The investigation of the electronic, elastic and vibrational properties of cubic Fe2YSi (Y=Co, Cr, Mn ve Ni) heusler compounds within the density functional theory

In this thesis, the structural, electronic, elastic and vibrational properties of cubic Fe2YSi (Y=Co, Cr, Mn and Ni) Heusler compounds are computed using a combination of density-functional theory total energy methods and density-functional perturbation theory lattice dynamics in Generalized Gradient Approximations (GGA). The calculated lattice constants, bulk modulus and bohr magnetizations are reported, which are in good agreement with the available experimental data and the previous theoretical results. The elastic constants were obtained using the stress-strain relations. The electronic band structures are presented for these materials. Fe2CrSi and Fe2MnSi compounds are found to be ''half metallic ferromagnet'', i.e. they have a semiconducting gap in the minority-spin (spin-down) bands but metallic majority-spin (spin-up) bands. A linear response approach to density functional theory is used to derive phonon dispersion curves and the phonon density of states for Fe2YSi (Y=Co, Cr, Mn and Ni). It is found that Fe2MnSi is stable in L21 structure, but for the three compounds Fe2YSi (Y=Co, Cr and Ni), the acoustic phonon branches are unstable for all symmetry directions.Key Words: Fe2CoSi, Fe2CrSi, Fe2MnSi, Fe2NiSi, Density-functional theory, Electronic bant structure, Elastic Properties, Phonon