We report growth of various phase architectures of self-assembled BiFeO3-CoFe2O4 (BFO-CFO) thin films on differently oriented SrTiO3 (STO) substrates. CFO forms segregated square, stripe, and triangular nanopillars embedded in a coherent BFO matrix on (001)-, (110)-, and (111)-oriented STO substrates, respectively. Nanostructures with an aspect ratio of up to 5:1 with a prominent magnetic anisotropy were obtained on both (001) and (110) STO along out-of-plane and in-plane directions. Magnetic easy axis rotation from in-plane to out-of-plane directions was realized through aspect ratio control. An intractable in-plane anisotropy was fixed in CFO on (111) STO due to the triangular shape of the ferromagnetic phase nanopillars. These studies established a detailed relationship of magnetic anisotropy with specific shape and dimensions of ordered magnetic arrays. The results suggest a way to effectively control the magnetic anisotropy in patterned ferromagnetic oxide arrays with tunable shape, aspect ratio, and elastic strain conditions of the nanostructures.

Ion doping effects in multiferroic MnWO4 J. Appl. Phys. 111, 083906 (2012) Origin of ferromagnetism and oxygen-vacancy ordering induced cross-controlled magnetoelectric effects at room temperature J. Appl. Phys. 111, 073904 (2012) Synthesis and signature of M-E coupling in novel self-assembled CaCu3Ti4O12-NiFe2O4 nanocomposite structure J. Appl. Phys. 111, 074302 (2012) Quantum levitation of a thin magnetodielectric plate on a metallic plate using the repulsive Casimir force J. Appl. Phys. 111, 074304 (2012) Additional information on J. Appl. Phys. The present work shows good control of both magnetic and electric properties with electric and magnetic fields, respectively, for epitaxial CoFe 2 O 4 (CFO) films on Pb(Mg,Nb)O 3 -PbTiO 3 (PMN-PT). X-ray reciprocal space mapping revealed a transformation between a-and c-domains in the PMN-PT under electric field (E). Magnetic hysteresis loop and magnetic force microscopy (MFM) measurements showed a considerable change in the magnetic properties in specific areas of CFO layers poled by MFM probe tips. Furthermore, a pulsed electric field applied to the substrate was found to switch the magnetization of CFO between high and low values, depending on the polarity of E.

The magnetic and magnetostriction properties of Z-type cobalt-doped barium hexaferrite with perpendicular c-axis crystallographic texture are presented. The hexaferrite was utilized as a component in Co 2 Z/lead magnesium niobate-lead titanate multiferroic heterostructures whose tunability of permeability with electric field in terms of ferromagnetic resonance shift was supported by experiments and theoretical calculation. A permeability change of 16% was measured by an induced magnetic field of 38 Oe under the application of 6 kV/cm of electric field. These findings lay the foundation for the application of Z-type hexaferrites in tunable rf and microwave devices valued for sending, receiving, and manipulating electromagnetic signals.

Binary alloys of Fe and Co have among the highest magnetizations of any transition metal alloy systems, but their affinity to form oxides act to reduce the magnetization of nanoparticles as their size is reduced below ∼30 nm. Here, we demonstrate the synthesis of single phase, size-controlled FeCo nanoparticles having magnetization greater than 200 emu/g via a non-aqueous method in which ethylene glycol served as solvent and reducing agent as well as surfactant. Experiments indicated pure-phase FeCo nanoparticles, having saturation magnetization up to 221 emu/g for sizes of 20–30 nm, in single batch processes resulting in > 2 g/batch. Post-synthesis oxidation of nanoparticles was investigated until very stable nanoparticles were realized with constant magnetization over time.

Ferrite composites of nominal composition Ba3Co2+xIrxFe24−2xO41 were studied in order to achieve low magnetic and dielectric losses and equivalent permittivity and permeability over a frequency range of 0.3–1 GHz. Crystallographic structure was characterized by X-ray diffraction, which revealed a Z-type phase accompanied by increasing amounts of Y-type phase as the iridium amount was increased. The measured microwave dielectric and magnetic properties showed that the loss tan δε and loss tan δμ decreased by 80% and 90% at 0.8 GHz with the addition of iridium of x = 0.12 and 0.15, respectively. An effective medium approximation was adopted to analyze the composite ferrites having mixed phase structures. Moreover, adding Bi2O3 enabled equivalent values of real permittivity and real permeability over the studied frequency range. The resultant data give rise to low loss factors, i.e., tan δε/ε′ = 0.008 and tan δμ/μ′ = 0.037 at 0.8 GHz, while characteristic impedance was the same as that of free space.

Epitaxial growth of high piezoelectric constant Pb(Zr0.525, Ti0.475)O3 (PZT) thin films deposited on amorphous magnetic Metglas® substrates by pulsed laser deposition (PLD) is reported. Particularly, Pt or Au buffer layers were employed to initiate epitaxial growth of the PZT films from atop of an amorphous surface. The optimization of deposition conditions for the PZT films with different buffer layers was systematically investigated. The crystal structure, texturing, and surface morphology of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ferroelectric and piezoelectric properties were measured indicating high polarization 27 μC/cm2 and piezoelectric constant d33, 46 pm/V for the Pt buffered films. The PZT thin films grown on a magnetostrictive material have demonstrated high quality crystallographic structure and piezoelectric response, having potential for use in emerging magnetoelectric sensors.

Thick barium hexaferrite BaFe12O19 (BaM) films having thicknesses of ∼100 μm were epitaxially grown on GaN/Al2O3 substrates from a molten-salt solution by vaporizing the solvent. X-ray diffraction measurement verified the growth of BaM (001) textured growth of thick films. Saturation magnetization, 4πMs, was measured for as-grown films to be 4.6 ± 0.2 kG and ferromagnetic resonance measurements revealed a microwave linewidth of ∼100 Oe at X-band. Scanning electron microscopy indicated clear hexagonal crystals distributed on the semiconductor substrate. These results demonstrate feasibility of growing M-type hexaferrite crystal films on wide bandgap semiconductor substrates by using a simple powder melting method. It also presents a potential pathway for the integration of ferrite microwave passive devices with active semiconductor circuit elements creating system-on-a-wafer architectures.

Ion doping effects in multiferroic MnWO4 J. Appl. Phys. 111, 083906 (2012) Origin of ferromagnetism and oxygen-vacancy ordering induced cross-controlled magnetoelectric effects at room temperature J. Appl. Phys. 111, 073904 (2012) Synthesis and signature of M-E coupling in novel self-assembled CaCu3Ti4O12-NiFe2O4 nanocomposite structure J. Appl. Phys. 111, 074302 (2012) Quantum levitation of a thin magnetodielectric plate on a metallic plate using the repulsive Casimir force