Copyright (c) 2012 All rights reserved. http://works.bepress.com/nsun Recent documents in Nian X. Sun en-us Mon, 26 Nov 2012 03:30:33 PST 3600 http://works.bepress.com/nsun/12 http://works.bepress.com/nsun/12 Wed, 11 Apr 2012 23:16:06 PDT Different self-assembled magnetic nanowire arrays were achieved with similar to 100% trapping rate on templates with nanomagnet arrays under a low external magnetic field (∽10 Oe). The principles of magnetic charge matching and dimension matching between the magnetic nanowires to be assembled and the gaps between two nanomagnets were proposed and demonstrated to be crucial for achieving low magnetostatic energy and high trapping rate. This templated self-assembly technique and the proposed template design principles have great potential for nanomanufacturing of regular arrays of magnetic nanostructures.

]]> Ming Liu et al. http://works.bepress.com/nsun/11 http://works.bepress.com/nsun/11 Wed, 11 Apr 2012 23:16:02 PDT A series of (Fe_100−yGa_y)_1−xB_x (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 <1>Oe, high 4πM_s, self-biased ferromagnetic resonance (FMR) frequency of 1.85 GHz, narrow FMR linewidth (X band) of 16–20 Oe, and a high saturation magnetostriction constant of 70 ppm. The combination of these properties makes the FeGaB films potential candidates for tunable magnetoelectric microwave devices and other rf/microwave magnetic device applications.

]]> Jing Lou et al. Thin films--Magnetic properties http://works.bepress.com/nsun/10 http://works.bepress.com/nsun/10 Wed, 11 Apr 2012 23:15:59 PDT 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.

]]> Ming Liu et al. Ferrites (Magnetic materials) Nanowires http://works.bepress.com/nsun/9 http://works.bepress.com/nsun/9 Wed, 11 Apr 2012 23:15:55 PDT 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.

]]> Jinsheng Gao et al. http://works.bepress.com/nsun/8 http://works.bepress.com/nsun/8 Wed, 11 Apr 2012 23:15:51 PDT 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 degrees C for 2 h to cause embrittlement. They were found to have soft magnetic properties (4πM_s∽13 kG,ΔH ∽100 Oe, and H_c< 0.5 Oe). The brittle ribbons were ball milled using tungsten carbide vials and stainless steel balls in an inert atmosphere for various milling times. The sample milled for 10 h was found to have a 4πM_s of about 13 kG and a coercivity of about 73 Oe with an average particle size of about 5μm. The screen printed (as prepared and aligned) samples showed a linewidth (Δ H) of about 1000 Oe. Similar values were obtained for screen printed films annealed for 1 h at 200 and 400 degrees C.

]]> Ashish K. Baraskar et al. http://works.bepress.com/nsun/7 http://works.bepress.com/nsun/7 Wed, 11 Apr 2012 23:15:47 PDT Magnetoelectric interactions as a function of applied electric field have been studied in ferrite-ferroelectric heterostructures at microwave frequencies. The measurements are performed on 1.5–2.0 μm thick nickel ferrite (NiFe₂O₄) films grown heteroepitaxially on lead zinc niobate-lead titanate and lead magnesium niobate-lead titanate substrates using direct liquid injection chemical vapor deposition. Large shifts in the ferromagnetic resonance profile are observed in these heterostructures due to strong magnetoelectric coupling resulting from electrostatic field induced changes in the magnetic anisotropy field. Theoretical estimates of field shifts are in good agreement with the experimental data.

]]> Ning Li et al. http://works.bepress.com/nsun/6 http://works.bepress.com/nsun/6 Wed, 11 Apr 2012 23:15:42 PDT 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.

]]> Ming Liu et al. Ferrites (Magnetic materials) http://works.bepress.com/nsun/5 http://works.bepress.com/nsun/5 Wed, 11 Apr 2012 23:15:38 PDT Strong magnetoelectric (ME) coupling was demonstrated in Fe₃O₄/PZN–PT (lead zinc niobate–lead titanate) multiferroic heterostructures obtained through a sputter deposition process. The dependence of the magnetic anisotropy on the electric field (E-field) is theoretically predicted and experimentally observed by ferromagnetic resonance spectroscopy. A large tunable in-plane magnetic anisotropy of up to 600 Oe, and tunable out-of-plane anisotropy of up to 400 Oe were observed in the Fe₃O₄/PZN–PT multiferroic heterostructures, corresponding to a large ME coefficient of 100 Oe cm/kV in plane and 68 Oe cm/kV out of plane, which match well with predicted results. In addition, the electric field manipulation of magnetic anisotropy is also demonstrated by the electric fields dependence of magnetic hysteresis loops, showing a large squareness ratio change of 44%. These Fe₃O₄/PZN–PT multiferroic heterostructures exhibiting large E-field tunable magnetic properties provide great opportunities for novel electrostatically tunable multiferroic devices.

]]> Ming Liu et al. Ferromagnetic materials Ferromagnetic resonance http://works.bepress.com/nsun/4 http://works.bepress.com/nsun/4 Wed, 11 Apr 2012 23:15:35 PDT Next generation magnetic microwave devices require ferrite films to be thick (>300 μm), 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.

]]> Vincent Girard Harris (1962-) et al. Ferrites Thin films Microwave devices http://works.bepress.com/nsun/3 http://works.bepress.com/nsun/3 Wed, 11 Apr 2012 23:15:28 PDT 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.

]]> Aria Yang et al. http://works.bepress.com/nsun/2 http://works.bepress.com/nsun/2 Wed, 11 Apr 2012 23:15:23 PDT 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.

]]> Yajie Chen et al. http://works.bepress.com/nsun/1 http://works.bepress.com/nsun/1 Wed, 11 Apr 2012 23:15:17 PDT Nanocrystalline films of the Ni₁₁Co₁₁Fe₆₇₋ₓZr₇B₄Cux (x=0,1) composition were deposited on fused quartz substrates by pulsed laser deposition. For the films ofNi₁₁Co₁₁Fe₆₆Zr₇B₄Cu, the bcc grain size ranged from 5 to 8 nm 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 H_c < 5 Oe, 4πM_s ∽16 kG, and in-plane uniaxial anisotropy field (HA)∽25-30 Oe. The ferromagnetic resonance linewidth was measured to be 34 Oe and zero magnetic field ferromagnetic resonance at ∽2 GHz. These properties allow these films to be candidates for magnetic planar inductors operating from 0.5 to 2 GHz.

]]> Ashish K. Baraskar et al.