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Full-Text Articles in Physics

Elastic Properties Of Gd5si2ge2 Studied With An Ultrasonic Pulse-Echo Technique, O. Svitelskiy, A. Suslov, Deborah L. Schlagel, Thomas A. Lograsso, Karl A. Gschneidner Jr., Vitalij K. Pecharsky Nov 2006

Elastic Properties Of Gd5si2ge2 Studied With An Ultrasonic Pulse-Echo Technique, O. Svitelskiy, A. Suslov, Deborah L. Schlagel, Thomas A. Lograsso, Karl A. Gschneidner Jr., Vitalij K. Pecharsky

Ames Laboratory Publications

We present the results of a study of the elastic properties of Gd5Si2Ge2, an alloy with giant magnetocaloric, magnetostrictive, and colossal magnetoresistive properties. Sound wave velocities measured in a number of different geometries allowed us to determine the whole elastic tensor for the monoclinic phase of this material. The anisotropy of the crystal is explored using the polar plots of the variations in the main crystallographic planes of the sound speed, the Young’s modulus, the shear modulus, and the linear compressibility. The effect of hydrostatic pressure on the Gd5Si2Ge2 ...


Short-Range Anisotropic Ferromagnetic Correlations In The Paramagnetic And Antiferromagnetic Phases Of Gd5ge4, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso Sep 2006

Short-Range Anisotropic Ferromagnetic Correlations In The Paramagnetic And Antiferromagnetic Phases Of Gd5ge4, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

Signatures of short range anisotropic ferromagnetic correlations and ferromagnetic clustering, manifested as unusually large hysteresis and other anomalies of the low magnetic field dc magnetization and ac magnetic susceptibility, have been observed in both the antiferromagnetic and paramagnetic states of single crystal Gd5Ge4. Ferromagnetic correlations, which are most pronounced in a weak magnetic field applied along the b axis, are readily suppressed by fields exceeding ∼5 kOe and are believed to be related to a Griffiths-like phase that develops in Gd5Ge4 below TG≅240 K.


Magnetism Of (Dy0.5er0.5)Al2 Single Crystal In Ac And Dc Magnetic Fields, Evgenii M. Levin, Karl A. Gschneidner Jr., Thomas A. Lograsso, Deborah L. Schlagel Aug 2006

Magnetism Of (Dy0.5er0.5)Al2 Single Crystal In Ac And Dc Magnetic Fields, Evgenii M. Levin, Karl A. Gschneidner Jr., Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

The temperature (4.2–90 K), ac magnetic field (1.25–50 Oe), frequency (5–125 Hz), and bias dc magnetic field (0–10 kOe) dependencies of the real and imaginary components of the ac magnetic susceptibility, and the temperature (4.2–250 K) and dc magnetic field(0.1–50 kOe) dependencies of the dc magnetic susceptibility and magnetization of a(Dy0.5Er0.5)Al2 single crystal have been studied. Isothermal magnetization measurement in a dc magnetic field indicates that (Dy0.5Er0.5)Al2 orders ferromagnetically at 37 K. The ac ...


Characterization Of Aperiodic And Periodic Thin Cu Films Formed On The Five-Fold Surface Of I-Al70pd21mn9 Using Medium-Energy Ion Scattering Spectroscopy, J. A. Smerdon, J. Ledieu, R. Mcgrath, T. C. Q. Noakes, P. Bailey, M. Draxler, C. F. Mcconville, Thomas A. Lograsso, A. R. Ross Jul 2006

Characterization Of Aperiodic And Periodic Thin Cu Films Formed On The Five-Fold Surface Of I-Al70pd21mn9 Using Medium-Energy Ion Scattering Spectroscopy, J. A. Smerdon, J. Ledieu, R. Mcgrath, T. C. Q. Noakes, P. Bailey, M. Draxler, C. F. Mcconville, Thomas A. Lograsso, A. R. Ross

Ames Laboratory Publications

The elucidation of the local atomic structure of a pseudomorphic film of Cu deposited on the five-fold surface of i-Al70Pd21Mn9using medium-energy ion scattering spectroscopy is reported. Monte Carlo calculations, using the VEGAS code, have been utilized to simulate the blocking of 100 keV He+ ions scattered from the overlayer. The coordinates of the Cu atoms in the overlayer derived from this procedure are consistent with a structure occurring in five rotational domains. Each domain consists of nanoscale strips of fcc Cu(100) with the ⟨110⟩ azimuth aligned along the five-fold directions of the quasicrystalline ...


