Delaire, O. and Lucas, M. S. and dos Santos, A. M. and Subedi, A. and Sefat, A. S. and McGuire, M. A. and Mauger, L. and Muñoz, J. A. and Tulk, C. A. and Xiao, Y. and Somayazulu, M. and Zhao, J. Y. and Sturhahn, W. and Alp, E. E. and Singh, D. J. and Sales, B. C. and Mandrus, D. and Egami, T. (2010) Temperature and pressure dependence of the Fe-specific phonon density of states in Ba(Fe_(1−x)Co_x)_2As_2. Physical Review B, 81 (9). Art. No. 094504. ISSN 1098-0121 http://resolver.caltech.edu/CaltechAUTHORS:20100521-122100647
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The ^(57)Fe-specific phonon density of states (DOS) of Ba(Fe_(1−x)Co_x)_2As_2 single crystals (x=0.0,0.08) was measured at cryogenic temperatures and at high pressures with nuclear-resonant inelastic x-ray scattering. Measurements were conducted for two different orientations of the single crystals, yielding the orientation-projected ^(57)Fe-phonon density of states for phonon polarizations in-plane and out-of-plane with respect to the basal plane of the crystal structure. In the tetragonal phase at 300 K, a clear stiffening was observed upon doping with Co. Increasing pressure to 4 GPa caused a marked increase of phonon frequencies, with the doped material still stiffer than the parent compound. Upon cooling, both the doped and undoped samples showed a stiffening and the parent compound exhibited a discontinuity across the magnetic and structural phase transitions. These findings are generally compatible with the changes in volume of the system upon doping, increasing pressure, or increasing temperature, but an extra softening of high-energy modes occurs with increasing temperature. First-principles computations of the phonon DOS were performed and showed an overall agreement with the experimental results, but underestimate the Grüneisen parameter. This discrepancy is explained in terms of a magnetic Grüneisen parameter, causing an extra phonon stiffening as magnetism is suppressed under pressure.
|Additional Information:||© 2010 The American Physical Society. Received 15 December 2009; revised 8 February 2010; published 4 March 2010. We thank Steve Nagler for help with providing the isotopically enriched iron. Experimental work at ORNL was supported by the Scientific User Facilities Division and the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, DOE. Theory work at ORNL was supported by DOE, Division of Materials Sciences and Engineering. Use of the HPCAT facility was supported by DOE-BES, DOE-NNSA CDAC, NSF, DOD TACOM, and the W. M. Keck Foundation. Use of the APS was supported by DOE-BES under Contract No. DE-AC02-06CH11357.|
|Classification Code:||PACS: 74.25.Kc, 63.20.-e, 74.70.Xa, 74.62.Fj|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||21 May 2010 20:50|
|Last Modified:||26 Dec 2012 12:03|
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