The Structural, Electronic, Magnetic, Mechanical, and Lattice Dynamical Properties of the Novel Full-Heusler Alloys Mn2HfX (X = Si and Ge): Ab Initio Study

Through first-principles investigation, two new Mn2-based full-Heusler alloys, Mn2HfSi and Mn2HfGe, have been studied using the full-potential linearized augmented plane wave (FP-LAPW) approach as implemented in the WIEN2k code. Our study focuses on these compound’s stability (thermodynamic, dynamic, and mechanical), electronic, and magnetic properties. The L21 (Cu2MnAl-type) structure is shown to be more energetically favorable than the XA (Hg2CuTi-type) structure for both compounds, Mn2HfX (X = Si and Ge). We demonstrate that Mn2HfX (X = Si and Ge) are stable through the calculations of cohesive, formation energies, phonon dispersion curves, and the elastic constants, with the illustration of 3D and 2D bulk and Young’s moduli. Using GGA and GGA-mBJ calculations show that Mn2HfX (X = Si and Ge) are half-metallic ferrimagnets (HMFs), with indirect band gap through the altered Becke-Johnson (mBJ), GGA approximation: 0.689 eV for Mn2HfSi and 0.520 eV for Mn2HfGe. Furthermore, the electrons at the Fermi level (EF) were fully spin-polarized. The total magnetic moment in these two compounds was found to have an integer value of 2 µB per formula, which complies with the Slater-Pauling rule Mtot = Ztot − 24. These compounds are favorable materials for spintronic applications. It was revealed that Mn2HfSi and Mn2HfGe maintained their half-metallicity for lattice constants in the range of 5.7–6.2 Å and 5.75–6.2 Å, respectively.