Spintronic properties of the Ti2CoB Heusler compound by density functional theory

The electronic structure and magnetic properties of the Ti₂CoB Heusler compound with a high-ordered CuHg₂Ti structure were investigated using the self-consistent full potential linearized augmented plane wave (FPLAPW) method within the density functional theory (DFT). Spin-polarized calculations show that the Ti₂CoB compound is half-metallic ferromagnetic with a magnetic moment of 2 μ_B at the equilibrium lattice constant, a=5.74 Å. The Ti₂CoB Heusler compound is ferromagnetic below the equilibrium lattice constant and ferrimagnetic above the equilibrium lattice constant. A large peak in majority-spin DOS and an energy gap in minority-spin DOS are observed at the Fermi level, yielding a spin polarization of 100%. A spin polarization higher than 90% is achieved for a wide range of lattice constants between 5.6 and 6.0 Å.     

Half-metallicity in the full-Heusler Co2ScP compound: A density functional study

The electronic structure and magnetic properties of the Heusler compound Co₂ScP have been investigated by the generalized gradient approximation based on density functional theory. The results show that the ground state phase of the Co₂ScP compound possesses AlCu₂Mn-type crystal structure and exhibits half-metallic ferrimagnetism. The total spin moment is 2 μ_B at the equilibrium lattice constant a₀=5.83 Å, which agrees with the Slater–Pauling rule. The spin-up electrons are metallic, but the spin-down bands are semiconductor with a gap of 0.55 eV, and the spin-flip gap is of 0.07 eV.     

First-principles study of half-metallic properties of the Heusler alloy Ti2CoGe

First-principles calculations have been performed on the electronic structures and magnetic properties of a new Ti₂Co-based full-Heusler alloy Ti₂CoGe. The calculations predict the Ti₂CoGe is a half-metallic ferromagnet at the equilibrium lattice constant with the minority-spin energy gap of 0.60 eV. It is found that the total magnetic moment (M_t) and the number of valence electrons (Z_t) in Ti₂CoGe obey a new Slater–Pauling (SP) rule of M_t=Z_t−18 and the rule also can be applied to other Ti₂Co-based half-metallic full-Heusler alloys. The Ti₂CoGe alloy keeps a 100% polarization at Fermi level and maintains the half-metallic character for lattice constants ranging between 6.05 and 6.67 Å.     

A first-principle study of half-metallic ferrimagnetism in the Ti2CoGa Heusler compound

Electronic structure calculations based on density functional (DFT) theory within the generalized gradient approximation (GGA) for the Ti₂CoGa Heusler compound have been performed using the self-consistent full-potential linearized augmented plane wave (FPLAPW) method. The electronic band structures and density of states of the Ti₂CoGa compound show that the spin-up electrons are metallic, but the spin-down bands have a gap of 0.5 eV, resulting in stable half-metallic ferrimagnetic behavior with a magnetic moment of 2μ_B.     

Half-metallic properties of Ti2FeSi full-Heusler compound

In this study, the electronic structure and magnetic properties of novel half-metallic Ti₂FeSi full-Heusler compound with CuHg₂Ti-type structure were examined by density functional theory (DFT) calculations. The electronic band structures and density of states of the Ti₂FeSi compound show the spin-up electrons are metallic, but the spin-down bands are semiconductor with a gap of 0.45 eV, and the spin-flip gap is of 0.43 eV. Fe atom shows only a small magnetic moment and its magnetic moment is antiparallel to that of Ti atoms, which is indicative of ferrimagnetism in Ti₂FeSi compound. The Ti₂FeSi Heusler compound has a magnetic moment of 2 μ_B at the equilibrium lattice constant a=5.997 Å.     

Half-metallicity and magnetic properties of half-Heusler type Mn2Sn: Ab initio predictions

Ab initio calculations have been carried out to investigate the electronic structure and magnetism of the compound Mn₂Sn with the bcc half-Heusler structure. For the equilibrium lattice parameter 5.69 Å, Mn₂Sn is predicted to be a half-metallic fully compensated ferrimagnet (also called half-metallic antiferromagnet) with zero total spin moment. This zero moment agrees well with the Slater-Pauling curve and mainly comes from the compensated Mn (A) and Mn (B) spin moments in antiparallel configuration. The half-metallicity of Mn₂Sn is stable in a wide lattice-parameter range from 5.6 Å to 5.9 Å. Upon contraction of the lattice, a transition from half-metallicity to semimetallicity is observed.     

