Anomalies in the Optical and Electrical Properties of CrAl Alloys

Nomerovannaya, L. V.; Rassokhin, V. A.

doi:10.1002/pssa.2210790108

Cited by 11 publications

(20 citation statements)

References 9 publications

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“…3 is compatible with this possibility since a small but finite intensity is observed at zero binding energy. Previous PRL 105, 236404 (2010) P H Y S I C A L R E V I E W L E T T E R S week ending 3 DECEMBER 2010 results are also consistent with an incomplete gap, such as resistivity which is not exponential in temperature [8,9], an infrared ''gap'' showing finite reflectivity in the DC limit [7], and a nonzero electronic contribution to the specific heat [33].…”

Section: Prl 105 236404 (2010) P H Y S I C a L R E V I E W L E T T Esupporting

confidence: 53%

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Band Gap and Electronic Structure of an Epitaxial, SemiconductingCr0.80Al0.20Thin Film

et al. 2010

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Cr 1Àx Al x exhibits semiconducting behavior for x ¼ 0:15-0:26. This Letter uses hard x-ray photoemission spectroscopy and density functional theory to further understand the semiconducting behavior. Photoemission measurements of an epitaxial Cr 0:80 Al 0:20 thin film show several features in the valence band region, including a gap at the Fermi energy (E F ) for which the valence band edge is 95 AE 14 meV below E F . Theory agrees well with the valence band measurements, and shows an incomplete gap at E F due to the hole band at M shifting almost below E F . DOI: 10.1103/PhysRevLett.105.236404 PACS numbers: 71.20.Lp, 71.23.Àk, 71.28.+d, 79.60.Bm Intermetallic compounds containing transition metals and sp elements often form a gap at the Fermi energy (E F ) due to hybridization. This gap can be exploited for applications, making these compounds the subject of intense study. For example, intermetallic semiconductors are attractive for thermoelectric devices due to their typically small gaps and large Seebeck coefficients (e.g., ZrNiSn) [1]. In magnetic compounds, the gap is asymmetric with spin; if a gap occurs at E F for one spin but not the other, the result is a half-metal (e.g., Co 2 MnAl) [2]. Half-metals are important for spintronics circuits such as spin transistors and nonvolatile logic.Compounds of the form A 2 BD or A 3 D, where A and B are transition metals and D is an sp element, typically crystallize in the ternary (L2 1 ) or binary (D0 3 ) full-Heusler structures. These compounds are usually ferro-or ferrimagnetic, with the magnetic moment well predicted by a Slater-Pauling counting scheme: M ¼ Z À 24, where Z is the total number of valence electrons in the unit cell [3]. For Z ¼ 24, there is no net magnetization and a gap in both the majority and minority spin density of states (DOS), resulting in a semiconducting gap (e.g., pseudogap in Fe 2 VAl) [4]. This tunability and predictability of parameters with Z makes Heusler compounds an attractive class of materials to work with.Cr 3 AlðCr 1Àx Al x with x % 0:25Þ is an exception to this scheme. According to the Slater-Pauling counting scheme Z ¼ 21 so it should be a metal with M ¼ À3. Instead, Cr 1Àx Al x is found to be antiferromagnetic for x ¼ 0-0:50. Cr is an antiferromagnet with a spin-density wave (SDW) incommensurate with the lattice. The addition of Al causes the SDW to become commensurate, i.e., a simple antiferromagnetic structure, for x ! 0:03. For x ¼ 0:15-0:26, the Cr magnetic moment reaches 1 B with a high Néel temperature of about 800 K [5].In the same range of x, Cr 1Àx Al x displays semiconducting behavior not yet adequately explained by theory [6]. The gap has been estimated to be between 6 and 60 meV, making Cr 1Àx Al x a narrow-gap semiconductor [7][8][9].In this Letter, we probe the electronic structure of Cr 0:80 Al 0:20 through hard x-ray photoemission spectroscopy (HXPS) and density functional theory (DFT). Hard x rays are advantageous over soft x rays due to enhanced bulk sensitivity and relatively enhanced photoionization ...

