High-resolution photoelectron spectroscopy of Heusler-type Fe₂VAl alloy

Abstract

The electronic structure of Heusler-type Fe 2 VAl has been studied by high-resolution photoelectron spectroscopy with the excitation photon energy h# ranging from 21.2 eV (the He I laboratory light source) to 904 eV (the soft X-ray synchrotron light source) for clean surfaces prepared by scraping or fracturing polycrystalline and single crystalline specimens. Photoelectron spectra recorded for the fractured surfaces show a 10 eV-wide valence band with ®ne structures and a clear decrease in the intensity towards the Fermi level E F , while a high intensity at E F and no ®ne structures are observed for the scraped surface. Comparison with the theoretical density of states (DOS) indicates that the vacuum ultraviolet photoelectron spectra emphasize the transition-metal 3d bands but the soft X-ray photoelectron spectra agree remarkably well with the DOS including the ®ne structures and the pseudogap at E F . The present results suggest that the electronic structure of Fe 2 VAl is highly sensitive to possible strain and defects induced by scraping. Bulk electronic structures of Fe 2 VAl are discussed in relation to the reported fascinating transport properties.

High-resolution soft x-ray photoelectron study of density of states and thermoelectric properties of the Heusler-type alloys(Fe2∕3V1∕3Soda1, Murayama2, Shimba3 et al. 2005Phys. Rev. B343140View full textAdd to dashboardCite

“…Here, we sub- tracted the background from the experimental photoelectron spectrum with an iteration method, 28 while we did not take account of the difference in the subshell ionization cross sections nor the lifetime broadening dependent on the binding energy of the created photohole in obtaining the theoretical spectrum. As already reported, 24 the overall feature of the spectrum agrees remarkably well with the predicted spectrum. In particular, the spectrum exhibits steep decrease in the intensity toward E F , i.e., the indication of a pseudogap across E F , as well as a 10 eV wide valence band with several fine structures corresponding to the features in the calculated spectrum.…”

“…30 As for the surface effects, in fact, the spectra recorded at the high detection angle from the surface normal, i.e., with the shallow effective probing depth, indicate the enhancement of the spectral weight from E b Ӎ 1 eV to E F . However, their contribution to the normal emission spectra is estimated to be ϳ10% at most, 24 and will not affect the discussion below so much.…”

“…In the early photoelectron measurements, 1,23 a clear Fermi edge with large intensity was observed even at the high-excitation photon energy. Recently, however, we have successfully obtained the spectra representing the bulk electronic structure with use of the high-resolution soft x-ray photoelectron spectroscopy ͑HRXPS͒ for clean surfaces prepared by in situ fracturing specimens instead of scraping them, 24 which adequately preserves the bulk electronic structure and suppresses the surface effects. The Fe and V L 2,3 x-ray absorption spectra also reveal sharp and clear features for the in situ fractured specimens of Fe 2 VAl in contrast to the scraped ones.…”

Thermoelectric Properties of Heusler Fe2TiSn Alloys

“…There is a pseudogap in which the conduction band and valence band state densities slightly overlap near the Fermi level when the VEC per atom is 6 4 . The pseudogap has been confirmed by X-ray photoelectron spectroscopy 5 , the photoelectric effect 6 , nuclear magnetic resonance 7,8 , the Hall effect 9 , and first-principles calculations [10][11][12][13][14][15][16][17] . Owing to the pseudogap, a Heusler alloy behaves as a semimetal that exhibits semiconductive behavior, even though it is a metal, so that the Seebeck coefficient S of the metal can be approximated by Mott's theory 18 , i.e.,…”

Thermoelectric Properties of the Off-Stoichiometric Heusler Alloys Fe_{2&minus;<i>y</i>}V_{1+<i>x</i>+<i>y</i>}Al_{1&minus;<i>x</i>}

“…ホイスラー型 Fe 2 VAl 合金は，金属元素のみから構成され ているにもかかわらず半導体的な電気抵抗率の温度依存性を 示す金属間化合物であり 1) ，バンド計算によるとフェルミ準 位に鋭い擬ギャップをもつ非磁性半金属であることが予測さ れ て い る 2 5) ． 赤 外 分 光 6,7) お よ び 光 電 子 分 光 8,9) 測 定 か ら 16,20,21) Al 16,20,21) では，第 4 元素置換の場合とは異なり電 子ドープの場合には正のゼーベック係数，ホールドープの場 Fig. 1 Compositional ternary diagram of various off stoichiometric Fe 2 VAl alloys, such as (Fe 2 V) 1＋x Al 1-x alloys (A A′ line ) , 19) Fe 2-y V 1＋y Al alloys ( B B ′ line ) 16,20,21) and Fe 2 V 1＋x Al 1-x alloys (C C′ line).…”