Temperature And Magnetic-Field Dependence Of The Elastic Constants Of Ni-Mn-Al Magnetic Heusler Alloys, Xavier Moya, Lluís Mañosa, Antoni Planes, Thorsten Krenke, Mehmet Acet, Michel Morin, Jerel L. Zarestky, Thomas A. Lograsso Jul 2006

Temperature And Magnetic-Field Dependence Of The Elastic Constants Of Ni-Mn-Al Magnetic Heusler Alloys, Xavier Moya, Lluís Mañosa, Antoni Planes, Thorsten Krenke, Mehmet Acet, Michel Morin, Jerel L. Zarestky, Thomas A. Lograsso

Ames Laboratory Publications

We report on measurements of the adiabatic second-order elastic constants of the off-stoichiometric Ni54Mn23Al23 single-crystalline Heusler alloy. The variation in the temperature dependence of the elastic constants has been investigated across the magnetic transition and over a broad temperature range. Anomalies in the temperature behavior of the elastic constants have been found in the vicinity of the magnetic phase transition. Measurements under applied magnetic field, both isothermal and variable temperature, show that the value of the elastic constants depends on magnetic order, thus giving evidence for magnetoelastic coupling in this alloy system.


Magnetic Anisotropy And Magnetic Phase Diagram Of Gd5ge4, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso Jul 2006

Magnetic Anisotropy And Magnetic Phase Diagram Of Gd5ge4, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

The magnetization of single crystal Gd5Ge4, which in a zero magnetic field orders antiferromagnetically at 128 K, indicates a reversible spin-flop transition when the magnetic field is along the c axis and the absence of similar transformations when the magnetic field vector is perpendicular to the c axis. This anisotropic behavior is due to variation of magnetization energy between the c axis and the a or b axes of the orthorhombic crystal caused by a different alignment of the Gd moments with respect to the magnetic field vector. The anisotropy of the antiferromagnetic state diminishes with the ...


Large Magnetically Induced Strains In Ni50mn28.7ga21.3 Driven With Collinear Field And Stress, A. Malla, M. J. Dapino, Thomas A. Lograsso, Deborah L. Schlagel Mar 2006

Large Magnetically Induced Strains In Ni50mn28.7ga21.3 Driven With Collinear Field And Stress, A. Malla, M. J. Dapino, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

Despite the huge magnetic-field-induced strain (MFIS) of up to 9.5% exhibited by certain Ni–Mn–Ga alloys, their usefulness in applications is severely hindered by the electromagnet device needed for driving the alloys with a magnetic field and orthogonal loading stress. In this paper we present macroscopic measurements obtained from a single crystal of Ni50Mn28.7Ga21.3 which demonstrate a large reversible MFIS of −4100 ppm when the alloy is driven with quasistatic magnetic fields and fixed compressive stresses applied collinearly along the [001] axis. This collinear configuration marks a fundamental difference with prior ...


Lattice Dynamics And Phonon Softening In Ni-Mn-Al Heusler Alloys, Xavier Moya, Lluís Mañosa, Antoni Planes, Thorsten Krenke, Mehmet Acet, V. O. Garlea, Thomas A. Lograsso, Deborah L. Schlagel, Jerel L. Zarestky Feb 2006

Lattice Dynamics And Phonon Softening In Ni-Mn-Al Heusler Alloys, Xavier Moya, Lluís Mañosa, Antoni Planes, Thorsten Krenke, Mehmet Acet, V. O. Garlea, Thomas A. Lograsso, Deborah L. Schlagel, Jerel L. Zarestky

Ames Laboratory Publications

Inelastic and elastic neutron scattering have been used to study a single crystal of the Ni54Mn23Al23 Heusler alloy over a broad temperature range. The paper reports the experimental determination of the low-lying phonon dispersion curves for this alloy system. We find that the frequencies of the TA2 modes are relatively low. This branch exhibits an anomaly (dip) at a wave numberξ0=1∕3≈0.33, which softens with decreasing temperature. Associated with this anomalous dip at ξ0, an elastic central peak scattering is also present. We have also observed satellites due to ...


