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Iowa State University

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Materials Science and Engineering

Solid-state phase transformations

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Full-Text Articles in Physics

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 ...


Field-Driven Structural Phase Transition And Sign-Switching Magnetocaloric Effect In Ni–Mn–Sn, M. Pasquale, C. P. Sasso, L. Giudici, Thomas A. Lograsso, Deborah L. Schlagel Sep 2007

Field-Driven Structural Phase Transition And Sign-Switching Magnetocaloric Effect In Ni–Mn–Sn, M. Pasquale, C. P. Sasso, L. Giudici, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

Depending on the starting equilibrium temperature, the application of a magnetic field on a sample of Ni–Mn–Sn produces sample heating or cooling during adiabatic experiments. The competition between endothermal and exothermal effects is observed close to the martensite-to-austenite magnetostructural phase transition. A model assuming the coexistence of two phases and a field dependence of their volume allows to compute the evolution of entropy and heat capacity during the phase transition. The correct fitting of the results suggests that the field-induced reduction of the martensite-to-austenite transition temperature is responsible for the observed sign switching of the magnetocaloric effect.


Spontaneous Generation Of Voltage In Single-Crystal Gd5si2ge2 During Magnetostructural Phase Transformations, Min Zou, H. Tang, Deborah L. Schlagel, Thomas A. Lograsso, Karl A. Gschneidner Jr., Vitalij K. Pecharsky Apr 2006

Spontaneous Generation Of Voltage In Single-Crystal Gd5si2ge2 During Magnetostructural Phase Transformations, Min Zou, H. Tang, Deborah L. Schlagel, Thomas A. Lograsso, Karl A. Gschneidner Jr., Vitalij K. Pecharsky

Ames Laboratory Conference Papers, Posters, and Presentations

The spontaneous generation of voltage (SGV) in single-crystal and polycrystallineGd5Si2Ge2 during the coupled magnetostructural transformation has been examined. Our experiments show reversible, measurable, and repeatable SGV responses of the materials to the temperature and magnetic field. The parameters of the response and the magnitude of the signal are anisotropic and rate dependent. The magnitude of the SGV signal and the critical temperatures and critical magnetic fields at which the SGV occurs vary with the rate of temperature and magnetic-field changes.


Dynamics Of The Magnetic Field-Induced First Order Magnetic-Structural Phase Transformation Of Gd5(Si0.5ge0.5)4, J. Leib, J. E. Snyder, Thomas A. Lograsso, Deborah L. Schlagel, David C. Jiles Jun 2004

Dynamics Of The Magnetic Field-Induced First Order Magnetic-Structural Phase Transformation Of Gd5(Si0.5ge0.5)4, J. Leib, J. E. Snyder, Thomas A. Lograsso, Deborah L. Schlagel, David C. Jiles

Ames Laboratory Conference Papers, Posters, and Presentations

The system Gd5(SixGe1−x)4 for 0.4⩽x⩽0.5 has been shown to have an unusual first order, coupled magnetic-structural phase transformation at the Curie temperature. Above the transformation temperature Tc, the material is paramagnetic with a monoclinic structure; below Tc, it is ferromagnetic with an orthorhombic structure. Another unusual feature of this phase transformation is that an applied magnetic field can increase Tc by 5 K per tesla. In this study, the magnetic-structural transformation in single crystalGd5Si2Ge2 was triggered by holding the sample at ...


Giant Magnetostriction Behavior At The Curie Temperature Of Single Crystal Gd5(Si0.5ge0.5)4, M. Han, David C. Jiles, J. E. Snyder, Thomas A. Lograsso, Deborah L. Schlagel Jun 2004

Giant Magnetostriction Behavior At The Curie Temperature Of Single Crystal Gd5(Si0.5ge0.5)4, M. Han, David C. Jiles, J. E. Snyder, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Conference Papers, Posters, and Presentations

We report results of thermal expansion (TE) and magnetostriction (MS) measurements on a single crystal sample of Gd5(Si0.5Ge0.5)4 prepared by the Bridgman method. TE and MS were measured along the c axis by the strain gauge method and the temperature was controlled using a closed cycle helium refrigerator. From the TE measurements the magnetic structural phase transition temperature was found to be 259.5 K on cooling and 261.5 K on heating. The abrupt change in strain and the temperature hysteresis indicate that it is a first order transition. MS measurements ...