Electronic structure of possible 3d `heavy-fermion' compound

Guo, Guang‐Yu; Botton, Gianluigi A.; Nishino, Yoichi

doi:10.1088/0953-8984/10/8/002

Cited by 132 publications

(134 citation statements)

References 24 publications

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“…The calculated DOS at the Fermi energy for the undoped system is 0.27 eV −1 /f.u. This gives a γ value for the linear heat capacity of 0.63 mJ mol −1 K −2 , nearly the same as 0.69 mJ mol −1 K −2 reported by Guo et al 8 The small difference between the two theoretical values is due to the different lattice constants and different methods used. However, both these values are order of magnitude smaller than the experimentally measured low-T γ value of 14 mJ mol −1 K −2 .…”

Section: Resultssupporting

confidence: 81%

Effect of onsite Coulomb repulsion on thermoelectric properties of full-Heusler compounds with pseudogaps

Lee

Mahanti

2011

Phys. Rev. B

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Electronic structure calculations using local density and generalized gradient(LDA/GGA) approximations for the full Heusler compound Fe2VAl show that it is a pseudo-gap (negative gap) system with very small density of states (DOS) at the Fermi level but rapidly rising DOS away from it, a feature that makes this compound a promising thermoelectric material. Thermopower (S) measurements in nominally pure and n-doped Fe2VAl give indeed large values of S (∼-150 µV/K at 200 K). To improve on the inadequacy of LDA/GGA in handling d-electron systems and to understand the origin of large thermopowers measured, we have carried out electronic structure calculations using GGA+U method with several values of the on-site Coulomb interaction parameter U including the ones calculated using constrained density functional theory (DFT). For the latter, we found Fe2VAl to be a narrow band gap semiconductor with a gap of 0.55 eV. With the calculated band structures, we have studied the carrier concentration and temperature dependence of S using Boltzmann transport equation in constant relaxation time approximation for both the pseudo-gap and gapped cases.Comparison between theory and experiment suggests that neither the pseudo-gap nor the finite gap (0.55 eV) model can explain all the transport properties consistently. Therefore treatment of U beyond simple mean-field approach (done in GGA+U) and/or inclusion of defect induced changes in the host electronic structure might be important in understanding the experiments.

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Section: Resultssupporting

confidence: 81%

Effect of onsite Coulomb repulsion on thermoelectric properties of full-Heusler compounds with pseudogaps

Lee

Mahanti

2011

Phys. Rev. B

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“…In particular, the anomalous low temperature specific heat has been attributed to ferromagnetic clusters with a density of 0.003-0.004/unit cell, consistent with the results from NMR experiments. These works, as well, are in broad agreement with the results from band structure calculations, which predict that via Fe/V site exchange or crystallographic superstructure formation ferromagnetic clusters or long-range order might be generated in Fe 2 VAl [6][7][8]. Recently, it has been claimed that such impurity induced ferromagnetism was observed in the related Heusler compound Fe 2 TiSn [12].…”

supporting

confidence: 85%

“…For x = 1, that is for Fe 2 VAl, this leads to a fully ordered Heusler lattice, with Fe, V and Al each occupying separate cubic sublattices. Band structure calculations [6][7][8] indicated that in Fe 2 VAl each Fe ion occupying an Fe I site carries a magnetic moment. This requires a site exchange of V with an Fe II ion, which might cause, either via superstructure formation (i.e., V occupying exclusively one Fe II site) or a sufficiently large level of random Fe II/V site exchanges, a magnetically ordered state or anomalous behaviour from diluted magnetic clusters.…”

Section: )mentioning

confidence: 99%

Structure and magnetic order in Fe_2+xV_1−xAl

Maksimov

Baabe

Klauss

et al. 2001

J. Phys.: Condens. Matter

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Abstract:We present a detailed structural investigation via neutron diffraction of differently heat treated samples Fe 2 VAl and Fe 2+x V 1−x Al. Moreover, the magnetic behaviour of these materials is studied by means of µSR and Mössbauer-experiments. Our structural investigation indicates that quenched Fe 2 VAl, exhibiting the previously reported "Kondo insulating like" behaviour, is off-stoichiometric (6% ) in itsAl content. Slowly cooled Fe 2 VAl is structurally better ordered and stoichiometric, and the microscopic magnetic probes establish long range ferromagnetic order below T C = 13K, consistent with results from bulk experiments. The magnetic state can be modelled as being generated by diluted magnetic ions in a non-magnetic matrix. Quantitatively, the required number of magnetic ions is too large as to be explained by a model of Fe/V site exchange. We discuss the implications of our findings for the ground state properties of Fe 2 VAl, in particular with respect to the role of crystallographic disorder. ) IntroductionRecently, the magnetic phase diagram of the alloying series (Fe 1−x V x ) 3 Al has been the focus of various detailed studies [1,2]. In particular, Heuslertype Fe 2 VAl has been reported to exhibit a very unusual behaviour for an intermetallic compound, namely a semiconductor-like resistivity close to a magnetic instability [1]. This was interpreted in terms of Kondo-insulating behaviour, analogous to the system FeSi [3,4]. In contrast, optical conductivity studies provided evidence for a pseudogap in the density of states of 1 Fe 2 VAl of 0.1-0.2eV [5], a view supported by various band structure calculations [6][7][8]. Notably, no temperature dependence of the gap features has been detected in these studies, apparently contradicting a Kondo insulator scenario for Fe 2 VAl. However, the pseudogap scenario itself does not account for the unusual resistivity of Fe 2 VAl, as in the absence of magnetic correlations it should predict no or a positive metallic magnetoresistance, in conflict with experimental observations [2,9]. Therefore, in Ref. 5 it has been speculated that the (magneto)resistivity of Fe 2 VAl reflects a mixture of electron excitation processes over the pseudogap and spin dependent scattering from impurities.Independently, on basis of specific heat and NMR-experiments it has been demonstrated that in Fe 2 VAl crystallographic disorder, assumed to be present in form of atomic site exchange between Fe and V atoms, substantially affects the ground state properties of this compound [10,11]. In particular, the anomalous low temperature specific heat has been attributed to ferromagnetic clusters with a density of 0.003-0.004/unit cell, consistent with the results from NMR experiments. These works, as well, are in broad agreement with the results from band structure calculations, which predict that via Fe/V site exchange or crystallographic superstructure formation ferromagnetic clusters or long-range order might be generated in Fe 2 VAl [6][7][8]. Recently, it has been claimed that s...

