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Full-Text Articles in Physics

Intelligent Metasurfaces With Continuously Tunable Local Surface Impedance For Multiple Reconfigurable Functions, Fu Liu, Odysseas Tsilipakos, Alexandros Pitilakis, Anna C. Tasolamprou, Mohammad Sajjad Mirmoosa, Nikolaos V. Kantartzis, Do-Hoon Kwon, Maria Kafesaki, Costas M. Soukoulis, Sergei A. Tretyakov Apr 2019

Intelligent Metasurfaces With Continuously Tunable Local Surface Impedance For Multiple Reconfigurable Functions, Fu Liu, Odysseas Tsilipakos, Alexandros Pitilakis, Anna C. Tasolamprou, Mohammad Sajjad Mirmoosa, Nikolaos V. Kantartzis, Do-Hoon Kwon, Maria Kafesaki, Costas M. Soukoulis, Sergei A. Tretyakov

Ames Laboratory Accepted Manuscripts

Electromagnetic metasurfaces can be characterized as intelligent if they are able to perform multiple tunable functions, with the desired response being controlled by a computer influencing the individual electromagnetic properties of each metasurface inclusion. In this paper, we present an example of an intelligent metasurface that operates in the reflection mode in the microwave frequency range. We numerically show that, without changing the main body of the metasurface, we can achieve tunable perfect absorption and tunable anomalous reflection. The tunability features can be implemented using mixed-signal integrated circuits (ICs), which can independently vary both the resistance and reactance, offering complete ...


Tailoring Bandgap Of Perovskite Batio3 By Transition Metals Co-Doping For Visible-Light Photoelectrical Applications: A First-Principles Study, Fan Yang, Liang Yang, Changzhi Ai, Pengcheng Xie, Shiwei Lin, Cai-Zhuang Wang, Xihong Lu Jun 2018

Tailoring Bandgap Of Perovskite Batio3 By Transition Metals Co-Doping For Visible-Light Photoelectrical Applications: A First-Principles Study, Fan Yang, Liang Yang, Changzhi Ai, Pengcheng Xie, Shiwei Lin, Cai-Zhuang Wang, Xihong Lu

Ames Laboratory Accepted Manuscripts

The physical and chemical properties of V-M″ and Nb-M″ (M″ is 3d or 4d transition metal) co-doped BaTiO3were studied by first-principles calculation based on density functional theory. Our calculation results show that V-M″ co-doping is more favorable than Nb-M″ co-doping in terms of narrowing the bandgap and increasing the visible-light absorption. In pure BaTiO3, the bandgap depends on the energy levels of the Ti 3d and O 2p states. The appropriate co-doping can effectively manipulate the bandgap by introducing new energy levels interacting with those of the pure BaTiO3. The optimal co-doping effect comes from the ...


Antimatched Electromagnetic Metasurfaces For Broadband Arbitrary Phase Manipulation In Reflection, Odysseas Tsilipakos, Thomas Koschny, Costas M. Soukoulis Jan 2018

Antimatched Electromagnetic Metasurfaces For Broadband Arbitrary Phase Manipulation In Reflection, Odysseas Tsilipakos, Thomas Koschny, Costas M. Soukoulis

Ames Laboratory Accepted Manuscripts

Metasurfaces impart phase discontinuities on impinging electromagnetic waves that are typically limited to 0–2π. Here, we demonstrate that multiresonant metasurfaces can break free from this limitation and supply arbitrarily large, tunable time delays over ultrawide bandwidths. As such, ultrathin metasurfaces can act as the equivalent of thick bulk structures by emulating the multiple geometric resonances of three-dimensional systems that originate from phase accumulation with effective material resonances implemented on the surface itself via suitable subwavelength meta-atoms. We describe a constructive procedure for defining the required sheet admittivities of such metasurfaces. Importantly, the proposed approach provides an exactly linear phase ...


