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Varying amounts of boron were added to the host FeGa alloy to investigate its impact upon local atomic structure and magnetic and microwave properties. The impact of B upon the local atomic structure in FeGaB films was investigated by extended x-ray absorption fine structure (EXAFS) analysis. The EXAFS fitting results revealed a contraction of lattice parameters with the introduction of B. The Debye–Waller factor determined from EXAFS fitting increases as a function of boron addition and abruptly changes during the structural evolution from crystalline to amorphous that occurs near 9% B. Upon the onset of this transition the static and microwave magnetic properties became exceptionally soft, with values of coercivity and ferromagnetic linewidth reducing to less than 1 Oe and 25 Oe, respectively.

A strong magnetoelectric (ME) interaction is presented in a magnetostrictive-semiconductor-piezoelectric heterostructure that consists of the Huesler alloy, Co2MnAl, GaAs, and lead magnesium niobate-lead titanate (PMN-PT). The laminated Co2MnAl/GaAs/PMN-PT structure, having a thickness of 19 nm/180 μm/500 μm, demonstrates a ferromagnetic resonance (FMR) field shift of 28 Oe with an external electric field of 200 V across the PMN-PT substrate. This corresponds to a resonance frequency shift of ∼125 MHz at X-band. It yields a large ME coupling (7 Oe cm/kV) and microwave tunability (∼32 MHz/kV cm−1), compared to other trilayer multiferroic composite structures. In addition, static magnetization measurement indicates a reduction in the remanence magnetization while applying the electric field, which corroborates the ME interactions mediated by the translation of magnetoelastic forces in this structure. This work explores the potential of multiferroic heterostrucuture transducers for use in FMR microwave devic...

We investigated the magnetic anisotropic properties and the spin wave relaxation in trilayer films of CoFe/PtMn/CoFe grown on the seed layer Ru or NiFeCr with CoFe compositions being Co–16 at. % Fe. The measurements were taken in samples with the ferromagnetic layers of CoFe varying from 10 to 500 A by the ferromagnetic resonance (FMR) technique. The magnetic anisotropic parameters were investigated by rotating the field aligned axis with respect to the spectral field in the configurations of both in plane and out of plane. We determine the effective in-plane anisotropy field of ∼0.005 T, the uniaxial out-of-plane anisotropy of ∼−0.3 T, and the exchange stiffness D of ∼512 meV A2. Moreover, spin wave damping was estimated by analyzing the FMR linewidth and line shape as a function of the angle between the external field and easy axis and as a function of the thickness of the CoFe layers. We identify an extrinsic contribution of the damping parameter dominated by two-magnon scattering in addition to the in...

Strong magnetoelectric (ME) interaction was demonstrated at both dc and microwave frequencies in a novel Zn0.1Fe2.9O4/PMN‐PT (lead magnesium niobate‐lead titanate) multiferroic heterostructure, which was prepared by spin-spray depositing a Zn0.1Fe2.9O4 film on a single-crystal PMN‐PT substrate at a low temperature of 90 ◦ C. A large electric-field induced ferromagnetic resonance field shift up to 140Oe was observed, corresponding to an ME coefficient of 23OecmkV −1 . In addition, a large electrostatic field tuning of the magnetic hysteresis loops was observed with a large squareness ratio change of 18%. The spin-spray deposited ferrite/piezoelectric multiferroic heterostructures exhibiting strong ME interactions at both dc and microwave frequencies provide great opportunities for novel electrostatically tunable microwave magnetic devices synthesized at a low temperature. (Some figures in this article are in colour only in the electronic version)

The multiferroic properties of a laminated heterostructure consisting of magnetostrictive Ni2MnGa ribbon and piezoelectric lead-magnesium-niobate-lead titanate crystal are reported. A tunability of the electric field-induced magnetic field was measured by a shift in the ferromagnetic resonance (FMR) field by 230 Oe at X-band while applying an electric field of 6 kV/cm. Concomitantly, a frequency shift in the FMR of 370 MHz was observed. The sensitive tunability stems from a large linear magnetoelectric coupling coefficient, A=41 Oe cm/kV, measured in the heterostructure. This represents a new class of metallic multiferroic heterostructures that operate at microwave frequencies.

