First-principles theoretical studies of half-metallic ferromagnetism in CrTe

Abstract

Using full-potential linear augmented plane wave method (FP-LAPW) and the density functional theory, we have carried out a systematic investigation of the electronic, magnetic, and cohesive properties of the chalcogenide CrTe in three competing structures: rock-salt (RS), zinc blende (ZB) and the NiAs-type (NA) hexagonal. Although the ground state is of NA structure, RS and ZB are interesting in that these fcc-based structures, which can possibly be grown on many semiconductor substrates, exhibit half-metallic phases above some critical values of the lattice parameter. We find that the NA structure is not half-metallic at its equilibrium volume, while both ZB and RS structures are. The RS structure is more stable than the ZB, with an energy that is lower by 0.25 eV/atom. While confirming previous results on the half-metallic phase in ZB structure, we provide hitherto unreported results on the half-metallic RS phase, with a gap in the minority channel and a magnetic moment of 4.0 µB per formula unit. A comparison of total energies for the ferromagnetic (FM), nonmagnetic (NM), and antiferromagnetic (AFM) configurations shows the lowest energy configuration to be FM for CrTe in all the three structures. The FP-LAPW calculations are supplemented by linear muffin-tin orbital (LMTO) calculations using both local density approximation (LDA) and LDA+U method. The exchange interactions and the Curie temperatures calculated via the linear response method in ZB and RS CrTe are compared over a wide range of the lattice parameter. The calculated Curie temperatures for the RS phase are consistently higher than those for the ZB phase.

The effect of pressure and alloying on half-metallicity of quaternary Heusler compounds CoMnYZ (Z = Al, Ga, and In)

“…The half-metallic gap reported in Table 2, which is determined as the minimum between the lowest energy of majority (minority) spin conduction bands with respect to the Fermi level, and the absolute values of the highest energy of the majority (minority) spin valence bands, are 0.158 eV, 0.294 eV and 0.195 eV, for CoMnYAl, CoMnYGa and CoMnYIn, respectively. On the other hand, the large gaps in these compounds containing localized magnetic orbitals due to d-d hybridization between the transition metal atoms [26] is essential for the gap formation as the p-d hybridization previously discussed [1]. According to Slater-Pauling rule the calculated magnetic moment has to be an integer value for a compound to be a half metal ferromagnet.…”

Half-metallicity and ferromagnetism of TcX (X=C, Si and Ge) in zinc blende structure

“…For the equilibrium lattice parameters we estimate the T c values to be around 100 K, 200 K, and 300 K for TcC, TcSi and TcGe, respectively. These values are relatively lower than those estimated for some of the 3d-transition metal based chalocogenides and pnictides [20,19], which have 3-4 times larger [10] magnetic moments.…”

“…Several details/ issues related to this mapping appear in our previous publications [19,20]. The representation of the total energy via an effective Heisenberg model itself can be and has been justified [51,57] for metallic (itinerant) ferromagnets as follows.…”

“…The aim is to search for half-metals with simple structure, and high Curie temperature. Recently Liu et al [19] and Bose and Kudrnovský [20] have presented extensive studies of exchange interactions and the Curie temperatures as a function of lattice parameter for some Cr-based chalcogenides and pnictides exhibiting half-metallicity. HM compounds which do not involve transition metals have also been considered.…”

Electronic and Magnetic Properties of the Bulk and Surfaces of Rock salt KM (M = Se and Te): A Density Functional Theory Study

“…The half-metallic (HM) gaps, which are the energy differences between the Fermi level and the maximum of the conduction band for the spin-up state, are found to be 0.23 and 0.32 eV for rs and zb structures of KSe and 0.1 and 0.23 eV for rs and zb structures of KTe, respectively. Here, we consider the electronic and magnetic properties of these compounds in rs structure because they are more stable in this structure than in the zb structure, and as a result, one can grow them in metastable rs structure over the semiconductors with the rs structure easier than the zb structure [26].…”