Co2fega Case Study

3.2 (001) surfaces of Co2FeGa
3.2.1. Structure and relaxation
To discuss the electronic structure and magnetic properties of the Co2FeGa (001) surface with L21 structure, we simulate the (001) surface properties of Co2FeGa full ̶ Heusler alloy, we built a slab containing fifteen atomic layers for ideal Co–Co and Fe–Ga terminations and modified Co- termination, and in order to avoid the interactions of nearby slabs, we added a 15 Å vacuums on top of the all surfaces. We examine three different possible surface terminations: the Co– termination on a FeGa subsurface layer as shown in Fig. 4 whiles the Fe–Ga and Co–Co terminations with the order of the layers, as shown in Fig 4. We determine the surface equilibrium structure for all termination
5 shows the total density of states of the majority and minority spin channels of the all terminations of the (001) surface Co2FeGa for a slab of 15 layers and 15 Å vacuums have been used successfully to study the surface properties, because the layers are thick enough to reproduce the bulk properties of Co2FeGa compound around the middle of the slabs. We note the total density of states of the majority and minority spin channels of Co2FeGa full–Heusler alloy surfaces. From these figures, we can see that the half metallicity is lost for all terminations and the DOS plots in the spin-minority channel do not show a band gap because the finite electronic states are newly developed at the Fermi level located between the t2g and eg orbital’s, also it can be seen in all terminated surfaces that both the majority and minority are metallic. When the depth increases the majority states are still metallic and have no distinct change at the Fermi level, while the minority states of each atom decrease relative to those of the atoms in the surface. For the Co-Co surface is lost the half–metallic (HM) properties of the bulk system with the spin polarization about –42%. The total density of states (DOS) as well as the projected density of states (PDOS) is shown in Fig. 5. Compared with to the case of bulk Co2FeGa full–Heusler alloy, we note the states of the majority spin channel move towards higher energies, which leading to a decrease of the energy states at the Fermi level, and the states in the minority spin channel change to lower energy levels from the d-band PDOS of Co and Fe, This means that the surface states at the Co-Co terminated surface is caused by the decrease of the bonding- antibonding splitting because the effect of symmetry breaking at the surface [31–32],therefore the half metallicity of the surfaces and also the subsurfaces Fe(S–1), Ga(S–1) and Co(S–2) are lost. The bonding states below the Fermi level are dominated by the d-bands of Co surface atoms.