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Full-Text Articles in Physics

Texture And Grain Morphology Dependencies Of Saturation Magnetostriction In Rolled Polycrystalline Fe83ga17, R. A. Kellogg, A. B. Flatau, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso May 2013

Texture And Grain Morphology Dependencies Of Saturation Magnetostriction In Rolled Polycrystalline Fe83ga17, R. A. Kellogg, A. B. Flatau, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

Textured polycrystalline Fe-Ga alloys exhibit magnetostrictive strains of 100 ppm or greater and may function as a mechanically robust actuator/sensing material. Current efforts seek to combine the 300+ ppm magnetostrictive strain performance of [100] oriented single crystals with the mechanical properties of polycrystalline forms. One approach to combining these properties is to control the crystallographic texture through deformation processing such as rolling. To determine the relationship between saturation magnetostriction, degree of texturing, and grain morphology we compare the results of three-dimensional finite element simulations with the analytical solution for a random polycrystal and the experimental responses of rolled polycrystalline ...


Magnetism Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, Steven E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon Apr 2013

Magnetism Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, Steven E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon

Ames Laboratory Conference Papers, Posters, and Presentations

The phonon dispersion was measured at room temperature (above the Néel temperature TN) along (0,0,L) in the tetragonal phase of LaFeAsO using inelastic x-ray scattering. Magnetostructural effects are well documented in the AFe2As2-based (A = Ca, Sr, Ba, Eu) systems. Only recently have single crystals of LaFeAsO become available. The experimentally observed splitting between two A1g phonon modes at 22 and 26 meV is only reproduced in spin-polarized calculations. Magnetostructural effects similar to those observed in the AFe2As2 materials are confirmed to be present in LaFeAsO. This is discussed ...


Temperature Dependence Of Magnetoelastic Properties Of Fe100−Xsix (5 < X < 20), G. Petculescu, P. K. Lambert, A. E. Clark, K. B. Hathaway, Qingfeng Xing, Thomas A. Lograsso, J. B. Restorff, M. Wun-Fogle Feb 2012

Temperature Dependence Of Magnetoelastic Properties Of Fe100−Xsix (5 < X < 20), G. Petculescu, P. K. Lambert, A. E. Clark, K. B. Hathaway, Qingfeng Xing, Thomas A. Lograsso, J. B. Restorff, M. Wun-Fogle

Ames Laboratory Conference Papers, Posters, and Presentations

Tetragonal magnetostriction (λγ,2) and elastic constants (c′, c44, and c11) for Fe100−xSixwere measured as a function of temperature (T). Compositions corresponding to the disordered A2 (x = 5), ordered D03 (x = 19.8), and mixed (x = 11.6) phases, were investigated. The magnetoelastic coupling (−b1) was determined for 77 < T < 300 K and compared with those of Fe-Ga, Fe-Ge, and Fe-Al. Both λγ,2(T) and −b1(T) of Fe-Si behave similarly to those of Fe-Ge, while other notable differences exist between the measured properties of Fe-Si and those of the other three alloys. Due to the early establishment of short ...


Magnetostriction, Elasticity, And D03 Phase Stability In Fe–Ga And Fe–Ga–Ge Alloys, G. Petculescu, K. L. Ledet, Mianliang Huang, Thomas A. Lograsso, Y. N. Zhang, R. Q. Wu, M. Wun-Fogle, J. B. Restorff, A. E. Clark, K. B. Hathaway Mar 2011

Magnetostriction, Elasticity, And D03 Phase Stability In Fe–Ga And Fe–Ga–Ge Alloys, G. Petculescu, K. L. Ledet, Mianliang Huang, Thomas A. Lograsso, Y. N. Zhang, R. Q. Wu, M. Wun-Fogle, J. B. Restorff, A. E. Clark, K. B. Hathaway

Ames Laboratory Conference Papers, Posters, and Presentations

The contrast between the saturation tetragonal magnetostriction, λγ,2 = (3/2)λ100, of Fe1−xGax and Fe1−yGey, at compositions where both alloys exhibit D03 cubic symmetry (second peak region), was investigated. This region corresponds to x = 28 at. % Ga and y = 18 at. % Ge or, in terms of e/a = 2 x + 3 y + 1, to an e/a value of ∼1.55 for each of the alloys. Single crystal, slow-cooled, ternary Fe1−xy GaxGey alloys with e/a ∼1.55 and gradually increasing y ...


