Copyright (c) 2013 Northeastern University All rights reserved. http://iris.lib.neu.edu/elec_comp_fac_pubs Recent documents in Electrical and Computer Engineering Faculty Publications en-us Tue, 21 May 2013 16:35:14 PDT 3600 http://iris.lib.neu.edu/elec_comp_fac_pubs/147 http://iris.lib.neu.edu/elec_comp_fac_pubs/147 Wed, 13 Feb 2013 14:16:35 PST This paper reports on the first demonstration of an ultra-miniaturized, high frequency (215 MHz) and high sensitivity MEMS resonant magnetic field sensor based on an AlN/FeGaB bilayer nano-plate resonator capable of detecting magnetic field at nano-Tesla level. Despite of the reduced volume and the high operating frequency of the sensor, high electromechanical performances were achieved (quality factor Q ≈ 511 and electromechanical coupling coefficient k_t² ≈ 1.63%). This first prototype was characterized for different magnetic field levels from 0 to 152 Oe showing a frequency sensitivity of ~ 1 Hz/nT and a limit of detection of ~ 10 nT.

... ]]> Yu Hui http://iris.lib.neu.edu/elec_comp_fac_pubs/146 http://iris.lib.neu.edu/elec_comp_fac_pubs/146 Wed, 13 Feb 2013 14:04:33 PST Modern power systems represent the largest man-made system in existence from the view point of invested capital. With the current rise in the demand of electrical energy, present-day power systems which are large and complex, will continue to grow both in size and complexity. Also, our dependence on electrical energy is so great that it is essential to have uninterrupted supply of electrical power within set limits of frequency and voltage levels, and that it becomes a dire necessity to develop methods for effective control and operation of power systems. Continual modification and improvement of power-system simulation are required to... ]]> Mulukutla S. Sarma http://iris.lib.neu.edu/elec_comp_fac_pubs/145 http://iris.lib.neu.edu/elec_comp_fac_pubs/145 Wed, 13 Feb 2013 14:04:30 PST Mulukutla S. Sarma http://iris.lib.neu.edu/elec_comp_fac_pubs/144 http://iris.lib.neu.edu/elec_comp_fac_pubs/144 Wed, 06 Feb 2013 08:32:55 PST This paper presents the theoretical modeling and experimental verification of an innovative Nano Electro Mechanical System (NEMS) technology suitable for the implementation of ultra-fast and high resolution un-cooled thermal detectors. Fundamental challenges associated to the implementation of mechanically resonant thermal detectors are overcome with the introduction of an innovative technology platform in which a temperature sensitive Aluminum Nitride (AlN) nano-plate resonator and a monolithically integrated micromachined suspended heat absorbing element are perfectly overlapped but separated by a sub-micron air gap. By placing the absorbing element outside the body of the resonator (but suspended over it) the electromechanical performance of the... ]]> Yu Hui http://iris.lib.neu.edu/elec_comp_fac_pubs/143 http://iris.lib.neu.edu/elec_comp_fac_pubs/143 Tue, 01 May 2012 13:54:35 PDT We report on voltage impulse induced reversible bistable magnetization switching in FeGaB/lead zirconate titanate (PZT) multiferroic heterostructures at room temperature. This was realized through strain-mediated magnetoelectric coupling between ferroelectric PZT and ferromagnetic FeGaB layer. Two reversible and stable voltage-impulse induced mechanical strain states were obtained in the PZT by applying an electric field impulse with its amplitude smaller than the electric coercive field, which led to reversible voltage impulse induced bistable magnetization switching. These voltage impulse induced bistable magnetization switching in multiferroic heterostructures provides a promising approach to power efficient bistable magnetization switching that is crucial for information storage.

... ]]> T. X. Nan Ferromagnetic materials Gallium alloys Iron alloys Lead compounds Magnetization http://iris.lib.neu.edu/elec_comp_fac_pubs/142 http://iris.lib.neu.edu/elec_comp_fac_pubs/142 Mon, 23 Apr 2012 13:16:32 PDT The present work shows good control of both magnetic and electric properties with electric and magnetic fields, respectively, for epitaxial CoFe₂O₄ (CFO) films on Pb(Mg,Nb)O₃-PbTiO₃ (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.

... ]]> Zhiguang Wang Heterostructures Electric fields Magnetic fields Magnetic force microscopy Hysteresis loop http://iris.lib.neu.edu/elec_comp_fac_pubs/141 http://iris.lib.neu.edu/elec_comp_fac_pubs/141 Mon, 23 Apr 2012 13:16:29 PDT The fringe magnetic field, induced by magnetoelectric coupling in a bilayer Fe-Ga/Pb(Mg_1/3Nb_2/3)O₃^_PbTiO₃ (PMN-PT) multifunctional composite, was investigated. The induced external field is characterized as having a butterfly hysteresis loop when tuned by an applied electric field. A tuning coefficient of the electrically induced fringe magnetic field is derived from the piezoelectric and magnetostrictive properties of the composite. A measured maximum tuning coefficient, 4.5 Oe/(kV cm⁻¹), is found to agree well with theoretical prediction. This work establishes a foundation in the design of transducers based on the magnetoelectric effect.

