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 Magnetic materials (13)
 Magnetic hysteresis (8)
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 Annealing (4)

 CNDE (4)
 Microstructural properties (3)
 Coercive force (3)
 Materials modification (2)
 Thin film structure (2)
 Magnetostriction (2)
 Microanalytical Instrumentation Center (2)
 Barkhausen effects (2)
 Alternating current power transmission (2)
 Domain walls (2)
 Materials analysis (2)
 Thermal properties (2)
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 Composite materials (2)
 Ferrofluids (2)
 Microelectronics Research Center (2)
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 Ferromagnetism (2)
 Magnetic field measurements (2)
 Magnetic anisotropy (2)
 Atmospheric pressure (1)
 Alloys (1)
 Advanced materials (1)
 Amorphous magnetic materials (1)
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Articles 1  26 of 26
FullText Articles in Physics
Influence Of Mn Concentration On Magnetic Topological Insulator Mnxbi2−Xte3 ThinFilm HallEffect Sensor, Ravi L. Hadimani, S. Gupta, S. M. Harstad, Vitalij K. Pecharsky, David C. Jiles
Influence Of Mn Concentration On Magnetic Topological Insulator Mnxbi2−Xte3 ThinFilm HallEffect Sensor, Ravi L. Hadimani, S. Gupta, S. M. Harstad, Vitalij K. Pecharsky, David C. Jiles
Ames Laboratory Publications
Halleffect (HE) sensors based on highquality Mndoped 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, MnxBi2xTe3, 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 ...
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
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 vaporcompression 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 wellknown alloys that present both giant magnetocaloric and colossal magnetostriction effects. Despite their ...
Design Of HighMagnetic 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
Design Of HighMagnetic 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 ferrofluidactuated 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 FerrofluidBased Actuator, Y. Melikhov, S. J. Lee, David C. Jiles, D. H. Schmidt, Marc D. Porter, Ruth Shinar
Microelectromagnetic FerrofluidBased 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 ferrofluidbased 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 onchip 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 ...
Composite Magnetostrictive Materials For Advanced Automotive Magnetomechanical Sensors, R. William Mccallum, Kevin W. Dennis, David C. Jiles, John E. Snyder, Y. H. Chen
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 liquidphasesintering 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.
Superparamagnetic Magnetization Equation In Two Dimensions, David C. Jiles, S. J. Lee, J. M. Kenkel, K. L. Metlov
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 twodimensional (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 onedimensional (axially anisotropic) and threedimensional (isotropic) cases. Nevertheless, in the lowfield limit, the series can be effectively truncated to give an approximate solution, while, in the highfield 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
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 FatigueInduced 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
Effects Of FatigueInduced 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, stressrelief 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 ...
Microstructure And Magnetic Properties Of AsQuenched And HeatTreated (Nd,Dy)Feb Powders Produced By High Pressure Gas Atomization, John E. Snyder, Chester C.H. Lo, X. Fang, B. Kriegermeier, David C. Jiles
Microstructure And Magnetic Properties Of AsQuenched And HeatTreated (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 asquenched and heattreated inert gas atomized (IGA) rareearth 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 asquenched particles consisted of an underquenched dendriticlike structure with the majority phase RE2Fe14B, and a fine network of RErich material between the grains. The heattreated 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
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 ascast and annealed Fe amorphous alloys. In the case of NO Fe–Si, the modeling parameter k defined by the volume ...
Effect Of The Elastic Modulus Of The Matrix On Magnetostrictive Strain In Composites, Y. Chen, John E. Snyder, Carl R. Schwichtenberg, Kevin W. Dennis, D. K. Falzgraf, R. William Mccallum, David C. Jiles
Effect Of The Elastic Modulus Of The Matrix On Magnetostrictive Strain In Composites, Y. Chen, John E. Snyder, Carl R. Schwichtenberg, Kevin W. Dennis, D. K. Falzgraf, R. William Mccallum, David C. Jiles
Ames Laboratory Publications
The effect of the matrix material on the magnetostriction of composites containing highly magnetostrictive particles has been studied. Experimental results showed that the elastic modulus of the matrix is an important factor determining the bulk magnetostriction of the composite. For a series of composites with the same volume fraction of magnetostrictive particles but different matrix materials, the bulk magnetostriction was found to increase systematically with decreasing elastic modulus of the matrix. A modeltheory for the magnetostriction of such composites has been developed, based on two limiting assumptions: uniform strain or uniform stress inside the composite. The theory was then used ...
