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Full-Text Articles in Physics

Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho Jun 2017

Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho

Gary Tuttle

A directional antenna made with photonic band gap structures has been presented. The directional antenna is formed with two photonic band gap structures oriented back to back and separated from each other by a distance to form a resonant cavity between the photonic band gap structures. An antenna element is placed in the resonant cavity. The resonant frequency of the cavity is tuned by adjusting the distance between the photonic band gap structures. The resonant cavity can be asymmetrical or symmetrical.


Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles Jun 2017

Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles

Gary Tuttle

We investigated the effect of magnetic doping on magnetic and transport properties of Bi2Te3thin films. CrxBi2−xTe3 thin films with x = 0.03, 0.14, and 0.29 were grown epitaxially on mica substrate with low surface roughness (∼0.4 nm). It is found that Cr is an electron acceptor in Bi2Te3 and increases the magnetization of CrxBi2−xTe3. When x = 0.14 and 0.29,ferromagnetism appears in CrxBi2−xTe3 thin films, where anomalous Hall effect and weak localization of magnetoconductance were observed. The Curie temperature, coercivity, and remnant Hall resistance of thin films increase with increasing Cr concentration ...


Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles Jan 2015

Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles

Electrical and Computer Engineering Publications

Gd5(Six Ge 1−x)4 has mixed phases in the composition range 0.32 < x < 0.41, which have not been widely studied. In this paper, we have synthesized and indexed single crystal samples of Gd5Si1.3 Ge 2.7 and Gd5Si1.4 Ge 2.6. We have investigated the first order and second orderphase transition temperatures of these samples using magnetic moment vs. temperature andmagnetic moment vs. magnetic field at different temperatures. We have used a modified Arrott plot technique that was developed and reported by us previously to determine the “hidden” second order phase transition temperature of the orthorhombic II phase.


Deep Brain Transcranial Magnetic Stimulation Using Variable “Halo Coil” System, Y. Meng, Ravi L. Hadimani, Lawrence J. Crowther, Z. Xu, J. Qu Jan 2015

Deep Brain Transcranial Magnetic Stimulation Using Variable “Halo Coil” System, Y. Meng, Ravi L. Hadimani, Lawrence J. Crowther, Z. Xu, J. Qu

Electrical and Computer Engineering Publications

Transcranial Magnetic Stimulation has the potential to treat various neurological disorders non-invasively and safely. The “Halo coil” configuration can stimulate deeper regions of the brainwith lower surface to deep-brain field ratio compared to other coil configurations. The existing “Halo coil” configuration is fixed and is limited in varying the site of stimulation in the brain. We have developed a new system based on the current “Halo coil” design along with a graphicaluser interface system that enables the larger coil to rotate along the transverse plane. The new system can also enable vertical movement of larger coil. Thus, this adjustable “Halo ...


Analysis Of Ringing Effects Due To Magnetic Core Materials In Pulsed Nuclear Magnetic Resonance Circuits, Neelam G. Prabhu Gaunkar, N. R. Y. Bouda, Ikenna C. Nlebedim, Ravi L. Hadimani, I. Bulu, K. Ganesan, Y. Q. Song, Mani Mina, David C. Jiles Jan 2015

Analysis Of Ringing Effects Due To Magnetic Core Materials In Pulsed Nuclear Magnetic Resonance Circuits, Neelam G. Prabhu Gaunkar, N. R. Y. Bouda, Ikenna C. Nlebedim, Ravi L. Hadimani, I. Bulu, K. Ganesan, Y. Q. Song, Mani Mina, David C. Jiles

Electrical and Computer Engineering Publications

This work presents investigations and detailed analysis of ringing in a non-resonant pulsednuclear magnetic resonance (NMR) circuit. Ringing is a commonly observed phenomenon in high power switching circuits. The oscillations described as ringing impede measurements in pulsed NMR systems. It is therefore desirable that those oscillations decay fast. It is often assumed that one of the causes behind ringing is the role of the magnetic core used in theantenna (acting as an inductive load). We will demonstrate that an LRC subcircuit is also set-up due to the inductive load and needs to be considered due to its parasitic effects. It ...