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.


The Effect Of Partial Substitution Of Ge For Ga On The Elastic And Magnetoelastic Properties Of Fe–Ga Alloys, G. Petculescu, A. O. Mandru, William M. Yuhasz, Thomas A. Lograsso, M. Wun-Fogle, J. B. Restorff, A. E. Clark, K. B. Hathaway Apr 2010

The Effect Of Partial Substitution Of Ge For Ga On The Elastic And Magnetoelastic Properties Of Fe–Ga Alloys, G. Petculescu, A. O. Mandru, William M. Yuhasz, Thomas A. Lograsso, M. Wun-Fogle, J. B. Restorff, A. E. Clark, K. B. Hathaway

Ames Laboratory Conference Papers, Posters, and Presentations

Both components of the tetragonal magnetoelastic constant b1: the saturation magnetostriction, λγ,2 = (3/2)λ100, and the magnetic-field saturated shear elasticity, c′ = (c11c12)/2, were investigated over a wide temperature range for the magnetostrictiveFe1−xyGaxGey alloys, (x+y ≅ 0.125, 0.185, and 0.245; x/y ≅ 1 and 3). The magnetostriction was measured from 77 to 425 K using standard strain gage techniques. Both shear elastic constants (c′ and c44) were measured from 5 to 300 K using resonant ultrasound spectroscopy. Six alloy compositions were ...


Magnetostrictive And Elastic Properties Of Fe100−Xmox (2, Mianliang Huang, A. O. Mandru, G. Petculescu, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso Apr 2010

Magnetostrictive And Elastic Properties Of Fe100−Xmox (2, Mianliang Huang, A. O. Mandru, G. Petculescu, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

In this paper we investigate the magnetostrictive [(3/2)λ100 and (3/2)λ111] and elastic (c′and c44) behavior of single crystalline alloys Fe100−xMox for 21 and −b2) are computed from the measurements. Similar to other Fe–X (X = Al, Ga, and Ge) alloys, the tetragonal magnetostriction (3/2)λ100 increases monotonically from ∼ 70×10−6 at ∼ 2.5 at. % Mo to a maximum of either ∼ 100×10−6 at ∼ 8 at. % Mo for the slow cooled crystals or ∼ 125×10−6 at ∼ 11 at. % Mo for quenched crystals. A ...


Magnetoelasticity Of Fe–Si Single Crystals, Qingfeng Xing, D. Wu, Thomas A. Lograsso Apr 2010

Magnetoelasticity Of Fe–Si Single Crystals, Qingfeng Xing, D. Wu, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

The tetragonal magnetostriction constant, (3/2)λ100, of Fe–Si single crystals was measured and was found to be structure dependent. Similar to that of Fe–Ge single crystals, (3/2)λ100 is positive in the single phase A2 regime, becomes negative in the single phase D03 regime, and changes from positive to negative between the two regimes. Short-range order in the A2 regime decreases the magnetostriction prior to the onset of long range order. In the single phase regions of both A2 and D03, thermal history does not show any obvious effect on the magnetostriction ...


Magnetoelastic Coupling In Fe100−Xgex Single Crystals With 4, G. Petculescu, J. B. Leblanc, M. Wun-Fogle, J. B. Restorff, William M. Yuhasz, Thomas A. Lograsso, A. E. Clark Mar 2009

Magnetoelastic Coupling In Fe100−Xgex Single Crystals With 4, G. Petculescu, J. B. Leblanc, M. Wun-Fogle, J. B. Restorff, William M. Yuhasz, Thomas A. Lograsso, A. E. Clark

Ames Laboratory Conference Papers, Posters, and Presentations

In this paper we examine the elastic (c′ and c44) and magnetostrictive (λ100 and λ111) behaviors of Fe100−xGex for 4<x<18, quantities used further to find the fundamental magnetoelastic coupling constants b1 and b2 at room temperature. The x dependence ofb1 and b2 for Fe100−xGex is contrasted to those of Fe100−xGax and Fe100−xAlx. While the rhombohedral shear elastic constant c44 is almost insensitive to the type and amount of solute, the tetragonal shear constant c′ shows a pronounced and rapid softening with increasing x for ...


