d 0 Half-Metallic Ferromagnetism in GeNaZ (Z = Ca, Sr, and Ba) Ternary Half-Heusler Alloys: an Ab initio Investigation
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ORIGINAL PAPER
d0 Half-Metallic Ferromagnetism in GeNaZ (Z = Ca, Sr, and Ba) Ternary Half-Heusler Alloys: an Ab initio Investigation L. Beldi 1 & Y. Zaoui 1 & K. O. Obodo 2 & H. Bendaoud 1 & B. Bouhafs 1 Received: 4 April 2020 / Accepted: 4 June 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract First-principles approach based on density functional theory was applied to investigate the structural, elastic, phonon dynamics, thermodynamics, electronic, and magnetic properties of GeNaZ (where Z = Ca, Sr and Ba) ternary Heusler alloys. The PerdewBurke-Ernzerhof generalized gradient approximation (GGA) and the modified Becke-Johnson (mBJ-GGA) were used for the exchange-correlation energy and potential. The GeNaZ ternary Heusler alloys were found to be half-metallic and stable in the ferromagnetic α phase. The alloys were found to satisfy the criteria for dynamic and elastic stabilities. Thus, they are dynamically and elastically stable. The calculated spin-polarized electronic band structure and density of states using GGA (mBJ-GGA) reveal that the minority spin channel has metallic character and the majority spin channel having an electronic band gap of 0.26 (0.59), 0.39 (0.66), and 0.08 (0.33) eV for the GeNaCa, GeNaSr, and GeNaBa ternary Heusler alloys, respectively. The considered alloys all result in a stable ferromagnetic half-metallic ground state structure with a magnetic moment of 1 μB/cell. The density of states and the spin-charge density of these alloys show that the magnetization originates primarily from the 4p states of the Ge atoms. The GeNaZ ternary Heusler alloys do not have any magnetic elements, and their induced magnetism makes them very promising materials for spintronic devices. Keywords Density functional theory . Phase stability . Half-Heusler alloys . Half-metallicity . Ferromagnetism
1 Introduction Heusler alloys [1–3] is a subject of continuing scientific and technological interest. Also, the devices based on Heusler alloys require the development of new structures with ferromagnetic behavior using transition metal elements [4–7] or elements that are intrinsically nonmagnetic [8–22]. The half-Heusler XYZ and the fullHeusler X2YZ alloys without transition metals, mainly referred to as d0 half-metallic Ferro-magnets (HMF), are a field of active research [23, 24]. Of particular interest is that their ferromagnetic character does not arise from
* B. Bouhafs [email protected] 1
Modeling and Simulation in Materials Science Laboratory, Physics Department, Djillali Liabès University of Sidi Bel-Abbès, 22000 Sidi Bel-Abbes, Algeria
2
HySA Infrastructure Centre of Competence, Faculty of Engineering, North-West University, South Africa (NWU), Vanderbijlpark 2531, South Africa
magnetic elements as well as the half-metallic (HM) nature with possible applications in spintronic systems [25–29]. This class of materials is strongly ferromagnetic and as mentioned above is composed of non-magnetic elements [30–32] compared with those predicted by Groot et al. in 1983 [3]
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