Thermal Effects On The Magnetic Properties Of Titanium Modified Cobalt Ferrite, Ikenna C. Nlebedim, David C. Jiles Jan 2015

Thermal Effects On The Magnetic Properties Of Titanium Modified Cobalt Ferrite, Ikenna C. Nlebedim, David C. Jiles

Electrical and Computer Engineering Publications

The temperature dependence of the magnetic properties of titanium modified cobalt ferrite is presented. The change of maximum magnetization obtained at H ≈ 2.4 MA/m between any two temperatures increases systematically with composition, which is desirable for applications in devices. Variation in magnetocrystalline anisotropy and coercivity were different from previous studies on cation substituted cobalt ferrite. At lower concentrations, the effect of lower thermal energy dominated the effect of non-magnetic cation substitutions in controlling the anisotropy.The reverse was the case at higher concentrations. The temperature dependence of coercivity is dominated by the contribution of magnetocrystalline anisotropy to coercivity ...


Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles Jan 2015

Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles

Electrical and Computer Engineering Publications

We investigated the effect of magnetic doping on magnetic and transport properties of Bi2Te3thin films. CrxBi2−xTe3 thin films with x = 0.03, 0.14, and 0.29 were grown epitaxially on mica substrate with low surface roughness (∼0.4 nm). It is found that Cr is an electron acceptor in Bi2Te3 and increases the magnetization of CrxBi2−xTe3. When x = 0.14 and 0.29,ferromagnetism appears in CrxBi2−xTe3 thin films, where anomalous Hall effect and weak localization of magnetoconductance were observed. The Curie temperature, coercivity, and remnant Hall resistance of thin films increase with increasing Cr concentration ...


Influence Of Ga-Concentration On The Electrical And Magnetic Properties Of Magnetoelectric Cogaxfe2− Xo4/Batio3 Composite, Yan Ni, Zhen Zhang, Cajetan I. Nlebedim, David C. Jiles Jan 2015

Influence Of Ga-Concentration On The Electrical And Magnetic Properties Of Magnetoelectric Cogaxfe2− Xo4/Batio3 Composite, Yan Ni, Zhen Zhang, Cajetan I. Nlebedim, David C. Jiles

Electrical and Computer Engineering Publications

Multiferroic materials exhibit magnetoelectric (ME) coupling and promise new device applications including magnetic sensors, generators, and filters. An effective method for developing ME materials with enhanced ME effect is achieved by the coupling through the interfacial strain between piezoelectric and magnetostrictive materials. In this study, the electrical and magnetic properties of Ga doped magnetoelectric CoGaxFe2−xO4/BaTiO3composite are studied systematically. It is found that Ga doping improves the sensitivity of magnetoelastic response and stabilizes the magnetic phase of the composites. More importantly, Ga doping reduces the electrical conductivity of composite, as well as the dielectric loss. An enhancement of the ...


Growth And Characterization Of Pt-Protected Gd5si4 Thin Films, Ravi L. Hadimani, Yaroslav Mudryk, Timothy E. Prost, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., David C. Jiles Jan 2014

Growth And Characterization Of Pt-Protected Gd5si4 Thin Films, Ravi L. Hadimani, Yaroslav Mudryk, Timothy E. Prost, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., David C. Jiles

Electrical and Computer Engineering Publications

Successful growth and characterization of thin films of giant magnetocaloric Gd5(SixGe1−x)4were reported in the literature with limited success. The inherent difficulty in producing this complex material makes it difficult to characterize all the phases present in the thin films of this material. Therefore, thin film of binary compound of Gd5Si4 was deposited by pulsed laser deposition. It was then covered with platinum on the top of the film to protect against any oxidation when the film was exposed to ambient conditions. The average film thickness wasmeasured to be approximately 350 nm using a scanning electron microscopy, and ...


Enhancement Of Magnetocaloric Effect In The Gd2al Phase By Co Alloying, Z. Y. Huang, H. Fu, Ravi L. Hadimani, E. Agurgo Balfour, S. N. Dembele, B. H. Teng, David C. Jiles Jan 2014

Enhancement Of Magnetocaloric Effect In The Gd2al Phase By Co Alloying, Z. Y. Huang, H. Fu, Ravi L. Hadimani, E. Agurgo Balfour, S. N. Dembele, B. H. Teng, David C. Jiles

Electrical and Computer Engineering Publications

To understand the effect of Co doping on the magnetic entropy changes in Gd2 Al phase, a series of Gd2AlCox alloys with 0 ≤ x ≤ 0.6 were synthesized by arc-melting and the crystal structure was analyzed by XRD. The magnetic properties were investigated, and the entropychanges were calculated for a magnetic field change of 50 kOe. All the as-cast alloys dopedwith Co exhibited greater magnetic entropy changes than the original binary Gd2 Al phase. The main reasons attributed to this are the increase of ferromagnetic interaction indicated by the disappearance of cusp and sharp drop in magnetization and the reduction ...


