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Full-Text Articles in Physics

Angular Dependence Of The Spin-Flop Transition And A Possible Structure Of The Spin-Flop Phase Of Gd5ge4, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso Oct 2007

Angular Dependence Of The Spin-Flop Transition And A Possible Structure Of The Spin-Flop Phase Of Gd5ge4, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

The angular dependence of the spin-flop transition in Gd5Ge4 has been examined by magnetization measurements of a single crystal. When the magnetic field vector is tilted away from the antiferromagnetic easy axis (c axis) toward the b axis, the spin-flop transition always remains first order in nature. However, when the field vector is tilted away from the c axis toward the a axis, the first order spin-flop transition is only observed over a narrow range of tilt angles (0<θ<20°), which serves as evidence that the Gd moments “flop” from the c axis to the a axis during the spin-flop transformation.


Field Step Size And Temperature Effects On The Character Of The Magnetostructural Transformation In A Gd5ge4 Single Crystal, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso Oct 2007

Field Step Size And Temperature Effects On The Character Of The Magnetostructural Transformation In A Gd5ge4 Single Crystal, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

The critical magnetic fields required to induce the magnetostructural transformation below ∼30 K in Gd5Ge4 are dependent on the size of the magnetic-field step employed during isothermal measurements of magnetization: the smaller the step, the lower the critical field. The influence of the magnetic-field step size on the character of the magnetostructural transition in Gd5Ge4 diminishes as temperature increases, nearly disappearing above ∼30 K. Decreasing the size of the field step also leads to the formation of multiple steps in the magnetization. The steps are reproducible in the same sample at low temperatures (below ...


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.


Anomalous Phonon Behavior In The High-Temperature Shape-Memory Alloy Ti50pd50−Xcrx, S. M. Shapiro, Guangyong Xu, Deborah L. Schlagel, Thomas A. Lograsso, R. Erwin Aug 2007

Anomalous Phonon Behavior In The High-Temperature Shape-Memory Alloy Ti50pd50−Xcrx, S. M. Shapiro, Guangyong Xu, Deborah L. Schlagel, Thomas A. Lograsso, R. Erwin

Ames Laboratory Publications

Ti50Pd50−xCrx is a high-temperature shape-memory alloy with a martensitic transformation temperature strongly dependent on the Cr composition. Prior to the transformation, a premartensitic phase is present with an incommensurate modulated cubic lattice with wave vector of q0=(0.22,0.22,0). The temperature dependence of the diffuse scattering in the cubic phase is measured as a function temperature for x=6.5, 8.5, and 10 at. %. The lattice dynamics has been studied and reveals anomalous temperature andq dependences of the [110]-TA2 transverse phonon branch. The phonon linewidth is broad ...


Magnetic Phase Transition In The Itinerant Helimagnet Mnsi: Thermodynamic And Transport Properties, Sergei M. Stishov, Alla E. Petrova, S. Khasonov, G. Kh. Panova, Anatoly A. Shikov, Jason C. Lashley, D. Wu, Thomas A. Lograsso Aug 2007

Magnetic Phase Transition In The Itinerant Helimagnet Mnsi: Thermodynamic And Transport Properties, Sergei M. Stishov, Alla E. Petrova, S. Khasonov, G. Kh. Panova, Anatoly A. Shikov, Jason C. Lashley, D. Wu, Thomas A. Lograsso

Ames Laboratory Publications

A careful study of thermodynamic and transport properties of a high-quality single crystal of MnSi at ambient pressure suggests that its transition to a helical magnetic state near 29 K is weakly first order. The heat capacity, temperature derivative of resistivity, thermal expansion, and magnetic susceptibility exhibit a specific structure around the phase transition point, interpreted as a combination of first- and second-order features. Striking mirror symmetry between the temperature derivative of resistivity and the thermal expansion coefficient is observed. Conclusions drawn from these experiments question prevailing views on the phase diagram of MnSi.