DomainWall Motion In Random Potential And Hysteresis Modeling, M. Pasquale, V. Basso, G. Bertotti, David C. Jiles, Y. Bi
DomainWall Motion In Random Potential And Hysteresis Modeling, M. Pasquale, V. Basso, G. Bertotti, David C. Jiles, Y. Bi
Ames Laboratory Publications
Two different approaches to hysteresis modeling are compared using a common ground based on energy relations, defined in terms of dissipated and stored energy. Using the Preisach model and assuming that magnetization is mainly due to domainwall motion, one can derive the expression of magnetization along a major loop typical of the Jiles–Atherton model and then extend its validity to cases where meanfield effects and reversible contributions are present.
Magnetomechanical Effect In Nickel And Cobalt, Michael K. Devine, David C. Jiles
Magnetomechanical Effect In Nickel And Cobalt, Michael K. Devine, David C. Jiles
Ames Laboratory Publications
The change in magnetization as a result of applied uniaxial stress has been measured in nickel and cobalt. Both tensile and compressive stresses were applied up to 125 MPa. Magnetostriction and anhysteretic magnetization as a function of stress were also measured. The change in magnetization with stress depended on the applied stress and the displacement between the prevailing magnetization and anhysteretic. At the loop tips, nickel showed a +6 mT (compression) and −6 mT (tension) magnetization change while cobalt displayed a +15 mT (compression) and −15 mT (tension) magnetization change. At remanence,nickel decreased in magnetization by 45 mT under ...
Modeling Of Permanent Magnets: Interpretation Of Parameters Obtained From The Jiles–Atherton Hysteresis Model, L. H. Lewis, J. Gao, David C. Jiles, D. O. Welch
Modeling Of Permanent Magnets: Interpretation Of Parameters Obtained From The Jiles–Atherton Hysteresis Model, L. H. Lewis, J. Gao, David C. Jiles, D. O. Welch
Ames Laboratory Publications
The Jiles–Atherton theory is based on considerations of the dependence of energy dissipation within a magnetic material resulting from changes in its magnetization. The algorithm based on the theory yields five computed model parameters, M _{S }, a, α, k, and c, which represent the saturation magnetization, the effective domain density, the mean exchange coupling between the effective domains, the flexibility of domain walls and energy‐dissipative features in the microstructure, respectively. Model parameters were calculated from the algorithm and linked with the physical attributes of a set of three related melt‐quenched permanent magnets based on the Nd_{2 ...}
Dependence Of Energy Dissipation On Annealing Temperature Of Melt–Spun Ndfeb Permanent Magnet Materials, Z. Gao, David C. Jiles, Daniel J. Branagan, R. William Mccallum
Dependence Of Energy Dissipation On Annealing Temperature Of Melt–Spun Ndfeb Permanent Magnet Materials, Z. Gao, David C. Jiles, Daniel J. Branagan, R. William Mccallum
Ames Laboratory Publications
A model of magnetic hysteresis which was developed originally for soft magnetic materials has been applied to melt–spun ribbons of Nd_{2}Fe_{14}B‐based material. The crucial ideas in the model description of hysteresis center on a dissipation of energy due to hysteresis which is proportional to the change in magnetization. The Nd_{2}Fe_{14}B material was melt–spun amorphous and then annealed for a period of 24 h at temperatures ranging from 700 to 950 °C. This resulted in different grain sizes, depending on annealing temperature. Consequently the hysteresis curves represent the properties of ...
The Magnetomechanical Effect In Electrolytic Iron, Michael K. Devine, David C. Jiles
The Magnetomechanical Effect In Electrolytic Iron, Michael K. Devine, David C. Jiles
Ames Laboratory Publications
The effect of stress on the magnetization of high purity iron has been studied systematically at different locations on the M,H plane corresponding to a variety of magnetic states of the material. The results confirm earlier studies that show the sign of the derivative dM/dσ changes at different locations on the M,H plane, and can even change as a result of a monotonic increase of stress either in compression or tension. The observed behavior can be explained on the basis of a recent theory which predicts that the irreversible changes in magnetization resulting from changes in ...
