Structural, Electronic, Magnetic, and Elastic Properties of CoX′CrZ (X′ = Sc, Ti; Z = Al, Ga) Quaternary Heusler Alloys: First‐Principles Study

Abstract

To find new spin‐gapless semiconductors (SGSs) or half‐metallic materials to promote the development of spintronics, the stable, electronic, magnetic, and mechanical properties of quaternary Heusler alloys CoX′CrZ (X′ = Sc, Ti; Z = Al, Ga) are studied by first principles. Findings show the ground state structure of all alloys is the T‐II structure, and their equilibrium lattice constants are CoScCrAl (6.15 Å), CoScCrGa (6.14 Å), CoTiCrAl (5.94 Å), and CoTiCrGa (5.93 Å), respectively, indicating that the T‐II structure is easily synthesized. The new SGSs of CoScCrAl and CoScCrGa have an indirect bandgap at the Fermi level in spin‐down channels. The indirect bandgap values are 0.52 and 0.56 eV, respectively, and the origin of the bandgap is analyzed. The spin polarization of all alloys is more than 90%, and CoScCrAl and CoScCrGa are suitable for room temperature applications due to their high Curie temperature and strict compliance with the Slater–Pauling rule. CoTiCrAl and CoTiCrGa conform to the Slater–Pauling rule when the lattice constant reaches 6.30 Å, and the half‐metallicity can be improved by doping or strain. All alloys have unique mechanical properties and are mechanically stable. Moreover, CoScCrAl and CoScCrGa exhibit brittle behavior, whereas CoTiCrAl and CoTiCrGa exhibit ductility.

Revealing the electronic, optical, elastic, mechanical, anisotropic, and thermoelectric responses of Sc2NiZ (Z = Si, Ge, and Sn) Heusler alloys via DFT calculations

“…Heusler alloys can be divided into four main groups according to their valence electron numbers as half, full, inverse and quaternary Heusler alloys. Also, half Heusler alloys have the XYZ atom order, where X and Y represent the metals from the d‐block of the periodic table of the elements and Z symbolizes any non‐metallic p‐block member [2, 5–9]. The full Heusler alloys, however, have the X 2 YZ formula where X atom valence electrons are higher than the Y atom.…”

“…Inverse Heusler alloys also display X 2 YZ structure and the Y atom holds more valence electrons than X atoms obeying the Slater‐Pauling rule. In the last group, quaternary Heusler alloys have XX'YZ atoms with the X > X′ > Y valence electron sequence [1–9]. Depending on their compositions, Heusler alloys exhibit desired advantages i.e., superconductivity, heavy fermion behavior, thermoelectricity, high‐magnetic moments, high‐magnetic anisotropy, etc.…”

“…Including both former experimental and theoretical inquiries [2,[5][6][7][8][9], the existing literature does not still report any detailed research regarding Sc 2 NiZ Heusler alloys even though they were first introduced in 2019 [10]. We aim to end this shortage and contribute to the interested audience by analyzing the titled properties of Sc 2 NiZ Heusler alloys.…”