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“…6,8 Stimulated by these findings, theoretical work claimed Fe 2 VAl is a nonmagnetic semimetal with the pseudogap at the Fermi level. [15][16][17] The considerable mass enhancement of the conduction carriers was attributed to excitonic correlations 16 or spin fluctuations. 17 However, subsequent specific heat, C͑T͒, measurements in applied magnetic fields showed that the upturn in C / T at low temperatures results from a Schottky contribution of magnetic clusters in Fe 2 VAl.…”

Section: Introductionmentioning

confidence: 99%

“…[15][16][17] The considerable mass enhancement of the conduction carriers was attributed to excitonic correlations 16 or spin fluctuations. 17 However, subsequent specific heat, C͑T͒, measurements in applied magnetic fields showed that the upturn in C / T at low temperatures results from a Schottky contribution of magnetic clusters in Fe 2 VAl. 8 The effects of off-stoichiometry have not been investigated quantitatively in the framework of nearly and weak ferromagnetism at x Ϸ 0 and ␦ Ϸ 0 yet.…”

Section: Introductionmentioning

confidence: 99%

Weak itinerant ferromagnetism in Heusler-typeFe2VAl0.95

et al. 2010

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Weak itinerant ferromagnetism in Sato, K.; Naka, T.; Taguchi, M.; Nakane, T.; Ishikawa, F.; Yamada, Y.; Takaesu, Y.; Nakama, T.; de Visser, A.; Matsushita, A. Published in:Physical Review B DOI:10.1103/PhysRevB.82.104408 Link to publicationCitation for published version (APA): Sato, K., Naka, T., Taguchi, M., Nakane, T., Ishikawa, F., Yamada, Y., ... Matsushita, A. (2010 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We report measurements of the magnetic, transport, and thermal properties of the Heusler-type compound Fe 2 VAl 0.95 . We show that while stoichiometric Fe 2 VAl is a nonmagnetic semimetal a 5% substitution on the Al site with the 3d elements Fe and V atoms leads to a ferromagnetic ground state with a Curie temperature T C =33Ϯ 3 K and a small ordered moment s = 0.12 B / Fe in Fe 2 VAl 0.95 . The reduced value of the ratio s / p = 0.08, where p = 1.4 B / Fe is the effective Curie-Weiss moment, together with the analysis of the magnetization data M͑H , T͒, show magnetism is of itinerant nature. The specific heat shows an unusual temperature variation at low temperatures with an enhanced Sommerfeld coefficient, ␥ =12 mJ K −2 mol −1 . The resistivity, ͑T͒, is metallic and follows a power law behavior = 0 + AT n with n Ϸ 1.5 below T C . With applying pressure, T C decreases with the rate of ͑1 / T C ͒͑dT C / dP͒ = −0.061 GPa −1 . We conclude substitution on the Al site with Fe and V atoms results in itinerant ferromagnetism with a low carrier density.

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Electronic structure of possible 3d `heavy-fermion' compound

Cited by 132 publications

References 24 publications

Effect of onsite Coulomb repulsion on thermoelectric properties of full-Heusler compounds with pseudogaps

Effect of onsite Coulomb repulsion on thermoelectric properties of full-Heusler compounds with pseudogaps

Structure and magnetic order in Fe_2+xV_1−xAl

Weak itinerant ferromagnetism in Heusler-typeFe2VAl0.95

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Electronic structure of possible 3d `heavy-fermion' compound

Cited by 132 publications

References 24 publications

Effect of onsite Coulomb repulsion on thermoelectric properties of full-Heusler compounds with pseudogaps

Effect of onsite Coulomb repulsion on thermoelectric properties of full-Heusler compounds with pseudogaps

Structure and magnetic order in Fe2+xV1−xAl

Weak itinerant ferromagnetism in Heusler-typeFe2VAl0.95

Contact Info

Product

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Structure and magnetic order in Fe_2+xV_1−xAl