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Title: X-ray 2p photoelectron and L-alpha resonant x-ray emission spectraof the 3d metals in Ni2MnZ (Z=In,Sn,Sb) Heusler alloys

Abstract

Magnetic and chemical bonding effects in Heusler alloysNi2MnIn, Ni2MnSn, and Ni2MnSb were studied by soft x-ray spectroscopy.Exchange splitting detected in Mn 2p core-level x-ray photoelectronspectra and an increase of the Mn L-beta/L-alpha intensity ratio innonresonant x-ray emission spectra show that atomic magnetic moment at Mnis higher than that of pure metal. Spin polarized density of statescalculations and comparative analysis of Mn and Ni L-alpha resonant x-rayemission spectra RXES demonstrate that the spin splitting in Mn 3d shellis larger than in Ni 3d shell. The d-d transitions observed in L-alphaRXES of Mn and Ni are suggested to be more intensive for Mn than for Nivalence electrons when initiated by off-resonant excitations.Experimental findings are supported by photoelectron spectra calculationsand developed two-step model of resonant x-ray emission. The interplaybetween Mn L-alpha RXES and calculated magnetic moments of Mn atoms inalloys as a function of the type of Z element is discussed.

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
COLLABORATION - U.Saskatchewan/Canada
OSTI Identifier:
923008
Report Number(s):
LBNL-61311
R&D Project: 0; BnR: YN0100000; TRN: US200804%%838
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: PHYSICAL REVIEW B; Journal Volume: 74; Related Information: Journal Publication Date: 08/01/2006
Country of Publication:
United States
Language:
English
Subject:
75; ALLOYS; ATOMS; BONDING; ELECTRONS; EMISSION SPECTRA; HEUSLER ALLOYS; MAGNETIC MOMENTS; SPECTRA; SPIN; VALENCE; X-RAY SPECTROSCOPY; Heusler alloys soft x-ray emission x-ray photoelectronspectroscopy