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 ...


Effect Of Interstitial Additions On Magnetostriction In Fe–Ga Alloys, Mianliang Huang, Thomas A. Lograsso, A. E. Clark, J. B. Restorff, M. Wun-Fogle Jan 2008

Effect Of Interstitial Additions On Magnetostriction In Fe–Ga Alloys, Mianliang Huang, Thomas A. Lograsso, A. E. Clark, J. B. Restorff, M. Wun-Fogle

Ames Laboratory Conference Papers, Posters, and Presentations

The additions of trace amounts of small interstitial atoms (carbon, boron, and nitrogen) to Fe–Ga (Galfenol) alloys have a small but beneficial effect on the magnetostriction of Fe–Ga alloys especially at high Ga compositions. The saturated magnetostrictions [(3/2)λ100’s] of both slow cooled and quenched single crystal Fe–Ga–C alloys with Ga contents >18 at. % are about 10%–30% higher than those of the comparable binary Fe–Ga alloys. For boron and nitrogen additions, the magnetostrictions of slow cooled alloys with Ga content >18 at. % were approximately 20% higher than those of the binary ...


Temperature Dependence Of The Magnetostriction And Magnetoelastic Coupling In Fe100−Xalx (X = 14.1,16.6,21.5,26.3) And Fe50co50, A. E. Clark, J. B. Restorff, M. Wun-Fogle, D. Wu, Thomas A. Lograsso Jan 2008

Temperature Dependence Of The Magnetostriction And Magnetoelastic Coupling In Fe100−Xalx (X = 14.1,16.6,21.5,26.3) And Fe50co50, A. E. Clark, J. B. Restorff, M. Wun-Fogle, D. Wu, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

In this paper, we report magnetostriction measurements, (λ100) on Fe-rich Fe–Al alloys and Fe50Co50 as functions of temperature from 77 K to room temperature (RT). From these measurements and elastic constant (c′) measurements, the tetragonal magnetoelastic coupling constants (b1’s) were calculated. Significant differences were found between our RT measurements and earlier magnetostriction measurements for the higher Al concentration alloys (16.6%, 21.5%, 26.3% Al) and the Fe50Co50 alloy. Reminiscent of the temperature dependence of λ100 for pure Fe, magnetostriction changes with temperature are minimal for Fe–Al ...


Magnetostriction Of Iron-Germanium Single Crystals, D. Wu, Qingfeng Xing, R. William Mccallum, Thomas A. Lograsso Jan 2008

Magnetostriction Of Iron-Germanium Single Crystals, D. Wu, Qingfeng Xing, R. William Mccallum, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

The addition of nonmagnetic Ga into body-centered cubic Fe enhances the magnetostriction constant λ100 over tenfold. Literature reports for substitution of Ge at low concentrations suggest that the addition of Ge also enhances the magnetostriction. In this work, the magnetostriction and microstructure of Fe–Ge were investigated to correlate magnetostriction with microstructure. The magnetostriction of Fe100−xGexsingle crystals with x between 0.05 and 0.18 varies with Ge concentration and correlates with phase changes. The value of (3/2)λ100 increases with Ge additions in the A2 single phase region (up to x ...


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 ...


Variation Of Magnetostriction With Temperature In Tb5si2.2ge1.8 Single Crystal, A. P. Ring, H. L. Ziegler, Thomas A. Lograsso, Deborah L. Schlagel, J. E. Snyder, David C. Jiles Apr 2006

Variation Of Magnetostriction With Temperature In Tb5si2.2ge1.8 Single Crystal, A. P. Ring, H. L. Ziegler, Thomas A. Lograsso, Deborah L. Schlagel, J. E. Snyder, David C. Jiles

Ames Laboratory Conference Papers, Posters, and Presentations

The Tb5(SixGe4−x) alloy system is similar to the better known Gd5(SixGe4−x), except it has a more complex magnetic and structural phase diagram. Gd5(SixGe1−x)4 has received much attention recently due to its giant magnetocaloric effect, colossal magnetostriction and giant magnetoresistance in the vicinity of a first order combined magnetic-structural phase transition. The magnetostriction changes that accompany the phase transitions of single crystal Tb5(Si2.2Ge1.8) have been investigated at temperatures between 20 and150 K by measurements of ...