Electronic structure and magnetism in full-Heusler compound Mn2ZnGe

The first-principle calculations within density functional theory are used to investigate the electronic structure and magnetism of the Mn₂ZnGe Heusler alloy with CuHg₂Ti-type structure. The half-metallic ferrimagnets (HMFs) in Mn₂ZnGe are predicted. The energy gap lies in the minority-spin band for the Mn₂ZnGe alloy. The calculated total spin magnetic moment is −2μ_B per unit cell for Mn₂ZnGe alloy, the magnetic moments of Zn and Mn(B) are antiparallel to that of Mn(A), and we also found that the half-metallic properties of Mn₂ZnGe are insensitive to the dependence of lattice within the wide range of 5.69 and 5.80 Å where exhibiting perfect 100% spin polarization at the Fermi energy.     

Half-metallic properties of the CuHg2Ti-type Mn2ZnSi full-Heusler compound

The half-metallic properties of novel CuHg₂Ti-type Mn₂ZnSi full-Heusler compound were examined by density functional theory (DFT) calculations. The electronic band structures and density of states of the Mn₂ZnSi compound show that spin-up electrons are metallic, but the spin-down bands are semiconductor with a gap of 0.48 eV, and the spin-flip gap is of 0.28 eV. The Mn₂ZnSi Heusler compound has a magnetic moment of 2 μ_B at the equilibrium lattice constant a = 5.80 Å. The Mn₂ZnSi full-Heusler compound is ferrimagnetic and maintains the half-metallic character having 100% polarization for lattice constants ranging between 5.62 and 6.91 Å.     

Magnetism in the new full-Heusler compound,Zr2CoAl: A first-principles study

The electronic structure and magnetic properties of Zr₂CoAl bulk material were investigated within the Density Functional Theory (DFT) framework. The material, basically a complete spin polarized half-metallic ferromagnet in the ground state, crystallizes in the ordered full-Heusler inverse structure (Hg₂CuTi-type structure). The energy band gap, localized in minority spin channel is 0.48 eV at equilibrium lattice parameter, 6.54 Å. The total magnetic moment calculated, equal to 2 μ_B/f.u., is an integral, in agreement with the Slater-Pauling curve for full-Heusler alloys.     

Structural,electronic, magnetic and thermoelectric properties of inverse Heusler alloys Ti2CoSi,Mn2CoAl and Cr2ZnSi by employing Ab initio calculations

ABSTRACT

The inverse Heusler alloys such as Ti₂CoSi, Mn₂CoAl and Cr₂ZnSi were studied in the framework of density functional theory using FP-LAPW linearised augmented plane wave method in order to determine the different physical properties such as structural, electronic, magnetic and thermoelectric. The generalised gradient approximation (GGA) was used to treat the exchange–correlation energy and the Beck-Johnson (mBJ) approach was used to calculate the electronic properties. In all studied compounds, the stable type Hg₂CuTi was energetically more favourable than Cu₂MnAl type structure. The results show that two compounds (Ti₂CoSi and Mn₂CoAl) are both ferromagnetic (FM) while Cr₂ZnSi is antiferromagnetic (AFM). The compounds Ti₂CoSi and Mn₂CoAl have a total magnetic moment of 3 and 2?μ_B, respectively, whereas the Cr₂ZnSi alloy has a total magnetic moment equals zero. The Ti₂CoSi, Mn₂CoAl and Cr₂ZnSi compounds exhibit half-metallic (HM) character with 100% spin polarisation at the Fermi level. Finally, the semi-classical Boltzmann theory implicit in the BoltzTraP code was used to calculate the electronic transport coefficients such as thermal and electrical conductivity, the Seebeck coefficient and the factor of merit.     

Band structure calculations for Heusler phase Co2YBi and half-Heusler phase CoYBi (Y=Mn, Cr)

We have studied the electron structure and magnetic properties of Heusler phase Co₂YBi and half-Heusler phase CoYBi (Y=Mn, Cr) by using the full-potential linearized-augmented plane-wave (FLAPW) method. Co₂MnBi and Co₂CrBi are predicted to be half-metallic magnetism with a total magnetic moment of 6 and 5 μ_B, respectively, well consistent with the Slater-Pauling rule. We also predict CoMnBi to be half-metallic magnetism with a slight compression. The gap origin for Co₂MnBi and Co₂CrBi is due to the 3d electron splitting of Mn (Cr) and Co atoms, and the gap width depends on Co electron splitting. The atom coordination surroundings have a great influence on the electron structure, and consequently the Y site in the X₂YZ structure has a more remarkable electron splitting than the X site due to the more symmetric surroundings. The investigation regarding the lattice constant dependence of magnetic moment shows that the Co magnetic moment exhibits an opposite behavior with the change of the lattice constant for Heusler and half-Heusler alloys, consequently leading to the different variation trends for total magnetic moment. The variation of total and atom magnetic moment versus lattice constant can be explained by the extent of 3d electron splitting and localization of Mn (Cr) and Co atoms for both the series of alloys.     