Influence Of Mn Concentration On Magnetic Topological Insulator Mnxbi2−Xte3 Thin-Film Hall-Effect Sensor, Ravi L. Hadimani, S. Gupta, S. M. Harstad, Vitalij K. Pecharsky, David C. Jiles Nov 2015

Influence Of Mn Concentration On Magnetic Topological Insulator Mnxbi2−Xte3 Thin-Film Hall-Effect Sensor, Ravi L. Hadimani, S. Gupta, S. M. Harstad, Vitalij K. Pecharsky, David C. Jiles

Ames Laboratory Publications

Hall-effect (HE) sensors based on high-quality Mn-doped Bi2Te3 topological insulator (TI) thin films have been systematically studied in this paper. Improvement of Hall sensitivity is found after doping the magnetic element Mn into Bi2Te3. The sensors with low Mn concentrations, MnxBi2-xTe3, x = 0.01 and 0.08 show the linear behavior of Hall resistance with sensitivity about 5 Ω/T. And their Hall sensitivity shows weak dependence on temperature. For sensors with high Mn concentration (x = 0.23), the Hall resistance with respect to magnetic field shows a hysteretic behavior. Moreover, its sensitivity shows almost eight times as high as ...


Magnetic Interaction And Electronic Transport In La0.4bi0.6mn0.5ti0.5o3 Manganite, Vijaylakshmi Dayal, Punith Kumar V., Ravi L. Hadimani, E. A. Balfour, H. Fu, David C. Jiles May 2015

Magnetic Interaction And Electronic Transport In La0.4bi0.6mn0.5ti0.5o3 Manganite, Vijaylakshmi Dayal, Punith Kumar V., Ravi L. Hadimani, E. A. Balfour, H. Fu, David C. Jiles

Electrical and Computer Engineering Publications

We report magnetic interactions and electronic transport properties in La0.4Bi0.6Mn0.5Ti0.5O3 perovskite manganite synthesized using solid-state route. After characterizing the samples structurally, the systematic investigations of magnetic and electrical transport behaviors have been undertaken. It has been observed that at low temperatures near TC, the sample is magnetically frustrated leading to the second-order magnetic transition. A justification for the observed magnetic behavior has been explained based on Arrott's plot study. The resistivity as a function of temperature in the absence and the presence of applied magnetic field suggests semiconducting nature of the sample. The conduction of ...


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 ...


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.


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 ...


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 ...


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 ...


Gd5(Si,Ge)4 Thin Film Displaying Large Magnetocaloric And Strain Effects Due To Magnetostructural Transition, Ravi L. Hadimani, Joao H. B. Silva, Andre M. Pereira, Devo L. Schlagel, Thomas A. Lograsso, Yang Ren, David C. Jiles, Joao P. Araújo Jan 2015

Gd5(Si,Ge)4 Thin Film Displaying Large Magnetocaloric And Strain Effects Due To Magnetostructural Transition, Ravi L. Hadimani, Joao H. B. Silva, Andre M. Pereira, Devo L. Schlagel, Thomas A. Lograsso, Yang Ren, David C. Jiles, Joao P. Araújo

Ames Laboratory Publications

Magnetic refrigeration based on the magnetocaloric effect is one of the best alternatives to compete with vapor-compression technology. Despite being already in its technology transfer stage, there is still room for optimization, namely, on the magnetic responses of the magnetocaloric material. In parallel, the demand for different magnetostrictive materials has been greatly enhanced due to the wide and innovative range of technologies that emerged in the last years (from structural evaluation to straintronics fields). In particular, the Gd5(Six Ge1−x)4 compounds are a family of well-known alloys that present both giant magnetocaloric and colossal magnetostriction effects. Despite their ...


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 ...


Phenomenological Modelling Of First Order Phase Transitions In Magnetic Systems, Yevgen Melikhov, Ravi L. Hadimani, Arun Raghunathan Jan 2014

Phenomenological Modelling Of First Order Phase Transitions In Magnetic Systems, Yevgen Melikhov, Ravi L. Hadimani, Arun Raghunathan

Electrical and Computer Engineering Publications

First order phase transitions may occur in several magnetic systems, with two structural phases having different magnetic properties each and a structural transition between them. Here, a novel physics based phenomenological model of such systems is proposed, in which magnetization is represented by the volumetric amounts of ferromagnetism (described by extended Jiles-Atherton theory) and paramagnetism (described by the Curie-Weiss law) in respective phases. An identification procedure to extract material parameters from experimental data is proposed. The proposed phenomenological approach was successfully applied to magnetocaloric Gd5(Six Ge 1−x)4 system and also has the potential to describe the behavior ...


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.