Ordering Of Si Atoms On The Fivefold Al-Pd-Mn Quasicrystal Surface, J. Ledieu, P. Unsworth, Thomas A. Lograsso, A. R. Ross, R. Mcgrath Jan 2006

Ordering Of Si Atoms On The Fivefold Al-Pd-Mn Quasicrystal Surface, J. Ledieu, P. Unsworth, Thomas A. Lograsso, A. R. Ross, R. Mcgrath

Ames Laboratory Publications

Silicon atoms are found to form an ordered overlayer on the fivefold surface of the icosahedral Al-Pd-Mn quasicrystal. Using scanning tunneling microscopy, the adsorption site is identified as the center of truncated clusters which are building blocks of the bulk structure. Comparison with theoretical models suggests that this site is favored because of bonding to Mn atoms.


Spectroscopic Ellipsometry Study Of Optical Anisotropy In Gd5si2ge2 And Comparison With Reflectance Difference Spectra, Joong Mok Park, David W. Lynch, S. J. Lee, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Tsokol, J. E. Snyder, David C. Jiles Jan 2006

Spectroscopic Ellipsometry Study Of Optical Anisotropy In Gd5si2ge2 And Comparison With Reflectance Difference Spectra, Joong Mok Park, David W. Lynch, S. J. Lee, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Tsokol, J. E. Snyder, David C. Jiles

Ames Laboratory Publications

The complex dielectric functions of single crystals of Gd5Si2Ge2 were obtained using spectroscopic ellipsometry (SE) in the photon energy range of 1.5–5.0 eV at room temperature. Reflectance difference (RD) spectra for the a‐b and b‐c planes of single crystals of Gd5Si2Ge2 were derived from these dielectric functions and compared to those obtained from reflectance difference spectroscopy (RDS) at near-normal incidence. The two experimental RD spectra from SE and RDS agreed well. The in-plane optical anisotropy of the sample is mainly due to intrinsic bulk properties ...


Small Sealed Ta Crucible For Thermal Analysis Of Volatile Metallic Samples, Y. Janssen, M. Angst, Kevin W. Dennis, Paul C. Canfield, R. William Mccallum Jan 2006

Small Sealed Ta Crucible For Thermal Analysis Of Volatile Metallic Samples, Y. Janssen, M. Angst, Kevin W. Dennis, Paul C. Canfield, R. William Mccallum

Ames Laboratory Publications

Differential thermal analysis on metallic alloys containing volatile elements can be highly problematic. Here we show how measurements can be performed in commercial, small-sample equipment without modification. This is achieved by using a sealed Ta crucible, easily fabricated from Ta tubing and sealed in a standard arc furnace. The crucible performance is demonstrated by measurements on a mixture of Mg and MgB2, after heating up to 1470°C. We also show data, measured on an alloy with composition Gd40Mg60, that clearly show both the liquidus and a peritectic and are consistent with published phase-diagram data.


Versatile And Compact Capacitive Dilatometer, G. M. Schmiedeshoff, A. W. Lounsbury, D. J. Luna, S. J. Tracy, A. J. Schramm, S. W. Tozer, V. F. Correa, S. T. Hannahs, T. P. Murphy, E. C. Palm, A. H. Lacerda, Sergey L. Bud'ko, Paul C. Canfield, J. L. Smith, J. C. Lashley, J. C. Cooley Jan 2006

Versatile And Compact Capacitive Dilatometer, G. M. Schmiedeshoff, A. W. Lounsbury, D. J. Luna, S. J. Tracy, A. J. Schramm, S. W. Tozer, V. F. Correa, S. T. Hannahs, T. P. Murphy, E. C. Palm, A. H. Lacerda, Sergey L. Bud'ko, Paul C. Canfield, J. L. Smith, J. C. Lashley, J. C. Cooley

Ames Laboratory Publications

We describe the design, construction, calibration, and operation of a relatively simple differential capacitive dilatometer suitable for measurements of thermal expansion and magnetostriction from 300 to below 1K with a low-temperature resolution of about 0.05Å. The design is characterized by an open architecture permitting measurements on small samples with a variety of shapes. Dilatometers of this design have operated successfully with a commercial physical property measurement system, with several types of cryogenic refrigeration systems, in vacuum, in helium exchange gas, and while immersed in liquid helium(magnetostriction only) to temperatures of 30mK and in magnetic fields to 45T.