Crystal chemistry of layered carbide, Ti3(Si0.43Ge0.57)C2

 The crystal structure of a layered ternary carbide, Ti₃(Si_0.43Ge_0.57)C₂, was studied with single-crystal X-ray diffraction. The compound has a hexagonal symmetry with space group P6₃/mmc and unit-cell parameters a=3.0823(1) Å, c=17.7702(6) Å, and V=146.21(1) Å³. The Si and Ge atoms in the structure occupy the same crystallographic site surrounded by six Ti atoms at an average distance of 2.7219 Å, and the C atoms are octahedrally coordinated by two types of symmetrically distinct Ti atoms, with an average C-Ti distance of 2.1429 Å. The atomic displacement parameters for C and Ti are relatively isotropic, whereas those for A (=0.43Si+0.57Ge) are appreciably anisotropic, with U₁₁ (=U₂₂) being about three times greater than U₃₃. Compared to Ti₃SiC₂, the substitution of Ge for Si results in an increase in both A-Ti and C-Ti bond distances. An electron density analysis based on the refined structure shows that each A atom is bonded to 6Ti atoms as well as to its 6 nearest neighbor A site atoms, whether the site is occupied by Si or Ge, suggesting that these bond paths may be significantly involved with electron transport properties.     

Structural phase transitions at high-temperature in double perovskite Sr2GdRuO6

The crystal structure evolution of the Sr₂GdRuO₆ complex perovskite at high-temperature has been investigated over a wide temperature range between 298 K≤T≤1273 K. Powder X-ray diffraction measurements at room temperature and Rietveld analysis show that this compounds crystallizes in a monoclinic perovskite-type structure with P2₁/n (#14) space group and the 1:1 ordered arrangement of Ru⁵⁺ and Gd³⁺ cations over the six-coordinate M sites, with lattice parameters a=5.81032(8) Å, b=5.82341(4) Å, c=8.21939(7) Å, V=278.11(6) Å³ and angle β=90.311(2)^o. The high-temperature analysis shows that this material suffers two-phase transitions. At 373 K it adopts a monoclinic perovskite structure with I2/m space group, and lattice parameters a=5.81383(2) Å, b=5.82526(4) Å, c=8.22486(1) Å, V=278.56(2) Å³ and angle β=90.28(2)^o. Above of 773 K, it suffers a phase transition from monoclinic I2/m to tetragonal I4/m, with lattice parameters a=5.84779(1) Å, c=8.27261(1) Å, V=282.89(5) Å³ and angle β=90.02(9)^o. The high-temperature phase transition from monoclinic I2/m to tetragonal I4/m is characterized by strongly anisotropic displacements of the anions.     

Structural, elastic and electronic properties of a new ternary-layered Ti2SiN

The structural, elastic and electronic properties of Ti₂SiN were studied by first-principle calculations. The calculated bond lengths of Ti-Si and Ti-C are 2.65 and 2.09 Å, respectively. The results show Ti₂SiN is mechanically stable, and its bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio μ and anisotropy factor A are determined to be 182 GPa, 118 GPa, 291 GPa, 0.233 and 1.57, respectively. The calculated electronic structure indicates that Ti₂SiN is anisotropic and conductive.     

Half-metallic antiferromagnetism in the ordered Cr1 − xCaxSb alloy from first-principles calculations

Compared to half-metallic ferromagnets, half-metallic antiferromagnets (precisely called half-metallic fully compensated ferrimagnets) are more promising candidates for spintronic applications since their zero magnetization leads to lower stray fields and thus tiny energy losses. Using the first-principles calculations, we have systematically investigated the electronic and magnetic properties of the ordered Cr_1 − xCa_xSb alloy. It is found that Cr_1 − xCa_xSb with x=0.125, 0.25, 0.5 and 0.75 all are half-metals like zinc-blende CrSb and CaSb. Interestingly, Cr_0.25Ca_0.75Sb is a half-metallic antiferromagnet with complete spin polarization, and the half-metallic antiferromagnetism is robust against the lattice compression and expansion and the choice of electronic exchange and correlation functional.     

Structural,electronic and magnetic properties of the double perovskite Pb2FeReO6

The structural, electronic and magnetic properties of the double perovskite Pb₂FeReO₆ have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as taking into account the on-site Coulomb repulsive and exchange coupling interactions (GGA+U). The optimized crystal structure of the Pb₂FeReO₆ is a body-centered tetragonal (BCT) with a space group of I4/m and the lattice constants of a=b=5.59 Å and c=7.93 Å, consistent with the experimental results. The two axial transition metal and oxygen (TM–O) distances are slightly larger than the four equatorial TM–O distances and shows the existence of the Jahn–Teller structural distortion in FeO₆ and ReO₆ octahedra. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.929 and −0.831μ_B respectively and thus antiferromagnetic (AFM) coupling via oxygen between them. The half-metallic (HM) ferromagnetic (FM) nature implies a potential application of this new compound in magnetoelectronic and spintronics devices.     