Magnetostructural Transitions And Adiabatic Temperature Variation In Polycrystal And Single-Crystal Ni2mnga Alloys, C. P. Sasso, M. Pasquale, L. Giudici, S. Besseghini, E. Villa, L. H. Lewis, Thomas A. Lograsso, Deborah L. Schlagel Apr 2006

Magnetostructural Transitions And Adiabatic Temperature Variation In Polycrystal And Single-Crystal Ni2mnga Alloys, C. P. Sasso, M. Pasquale, L. Giudici, S. Besseghini, E. Villa, L. H. Lewis, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Conference Papers, Posters, and Presentations

The magnetocaloric response of off-stoichiometric Ni2MnGa polycrystal and single-crystal samples with a Curie temperature coincident with the martensitic transition temperature was investigated. The direct measurement of temperature change (ΔTad) during an adiabatic transformation under a maximum field variation ΔH = 5.6×106 A/m (7 T) was performed. The polycrystalline sample shows a maximum ΔTad ≈ 1.5 K at a temperature close to the structural transition. The value of ΔTad and the 20 K span of the ΔTad peak encourage further studies of the effect of microstructure on ...


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.


Lattice And Spin Dynamics In Bcc Fe, 10 At. % Be, P. Zhao, J. Cullen, M. Wuttig, H. J. Kang, J. W. Lynn, Thomas A. Lograsso, O. Moze Apr 2006

Lattice And Spin Dynamics In Bcc Fe, 10 At. % Be, P. Zhao, J. Cullen, M. Wuttig, H. J. Kang, J. W. Lynn, Thomas A. Lograsso, O. Moze

Ames Laboratory Conference Papers, Posters, and Presentations

Body centered cubic Fe1−xBex alloys are known to display an enhanced tetragonal magnetostriction compared to Fe. In order to characterize the enhanced magnetoelasticity observed in this alloy system, we present detailed inelastic neutron scattering measurements of the phonon dispersion relations of a single crystal of bcc Fe, 10 at. %Be along the high symmetry directions [100], [110], and [111] at room temperature. We observe in particular that the frequency of transverse phonons propagating along the [110] direction with a [10] polarization at the zone boundary is reduced by 10% with respect to bcc Fe (the corresponding ...


Magnetic Field Dependence Of Galfenol Elastic Properties, G. Petculescu, K. B. Hathaway, Thomas A. Lograsso, M. Wun-Fogle, A. E. Clark May 2005

Magnetic Field Dependence Of Galfenol Elastic Properties, G. Petculescu, K. B. Hathaway, Thomas A. Lograsso, M. Wun-Fogle, A. E. Clark

Ames Laboratory Conference Papers, Posters, and Presentations

Elastic shear moduli measurements on Fe100−xGax (x = 12–33) single crystals (via resonant ultrasound spectroscopy) with and without a magnetic field and within 4–300 K are reported. The pronounced softening of the tetragonal shear modulus c′ is concluded to be, based on magnetoelastic coupling, the cause of the second peak in the tetragonal magnetostriction constant λ100 near x = 28. Exceedingly high ΔE effects ( ∼ 25%), combined with the extreme softness in c′ (c′<10 GPa), suggest structural changes take place, yet, gradual in nature, as the moduli show a smooth dependence on Ga concentration, temperature, and magnetic field. Shear anisotropy (c44/c′) as high as 14.7 was observed for Fe71.2Ga28.8.


