EXPLORING THE STRUCTURAL, MECHANICAL, ELECTRONIC, MAGNETIC, OPTICAL AND THERMOELECTRIC PROPERTIES OF QUATERNARY HEUSLER ALLOYS FEMNSCGA, FEMNSCAL AND FEMNCRGE
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Date
2025-04-27
Authors
Masri, Hasan
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An-Najah National University
Abstract
This dissertation presents a comprehensive analysis of the structural, electronic, magnetic, optical, and thermoelectric properties of three quaternary Heusler compounds: FeMnCrGe (Iron-Manganese-Chromium-Germanium), FeMnScAl (Iron Manganese-Scandium-Aluminum), and FeMnScGa (Iron-Manganese-Scandium-Gallium), using first-principles theoretical frameworks. This research relies on the density functional theory (DFT). The calculations use the Perdew–Burke–Ernzerhof (GGA-PBE) functional. This approach uses a generalized gradient approximation. It ensures precise electronic structure analysis. Additionally, it uses the modified Becke-Johnson (mBJ) functional. These approaches help to evaluate the material's potential applications in spintronics and energy conversion devices. All three compounds have a face-centered cubic structure with adherence to the Fm-3m space group. A negative formation energy characterizes their stable configurations. This confirms their stability. Moreover, they comply with mechanical stability conditions.
FeMnCrGe (Type 1 structure), FeMnScAl, and FeMnScGa (Type 2 structures) all meet mechanical stability requirements and exhibit structural stability through a hybrid ionic-covalent bonding framework. The electronic structure analysis depicts strong half-metallic behavior for all compounds studied, with 100% spin polarization. The FeMnCrGe compound has a spin-down bandgap value calculated as 0.974 eV with a modified Becke-Johnson potential, compared with a 0.1574 eV bandgap for FeMnScAl and 0.442 eV for FeMnScGa. As per the Slater-Pauling rule, magnetic moments have been calculated. The FeMnCrGe compound illustrates a magnetic moment value per formula unit as 1.00 μB, with FeMnScAl and FeMnScGa having magnetic moments of 3.00 μB each. Such a fluctuation is attributed to strong ferromagnetic behavior, which is substantiated through strong magnetic interactions from manganese. Investigation of the thermoelectric properties reveals high efficiency in energy conversion. The material FeMnScAl has a peak value for ZT of 0.689 at 150 K, and FeMnCrGe has a value of 0.42 at 500 K.
Also, the optical properties of all three compounds demonstrate high ultraviolet absorption, with FeMnScGa having absorption coefficients above 180 × 10⁴/cm. Additionally, all materials exhibit a high refractive index, and large interband transitions are present. These characteristics suggest excellent potential for optoelectronic devices. Their impact could be significant in advanced applications. These materials offer significant potential. They could advance spintronic, thermoelectric, and optoelectronic technologies. These materials exhibit half-metallicity, stable magnetism, and strong thermoelectric properties. This unique combination creates new opportunities. It helps to address challenges in conventional electronics and energy harvesting. The theoretical framework as a whole presents a solid foundation for future empirical research, as well as for real applications of these flexible materials for constructing novel technological advancements.