Narrow Results

We present a comprehensive investigation of the equilibrium structural, electronic and magnetic properties of Co₂MnSi and Co₂FeSi by density-functional theory (DFT) within the generalized gradient approximation (GGA) using the projected augmented wave (PAW) method. The on-site Coulomb interaction has also taken into account (GGA+U) approach to unravel the correlation effects on the electronic structure. The change of the energy gap, "spin gap", Fermi energy level and magnetic moments with the lattice parameters is investigated. We found that the on-site correlation interaction in Co₂FeSi is stronger than in Co₂MnSi. So on-site electronic correlation is necessary for Co₂FeSi and the magnetic moments reproduce experimental results well by GGA+U. Further we also found that a moderate change of the lattice parameters does not change the half-metallic ferromagnet (HMF) behavior for both materials. Appearance of half-metallicity is consistent with the integral magnetic moments, which also agrees with the experiment measurements.

The structural optimization was followed by the calculation of electronic structure and magnetic properties on Co₂CrAl and Co₂CrGa. The structure optimization was based on generalized gradient approximation (GGA). The calculation of electronic structure was based on full potential linear augmented plane wave (FPLAPW) method within local spin density approximation (LSDA). We studied the electronic structure and magnetic properties. Results of density of states (DOS) and band structures shows that Co₂CrAl and Co₂CrGa are half-metallic ferromagnets (HMFS). The calculated magnetic moments of Co₂CrAl and Co₂CrGa are 2.915 and 3.075 μ_B, respectively. We have calculated the onsite d–d coulomb and exchange interaction (U) For 3d elements like Co and Cr. The strongly localized d states were treated with LSDA+U method.

The ground state geometric structures of the nanoparticles or clusters CO_n(n = 1-6) were given based on the first-principles calculations. Then the magnetic properties of the clusters CO_n(n = 1-6) and (CO_n)^-2(n = 1-6) were calculated in system. Results show that their ground state structures are closely related to the numbers of O-ions. These clusters have no magnetic moments and half-metallicity if they are electroneutral. However, they have magnetic moments if they have positive or negative charges. The total magnetic moments of the clusters (CO_n)^-2(n = 1-6, but n≠3) are all 2.0000 μ_B, and all their ions have contributions to the total magnetic moments. The main reason is that the molecular orbitals with lower energy filled with paired electrons and the molecular orbitals with higher energy are occupied by two electrons in parallel.

Density functional theory with pesudo potential approximation is used to study XBaB ($X=\mathrm{\text{Li}}$, Na, K) half-Heusler compounds structural, magnetic and electrical property using Quantum espresso code and thermoelectric properties were studied using BoltzTrap code. Total energy calculations were carried out in the $\alpha$, $\beta$ and $\gamma$ phases of XBaB compounds in ${C1}_b$ type structure. The compounds were stable in $\alpha$-phase and hence further calculations were focused only on $\alpha$ phase. From the spin polarization calculations, magnetic state was stable than nonmagnetic state and exhibits ferromagnetism at the equilibrium lattice constant with an integer magnetic moment of 2 ${\mu }_B$. From the band structure calculations and through density of states, all the three compounds exhibit half-metallicity with 100% spin polarization by showing semi-conductivity for majority spin and metallicity for minority spin. In addition, thermoelectric properties were investigated for all three compounds. LiBaB is found to have high Seebeck coefficient of 2462$\mu$VK${}^{-1}$ and ZT value of 1, compared to other compounds. These materials were found to have high ZT value and hence they can be used for thermoelectric applications.

In this work, using the single-band Hubbard model, we numerically study the magnetic ordering in zigzag graphene nanoribbons (ZGNRs). We calculate density of states and charge density distribution in the ZGNR, and show the nontrivial behavior of its electronic band structure in the presence of an external transverse electric field. Then, the robustness of such edge magnetic ordering and consequent half-metallicity is investigated for nanoribbons defected with single-atom vacancies. Our results show that the nontrivial magnetic properties of ZGNRs are robust to an acceptable percentage of single atom vacancies.