Design Of High-Magnetic Field Gradient Sources For Controlling Magnetically Induced Flow Of Ferrofluids In Microfluidic Systems, W. He, S. J. Lee, David C. Jiles, D. H. Schmidt, Marc D. Porter, Ruth Shinar May 2003

Design Of High-Magnetic Field Gradient Sources For Controlling Magnetically Induced Flow Of Ferrofluids In Microfluidic Systems, W. He, S. J. Lee, David C. Jiles, D. H. Schmidt, Marc D. Porter, Ruth Shinar

Ames Laboratory Publications

The use of miniature electromagnets for ferrofluid-actuated liquid dispensing into microfluidic channels has been investigated by numerical simulations using the finite element method and measurements of fluid displacement and flow rate. The simulations illustrate the effect of structural and geometrical parameters of single and paired solenoid coils on the magnetic force experienced by the ferrofluid. Dual solenoids were used for extended fluid displacement. Ferrofluid positioning and flow rates were controlled also by using a solenoid with an iron core. The experimental measurements of fluidflow in capillaries were used to validate the modeling calculations. The results can be used as a ...


Microelectromagnetic Ferrofluid-Based Actuator, Y. Melikhov, S. J. Lee, David C. Jiles, D. H. Schmidt, Marc D. Porter, Ruth Shinar May 2003

Microelectromagnetic Ferrofluid-Based Actuator, Y. Melikhov, S. J. Lee, David C. Jiles, D. H. Schmidt, Marc D. Porter, Ruth Shinar

Ames Laboratory Publications

Computer simulations were used to investigate the performance of a microscale ferrofluid-based magnetic actuator developed for liquid dispensing in microfluidic channels. The actuation was based on the movement of a ferrofluid plug in a magnetic field gradient generated by on-chip effectively infinite parallel conductors. The movement, positioning, and retaining of ferrofluid plugs with different lengths at various locations along a microfluidic channel were investigated for two cases. In case (a), the magnetic field gradient was generated by a single conductor; when the ferrofluid reached its equilibrium position, the current was switched off and the nearest neighbor conductor was energized. A ...


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 ...


Examination Of The Relationship Between The Parameters Of Barkhausen Effect Model And Microstructure Of Magnetic Materials, Chester C.H. Lo, S. J. Lee, L. C. Kerdus, David C. Jiles May 2002

Examination Of The Relationship Between The Parameters Of Barkhausen Effect Model And Microstructure Of Magnetic Materials, Chester C.H. Lo, S. J. Lee, L. C. Kerdus, David C. Jiles

Center for Nondestructive Evaluation Publications

A relationship between the parameters of a hysteretic-stochastic process model of the Barkhausen effect (BE) and the microstructural features of a series of ferritic/pearlitic steel samples has been identified. The root-mean-square values and pulse height distributions of the experimental and modeled BE signals showed similar dependence on the pearlite content. The correlation length parameter ξ of the model, which represents the range of interaction of domain walls with pinning sites, was found to obey ξ=AVfDf+BVpDp where Vf(Vp)and Df(Dp) are the volume fraction and grain size of ferrite (pearlite).


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 ...


Composite Magnetostrictive Materials For Advanced Automotive Magnetomechanical Sensors, R. William Mccallum, Kevin W. Dennis, David C. Jiles, John E. Snyder, Y. H. Chen Apr 2001

Composite Magnetostrictive Materials For Advanced Automotive Magnetomechanical Sensors, R. William Mccallum, Kevin W. Dennis, David C. Jiles, John E. Snyder, Y. H. Chen

Ames Laboratory Publications

In this paper we present the development of a composite magnetostrictive material for automotive applications. The material is based on cobaltferrite,CoO⋅Fe2O3, and contains a small fraction of metallic matrix phase that serves both as a liquid-phasesintering aid during processing and enhances the mechanical properties over those of a simple sinteredferrite ceramic. In addition the metal matrix makes it possible to braze the material, making the assembly of a sensor relatively simple. The material exhibits good sensitivity and should have high corrosion resistance, while at the same time it is low in cost.


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 ...


Superparamagnetic Magnetization Equation In Two Dimensions, David C. Jiles, S. J. Lee, J. M. Kenkel, K. L. Metlov Aug 2000

Superparamagnetic Magnetization Equation In Two Dimensions, David C. Jiles, S. J. Lee, J. M. Kenkel, K. L. Metlov

Ames Laboratory Publications

An equation for the dependence of magnetization on magnetic field in the case of two-dimensional (base plane) anisotropy has been derived. The resulting equation is expressed as an infinite series of modified Bessel functions, unlike the elementary function expressions that are applicable to the one-dimensional (axially anisotropic) and three-dimensional (isotropic) cases. Nevertheless, in the low-field limit, the series can be effectively truncated to give an approximate solution, while, in the high-field limit, an alternative expression has been derived which represents the limiting function as the field strength tends to infinity. The resulting expressions can be used to describe the superparamagnetic ...


