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Pressure Induces Invar Behavior in Unexpected Compositions PDF Print E-mail
Over 100 years ago Charles Edouard Guillaume, working at the International Bureau of Weights and Measures in France, discovered that certain alloys did not expand when heated, a behavior that came to be known as the Invar effect. Guillaume’s discovery found immediate and lasting technological applications, and he was awarded the Nobel Prize in Physics in 1920. Guillaume’s original work was carried out on an Ni-Fe alloy, but thermal Invar behavior has been found in a number of other alloy systems, all of which require precise control of composition.

Researchers from the California Institute of Technology, the National Synchrotron Light Source, the Geophysical Laboratory, and the Advanced Photon Source have discovered Invar behavior at high pressures in Pd-25 at.% Fe, a composition far from the Invar composition of Pd-75 at.% Fe. The group, led by CDAC graduate student Mike Winterrose, used density functional theory calculations, energy-dispersive x-ray diffraction, and synchrotron Mössbauer spectroscopy to investigate the mechanical and magnetic properties of Pd-25 at.% Fe through the Invar transition in the resistively heated diamond anvil cell. The synchrotron Mössbauer measurements revealed a collapse of the 57Fe magnetic moment between 8.9 and 12.3 GPa at 300 K, coinciding with a transition in bulk modulus found by x-ray diffraction measurements. Heating the sample under a pressure of 7 GPa showed negligible thermal expansion from 300 to 523 K (Fig. 1), demonstrating that Invar behavior can be induced by pressure in an alloy composition very different from those exhibiting Invar behavior at ambient pressure. The first-principles calculations show that pressure causes the electronic structure near the Fermi level in Pd-25 at.% Fe to become similar to that of classic thermal Invar alloys. By tuning the electronic structure, pressure should cause materials of many chemical compositions to exhibit Invar behavior. This work has been published in Physical Review Letters [M. L. Winterrose, et al., Phys. Rev. Lett., 102, 237202 (2009)].

  • More information on this work is posted here.
Colossal Magnetic Effects at High Pressure PDF Print E-mail
Understanding and ultimately controlling the intricate coupling between electrical conductivity and magnetism in colossal magnetoresistance (CMR) manganites remains a challenge, due to the coupling between lattice, charge, spin, and orbital degrees of freedom. Scientists from Carnegie, APS and Argonne, led by Yang Ding (HPSync) report new progress in using high pressure techniques to unravel its subtleties, with recent work showing that the CMR manganite (La0.75Ca0.25MnO3) is subject to a magnetic transition coupled with a Jahn-Teller distortion at approximately 23 GPa.

To study the material, the researchers used x-ray magnetic circular dichroism (XMCD) and angular-dispersive diffraction techniques at the APS. XMCD is a newly- developed technique that uses high-brilliance, circularly polarized x-rays to probe the magnetic state of materials under pressure in the diamond anvil cell.

The current study shows that the predominant effect of the applied external pressure is an increase in the strength of the superexchange interaction relative to the double exchange interaction. As a result, the system tends to increase the number of through-bond antiferromagnetic interactions by decreasing the dimension of the ferromagnetic region from three to two. This leads to an anisotropic redistribution of the 3d-eg electrons in the Mn atoms. The resultant non-uniform electron density couples to the lattice via the Jahn-Teller effect causing a strained distortion of the crystal structure even under a uniform hydrostatic pressure. Ultimately, manganite transforms from an F-type ferromagnet to an A-type antiferromagnet at 23 GPa.

This discovery once again highlights the key role of pressure in understanding the physics of magnetism in dense matter. The results of this study have been published in Physics Review Letters [Y. Ding, et al., Phys. Rev. Lett., 102, 237201 (2009)].
Synchrotron Workshop Attracts Researchers from Around the World PDF Print E-mail
Nearly 100 attendees from around the world came together for the High Pressure Synchrotron Science symposium, held May 6-8, 2009 at the Advanced Photon Source in conjunction with the 2009 APS User's Meeting. The mission of the symposium, which was sponsored by several groups including CDAC and HPSynC, was to bring the user community together to discuss new ways of exploring the pressure variable in chemistry, physics, materials science, geoscience and biology using synchrotron radiation. In a program that spanned three days and included 35 invited talks, the state of the art in high pressure research was explored across this diverse range of fields.

