Induced ferromagnetism and magnetoelectric coupling in ion-beam synthesized BiFeO 3 –CoFe 2 O 4 nanocomposite thin films

Ferrimagnetic CoFe 2 O 4 (cobalt ferrite) is formed within an epitaxial BiFeO 3 (bismuth ferrite) thin film matrix by Co channeled ion implantation and subsequent annealing. The presence of nanoscale CoFe 2 O 4 crystals in the matrix is confirmed by x-ray diffraction using synchrotron radiation. The significantly increased magnetic moment and the low-temperature coercive field of the composite system evidence the formation of ferrimagnetic cobalt ferrite and its nanoscale character, respectively. The results demonstrate that ion beam synthesis is an appropriate method to controllably transform a planar system into a granular one, increasing the interface area between cobalt ferrite and bismuth ferrite. The ferroelectric nature of the BiFeO 3 –CoFe 2 O 4 composite is confirmed by several scanning probe microscopy techniques. At room temperature, the composite exhibits a magnetoelectric voltage coefficient of α ME = 17.5 V (cm · Oe) −1 , while a single-phase BiFeO 3 thin film shows a α ME value of 4.2 V (cm · Oe) −1 . The high magnetoelectric voltage coefficient is interpreted to be the result of the interfacial interaction between the ferrimagnetic CoFe 2 O 4 nanocrystallites and the multiferroic BiFeO 3 matrix.