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Section: Prl 105 236404 (2010) P H Y S I C a L R E V I E W L E T T Esupporting

confidence: 53%

“…The gap has been estimated to be between 6 and 60 meV, making Cr 1Àx Al x a narrow-gap semiconductor [7][8][9].…”

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confidence: 99%

Band Gap and Electronic Structure of an Epitaxial, SemiconductingCr0.80Al0.20Thin Film

et al. 2010

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“…[6][7][8] The large moment and high Néel temperature are thought to be due to increased localization of the d electrons in Cr 1−x Al x compared to Cr. 9 These signatures, occurring near x = 0.25, point toward a stoichiometric Cr 3 Al compound causing the anomalous behavior. Such a compound has been suggested by transmission electron microscopy (TEM), which showed nanometer-size domains of a chemically ordered, rhombohedrally distorted structure separated by antiphase boundaries.…”

Section: Introductionmentioning

confidence: 99%

“…1 A high resistivity, up to 3600 μ cm, and a large negative Hall constant both peak at x = 0.25. 2,3 In addition, the electronic contribution to the specific heat shows a minimum at x = 0.25. 4 The magnetism in Cr 1−x Al x shows anomalous behavior in the same range of x. Antiferromagnetism in Cr occurs in a spindensity wave (SDW) incommensurate with the lattice.…”

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confidence: 99%

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Antiferromagnetism in Cr3Al and relation to semiconducting behavior

et al. 2012

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Antiferromagnetism and chemical ordering have both been previously suggested as causes of the observed semiconductorlike behavior in Cr 3 Al. Two films of Cr 3 Al(001)/MgO(001) were grown under different conditions to achieve different types of chemical ordering and electronic properties: one X-phase structure (semiconducting) and one C11 b structure (metallic). The films were investigated by x-ray and neutron diffraction. Both films show commensurate antiferromagnetic order, with a high Néel temperature greater than 578 K, showing that the antiferromagnetism in Cr 3 Al is quite robust. Density-functional theory calculations were performed and it was shown that the well-known antiferromagnetic pseudogap in the density of states occurs for all types of chemical ordering considered. The conclusion of these studies is that the antiferromagnetism causes a pseudogap in the density of states, which is a necessary condition for the semiconductorlike transport behavior; however, that antiferromagnetism is seen in both metallic and semiconducting Cr 3 Al samples shows that antiferromagnetism is not a sufficient condition for semiconducting behavior. Chemical ordering is equally important.

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On the ordering of Cr_1‐xAl_x alloys (x < 0.33) leading to microprecipitations of X‐ and β‐phases

Dłużewski

1985

Cryst. Res. Technol.

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The analysis of electron diffractioii patterns of Crl-xAlx alloys with 0.16 5 2 5 0.24 has been performed. The diffraction vectors describing the position of X-phase spots wcre corrected to the new 0.769 0. 004 ( 1 1 1 ) value. The ordering model of Crl-xAlx alloys with 1~: < 0 . 3 3 is discussed in connection with physical properties. The new identification of the X-phase as Cr,AI displacive modulation structure is proposed.

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Anomalies in the Optical and Electrical Properties of CrAl Alloys

Cited by 11 publications

References 9 publications

Band Gap and Electronic Structure of an Epitaxial, SemiconductingCr0.80Al0.20Thin Film

Band Gap and Electronic Structure of an Epitaxial, SemiconductingCr0.80Al0.20Thin Film

Antiferromagnetism in Cr3Al and relation to semiconducting behavior

On the ordering of Cr_1‐xAl_x alloys (x < 0.33) leading to microprecipitations of X‐ and β‐phases

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Anomalies in the Optical and Electrical Properties of CrAl Alloys

Cited by 11 publications

References 9 publications

Band Gap and Electronic Structure of an Epitaxial, SemiconductingCr0.80Al0.20Thin Film

Band Gap and Electronic Structure of an Epitaxial, SemiconductingCr0.80Al0.20Thin Film

Antiferromagnetism in Cr3Al and relation to semiconducting behavior

On the ordering of Cr1‐xAlx alloys (x < 0.33) leading to microprecipitations of X‐ and β‐phases

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On the ordering of Cr_1‐xAl_x alloys (x < 0.33) leading to microprecipitations of X‐ and β‐phases