Citation Formats

Yablonskikh, M.V., Braun, J., Kuchel, M.T., Postnikov, A.V., Denlinger, J.D., Shreder, E.I., Yarmoshenko, Y.M., Neumann, M., and Moewes, A. X-ray 2p photoelectron and L-alpha resonant x-ray emission spectraof the 3d metals in Ni2MnZ (Z=In,Sn,Sb) Heusler alloys. United States: N. p., 2006. Web. doi:10.1103/PhysRevB.74.085103.
Yablonskikh, M.V., Braun, J., Kuchel, M.T., Postnikov, A.V., Denlinger, J.D., Shreder, E.I., Yarmoshenko, Y.M., Neumann, M., & Moewes, A. X-ray 2p photoelectron and L-alpha resonant x-ray emission spectraof the 3d metals in Ni2MnZ (Z=In,Sn,Sb) Heusler alloys. United States. doi:10.1103/PhysRevB.74.085103.
Yablonskikh, M.V., Braun, J., Kuchel, M.T., Postnikov, A.V., Denlinger, J.D., Shreder, E.I., Yarmoshenko, Y.M., Neumann, M., and Moewes, A. Tue . "X-ray 2p photoelectron and L-alpha resonant x-ray emission spectraof the 3d metals in Ni2MnZ (Z=In,Sn,Sb) Heusler alloys". United States. doi:10.1103/PhysRevB.74.085103.
@article{osti_923008,
title = {X-ray 2p photoelectron and L-alpha resonant x-ray emission spectraof the 3d metals in Ni2MnZ (Z=In,Sn,Sb) Heusler alloys},
author = {Yablonskikh, M.V. and Braun, J. and Kuchel, M.T. and Postnikov, A.V. and Denlinger, J.D. and Shreder, E.I. and Yarmoshenko, Y.M. and Neumann, M. and Moewes, A.},
abstractNote = {Magnetic and chemical bonding effects in Heusler alloysNi2MnIn, Ni2MnSn, and Ni2MnSb were studied by soft x-ray spectroscopy.Exchange splitting detected in Mn 2p core-level x-ray photoelectronspectra and an increase of the Mn L-beta/L-alpha intensity ratio innonresonant x-ray emission spectra show that atomic magnetic moment at Mnis higher than that of pure metal. Spin polarized density of statescalculations and comparative analysis of Mn and Ni L-alpha resonant x-rayemission spectra RXES demonstrate that the spin splitting in Mn 3d shellis larger than in Ni 3d shell. The d-d transitions observed in L-alphaRXES of Mn and Ni are suggested to be more intensive for Mn than for Nivalence electrons when initiated by off-resonant excitations.Experimental findings are supported by photoelectron spectra calculationsand developed two-step model of resonant x-ray emission. The interplaybetween Mn L-alpha RXES and calculated magnetic moments of Mn atoms inalloys as a function of the type of Z element is discussed.},
doi = {10.1103/PhysRevB.74.085103},
journal = {PHYSICAL REVIEW B},
number = ,
volume = 74,
place = {United States},
year = {Tue Mar 21 00:00:00 EST 2006},
month = {Tue Mar 21 00:00:00 EST 2006}
}
  • No abstract prepared.
  • We show that Rh substitution at the Co site in Zr{sub 0.5}Hf{sub 0.5}Co{sub 1-x}Rh{sub x}Sb{sub 0.99}Sn{sub 0.01} (0<=x<=1) half-Heusler alloys strongly reduces the thermal conductivity with a simultaneous, significant improvement of the power factor of the materials. Thermoelectric properties of hot-pressed pellets of several compositions with various Rh concentrations were investigated in the temperature range from 300 to 775 K. The Rh 'free' composition shows n-type conduction, while Rh substitution at the Co site drives the system to p-type semiconducting behavior. The lattice thermal conductivity of Zr{sub 0.5}Hf{sub 0.5}Co{sub 1-x}Rh{sub x}Sb{sub 0.99}Sn{sub 0.01} alloys rapidly decreased with increasing Rh concentrationmore » and lattice thermal conductivity as low as 3.7 W/m*K was obtained at 300 K for Zr{sub 0.5}Hf{sub 0.5}RhSb{sub 0.99}Sn{sub 0.01}. The drastic reduction of the lattice thermal conductivity is attributed to mass fluctuation induced by the Rh substitution at the Co site, as well as enhanced phonon scattering at grain boundaries due to the small grain size of the synthesized materials. - Graphical abstract: Significant reduction of the lattice thermal conductivity with increasing Rh concentration in the p-type Zr{sub 0.5}Hf{sub 0.5}Co{sub 1-x}Rh{sub x}Sb{sub 0.99}Sn{sub 0.01} half-Heusler materials prepared by solid state reaction at 1173 K.« less
  • Several compositions of the p-type half-Heusler alloys Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb 1–xSn x (0≤x≤0.4) were synthesized by mechanically alloying high purity elemental powders using hardened steel jars and balls on a high energy shaker mill. Powder X-ray diffraction (XRD) investigations of several aliquots taken after regularly spaced milling time suggested that single phase products with half-Heusler (HH) structure can be obtained after 10 h. However, XRD and transmission electron microscopy (TEM) studies of several specimens obtained from compacted polycrystalline powders of Z₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb 1–xSn x alloys using a uniaxial hot press (HP) revealed the presence of CoSb inclusions with various sizes embedded inside themore » HH matrix. Hall effect, electrical conductivity, and thermopower data collected between 300 K and 775 K on several compositions suggested that electronic transport in the synthesized Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb 1–xSn x/CoSb composites strongly depends on the average size and/or mole fraction of the embedded CoSb inclusions rather than the fraction (x) of Sn substituting for Sb. Among the samples investigated, the nanocomposite with x=0.2, which contains nanometer-scale CoSb inclusions, showed the largest power factor (800 μW/K² m at 775 K) and the lowest lattice thermal conductivity (~2.2 W/m K at 775 K) leading to a six-fold enhancement in the figure of merit when compared to the Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb₀.₉₉Sn₀.₀₁ bulk matrix. - Graphical abstract: CoSb nanoinclusions embedded into a p-type Zr₀.₅Hf₀.₅Co₀.₄Rh₀.₆Sb 1–xSn x half-Heusler matrix simultaneously boost the thermopower and carrier mobility leading to a drastic enhancement of the power factor of the resulting bulk nanostructured materials. Highlights: • The phase composition of half-Heusler (HH) alloy is very sensitive to the synthesis method. • Mechanical alloying (MA) of elements results in bulk HH matrix with CoSb inclusions. • CoSb nanoinclusions simultaneously boost the thermopower and carrier mobility with the HH matrix. • The MA process reduces lattice thermal conductivity due to high density of grain boundaries.« less
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