Enhancement Of Piezomagnetic Response Of Highly Magnetostrictive Rare Earth‐Iron Alloys At Khz Frequencies, Patricia P. Pulvirenti, David C. Jiles, R. D. Greenough, I. M. Reed
Enhancement Of Piezomagnetic Response Of Highly Magnetostrictive Rare Earth‐Iron Alloys At Khz Frequencies, Patricia P. Pulvirenti, David C. Jiles, R. D. Greenough, I. M. Reed
Ames Laboratory Publications
The effects of Al and Si additions on the frequency response of highly magnetostrictive Tb–Dy–Fe alloys have been studied. These elements reduced the electrical conductivity of the material, thereby increasing the depth of penetration of acmagnetic fields and extending the operational frequency range. Complex permeability measurements were made on doped and undoped polycrystalline samples with the objective of studying the improvement in energy conversion efficiency at kilohertz frequencies as a result of the alloying additions. The resulting complex permeability was compared with the values for single crystal specimens of Tb_{0.3}Dy_{0.7}Fe_{1.92 ...}
Recent Developments In Modeling Of The Stress Derivative Of Magnetization In Ferromagnetic Materials, David C. Jiles, Michael K. Devine
Recent Developments In Modeling Of The Stress Derivative Of Magnetization In Ferromagnetic Materials, David C. Jiles, Michael K. Devine
Ames Laboratory Publications
The effect of changing stress on the magnetization of ferromagnetic materials leads to behavior in which the magnetization may increase, or decrease, when exposed to the same stress under the same external conditions. A simple empirical law seems to govern the behavior when the magnetization begins from a major hysteresis loop. The application of the law of approach, in which the derivative of the magnetization with respect to the elastic energy supplied dM/dW is proportional to the magnetization displacement M _{an}−M, is discussed.
Frequency Dependence Of Hysteresis Curves In Conducting Magnetic Materials, David C. Jiles
Frequency Dependence Of Hysteresis Curves In Conducting Magnetic Materials, David C. Jiles
Ames Laboratory Publications
An extension of the hysteresis model has been developed that takes into account the effects on the hysteresis curves of eddycurrents in electrically conducting media. In the derivation presented it is assumed that the frequency of the applied field is low enough (or the thickness of the material medium small enough) that the skin effect can be ignored so that the magnetic field penetrates uniformly throughout the material. In this case, the dc hysteresis equation is extended by the addition of a classical eddy‐current‐loss term depending on (i) the rate of change of magnetization with time, (ii) the ...
Estimation Of Fatigue Exposure From Magnetic Coercivity, Z. J. Chen, David C. Jiles, J. Kameda
Estimation Of Fatigue Exposure From Magnetic Coercivity, Z. J. Chen, David C. Jiles, J. Kameda
Ames Laboratory Publications
An investigation of the effects of fatigue on A533B steel under constant load amplitude is reported in this paper. It was found that the plastic strain of the sample accumulated logarithmically with the number of stress cycles after initial fatigue softening. Based on the fact that plastic strain is often linearly related to the coercivity of material, at least for small changes of H _{c }, a phenomenological relationship has been developed and tested to correlate the number of stress cycles to this magnetic parameter. This result represents the first successful attempt to relate the fatigue exposure directly to a magnetic ...
Enhanced Differential Magnetostrictive Response In Annealed Terfenol‐D, N. Galloway, M. P. Schulze, R. D. Greenough, David C. Jiles
Enhanced Differential Magnetostrictive Response In Annealed Terfenol‐D, N. Galloway, M. P. Schulze, R. D. Greenough, David C. Jiles
Ames Laboratory Publications
The field and pressure dependencies of the magnetostriction of Tb_{0.316}Dy_{0.684}Fe_{1.982} have been measured in a grain‐oriented rod after thermally annealing for 1 day at 850 °C and for 4 days at 950 °C in an argon atmosphere. The results of the heat treatment are a fivefold increase in the strain coefficient d _{33}(=dλ/dH) and a 100% increase in the maximum strain (λ). There was also an increase in the λ‐vs‐Hhysteresis. Under compressive uniaxial stress there was virtually no bulk change in magnetostrictive strain until the ...