Irreversible Field Induced Magnetostriction At Temperatures Above And Below The Order-Disorder Transition In Single Crystal Tb5si2.2ge1.8, A. P. Ring, Thomas A. Lograsso, Deborah L. Schlagel, J. E. Snyder, David C. Jiles May 2007

Irreversible Field Induced Magnetostriction At Temperatures Above And Below The Order-Disorder Transition In Single Crystal Tb5si2.2ge1.8, A. P. Ring, Thomas A. Lograsso, Deborah L. Schlagel, J. E. Snyder, David C. Jiles

Ames Laboratory Conference Papers, Posters, and Presentations

This paper reports on the behavior of single crystal Tb5Si2.2Ge1.8 in the vicinity of its order-disorder and order-order phase transition from a higher temperature paramagnetic∕monoclinic state to a lower temperature ferromagnetic∕orthorhombic state. Measurements have been made of thermal and field induced changes in strain along the crystallographic a axis. The material exhibits large strains of up to 1500 ppm when a magnetic field is applied to it in its paramagnetic state but much smaller strains when a field is applied to it in its ferromagnetic state. These field induced strains are ...


Magnetostriction Of Ternary Fe–Ga–X (X = C,V,Cr,Mn,Co,Rh) Alloys, A. E. Clark, J. B. Restorff, M. Wun-Fogle, K. B. Hathaway, Thomas A. Lograsso, Mianliang Huang, E. Summers Apr 2007

Magnetostriction Of Ternary Fe–Ga–X (X = C,V,Cr,Mn,Co,Rh) Alloys, A. E. Clark, J. B. Restorff, M. Wun-Fogle, K. B. Hathaway, Thomas A. Lograsso, Mianliang Huang, E. Summers

Ames Laboratory Conference Papers, Posters, and Presentations

Binary iron-gallium (Galfenol) alloys have large magnetostrictions over a wide temperature range. Single crystal measurements show that additions of 2 at. % or greater of 3d and 4d transition elements with fewer (V, Cr, Mo, Mn) and more (Co, Ni, Rh) valence electrons than Fe, all reduce the saturation magnetostriction. Kawamiya and Adachi [J. Magn. Magn. Mater. 31–34, 145 (1983)] reported that the D03 structure is stabilized by 3dtransition elements with electron∕atom ratios both less than iron and greater than iron. IfD03 ordering decreases the magnetostriction, the maximum magnetostriction should ...


Spin-Wave Dispersion In Magnetostrictive Fe-Ga Alloys: Inelastic Neutron Scattering Measurements, Jerel L. Zarestky, O. Moze, J. W. Lynn, Y. Chen, Thomas A. Lograsso, Deborah L. Schlagel Feb 2007

Spin-Wave Dispersion In Magnetostrictive Fe-Ga Alloys: Inelastic Neutron Scattering Measurements, Jerel L. Zarestky, O. Moze, J. W. Lynn, Y. Chen, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

Fe-Ga alloys of appropriate Ga concentration and heat treatment show a very large enhancement in the tetragonal magnetostriction over that of pure α-Fe [λ100(Fe-Ga)∼15λ100(Fe)]. In order to gain further understanding of the extraordinary magnetoelastic characteristics of this system, the spin dynamics of two of these alloys, Fe1−xGax (x=0.160 and 0.225), were studied using inelastic neutron scattering techniques. The correlation of the spin-wave dispersion curve with the lattice constant and atomic radii of solute is examined for this and other Fe alloys.


Crystallography, Anisotropic Metamagnetism, And Magnetocaloric Effect In Tb5si2.2ge1.8, Min Zou, Yaroslav Mudryk, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso Jan 2007

Crystallography, Anisotropic Metamagnetism, And Magnetocaloric Effect In Tb5si2.2ge1.8, Min Zou, Yaroslav Mudryk, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

The metamagnetic-like transitions and giant magnetocaloric effect were observed with the magnetic field applied parallel to the aand c axes, but not the b axis in a Tb5Si2.2Ge1.8 single crystal. The in situ x-ray powder diffraction study indicates that these metamagnetic-like transitions are coupled to crystallographic phase transformations occurring via strong magnetoelastic interactions. The magnetocrystalline anisotropy plays an important role in this system. Magnetic fields less than 40 kOe cannot drive either the magnetic or the crystallographic phase transition to completion for Tb5Si2.2Ge1.8 powder due to ...