the CoFe2O4 pillars. Herein two methods are reported that can modulate the magnetic properties of nanocomposite thin films: changing the CoFe2O4 content in BiFeO3 and changing the aspect ratios of the CoFe2O4 pillars. The out-of-plane magnetic anisotropy of nanocomposites increased with decreasing CoFe2O4 ratio, and the anisotropy agreed with the value predicted from the strain effect. Nanocomposites with high-aspect-ratio CoFe2O4 pillars exhibited increased out-of-plane magnetic anisotropy as a result of their changing shape and increasing out-of-plane strain. Strain effects on the magnetic anisotropy of nanocomposites were confirmed by removing the BiFeO3 matrix via chemical etching.