Giant magnetoelectric coupling at both microwave frequencies and dc was observed in an FeGaB/lead magnesium niobate-lead titanate microwave multiferroic composite. A record high microwave frequency tunability of Delta f=900 MHz or Delta f/f=58% was demonstrated with the change of an external electric field from -6 to +2 kV/cm. A strong electric field dependence of magnetic hysteresis loops was also observed. Such multiferroic composite provides great opportunities for electrostatically tunable microwave devices. (C) 2008 American Institute of Physics. NSF ECCS-0746810, DMR-0603115 ONR N000140710761, N000140810526 Draper Laboratory through University UR&D program

Ni0.23Fe2.77O4 (NFO)/Pb(Zr,Ti)O3 (PZT) multiferroic composites were synthesized by spin-spray deposition of NFO film onto PZT at 90°C. Strong interface adhesion between NFO and PZT was observed, which was verified by high resolution transmission electron microscopy indicating excellent wetting between the NFO and PZT, and by the strong magnetoelectric coupling in the NFO/PZT multiferroic composite showing an electric field induced remnant magnetization change of 10%. This strong interface adhesion and low-temperature spin-spray synthesis of multiferroic materials provide an alternative route for novel integrated multiferroic materials and devices.

Thick films of the Ni11Co11Fe66Zr7B4Cu composition were synthesized via screen printing of the ball-milled ribbons of the above composition for possible use as planar inductors. The ribbons were obtained by rapid solidification. The resulting ribbon samples were annealed at 300°C for 2h to cause embrittlement. They were found to have soft magnetic properties (4πMs∼13kG, ΔH∼100Oe, and Hc

The magnetic, microwave, and the atomic structure properties of (Fe0.7Co0.3)1−xBx sputtered films on glass substrates were investigated. The addition of boron induced a decrease in coercivity and ferromagnetic resonance linewidth. The amorphous structure was formed at x∼0.075. Extended x-ray absorption fine structure (EXAFS) of Fe and Co showed the reduced Fourier transform (FT) amplitude, and increased Debye-Waller factors as x was increased, indicating the increased disorder due to the thermal and structural displacements. Possible Fe–B bonding was observed with a reduced bond length, which indicates boron atoms' preference for staying in the interstitial sites in bcc unit cell.

We studied exchange-dominated surface and bulk spin-wave modes in a single period of CoFe∕PtMn∕CoFe trilayer film grown on a seed layer of Ru with CoFe film compositions being Co‐16at.%Fe. The thickness of the ferromagnetic CoFe layers is ∼400A and that of the antiferromagnetic layer is 120A. Multimode spin-wave spectra were observed using the ferromagnetic resonance technique, as the sample plane was rotated with respect to the direction of the magnetic field. The effective magnetic anisotropy parameters and the g factor of the magnetic film were calculated from the field corresponding to the main (strongest) resonance peak at different angles. In addition, we identified a high-order standing spin wave in our spectra and found a “critical angle” in the multilayer sample. As H is significantly rotated away from the normal, there is a critical orientation where only a single acoustic spin-wave mode can be observed. We included an effective surface anisotropy field to describe our results. From the surface ...

Strong magnetoelectric coupling was observed at microwave frequencies in metallic magnetic film/lead zirconate titanate [Pb(Zr,Ti)O3] multiferroic composites, in which the magnetic films were either FeCoB or FeGaB with relatively high saturation magnetostriction constants between 40 and 70ppm and narrow ferromagnetic resonance linewidths of ∼20Oe at 10GHz. Large electrostatically induced ferromagnetic resonance frequency shifts of 50–110MHz at ∼2.3GHz were observed. These metallic magnetic film/Pb(Zr,Ti)O3 multiferroic composites with large electrostatic tunability of the ferromagnetic resonance frequency provide great opportunities for integrated microwave multiferroic devices.

Nanocrystalline structured films of the alloy Ni11Co11Fe66Zr7B4Cu1 were deposited by pulsed laser ablation deposition onto fused quartz substrates. A substrate temperature of 300°C was found to produce films consisting of body-centered-cubic (bcc) metallic grains suspended in an amorphous matrix. The bcc grain size ranged from 5–8nm for substrate temperatures up to 300°C. Measured values of coercivity were consistently below 4Oe for films having a saturation magnetization, as 4πMS, of ∼16kG with in-plane uniaxial anisotropy fields of 25to30Oe. The ferromagnetic resonance peak-to-peak derivative linewidth was measured to be 34Oe at a frequency of 9.61GHz. The zero magnetic field ferromagnetic resonance occurred at ∼2GHz. These films exhibit soft magnetic properties, high saturation induction, low microwave loss, and the structural stability desirable for thin film inductor applications.

This paper presents a circular loop antenna with self-biased magnetic film loading. The proposed circular loop antenna is realized by cascading a microstrip loop and a tuning stub. The self-biased magnetic films were used as a practical means to tune the working frequency of the antenna. Three different cases of antennas with films loading were designed and analyzed. Antennas with self-biased magnetic films loading working at 1.7 GHz with a tuning range of 50%~400% of the antenna bandwidth were achieved.