Structural, Magnetic, And Magnetoelastic Properties Of Magnesium Substituted Cobalt Ferrite, Cajetan Ikenna Nlebedim, Ravi L. Hadimani, Ruslan Prozorov, David C. Jiles Jan 2013

Structural, Magnetic, And Magnetoelastic Properties Of Magnesium Substituted Cobalt Ferrite, Cajetan Ikenna Nlebedim, Ravi L. Hadimani, Ruslan Prozorov, David C. Jiles

Electrical and Computer Engineering Publications

The effects of substituting Mg on the structural, magnetic, and magnetostrictive properties ofcobalt ferrite have been investigated. Comparable values of lattice parameter were obtained for the Mg-substituted samples. Saturation magnetization continuously decreased with increase inMg concentration. Peak-to-peak magnetostriction amplitude and strain sensitivity had a similar dependence on Mg concentration.


Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho Jul 2003

Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho

Iowa State University Patents

A directional antenna made with photonic band gap structures has been presented. The directional antenna is formed with two photonic band gap structures oriented back to back and separated from each other by a distance to form a resonant cavity between the photonic band gap structures. An antenna element is placed in the resonant cavity. The resonant frequency of the cavity is tuned by adjusting the distance between the photonic band gap structures. The resonant cavity can be asymmetrical or symmetrical.


In Situ Applied Field Imaging Of A Magnetic Tunnel Junction Using Magnetic Force Microscopy, J. S. Leib, Chester C.H. Lo, John E. Snyder, David C. Jiles May 2003

In Situ Applied Field Imaging Of A Magnetic Tunnel Junction Using Magnetic Force Microscopy, J. S. Leib, Chester C.H. Lo, John E. Snyder, David C. Jiles

Materials Science and Engineering Publications

Knowledge of domain behavior in magnetic tunnel junctions is an essential component, together with knowledge of the electron band structure, for understanding their magnetoelectronic properties. To this purpose, the magnetization reversal processes of a multilayertunnel junction of structure substrate/NiFe/AlOx/FeCo/CrPtMn/Al of tapered half-ellipsoid shape have been imaged using a magnetic force microscope(MFM) within situ applied magnetic fields. Stripe domains through both the stack and free layers observed at zero applied field were erased by a ∼100 Oe field applied to the left followed by applying a small field to the right. Magnetic domain structure ...


Lorentz Transmission Electron Microscopy And Magnetic Force Microscopy Characterization Of Nife/Al-Oxide/Co Films, Andrew C. C. Yu, Chester C.H. Lo, Amanda K. Petford-Long, David C. Jiles, Terunobu Miyazaki Jan 2002

Lorentz Transmission Electron Microscopy And Magnetic Force Microscopy Characterization Of Nife/Al-Oxide/Co Films, Andrew C. C. Yu, Chester C.H. Lo, Amanda K. Petford-Long, David C. Jiles, Terunobu Miyazaki

Materials Science and Engineering Publications

Magnetization reversal process of NiFe/Al-oxide/Co junction films was observed directly using Lorentztransmission electron microscopy (LTEM) and magnetic force microscopy(MFM).In situmagnetizing experiments performed in both LTEM and MFM were facilitated by a pair of electromagnets, which were mounted on the sample stages. A two-stage magnetization reversal process for the junction film was clearly observed in LTEM with NiFe magnetization reversed first via domain wall motion followed by Co magnetization reversal via moment rotation and domain wall motion. Reversal mechanism and domain characteristics of the NiFe and Co layers showed very distinctive features. The magnetization curve of ...


Magnetic Force Microscopy Study Of Magnetization Reversal In Sputtered Fesial(N) Films, Chester C.H. Lo, J. E. Snyder, J. S. Leib, R. Chen, B. Kriegermeier-Sutton, Matthew J. Kramer, David C. Jiles, M. T. Kief Mar 2001

Magnetic Force Microscopy Study Of Magnetization Reversal In Sputtered Fesial(N) Films, Chester C.H. Lo, J. E. Snyder, J. S. Leib, R. Chen, B. Kriegermeier-Sutton, Matthew J. Kramer, David C. Jiles, M. T. Kief

Materials Science and Engineering Publications

The magnetization reversal in a series of rf-sputtered FeSiAl(N) films has been studied using magnetic force microscopy. A system has been developed which has the capability to image domain structure while an in-plane magnetic field is applied in situ. All films exhibited a stripe domain structure in zero applied field which was indicative of a perpendicular component of domain magnetization which alternates in sign. All films showed a similar sequence of magnetization processes: on reducing the applied field from saturation a fine stripe domain structure nucleated and then coarsened as the field was decreased to zero. Local switching of ...


