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Articles 1 - 9 of 9

Full-Text Articles in Physics

Modulation On Ni2mnga(001) Surface, S. W. D'Souza, Abhishek Rai, J. Nayak, M. Maniraj, R. S. Dhaka, S. R. Barman, Deborah L. Schlagel, Thomas A. Lograsso Dec 2010

Modulation On Ni2mnga(001) Surface, S. W. D'Souza, Abhishek Rai, J. Nayak, M. Maniraj, R. S. Dhaka, S. R. Barman, Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

We report periodic modulation on (001) surface of Ni2MnGa ferromagnetic shape memory alloy. For the stoichiometric surface, analysis of the low energy electron diffraction (LEED) spot profiles shows that the modulation is incommensurate. The modulation appears at 200 K, concomitant with the first order structural transition to the martensitic phase.


Influence Of Annealing And Phase Decomposition On The Magnetostructural Transitions In Ni50mn39sn11, William M. Yuhasz, Deborah L. Schlagel, Qingfeng Xing, Kevin W. Dennis, R. William Mccallum, Thomas A. Lograsso Feb 2009

Influence Of Annealing And Phase Decomposition On The Magnetostructural Transitions In Ni50mn39sn11, William M. Yuhasz, Deborah L. Schlagel, Qingfeng Xing, Kevin W. Dennis, R. William Mccallum, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

Magnetic and structural transitions in the Ni50Mn50−xSnx (x = 10–25) ferromagnetic shape memory alloys are currently of interest. As in Ni–Mn–Ga, these alloys feature high-temperature austenite and low-temperature martensite phases, where the magnetic state is strongly composition dependent. To study the role of chemical ordering in fine-tuning their magnetostructural properties, they were first annealed for 4 weeks/1223 K to achieve structural and compositional homogeneity, and were then further annealed for 1 week ( ∼ 150 K below the reported B2 to L21 transition) at 773 K to increase the degree ...


Magnetic Force Microscopy Investigation Of Domain Structures In Fe–X At. % Ga Single Crystals (12, Feiming Bai, Jiefang Li, D. Viehland, D. Wu, Thomas A. Lograsso Jul 2005

Magnetic Force Microscopy Investigation Of Domain Structures In Fe–X At. % Ga Single Crystals (12, Feiming Bai, Jiefang Li, D. Viehland, D. Wu, Thomas A. Lograsso

Ames Laboratory Publications

The domain structure of furnace-cooled (FC) and post-annealed (PA) Fe–x at. % Ga (x = 12, 20, and 25) crystals has been investigated by magnetic force microscopy. For both FC and PA Fe–12 at. % Ga, the domains were found to be well-aligned and oriented along the [100] direction. For Fe–20 at. % Ga, although a preferred [100] orientation remained, a difference in morphology was found between FC and PA conditions—in the PA condition, clear dendritic domains were observed. For both FC and PA Fe–25 at. % Ga, a much reduced [100] preferred domain orientation was found, the domain size ...


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 ...


Relaxation In Glassforming Liquids And Amorphous Solids, C. Austin Angell, Kia L. Ngai, Greg B. Mckenna, Paul F. Mcmillan, Steve W. Martin Jan 2000

Relaxation In Glassforming Liquids And Amorphous Solids, C. Austin Angell, Kia L. Ngai, Greg B. Mckenna, Paul F. Mcmillan, Steve W. Martin

Materials Science and Engineering Publications

The field of viscousliquid and glassysolid dynamics is reviewed by a process of posing the key questions that need to be answered, and then providing the best answers available to the authors and their advisors at this time. The subject is divided into four parts, three of them dealing with behavior in different domains of temperature with respect to the glass transition temperature, Tg,and a fourth dealing with “short time processes.” The first part tackles the high temperature regime T>Tg, in which the system is ergodic and the evolution of the viscousliquid toward the condition at Tg is ...


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 ...


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 Apr 1996

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 Nd2Fe14B‐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 Nd2Fe14B 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 ...


Monitoring Neutron Embrittlement In Nuclear Pressure Vessel Steels Using Micromagnetic Barkhausen Emissions, Levent B. Sipahi, Madhav Rao Govindaraju, David C. Jiles May 1994

Monitoring Neutron Embrittlement In Nuclear Pressure Vessel Steels Using Micromagnetic Barkhausen Emissions, Levent B. Sipahi, Madhav Rao Govindaraju, David C. Jiles

Center for Nondestructive Evaluation Publications

In nuclear power plants, neutron embrittlement of pressure vessel steels has been one of the main concerns. The use of micromagnetic Barkhausen emissions is a promising method to monitor the variations in microstructural and subsurface stress states due to their influence on these emissions. Measurements of these emissions can reveal neutron irradiationdegradation in nuclear power plant components. Samples which were irradiated at differentneutron fluences and annealed at different temperatures were obtained from three reactor surveillance programs. The results of different neutron fluences and annealing procedures showed noticeable fractional changes in the magnetic Barkhausen effect signal parameter, ΔMBE/MBE, and in ...


Enhanced Differential Magnetostrictive Response In Annealed Terfenol‐D, N. Galloway, M. P. Schulze, R. D. Greenough, David C. Jiles Aug 1993

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 Tb0.316Dy0.684Fe1.982 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 ...