An Extended Model Of The Barkhausen Effect Based On The Abbm Model, D. M. Clatterbuck, V. J. Garcia, M. J. Johnson, David C. Jiles May 2000

An Extended Model Of The Barkhausen Effect Based On The Abbm Model, D. M. Clatterbuck, V. J. Garcia, M. J. Johnson, David C. Jiles

Ames Laboratory Publications

The Barkhausen model of Alessandro et al. [J. Appl. Phys. 68, 2901 (1990)] has been extended to nonstationary domain walldynamics. The assumptions of the original model limit, its use to situations where the differential permeability, and time derivative of applied field are constant. The later model of Jiles et al. assumes that the Barkhausen activity in a given time interval is proportional to the rate of change of irreversible magnetization which can be calculated from hysteresis models. The extended model presented here incorporates ideas from both of these. It assumes that the pinning field and domain wall velocity behave according ...


Effects Of Fatigue-Induced Changes In Microstructure And Stress On Domain Structure And Magnetic Properties Of Fe–C Alloys, Chester C.H. Lo, F. Tang, S. B. Biner, David C. Jiles May 2000

Effects Of Fatigue-Induced Changes In Microstructure And Stress On Domain Structure And Magnetic Properties Of Fe–C Alloys, Chester C.H. Lo, F. Tang, S. B. Biner, David C. Jiles

Ames Laboratory Publications

A study of the effects of microstructural changes on domain structure and magnetic properties as a result of fatigue has been made on Fe–C alloys subjected to either cold work, stress-relief annealing, or heat treatment that produced a ferritic/pearlitic structure. The magnetic properties varied with stress cycling depending on the initial condition of the samples. Variations in coercivity in the initial stage of fatigue were closely related to the changes in dislocation structure. In the intermediate stage of fatigue the observed refinement of domain structures was related to the development of dislocation cell structures and formation of slip ...


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 ...


Microstructure And Magnetic Properties Of As-Quenched And Heat-Treated (Nd,Dy)Feb Powders Produced By High Pressure Gas Atomization, John E. Snyder, Chester C.H. Lo, X. Fang, B. Kriegermeier, David C. Jiles Apr 1999

Microstructure And Magnetic Properties Of As-Quenched And Heat-Treated (Nd,Dy)Feb Powders Produced By High Pressure Gas Atomization, John E. Snyder, Chester C.H. Lo, X. Fang, B. Kriegermeier, David C. Jiles

Ames Laboratory Publications

The magnetic properties and microstructures of a series of as-quenched and heat-treated inert gas atomized (IGA) rare-earth rich (Nd,Dy)–Fe–B particles have been investigated. Heat treatment was found to substantially improve magnetic properties, with effects most pronounced in samples with higher Dy content and higher total rare earth (RE) content. The as-quenched particles consisted of an underquenched dendritic-like structure with the majority phase RE2Fe14B, and a fine network of RE-rich material between the grains. The heat-treated particles showed a change in microstructure which correlated with magnetic property changes. Particles which showed little change in magnetic properties showed no ...


Application Of The Preisach And Jiles–Atherton Models To The Simulation Of Hysteresis In Soft Magnetic Alloys, M. Pasquale, G. Bertotti, David C. Jiles, Y. Bi Apr 1999

Application Of The Preisach And Jiles–Atherton Models To The Simulation Of Hysteresis In Soft Magnetic Alloys, M. Pasquale, G. Bertotti, David C. Jiles, Y. Bi

Ames Laboratory Publications

his article describes the advances in unification of model descriptions of hysteresis in magnetic materials and demonstrates the equivalence of two widely accepted models, the Preisach (PM) and Jiles–Atherton (JA) models. Recently it was shown that starting from general energy relations, the JA equation for a loop branch can be derived from PM. The unified approach is here applied to the interpretation of magnetization measured in nonoriented Si–Fe steels with variable grain size ⟨s⟩, and also in as-cast and annealed Fe amorphous alloys. In the case of NO Fe–Si, the modeling parameter k defined by the volume ...