Thick film layered magnetoelectric composites consisting of ferromagnetic and ferroelectric phases have been synthesized with nickel ferrite (NFO), cobalt ferrite (CFO), La 0.7 Sr 0.3 MnO 3 (LSMO), or La 0.7 Ca 0.3 MnO 3 (LCMO) and lead zirconate titanate (PZT). Structural, magnetic and ferromagnetic resonance characterization shows evidence for defect free ferrites, but deterioration of manganite parameters. The resistivity and dielectric constants are smaller than expected values. The magnetoelectric effect (ME) is stronger in ferrite-PZT than in manganite-PZT. The ME voltage coefficient α E at room temperature is the highest in NFO-PZT and the smallest for LCMO-PZT. The transverse ME effect is an order of magnitude stronger than the longitudinal effect. Multilayer composites consisting of alternative layers of magnetostrictive and piezoelectric materials are observed to show a strong magnetoelectric (ME) effect and are of interest for studies on ME interactions and for potential use in devices [1][2][3][4][5]. Such structures when placed in an external ac magnetic field δH undergo deformation of the magnetic layer due to magnetostriction, resulting in an electrical polarization of the dielectric layer due to piezoelectric effect [6,7]. The ac electrical field δE produced in the structure is a "productproperty" and is proportional to the piezomagnetic and piezoelectric coefficients of the constituent phases [8]. The magnetoelectric voltage coefficient α E = δE/δH for such composites is in the range 50-5000 mV/Oe cm, depending on the nature and volume of the magnetic and piezoelectric phases [1][2][3][4]6,7]. These values far exceed the ME coefficient of 20 mV/Oe cm for Cr 2 O 3, the best single phase ME material [9].Theoretical models for a bilayer with parameters of nickel or cobalt ferrite and lead zirconate titanate predict coefficients as high as 1.5 V/Oe cm [7]. Although our studies reveal strong ME interactions in nickel ferrite -PZT samples, systems such as cobalt ferrite-PZT show a weak coupling [10]. The reason could be deterioration of physical properties of individual layers and poor mechanical coupling between the two phases due to defects at the interface formed during the sample processing [3,4,6]. A detailed and comprehensive investigation of structural, electrical and magnetic properties of the structures is important to elucidate the cause of magnetoelectric coefficient limitations.This report details the fabrication and characterization of multilayer thick film structures consisting of piezoelectric (lead zirconate titanate) and ferromagnetic (nickel ferrite, cobalt ferrite, and lanthanum-strontium or calcium manganite) phases. The choice of materials for the structures is due to the following reasons. All the materials, except the manganites, have ferromagnetic or ferroelectric phase transition temperatures well above the room temperature. Piezoelectric lead zirconate titanate (PZT) has high dielectric permeability and high piezoelectric coupling constants. Both nickel and cobalt fer...

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The problem of the physical mechanisms of collective magnetic behavior, both static and dynamic, of an assembly of ferromagnetic particles comprising a nanocomposite material has been addressed. Detailed measurements of magnetization curves and microwave absorption spectra of films prepared from chemically synthesized ͑polyol technique͒ Fe-Ni-Co particles of various shapes and sizes have been performed. It has been shown that the dipole-dipole interparticle interactions play an important role in the magnetic behavior of such systems. An original method, relying on the shift of the magnetization curves in parallel and perpendicular geometry due to the planar anisotropy, allowing estimation of the concentration of magnetic particles has been proposed. The measurements of microwave absorption spectra at 9.5 GHz have revealed the features typical of local resonances localized on individual nanoparticles ͑Kittel mode and the lowest SWR͒ as well as those that can be attributed to collective behavior due to dipole-dipole interactions. It has been demonstrated that magnetization reversal is accompanied by a microwave hysteresis.

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