A new magnetoelectric hybrid device composed of a nanoparticulate magnetostrictive iron oxide-cobalt ferrite film on a piezoelectric lead zirconic titanate crystal serving as both substrate and straining medium is described. Nano-Fe 3 O 4 / CoFe 2 O 4 particles, ranging from 5 to 42 nm, were prepared using a variation of the sol-gel method. A small electric field, 5 -10 kV cm −1 , applied at the coercive field of the nano-Fe 3 O 4 / CoFe 2 O 4 component modulates the film magnetization up to 10% of the saturation magnetization of ferrite. At the smallest particle size of 5 nm, the coercive field is as low as 25 Oe and the inverse ME E voltage coefficient is as high as ͑10.1 V / cm Oe͒ −1 . © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2841064͔The recent surge of papers describing magnetoelectric composites ͑MECs͒ may be divided into two groups; the first consisting of papers reporting on metal-oxide composites and the second containing those publications dealing with oxide-oxide structures. High MEC susceptibilities at low magnetic fields are achieved with metal-oxide MECs by choosing either glassy metals or designing highly magnetostrictive metallic components with zero demagnetization factor. 1,2 Similar approaches are not as readily accessible for oxide/oxide ME composites as these are predominantly fabricated by thin film technologies, e.g., 3 and the oxide featuring the highest magnetostriction, CoFe 2 O 4 ͑CFO͒, possesses a large magnetocrystalline anisotropy. The fully epitaxial self-assembled 3-1 CFO/BaTiO 3 ME composites 4 represent somewhat of an exception. Therefore, in an effort to reduce the effective magnetocrystalline anisotropy and thereby the coercive force of CFO, we developed a nanoFe 3 O 4 / CoFe 2 O 4 ʈ lead zirconic titanate ͑PZT͒ MEC, whose fabrication and properties are described in the following.To achieve a highly effective magnetoelectric signal, ME composites require high piezoelectric and magnetic susceptibilities. 5,6 Pb͑Zr 0.53 Ti 0.47 ͒O 3 is a well-understood piezoelectric material fulfilling this requirement. Ferromagnetic bulk Co ferrite is a good choice due to its high magnetostriction. However, because of its high magnetocrystalline anisotropy, 7 it has a low magnetostrictive initial susceptibility that results in a low magnetoelectric susceptibility d / dH. In nanoparticles, the effective magnetocrystalline anisotropy is lowered and d / dH can be increased while maintaining its high saturation 8 as has also been demonstrated for Co ferrite. 9 Therefore, in order to create an all-oxide MEC with a large ME coupling coefficient, a nanoFe 3 O 4 / CoFe 2 O 4 / Pb͑Zr 0.53 Ti 0.47 ͒O 3 was developed. This composite yields giant ME voltages under significantly lower magnetic bias fields than previously reported for CFO/PZT MECs. 10 Its manufacture and properties will be described next.The composite was manufactured by spinning a CFO sol-gel 11 onto a mirror polished PZT single crystal substrate, obtained from Fuji Ceramics, Inc. The deposition technique and substrate were ch...