Temperature Dependence Of The Magnetomechanical Effect In Metal-Bonded Cobalt Ferrite Composites Under Torsional Strain, Y. Chen, John E. Snyder, Kevin W. Dennis, R. William Mccallum, David C. Jiles May 2000

Temperature Dependence Of The Magnetomechanical Effect In Metal-Bonded Cobalt Ferrite Composites Under Torsional Strain, Y. Chen, John E. Snyder, Kevin W. Dennis, R. William Mccallum, David C. Jiles

Materials Science and Engineering Publications

Metal-bonded cobaltferrite composites are promising candidates for torquesensors and other magnetostrictive sensing and actuating applications. In the present study, the temperature dependence of the magnetomechanical effect in a ring-shape cobaltferrite composite under torsional strain has been investigated in the temperature range of −37 to 90 °C. The changes of external axial magnetic field were measured as a function of applied torque. Magnetomechanical sensitivity of ΔHext/Δτ=65 A N−1 m−2 was observed with a magnetomechanical hysteresis of Δτ=±0.62 N m at room temperature (22 °C). These were then measured as a function of temperature. Both decreased ...


Modeling Of Micromagnetic Barkhausen Activity Using A Stochastic Process Extension To The Theory Of Hysteresis, David C. Jiles, Levent B. Sipahi, G. Williams May 1993

Modeling Of Micromagnetic Barkhausen Activity Using A Stochastic Process Extension To The Theory Of Hysteresis, David C. Jiles, Levent B. Sipahi, G. Williams

Materials Science and Engineering Publications

Recent work by Bertotti [IEEE Trans. Magn. MAG‐24, 621 (1988)] and others has shown that it is possible to model the micromagnetic Barkhausen discontinuities at the coercive point using a two‐parameter stochastic model. However, the present formulation of the model is restricted to limited regions of the hysteresis curve over which dM/dH is approximately constant and whendH/dt is held at a constant rate. A natural extension of this model is to take the basic result, in which the level of Barkhausen activity in one time period is related to the activity in the previous time ...


Comprehensive Analysis Of Barkhausen Emission Spectra Using Pulse Height Analysis, Frequency Spectrum, And Pulse Wave Form Analysis, Levent B. Sipahi, David C. Jiles, D. Chandler May 1993

Comprehensive Analysis Of Barkhausen Emission Spectra Using Pulse Height Analysis, Frequency Spectrum, And Pulse Wave Form Analysis, Levent B. Sipahi, David C. Jiles, D. Chandler

Materials Science and Engineering Publications

The dependence of magnetic Barkhausen emissions (MBE) upon both field excitation and detection frequencies and excitation wave form was studied in order to investigate two of several crucial factors which affect the emissions. Sinusoidal, triangular, and square wave forms were used to generate the MBE and the pulse height spectra, frequency spectra, and pulse wave forms of these signals were analyzed. The frequency spectra of sinusoidal and triangular alternating field excitations showed similar behavior but the spectrum under square wave excitation was different due to the existence of high frequency components during square wave switching. As yet, no common standard ...


Interpretation Of The Magnetization Mechanism In Terfenol‐D Using Barkhausen Pulse‐Height Analysis And Irreversible Magnetostriction, David C. Jiles, S. Hariharan May 1990

Interpretation Of The Magnetization Mechanism In Terfenol‐D Using Barkhausen Pulse‐Height Analysis And Irreversible Magnetostriction, David C. Jiles, S. Hariharan

Electrical and Computer Engineering Publications

The ternary alloy Dy0.7Tb0.3Fe1.9, known as Terfenol‐D, is a highly magnetostrictive alloy with magnetostriction coefficients along the principal crystallographic directions of λ1 1 1=1640×10−6and λ1 0 0≤100(±30)×10−6. The bulk magnetostriction λ is dependent on the state of magnetization M, on the original domain configuration, and on the texture of the material. This paper reports on Barkhausen measurements and magnetostriction. The pulse‐height distribution of Barkhausen emissions revealed events occurring at a specific amplitude which were stress dependent. The magnetostriction results gave ...