... ]]> Trifon Fitchorov Heterostructures Magnetic fields Hysteresis loop http://iris.lib.neu.edu/elec_comp_fac_pubs/140 http://iris.lib.neu.edu/elec_comp_fac_pubs/140 Mon, 23 Apr 2012 13:16:26 PDT We demonstrate an equivalence between direct and converse magnetoelectric effects in two-phase systems comprising piezoelectric and magnetostrictive materials. This was achieved by recasting the Maxwell relation in terms of the effective electrical and magnetic dipole moments for the system and comparing coupling strengths at the same electrical and magnetic d.c. biases. Our findings therefore apply to magnetoelectric systems comprising more than two phases and correct the two widely held but opposing views that are compromised by incorrect parameterization or inconsistent bias conditions.

... ]]> Jing Lou Piezoelectric materials Dipole moments http://iris.lib.neu.edu/elec_comp_fac_pubs/139 http://iris.lib.neu.edu/elec_comp_fac_pubs/139 Wed, 04 Apr 2012 08:14:09 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 Ferromagnetic resonance Chemical vapor deposition Heterostructures http://iris.lib.neu.edu/elec_comp_fac_pubs/138 http://iris.lib.neu.edu/elec_comp_fac_pubs/138 Wed, 04 Apr 2012 07:59:34 PDT Ferromagnetic resonance (FMR) measurements have been performed over a broad frequency range on epitaxial films of Co and bcc α‐Fe grown onto epilayers of ZnSe by molecular‐beam‐epitaxy techniques on (001) and (110) GaAs substrates. In‐plane and perpendicular FMR results were used in deducing the magnetic parameters and spin‐wave resonance (SWR) dispersion of the films. The magnetic parameters deduced for Fe films agree with previous results obtained on the (001) Fe/ZnSe film. Well‐resolved SWR modes were observed in the Fe/ZnSe films, allowing extraction of the exchange stiffness constant. Few spin‐wave excitations were observed for the Co/ZnSe films. Both (110) Fe/ZnSe and... ]]> S. A. Oliver Ferromagnetic resonance Molecular beam epitaxy http://iris.lib.neu.edu/elec_comp_fac_pubs/137 http://iris.lib.neu.edu/elec_comp_fac_pubs/137 Tue, 03 Apr 2012 13:00:55 PDT This study is an extension of previous work dealing with single crystals of YIG/GGG/YIG grown in (110) layers. Ferromagnetic resonance (FMR) measurements for fields along the axis were performed. The microwave measurements reveal hysteretic behavior as the FMR frequency is measured for positive and negative magnetic fields H. For H in which the magnetic moment is zero (spin flop) the FMR frequency goes through a discrete and measurable jump or change. This discontinuity in the FMR frequency at the spin-flop condition is attributed to the magnetostatic interaction between the two YIG layers.

... ]]> K. Sun Ferromagnetism Ferromagnetic resonance Magnetic fields http://iris.lib.neu.edu/elec_comp_fac_pubs/136 http://iris.lib.neu.edu/elec_comp_fac_pubs/136 Tue, 03 Apr 2012 13:00:50 PDT X-band phased array antenna containing four linear microstrip patch elements has been fabricated and tested. The elements were fed through single-crystal yttrium-iron-garnet phase shifters. By varying the bias magnetic field the input phases to the antenna elements can thus be tuned, resulting in steering of the radiation beam in one dimension.

]]> H. How Phased array antennas Phase shifters http://iris.lib.neu.edu/elec_comp_fac_pubs/135 http://iris.lib.neu.edu/elec_comp_fac_pubs/135 Tue, 03 Apr 2012 13:00:44 PDT This work examines the material characteristics and magnetic properties of hexagonal M-type barium ferrite (BaFe₁₂O₁₉) films deposited by pulsed laser ablation deposition onto (111) magnesium oxide substrates at different oxygen growth pressures. X-ray diffraction data showed the lattice constant of the film grown at 300 mTorr c=23.23 Å increased to c=23.30 Å for the film grown at 20 mTorr. The saturation magnetization ranged from 4.03 to 4.33 kG and the magnetic uniaxial anisotropy field ranged from 16.73 to 19.49 kOe as the oxygen pressure was varied from 10 to 300 mTorr. The narrowest ferrimagnetic resonance (FMR) linewidths (ΔH) for as-produced... ]]> S. D. Yoon Barium films (Metal coating) Magnesium oxide http://iris.lib.neu.edu/elec_comp_fac_pubs/134 http://iris.lib.neu.edu/elec_comp_fac_pubs/134 Tue, 03 Apr 2012 13:00:39 PDT The dynamic time domain response of the converse magnetoelectric effect in a multiferroic Metglas®/Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) heterostructure, under the application of a square waveform electric field excitation of 8 kV/cm at a frequency of 0.4 Hz, is reported. The relaxation behavior followed a stretched power-law function allowing the calculation of an intrinsic time constant. Aging behavior of magnetoelectric coupling was observed after polarization switching of 1000 cycles. These phenomena are predominantly attributed to the temporal response of polarization within the PMN-PT crystal. Results elucidate the dynamic properties of relaxor-based multiferroic heterostructures and importantly define operational constraints for low frequency device operation.