Temperature Dependence Of The Magnetic Anisotropy And Magnetostriction Of Fe100−Xgax (X = 8.6, 16.6, 28.5), A. E. Clark, M. Wun-Fogle, J. B. Restorff, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum May 2005

Temperature Dependence Of The Magnetic Anisotropy And Magnetostriction Of Fe100−Xgax (X = 8.6, 16.6, 28.5), A. E. Clark, M. Wun-Fogle, J. B. Restorff, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum

Ames Laboratory Conference Papers, Posters, and Presentations

The temperature dependence of the lowest order magnetic anisotropy constant K1 and the lowest order saturation magnetostriction constant, (3/2)λ100, were measured from 4 K to 300 K for Fe91.4Ga8.6,Fe83.4Ga16.6, and Fe71.5Ga28.5 and were compared to the normalized magnetization power law, ml(l+1)/2. Fe91.4Ga8.6 maintains the magnetostriction anomaly of Fe (dλ100/dT>0) and K1 is a reasonable fit to the ml(l+1)/2power law with ...


Magnetic Anisotropy And Phase Transitions In Single-Crystal Tb5(Si2.2ge1.8), M. Han, J. E. Snyder, W. Tang, Thomas A. Lograsso, Deborah L. Schlagel, David C. Jiles May 2005

Magnetic Anisotropy And Phase Transitions In Single-Crystal Tb5(Si2.2ge1.8), M. Han, J. E. Snyder, W. Tang, Thomas A. Lograsso, Deborah L. Schlagel, David C. Jiles

Ames Laboratory Conference Papers, Posters, and Presentations

The Tb5(SixGe4−x) alloy system has many features in common with the Gd5(SixGe4−x)system although it has a more complex magnetic and structural phase diagram. This paper reports on the magnetic anisotropy and magnetic phase transition of single-crystalTb5(Si2.2Ge1.8) which has been investigated by the measurements of M-H and M-T along the a, b, and c axes. The variation of 1/χ vs T indicates that there is a transition from paramagnetic to ferromagnetic at Tc = 110 K. Below this ...


Thermal Expansion And Gruneisen Parameters In Some Pr–Ni–Si Compounds, S. H. Song, David C. Jiles, J. E. Snyder, A. O. Pecharsky, D. Wu, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum May 2005

Thermal Expansion And Gruneisen Parameters In Some Pr–Ni–Si Compounds, S. H. Song, David C. Jiles, J. E. Snyder, A. O. Pecharsky, D. Wu, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum

Ames Laboratory Conference Papers, Posters, and Presentations

In this study, the thermal expansion and Gruneisen parameter of polycrystalline “Pr5Ni2Si3” and “Pr15Ni7Si10” were investigated over the temperature range of 5–300 K. Calculations of the phonon contribution to thermal expansion were made, which allowed the magnetic contribution to thermal expansion to be calculated from the difference between the total thermal expansion and the phonon contribution. This resulted in a temperature-dependent magnetic contribution to thermal expansion that varied with the magnetic ordering of the material. The results show two magnetic transitions in each compound, the higher temperature transition corresponding ...


Magnetostriction And Elasticity Of Body Centered Cubic Fe100−Xbex Alloys, A. E. Clark, M. Wun-Fogle, J. B. Restorff, Thomas A. Lograsso, G. Petculescu Jun 2004

Magnetostriction And Elasticity Of Body Centered Cubic Fe100−Xbex Alloys, A. E. Clark, M. Wun-Fogle, J. B. Restorff, Thomas A. Lograsso, G. Petculescu

Ames Laboratory Conference Papers, Posters, and Presentations

Magnetostriction measurements from 77 K to room temperature on oriented (100) and (110) disk samples of Fe93.9Be6.1 and Fe88.7Be11.3 reveal substantial increases in λ100compared to iron. For the 11.3% alloy, λ100=110 ppm, a sixfold increase above that of α-Fe. For the 6.1% alloy, λ100=81 ppm, ∼40% and ∼170% greater than λ100 of comparable Fe–Ga and Fe–Al alloys, respectively, for H=15 kOe. Large differences exist between the values of λ100 and λ111 (λ100>0, λ111 ...


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 ...


Magnetic Field Induced Phase Transitions In Gd5(Si1.95ge2.05) Single Crystal And The Anisotropic Magnetocaloric Effect, H. Tang, A. O. Pecharsky, Deborah L. Schlagel, Thomas A. Lograsso, Vitalij K. Pecharsky, Karl A. Gschneidner Jr. May 2003

Magnetic Field Induced Phase Transitions In Gd5(Si1.95ge2.05) Single Crystal And The Anisotropic Magnetocaloric Effect, H. Tang, A. O. Pecharsky, Deborah L. Schlagel, Thomas A. Lograsso, Vitalij K. Pecharsky, Karl A. Gschneidner Jr.