Half-metallic ferromagnetism in rocksalt and zinc-blende MS (M=Li, Na and K): A first-principles study

First-principles full-potential linearized augmented plane-wave method is used to investigate the electronic structure and magnetic properties of hypothetical zinc-blende and rocksalt LiS, NaS and KS. We find that all the compounds except rocksalt LiS exhibit half-metallic ferromagnetism with an integer magnetic moment of 1.00 μ_B per formula unit. The ferromagnetism results from the spin-polarization of p states of anion S. Total energies calculations indicate the rocksalt phase is lower in energy than the zinc-blende one. The total energy differences are about 0.38, 0.36 and 0.32 eV per formula unit for LiS, NaS and KS, respectively. Meanwhile, it is shown that rocksalt NaS and KS have the half-metallic gaps of 0.22 and 0.41 eV, respectively, and the half-metallic gaps are 0.03, 0.46 and 0.65 eV for zinc-blende LiS, NaS and KS, respectively. We also find the half-metallicity is robust against the lattice contraction up to 7% and 13% for rocksalt NaS and KS, respectively. Although rocksalt LiS is nonmagnetic and metallic at the equilibrium lattice constant, it shows half-metallic ferromagnetism when the lattice constant is larger than 5.40 Å.     

Crystal structure,ionic conductivity and dielectric relaxation studies in the (C5H10N)2BiBr5 compound

The synthesis and crystal structure of the bis (3-dimethylammonium-1-propyne) pentabromobismuthate(III) salt are given in the present paper. After an X-ray investigation, it has been shown that the title compound crystallizes at 298 K in a centrosymmetric monoclinic system, in the space group C₂/c with the following lattice parameters a=12.9034(3) Å, b=19.4505(6) Å, c=8.5188(2) Å, β=102.449(2). Not only were the impedance spectroscopy measurements of (C₅H₁₀N)₂BiBr₅ carried out from 209 Hz to 5 MHz over the temperature range of 318 K–373 K, but also its ac conductivity evaluated. Besides, the dielectric relaxation was examined using the modulus formalism. Actually, the near values of activation energies obtained from the impedance and modulus spectra confirms that the transport is of an ion hopping mechanism, dominated by the motion of the H⁺ ions in the structure of the investigated material.     

Velocity modulation spectroscopy of molecular ions I: The pure rotational spectrum of TiCl (XΦr)

The pure rotational spectrum of the TiCl⁺ ion in its X³Φ_r ground state has been measured in the frequency range 323-424 GHz, using a combination of direct absorption and velocity modulation techniques. The ion was created in an AC discharge of TiCl₄ and argon. Ten, eleven, and nine rotational transitions were recorded for the ⁴⁸Ti³⁵Cl⁺, ⁴⁸Ti³⁷Cl⁺, and ⁴⁶Ti³⁵Cl⁺ isotopomers, respectively; fine structure splittings were resolved in every transition. The rotational fine structure pattern was irregular with the Ω = 4 component lying in between the Ω = 2 and 3 lines. This result is consistent with the presence of a nearby ³Δ_r state, which perturbs the Ω = 2 and 3 sub-levels, shifting their energies relative to the Ω = 4 component. The data for each isotopomer were analyzed in a global fit, and rotational and fine structure parameters were determined. The value of the spin-spin constant was comparable to that of the spin-orbit parameter, indicating a large second-order spin-orbit contribution to this interaction. The bond length established for TiCl⁺, r₀ = 2.18879 (7) Å, is significantly shorter than that of TiCl, which has r₀ = 2.26749 (4) Å. The shorter bond length likely results from a Ti²⁺Cl⁻ structure in the ion relative to the neutral, which is thought to be represented by a Ti⁺Cl⁻ configuration. The higher charge on the titanium atom shortens the bond.     

Electronic band structure matching for half- and full-Heusler alloys

We explore the lattice and the electronic band structures matching between the half-metallic Heusler alloys (half-Heusler NiMnSb and full-Heusler Co₂MnSi) and several hypothetical non-magnetic Heusler alloys by using first principle calculations. The lattice and band structure matching are almost perfectly satisfied between the two materials of similar crystal structures: (i) NiMnSb and XYSb and (ii) Co₂MnSi and X₂YSi, where X, Y=Ni or Cu. Owing to the high interface spin scattering asymmetry, these materials are promising to realize a high giant magnetoresistance at room temperature.