Measurements Of Magnetic Circuit Characteristics For Comprehension Of Intrinsic Magnetic Properties Of Materials From Surface Inspection, Z. J. Chen, Michael K. Devine, David C. Jiles
Measurements Of Magnetic Circuit Characteristics For Comprehension Of Intrinsic Magnetic Properties Of Materials From Surface Inspection, Z. J. Chen, Michael K. Devine, David C. Jiles
Ames Laboratory Publications
A transfer function is presented for calculating magnetic field and flux density inside a test material as a result of surface measurement. By considering flux leakage, we introduce a parameter η, called the leakage coefficient, which can be experimentally determined. It is introduced into the equations to make the transfer function more practical. The distribution of field inside a test material is then discussed in accordance with a surfacemagnetic charge model.
Magnescope: Applications In Nondestructive Evaluation, Michael K. Devine, David C. Jiles, A. R. Eichmann, David A. Kaminski, S. Hardwick
Magnescope: Applications In Nondestructive Evaluation, Michael K. Devine, David C. Jiles, A. R. Eichmann, David A. Kaminski, S. Hardwick
Ames Laboratory Publications
This paper describes recent results obtained with the Magnescope, which has been used on location in industrial environments and has successfully detected impending fatigue failure, creep damage, applied stress, and microstructural differences. It is concluded that the device provides a useful nondestructive method for evaluating the mechanical properties of materials through the measurement of their structure sensitive magnetic properties.
Analytic Model Calculation Of Magnetic Field In A Magnetic Half‐Space Due To Surface Magnetic Charge, Z. J. Chen, Madhav Rao Govindaraju, David C. Jiles
Analytic Model Calculation Of Magnetic Field In A Magnetic Half‐Space Due To Surface Magnetic Charge, Z. J. Chen, Madhav Rao Govindaraju, David C. Jiles
Ames Laboratory Publications
By analogy with electrostatic field, a simple analytic model is presented on the distribution of magnetic field inside a test material as a result of surface inspection with a magnetic probe. According to this model, the penetration depth of the magnetic field is defined and the permeability of the material at different depths is calculated. Finally, the magnetic flux inside the inspection head when placed on samples of different thicknesses is calculated and compared with experimental results.
Evaluation Of Fatigue Damage In Steel Structural Components By Magnetoelastic Barkhausen Signal Analysis, Madhav Rao Govindaraju, Andrew Strom, David C. Jiles, S. B. Biner, Z. J. Chen
Evaluation Of Fatigue Damage In Steel Structural Components By Magnetoelastic Barkhausen Signal Analysis, Madhav Rao Govindaraju, Andrew Strom, David C. Jiles, S. B. Biner, Z. J. Chen
Ames Laboratory Publications
This paper is concerned with using a magnetic technique for the evaluation of fatigue damage in steel structural components. It is shown that Barkhausen effect measurements can be used to indicate impending failure due to fatigue under certain conditions. The Barkhausen signal amplitude is known to be highly sensitive to changes in density and distribution of dislocations in materials. The sensitivity of Barkhausen signal amplitude to fatigue damage has been studied in the low‐cycle fatigue regime using smooth tensile specimens of a medium strength steel. The Barkhausen measurements were taken at depths of penetration of 0.02, 0.07 ...
Pressure Cell For Magnetostrictive Measurements, Jerome E. Ostenson, Douglas K. Finnemore, David C. Jiles
Pressure Cell For Magnetostrictive Measurements, Jerome E. Ostenson, Douglas K. Finnemore, David C. Jiles
Ames Laboratory Publications
A pressure cell has been designed to study the magnetostrictive properties of a material as a function of both pressure and magnetic field. For changes in length on the order of 2000 ppm, it is necessary to have a substantial compliance in the pressure cell to retain a constant stress over the length of travel.