A series of (Fe100−yGay)1−xBx (x=0–21 and y=9–17) films were deposited; their microstructure, soft magnetism, magnetostrictive behavior, and microwave properties were investigated. The addition of B changes the FeGaB films from polycrystalline to amorphous phase and leads to excellent magnetic softness with coercivity

Multiferroic CoFe2O4–Pb(Zr,Ti)O3 (CFO-PZT) composite films with nanoscale mixture of the two phases were prepared by a modified sol-gel process, in which a mixed precursor solution of both CFO and PZT was used. X-ray diffraction and transmission electron microscopy examinations revealed the coexistence of perovskite PZT and spinel CFO that were mixed in nanoscale with mean grain sizes of 5–10nm. Magnetic properties of the CFO-PZT nanocomposite were examined, which were consistent with their microstructures. The magnetoelectric coupling between CFO and PZT was demonstrated by an external magnetic field induced electric polarization change. This modified sol-gel processing provides an alternative for multiferroic composite films, which is simpler and easier to control compared to the conventional layer-layer sol-gel process for multiferroic composite films.

Nanocrystalline films of the Ni11Co11Fe67−xZr7B4Cux (x=0,1) composition were deposited on fused quartz substrates by pulsed laser deposition. For the films of Ni11Co11Fe66Zr7B4Cu, the bcc grain size ranged from 5to8nm in the films deposited at substrate temperatures from ambient to 300°C. Films grown at a substrate temperature of 300°C were found to have optimal magnetic properties including minima in the coercivity and ferromagnetic resonance (FMR) linewidth. The magnetic characterization studies showed coercivity Hc

A synthesis method was developed for producing core-shell nanowire arrays, which involved a combination of a modified sol-gel process, electrochemical deposition, and subsequent oxidization in anodized nanoporous alumina membranes. This method was applied to generate ordered arrays of one dimensional multiferroic NiFe2O4 core and Pb(Zr0.52Ti0.48)O3 (PZT) shell nanostructures. Extensive microstructural, magnetic, and ferroelectric characterizations confirmed that the regular arrays of core-shell multiferroic nanostructures were composed of a spinel NiFe2O4 core and perovskite PZT shell. This synthesis method can be readily extended to prepare different core-shell nanowire arrays and is expected to pave the way for one dimensional core-shell nanowire arrays.

Programmable defect-free self-assembled magnetic nanowire arrays were produced by using specially designed nano-magnet arrays and external magnetic field. Nickel nanowires were grown on nanoporous template using electrodeposition technique. Magnetic properties, structure and morphology were studied carefully by using vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Individual magnetic nanowires were successfully trapped between the nanomagnet pairs with a width of 200 nm and a thickness of 100 nm. Templated self-assembly of magnetic nanowires was successfully demonstrated with Permalloy nano-magnet arrays in both 1D and 2D.

AS new type of electronically tunable magnetic patch antennas with metal magnetic films was designed, fabricated, and tested at 2.1 GHz. The magnetic patch antennas showed an enhanced bandwidth of 50% over the non-magnetic patch antennas, a significantly enhanced directivity, and a large tunability of the radiation intensity of 4.23 dB at a low applied magnetic field of ∼20 Oe.

A new structure of integrated planar metal magnetic film coupled line (MMFCL) circulators is presented, in which a metal magnetic film is used instead of ferrite materials. Simulation was performed with HFSS based on coupled-mode theory. An insertion loss of 4 dB and isolation of −13.5 dB between S21 and S12 over a frequency band of 3 GHz (from 36.5 to 39.5 GHz) were realised for a three-port MMFCL circulator.

Single crystal Fe films were grown on Ge (001) substrates by using dc magnetron sputtering. It was found that the microstructures and magnetic properties of Fe films on Ge substrates were strongly dependent upon the substrate temperature during the deposition process. There existed a narrow substrate temperature window of 125±25°C for achieving single crystal Fe film on Ge. Lower substrate temperature led to polycrystalline Fe films due to limited mobility of Fe atoms, while higher substrate temperatures resulted in amorphous Fe–Ge alloy due to severe interdiffusion.

An analytical nonlinear hysteresis model was developed to describe the hysteresis loops of different magnetic materials, which was capable of fitting Permalloy films as an example. As a case study this model was applied in the sensitivity analysis of the fluxgate magnetometers where accurately capturing the nonlinear behavior of the magnetic core is crucial. Straightforward analytical equation of the output voltage signal as well as its harmonic decomposition was obtained for the fluxgate magnetometer as a function of hysteresis loop parameters. Sensitivity values predicted by the model were found to be consistent with the measured values published previously. The model allows the harmonic content distribution in the output signal of the fluxgate magnetometer to be studied analytically as a function of various device parameters, and thereby very useful in the selection of core materials in fluxgate devices.

