First-Principles Study of the Structural, Electronic, Magnetic and Thermal Properties of the Cr Doped Ge6Mn2Te8 and Ge6Fe2Te8 Systems

F. Semari a, N. Baki b, H. Khachai b, A. Yakoubi b, S. Méçabih c, R. Khenataa, A. Shankar d, D.P. Rai e and A. Bouhemadou f aLaboratoire de Physique Quantique de la Matiére et de Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 Mascara, Algeria bLaboratoire d'Étude des Matériaux et Instrumentations Optiques-Faculté des Sciences Exactes, Djillali Liabès University, 22000 Sidi Bel Abbès, Algeria cModelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes, Algeria dDepartment of Physics, University of North Bengal, Darjeeling-734013, India eDepartment of Physics, Pachhunga University College, Aizawl-796001, India fLaboratory for Developing New Materials and Their Characterization, Department of Physics, Faculty of Science, University of Setif 1, Setif 19000, Algeria

Received: June 6, 2016; In final form: May 22, 2017

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First-principles calculations have been used to study the structural, electronic, magnetic, and thermal properties of the Cr doped Ge6Mn2Te8 and Ge6Fe2Te8 systems. The calculations were performed using the full-potential linearized augmented plane wave plus local orbitals (FP-LAPW + LO) method based on the spin-polarized density functional theory. Additionally, the electronic exchange-correlation potential is approximated using the spin generalized gradient approximation. The structural properties of the Ge5Mn2CrTe8 and Ge5Fe2CrTe8 alloys are indicated by their corresponding lattice constants, values of the bulk moduli and their pressure derivatives. An analysis of the band structures and the densities of states indicate that for both alloys, they present nearly half-metallic ferromagnetism character. The band structure calculations are used to estimate the spin-polarized splitting energies, Δpx(d) and Δpx(pd) produced by the 3d Mn, 3d Fe and 3d Cr doped states as well as the s(p)-d exchange constants, N0α (conduction band) and N0β (valence band). It is observed that the p-d hybridization reduces the magnetic moment of the Mn and Fe atoms from their atomic charge values and create small local magnetic moments on the nonmagnetic Ge and Te sites. Furthermore, the calculations of the charge density indicate that both compounds have ionic bonding character. Through the quasi-harmonic Debye model, the effects of pressure P and temperature T on the bulk modulus B, the primitive cell volume V/V0, the Debye temperature θD, the Grüneisen parameter γ, the heat capacity CV, the entropy S, as well as the thermal expansion coefficient, α of the Ge6Mn2Te8, Ge5Mn2CrTe8, Ge6Fe2Te8 and Ge5Fe2CrTe8 alloys are predicted.

DOI: 10.12693/APhysPolA.132.1242 topics: first-principles calculations, half-metallic ferromagnetism, electronic properties, magnetic moment, spin-exchange splitting, thermodynamic properties