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## Full-Text Articles in Physics

Interphase Exchange Coupling In Fe/Sm-Co Bilayers With Gradient Fe Thickness, Ming-Hui Yu, Jason Hattrick-Simpers, Ichiro Takeuchi, Jing Li, Z. Wang, J. Liu, S. Lofland, Somdev Tyagi, J. Freeland, D. Giubertoni, M. Bersani, M. Anderle

#### Interphase Exchange Coupling In Fe/Sm-Co Bilayers With Gradient Fe Thickness, Ming-Hui Yu, Jason Hattrick-Simpers, Ichiro Takeuchi, Jing Li, Z. Wang, J. Liu, S. Lofland, Somdev Tyagi, J. Freeland, D. Giubertoni, M. Bersani, M. Anderle

*Jason R. Hattrick-Simpers*

We have fabricated Fe∕Sm–Co bilayers with gradient Fe thicknesses in order to systematically study the dependence of exchange coupling on the thickness of the Fe layer. The Fe layer was deposited at two different temperatures (150 and 300°C) to study the effect of deposition temperature on the exchange coupling. Magneto-optical Kerr effect and x-ray magnetic circular dichroism (XMCD) have been employed as nondestructive rapid characterization tools to map the magnetic properties of the gradient samples. Systematic enhancement in exchange coupling between the soft layer and the hard layer is observed as the soft layer thickness is decreased ...

Interphase Exchange Coupling In Fe/Sm-Co Bilayers With Gradient Fe Thickness, Ming-Hui Yu, Jason R. Hattrick-Simpers, Ichiro Takeuchi, Jing Li, Z. L. Wang, J. P. Liu, S. E. Lofland, Somdev Tyagi, J. W. Freeland, D. Giubertoni, M. Bersani, M. Anderle

#### Interphase Exchange Coupling In Fe/Sm-Co Bilayers With Gradient Fe Thickness, Ming-Hui Yu, Jason R. Hattrick-Simpers, Ichiro Takeuchi, Jing Li, Z. L. Wang, J. P. Liu, S. E. Lofland, Somdev Tyagi, J. W. Freeland, D. Giubertoni, M. Bersani, M. Anderle

*Faculty Publications*

We have fabricated Fe∕Sm–Co bilayers with gradient Fe thicknesses in order to systematically study the dependence of exchange coupling on the thickness of the Fe layer. The Fe layer was deposited at two different temperatures (150 and 300°C) to study the effect of deposition temperature on the exchange coupling. Magneto-optical Kerr effect and x-ray magnetic circular dichroism (XMCD) have been employed as nondestructive rapid characterization tools to map the magnetic properties of the gradient samples. Systematic enhancement in exchange coupling between the soft layer and the hard layer is observed as the soft layer thickness is decreased ...

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 ...

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 as-cast and annealed Fe amorphous alloys. In the case of NO Fe–Si, the modeling parameter *k* defined by the volume ...

Monitoring Fatigue Damage In Materials Using Magnetic Measurement Techniques, Chester C.H. Lo, F. Tang, Y. Shi, David C. Jiles, S. B. Biner

#### Monitoring Fatigue Damage In Materials Using Magnetic Measurement Techniques, Chester C.H. Lo, F. Tang, Y. Shi, David C. Jiles, S. B. Biner

*Center for Nondestructive Evaluation Publications*

Measurements of hysteresis and Barkhausen effect (BE) have been made on 0.1 wt % C Fe–C alloys subjected to strain-controlled fatigue at various strain amplitudes. A relationship between the fatigue lifetime and strain amplitude was observed. The hysteresis properties of the samples cycled at different strain amplitudes were found to vary systematically with expended fatigue life. These properties showed significant changes in the initial and final stages of fatigue, while between these stages they remained stabilized. In the stable stage the remanence was found to decrease, whereas the coercivity increased with increasing strain amplitude. Variations in BE signal during ...

Domain-Wall Motion In Random Potential And Hysteresis Modeling, M. Pasquale, V. Basso, G. Bertotti, David C. Jiles, Y. Bi

#### Domain-Wall 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 domain-wall 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 mean-field effects and reversible contributions are present.

Generalization Of Hysteresis Modeling To Anisotropic Materials, A. Ramesh, David C. Jiles, Y. Bi

#### Generalization Of Hysteresis Modeling To Anisotropic Materials, A. Ramesh, David C. Jiles, Y. Bi

*Materials Science and Engineering Publications*

An extension to the model of hysteresis has been presented earlier which included the effect of anisotropy in the modeling of the anhysteretic magnetization curves of uniaxially anisotropic single crystalline materials. Further exploration of this extension shown here considers different kinds of crystal anisotropy in materials. Theory considers that the differential susceptibility at any given field is determined by the displacement of the prevailing magnetization from the anhysteretic magnetization. Thus, it has been shown that the effect of anisotropy on magnetic hysteresis in materials can be incorporated into the model of hysteresis through the anisotropic anhysteretic. This extension is likely ...

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 ...

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 ...

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}(=*d*λ/*dH*) and a 100% increase in the maximum strain (λ). There was also an increase in the λ‐vs‐*H*hysteresis. Under compressive uniaxial stress there was virtually no bulk change in magnetostrictive strain until the ...

A Model For Hysteretic Magnetic Properties Under The Application Of Noncoaxial Stress And Field, Martin J. Sablik, S. W. Rubin, L. A. Riley, David C. Jiles, David A. Kaminski, S. B. Biner

#### A Model For Hysteretic Magnetic Properties Under The Application Of Noncoaxial Stress And Field, Martin J. Sablik, S. W. Rubin, L. A. Riley, David C. Jiles, David A. Kaminski, S. B. Biner

*Center for Nondestructive Evaluation Publications*

Although descriptions of the effect of stress on spontaneous magnetization within a single domain already exist, there remains no adequate mathematical model for the effects of noncoaxial magnetic field and stress on bulk magnetization in a multidomained specimen. This article addresses the problem and provides a phenomenological theory that applies to the case of bulk isotropic materials. The magnetomechanical hysteresis model of Sablik and Jiles is thus extended to treat magnetic properties in the case of noncoaxial stress and magnetic field in an isotropic, polycrystalline medium. In the modeling, noncollinearity between magnetization and magnetic field is taken into account. The ...

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

#### 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 when*dH*/*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 ...