... ]]> Yajie Chen Heterostructures http://iris.lib.neu.edu/elec_comp_fac_pubs/133 http://iris.lib.neu.edu/elec_comp_fac_pubs/133 Tue, 03 Apr 2012 13:00:15 PDT The deposition and characterization of thick M-type barium hexaferrite (BaFe₁₂O₁₉) films produced by a modified liquid phase epitaxy deposition technique are reported. The films are deposited on (111) oriented single crystal garnet (Gd₃Ga₅O₁₂) substrates. The thickness of the films ranged between 45 and 80 μm with growth rates of up to 40 μm/h. This growth rate is about five times greater than films grown on substrates of (111) magnesium oxide. Although the films are relatively thick, the ferrimagnetic resonance linewidth is remarkably narrow.

... ]]> C. Vittoria Thick films Epitaxy Ferromagnetic resonance http://iris.lib.neu.edu/elec_comp_fac_pubs/132 http://iris.lib.neu.edu/elec_comp_fac_pubs/132 Tue, 03 Apr 2012 13:00:08 PDT Amplification of echo signals in ordered magnetic materials was postulated by many authors in the middle sixties. However, theoretical estimates of amplification were invariably several orders of magnitude higher than observed in ferrimagnetic materials. We have reformulated the equation of motion to include the nonlocal dipole-dipole interaction to describe the dynamic response of an echo. Our estimates of amplification compare reasonably well with measured values.

]]> H. How Magnetic materials http://iris.lib.neu.edu/elec_comp_fac_pubs/131 http://iris.lib.neu.edu/elec_comp_fac_pubs/131 Tue, 03 Apr 2012 13:00:01 PDT The demagnetizing energy of spheroidal magnetic particles dispersed in cubic lattices has been calculated. The demagnetizing energy contains contributions from the demagnetizing self-energy and magnetostatic coupling energy between particles. The total demagnetizing energy can be conveniently expressed in terms of three demagnetizing factors whose sum equals unity. For low volume loading of particles the self-energy contribution is the dominant one, which is insensitive to particle coordinations and can be approximated by that of an isolated particle. However, when particle loading increases appreciably, significant differences arise for different particle lattices (sc, bcc, and fcc). One advantage of our formulation is that... ]]> H. How Composite materials Magnetic permeability http://iris.lib.neu.edu/elec_comp_fac_pubs/130 http://iris.lib.neu.edu/elec_comp_fac_pubs/130 Tue, 03 Apr 2012 12:59:57 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... ]]> Jinsheng Gao Boron Atomic structure Magnetism Thin films Extended X-ray absorption fine structure http://iris.lib.neu.edu/elec_comp_fac_pubs/129 http://iris.lib.neu.edu/elec_comp_fac_pubs/129 Tue, 03 Apr 2012 12:59:52 PDT The wave dispersion relations of the mixed polariton-photon modes along the surface of a semi-infinite layered structure consisting of alternating magnetic and nonmagnetic films are calculated. The magnetic films are magnetized to saturation by an external field parallel to the film plane and perpendicular to the wave propagation direction. Three different types of surpace modes are found and discussed. the surface-surface-type and (lower) surface-bulk-type modes can exist in a general layered structure which, when propogating in the positive k direction, corresponds in magnetostatic limit to those surface modes found by Camley et al. For negative k propagation of surface-surface-type modes,... ]]> H. How Surface waves Magnetic films http://iris.lib.neu.edu/elec_comp_fac_pubs/128 http://iris.lib.neu.edu/elec_comp_fac_pubs/128 Tue, 03 Apr 2012 12:59:47 PDT Thick barium hexaferrite [BaO∙(Fe₂O₃)₆] films, having the magnetoplumbite structure (i.e., Ba M), were epitaxially grown on c-axis oriented GaN/Al₂O₃ substrates by pulsed laser deposition followed by liquid phase epitaxy. X-ray diffraction showed (0,0,2n) crystallographic alignment with pole figure analyses confirming epitaxial growth. High resolution transmission electron microscopy images revealed magnetoplumbite unit cells stacked with limited interfacial mixing. Saturation magnetization, 4πM_s, was measured for as-grown films to be 4.1 ± 0.3 kG with a perpendicular magnetic anisotropy field of 16 ± 0.3 kOe. Ferromagnetic resonance linewidth, the peak-to-peak power absorption derivative at 53 GHz, was 86 Oe. These properties will prove... ]]> Z. Chen Thick films Liquid phase epitaxy Magnetic properties Pulsed laser deposition