Electronic structure and magnetic, electrical and optical properties of ferromagnetic Heusler alloys

Otto, M.; Feil, H.; Woerden, R.A.M. van; Wijngaard, J. H.; Valk, P. J. van der; Bruggen, C.F. van; Haas, C.

doi:10.1016/0304-8853(87)90354-4

Cited by 91 publications

(57 citation statements)

References 18 publications

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“…This strongly suggests that the primary contribution to the anomalous Hall effect is from the side jump mechanism, 26 which scales inversely with the mean free path. 27 If the carrier polarization is proportional to the magnetization as inferred from the anomalous Hall data for some half-metallic Heusler alloys, 28 then R S ϭ ⌬L/ ϰ 2 , where is the mean free path and ⌬L is the side jump distance ͑of order 1 Å͒; this suggests a T 4 dependence since ϰT 2 above 100 K. A more detailed analysis along the lines of Ref. 28 is made more difficult here by the presence of two bands, both of which may contribute to side jump, 29 and whose relative contributions are changing with temperature, as indicated by the Hall measurements.…”

Section: Figmentioning

confidence: 99%

Evidence for two-band magnetotransport in half-metallic chromium dioxide

et al. 2000

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Magnetotransport measurements were made on patterned, ͑110͒ oriented CrO 2 thin films grown by the high-pressure, thermal decomposition of CrO 3 onto rutile substrates. The low-temperature Hall effect exhibits a sign reversal from positive to negative as the magnetic field is increased above 1 T, which may be interpreted within a simple two-band model as indicating the presence of highly mobile ( h ϭ0.25 m 2 /V s) holes as well as a much larger number of less mobile electrons (nϭ0.4 electrons/Cr͒. Between 50 and 100 K, the field at which the sign reversal occurs rapidly increases and a contribution from the anomalous Hall effect becomes significant, while the large, positive transverse magnetoresistance ͑MR͒ observed at low temperatures changes over to a predominantly negative MR. These changes correlate with a thermally activated dependence in the resistivity of the form T 2 e Ϫ⌬/T with ⌬Ϸ80 K, reflecting the lack of temperature dependence in the resistivity at low temperatures and a T 2 behavior above 100 K. The high mobilities at low temperature which result in the observed positive MR reflect the suppression of spin-flip scattering expected for a half-metallic system. However, the changes in magnetotransport above the temperature ⌬ must be due to the onset of spin-flip scattering, even though k B ⌬ is much less than the expected energy gap in the minority spin density of states. The significance of ⌬ is discussed in terms of recent models for another half-metallic system, the perovskite manganites, and the possible formation of ''shadow bands.''

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Section: Figmentioning

confidence: 99%

Evidence for two-band magnetotransport in half-metallic chromium dioxide

et al. 2000

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“…The magnetic properties are due to magnetic moments localized at the Mn atoms, which interact via itinerant electrons in the conduction band. 6 It has been calculated that 9 out of total 22 valence electrons are located in spin-down bands, and thus the total spin magnetic moment of NiMnSb becomes exactly 4.0 B .…”

Section: Introductionmentioning

confidence: 99%

Synthesis and physical properties of arc melted NiMnSb

Gardelis

Androulakis

Migiakis

et al. 2004

Journal of Applied Physics

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Several polycrystalline samples of the half-Heusler alloy NiMnSb were grown by arc melting of stoichiometric and nonstoichiometric amounts of high-purity constituent elements. The structure and the phase-purity of the prepared samples were examined systematically by powder x-ray diffraction. The transport properties of the best sample, with saturation magnetization M s (5 K) ϭ4 B /formula unit, were studied by measuring electrical resistivity, thermal conductivity, and thermopower. Features in both magnetic and transport data are consistent with NiMnSb being in a half-metallic state at low temperatures, i.e., the conduction electrons are fully spin polarized. However, point-contact Andreev reflection measurements on the same sample at 4.2 K demonstrate only ϳ45% spin polarization.

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“…The real situation is intermediate, but the question arises whether half metals are closer to strong ferromagnetism or to VWI ferromagnetism. For half metals, the situation was analyzed by Otto et al [6], who advocated the local-band picture, that is, strong ferromagnetism (section 3). However, this view has not remained unchallenged and seems to be only partially adequate (section 5).…”

Section: Relation To Strong and Weak Ferromagnetismmentioning

confidence: 99%

“…Furthermore, real-structure features such as defects, surfaces, and interfaces may drastically reduce the spin polarization [3]. Electron states in half metals may be itinerant or localized, but even in the itinerant case, the fi nite-temperature behavior exhibits localized features [6], very similar to the situation encountered in ordinary itinerant ferromagnets [7,8]. A number of experimental and theoretical aspects of half metallics and some specifi c materials have been reviewed recently [2,3,[9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Finite-temperature depolarization in half metals

Skomski

2007

J. Phys.: Condens. Matter

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The temperature dependence of the spin polarization of type-I half-metallic ferromagnets is investigated and compared with that of other magnetic materials, such as semimetals, strong and weak ferromagnets, and exchange-enhanced Pauli paramagnets. Stable atomic moments, as realized by strong intra-atomic exchange, exhibit a nonzero spin-down density of states (DOS) at fi nite temperatures. This thermal spin mixing means that the conductivity of the "insulating" spin channel is always nonzero and that half-metallic ferromagnetism is an idealized limit. At zero temperature, similar effects are caused by intersublattice interactions, spin-orbit coupling and crystal imperfections. With increasing interatomic hopping, the moment becomes unstable, and Stoner-type thermal excitations yield an additional reduction of the spin polarization. In the Stoner limit, the hybridization gap closes far below the Curie temperature, and the corresponding transition temperature T* increases with increasing hybridization gap and decreasing band width. Correlations are analyzed by a version of the Kondo model and by an unrestricted Hartree-Fock approximation, and it is argued that correlations are less important than the leading one-electron contributions.

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Electronic structure and magnetic, electrical and optical properties of ferromagnetic Heusler alloys

Cited by 91 publications

References 18 publications

Evidence for two-band magnetotransport in half-metallic chromium dioxide

Evidence for two-band magnetotransport in half-metallic chromium dioxide

Synthesis and physical properties of arc melted NiMnSb

Finite-temperature depolarization in half metals

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