The vibrancy of the community was highlighted by the breadth of interesting talks and a notable number of contributions from areas not traditionally associated with high pressure research. These included a presentation on observations of a high density form of liquid water inside protein crystals at high pressure, several presentations on the possibilities of coherent diffraction imaging of single-particles under high hydrostatic pressures, and a presentation on x-ray photo chemistry under extreme conditions as a way of forming novel materials.

Exciting fundamental physics was also presented in the form of dramatic images of transparent, non-conducting sodium, and shock compression was shown to result in the metallization of He at densities exceeding 2.5 g/cm3. The rich possibilities of high pressure as a means of forming ultra-hard materials in the B-C-N system were explored, as were the structural properties of nano-polycrystalline diamond. Geophysics was also a main theme throughout the meeting: chemical reaction and partitioning at the core-mantle boundary were featured, as were the implications of the recently discovered spin transitions in iron-based minerals.


Three CDAC partners, Tom Duffy (Princeton), Yogesh Vohra (University of Albama – Birmingham), and Wendy Mao (Stanford), gave presentations at the meeting. Presentations were given by other CDAC affiliated scientists, including Alexander Goncharov and Viktor Struzhkin from the Geophysical Laboratory; Stanislav Sinogeikin, Wenge Yang, and Qiang Mei from HPCAT; and Lin Wang and Michael Lerche from HPSynC.

The diverse scientific program was structured around three technical sessions, each of which focused on the future of high pressure synchrotron research relative to a particular area of the field. The emerging role of in situ imaging of systems under extreme conditions raised the prospect of a new field of hierarchical structural/functional characterization. Meanwhile, a strong drive to push the frontiers of experimentation towards the nanoscale, with sub-micron beamsizes and high precision stages, was discussed in several presentations.

Proceedings of the meeting are to be published in a special issue of Journal of Physics: Condensed Matter.

 


  • Lee, M. S., J. A. Montoya, S. Scandolo, Thermodynamic stability of layered structures in compressed CO2, Phys. Rev. B, 79, 144102 (2009).
  • Al-Khatatbeh, Y., K. K. M. Lee, and B. Kiefer, High-pressure behavior of TiO2 as determined by experiment and theory, Phys. Rev. B, 79, 134114 (2009).
  • Debessai, M., T. Matsuoka, J. J. Hamlin, J. S. Schilling, K. Shimizu, Pressure-induced superconducting state of europium metal at low temperatures, Phys. Rev. Lett., 102, 197002 (2009).
  • Tsoi, G., A. K. Stemshorn, Y. K. Vohra, P. M. Wu, F. C. Hsu, Y. L. Huang, M. K. Wu, K. W. Yeh, and S. T. Weir, High pressure superconductivity in iron-based layered compounds studied using designer diamonds, J. Phys.: Condens. Matt., 21, 232201 (2009).
  • Zha, C. S., S. Krasnicki, Y. F. Meng, C. S. Yan, J. Lai, Q. Liang, H. K. Mao, and R. J. Hemley, Composite chemical vapor deposition diamond anvils for high-pressure/high-temperature experiments, High Press. Res., 29, 317-324 (2009).
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CDAC is an interdisciplinary center headquartered at the Geophysical Laboratory of the Carnegie Institution of Washington. Our goals are to advance and perfect an extensive set of high P-T techniques and unique facilities, to perform key studies on a broad range of important materials in newly-accessible P-T regimes, and to integrate and coordinate static, dynamic and theoretical results for Stewardship Science applications.