Ames Laboratory Conference Papers, Posters, and Presentations

Magnetization measurements using a Gd5(Si1.95Ge2.05) single crystal with the magnetic field applied along three crystallographic directions, [001], [010] and [100], were carried out as a function of the applied field (0–56 kOe) at various temperatures (∼5–320 K). The magnetic field (H)–temperature (T) phase diagrams were constructed for theGd5(Si1.95Ge2.05) single crystal with field along the three directions. A small anisotropy was observed. The magnetocaloric effect was calculated from isothermal magnetization data, and the observed anisotropy correlates with the HT phase diagrams. The results ...


Extraordinary Magnetoelasticity And Lattice Softening In Bcc Fe-Ga Alloys, A. E. Clark, K. B. Hathaway, M. Wun-Fogle, J. B. Restorff, Thomas A. Lograsso, V. M. Keppens, G. Petculescu, R. A. Taylor May 2003

Extraordinary Magnetoelasticity And Lattice Softening In Bcc Fe-Ga Alloys, A. E. Clark, K. B. Hathaway, M. Wun-Fogle, J. B. Restorff, Thomas A. Lograsso, V. M. Keppens, G. Petculescu, R. A. Taylor

Ames Laboratory Conference Papers, Posters, and Presentations

Extraordinary magnetostrictive behavior has been observed in Fe-Ga alloys with concentrations of Ga between 4% and 27%. λ100 exhibits two peaks as a function of Ga content. At room temperature, λ100 reaches a maximum of 265 ppm near 19% Ga and 235 ppm near 27% Ga. For compositions between 19% and 27%, λ100 drops sharply to a minimum near 24% Ga and exhibits an anomalous temperature dependence, decreasing by as much as a factor of 2 at low temperatures. This unusual magnetostrictive behavior is interpreted on the basis of a single maximum in the magnetoelastic coupling ∣b ...


Quadrupolar And Dipolar Contributions To X-Ray Magnetic Circular Dichroism At The Tb L3,2 Edges: Experiment Versus Theory, H. Wende, Z. Li, A. Scherz, G. Ceballos, K. Baberschke, A. Ankudinov, J. J. Rehr, F. Wilhelm, A. Rogalev, Deborah L. Schlagel, Thomas A. Lograsso May 2002

Quadrupolar And Dipolar Contributions To X-Ray Magnetic Circular Dichroism At The Tb L3,2 Edges: Experiment Versus Theory, H. Wende, Z. Li, A. Scherz, G. Ceballos, K. Baberschke, A. Ankudinov, J. J. Rehr, F. Wilhelm, A. Rogalev, Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

We investigate the x-ray magnetic circular dichroism (XMCD) at the L3,2 edges using a single crystal of Tb as a prototype system for a one-element magnet in order to ascertain the multipolar nature of the features in the dichroic spectra. The high resolution of the experimental data allows for a clear identification of the dipolar (E1: 2p→5d) and quadrupolar (E2: 2p→4f) transitions. On the basis of ab initio calculations we developed a simple procedure to extract the quadrupolar part by subtracting the derivative of the spin-averaged absorption spectra from the ...


Temperature And Stress Dependencies Of The Magnetic And Magnetostrictive Properties Of Fe0.81ga0.19, R. A. Kellogg, Alison B. Flatau, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso May 2002

Temperature And Stress Dependencies Of The Magnetic And Magnetostrictive Properties Of Fe0.81ga0.19, R. A. Kellogg, Alison B. Flatau, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

It was recently reported that the addition of nonmagnetic Ga increased the saturation magnetostriction (λ100) of Fe over tenfold while leaving the rhombohedral magnetostriction (λ111) almost unchanged. To determine the relationship between the magnetostriction and the magnetization we measured the temperature and stress dependence of both the magnetostriction and magnetization from −21 °C to +80 °C under compressive stresses ranging from 14.4 MPa to 87.1 MPa. For this study a single crystal rod of Fe0.81Ga0.19 was quenched from 800 °C into water to insure a nearly random distribution of Ga atoms ...