Next generation magnetic microwave devices require ferrite films to be thick (>300μm), self-biased (high remanent magnetization), and low loss in the microwave and millimeter wave bands. Here we examine recent advances in the processing of thick Ba-hexaferrite (M-type) films using pulsed laser deposition (PLD), liquid-phase epitaxy, and screen printing. These techniques are compared and contrasted as to their suitability for microwave materials processing and industrial production. Recent advances include the PLD growth of BaM on wide-band-gap semiconductor substrates and the development of thick, self-biased, low-loss BaM films by screen printing.

Films consisting of Zn1−xFexO were prepared by alternating-target laser ablation deposition. The Fe doping levels ranged from x=0.016to0.125at.%. X-ray diffraction and energy dispersive x-ray spectroscopy measurements showed only (002n) reflections of the ZnO host and confirmation of the Fe concentration, respectively. For films grown on (001) Al2O3 at 300K, room temperature average saturation magnetization, ⟨4πMs⟩, measured from superconducting quantum interference device (SQUID) hysteresis loops for x=0.125±0.025 was 172G. Although SQUID measurements were sensitive to the average value of the saturation magnetization, ferrimagnetic resonance measurements appeared to be sensitive only to the saturation magnetization of the so-called magnetic layer containing ferric ions. We believe that we have produced a host semiconductor material doped with impurities of ferrimagnetic ordering.

Structural and magnetic characterizations of nanocrystalline films of (Ni0.67Co0.25Fe0.08)89−xZr7B4Cux (x=0,1) alloys are reported. The films were grown on quartz substrates using pulsed laser deposition from homogeneous targets of the above compositions at substrate temperatures ranging from ambient to 600°C. Structural properties were measured by x-ray diffraction, atomic force microscopy, and transmission electron microscopy, whereas the magnetic properties were measured by vibrating sample magnetometry and ferromagnetic resonance. The resulting films exist as a two phase alloy with face-centered-cubic metallic grains suspended in an amorphous matrix. For both the x=1 and x=0 alloys, the softest magnetic properties (coercivity Hc

Plated high saturation magnetization soft magnetic FeCo films were annealed in magnetic field; their stress, microstructure, and magnetic properties were investigated. The FeCo films consistently showed a reduced tensile stress after magnetic annealing at temperatures above 255°C. The annealing temperature was found to be the primary factor in reducing the tensile stress, while annealing time was secondary. The FeCo films showed improved soft magnetic properties when subjected to an easy axis annealing with reduced coercivities along both the easy axis and hard axis. Hard axis annealing on these FeCo films caused a switched easy and hard axis in these films when the annealing temperature is above 255°C.Plated high saturation magnetization soft magnetic FeCo films were annealed in magnetic field; their stress, microstructure, and magnetic properties were investigated. The FeCo films consistently showed a reduced tensile stress after magnetic annealing at temperatures above 255°C. The annealing temperature was found to be the primary factor in reducing the tensile stress, while annealing time was secondary. The FeCo films showed improved soft magnetic properties when subjected to an easy axis annealing with reduced coercivities along both the easy axis and hard axis. Hard axis annealing on these FeCo films caused a switched easy and hard axis in these films when the annealing temperature is above 255°C.

An evident inequality between the enthalpy of crystallization of amorphous selenium, Delta H-x, and the enthalpy difference between the undercooled liquid and the conventional polycrystalline selenium, Delta Hl --> c, was observed, which is inconsistent with the widely accepted idea that the two enthalpies should be equal. The inequality between the two enthalpies is attributed to the excess enthalpy of the nanocrystallites selenium with respect to the conventional polycrystalline selenium. The maximum excess enthalpy of the nanocrystalline selenium amounts up to 30% of the heat of fusion. Based on the assumption that the excess enthalpy of the nanocrystalline sample is concentrated in the high density of grain boundaries, the grain-boundary enthalpies of the nanocrystalline selenium samples were determined. The obtained grain-boundary enthalpies of the nanocrystalline selenium samples are found to increase from 0.27 to 0.32 J/m(2) with the mean crystallite size increment from 9 to 22 nm. It is predicted that an inequality between the two enthalpies of Delta H-x and Delta Hl --> c will always occur in the nanocrystallization process of an amorphous solid and that the grain-boundary enthalpies of the nanocrystallized products can then be determined.