Electronic and elastic properties of the half-Heusler CoCrSn are calculated using first-principles method. The results show that CoCrSn is a half-metallic ferrimagnetism with the total magnetic moment of 1.00 ${\mu }_B$ per formula unit at equilibrium lattice constant. The results agree well with the Slatere–Pauling rule based on the relationship of valence electrons and total magnetic moment. The half-Heusler CoCrSn maintains the half-metallic stability within the lattice constants ranging from 5.17 Å to 5.91 Å in GGA, from 5.24 Å to 5.89 Å in GGA+SOC, and from the 4.63 Å to 6.18 Å in GGA+U, respectively. The mechanical parameters of CoCrSn, such as elastic constants, bulk modulus, shear modulus, Pough’s ratio, Frantesvich ratio, Young’s modulus, Poisson’s ratio, Kleinman parameter and Debye temperature are calculated for the first time, and the results show that it is mechanically stable and is a ductile material. The studies show that the half-Heusler CoCrSn is a promising half-metal in spintronics.

Half-metals and spin gapless semiconductors (SGSs), which exhibit 100% spin polarization at the Fermi level, are considered important candidates for spintronics. Using first-principles calculations, we have investigated the effects of uniform strain and tetragonal distortion on the half-metallicity and spin gapless feature of inverse Heusler Ti₂YSi (Y = Fe and Co) alloys. Results show that for uniform strains, the half-metallicity occurs in the ranges of lattice parameters from 5.938 Å to 6.535 Å for Ti₂FeSi and from 5.924 Å to 6.840 Å for Ti₂CoSi. Tetragonal distortions over the ranges of −2.0% to +2.5% and −2.6% to +4.1% could destroy the half-metallicity for Ti₂FeSi and Ti₂CoSi, respectively. On the other hand, Ti₂CoSi is an SGS at lattice constants of 5.968–6.023 Å. An interesting finding is that Ti₂CoSi reproduces the SGS character with increasing the lattice parameters to 6.784–6.840 Å. Small tetragonal distortions with ±0.2% will destroy the SGS character of Ti₂CoSi.

The structural, elastic, electronic and magnetic properties of the cubic ${\mathrm{\text{PtONa}}}_3$ anti-perovskite are investigated by means of the full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). We have used three approximations: the generalized gradient (GGA), the GGA+$U$, where $U$ is on-site Coulomb interaction correction, and the modified Becke–Johnson (mBJ-GGA). The elastic constants $(C_{ij})$ show that our compounds are ductile and anisotropic. The results obtained for the spin-polarized band structure and the density of states show a half-metallic behavior for the compounds using the GGA, GGA+$U$ and mBJ-GGA approaches. These results make ${\mathrm{\text{PtONa}}}_3$ a promising candidate for spintronics applications.

Searching two-dimensional (2D) magnetic materials with high spin polarization is important for the development and application of next-generation spintronic devices. Here, based on spin-polarized density functional theory calculations, the stability, electronic structure and magnetic properties of Mn-doped and Mn–NM (NM = B, C, N and S) co-doped monolayer WSe₂ are investigated in detail. The results indicate that the Mn–S co-doped MoSe₂ configuration has the lowest formation energy in the whole chemical potential range and easily spontaneously forms under thermodynamic equilibrium conditions. Obviously, the Mn-doped WSe₂ configuration exhibits magnetic half-metallicity characters with a completely spin polarization at the Femi level $(E_F)$, which can be attributed to that the electrons partially occupy the bonding states consisting of Mn $a_1$ states at the $E_F$. For the Mn–C and Mn–S co-doped configurations, the Mn $d_{xy}$ and $d_z^2$ orbitals strongly hybridize with the C or S spin-up $p_z$ orbital at the $E_F$, which induces strong spin exchange splitting and eventually gives rise to the magnetic semiconductor character. However, the Mn–B and Mn–N co-doped configurations exhibit completely symmetrical spin-up and spin-down channel of $a_1$, $a_2$, $a_3$ and $a_4$ states due to the effective charge compensation between Mn and B or N atoms. These studies provide a new class of 2D magnetic materials for future spintronics devices.

The effects of Fe–NM (NM=B, C, N) co-doping on the stability, electronic structures, magnetic and optical properties of 2H-WSe₂ monolayer are investigated in detail by spin-polarized density functional theory (DFT) calculations. The results show that the Fe-doped WSe₂ monolayer exhibits magnetic half-metallicity (HM) with a 100% spin polarization due to the electrons partially occupied Fe $e_1$ and $a_1$ bonding states at the Femi level $(E_F)$, and eventually induces a magnetic moment of 2 ${\mu }_B$. The Fe–B and Fe–N co-doped WSe₂ monolayers show obvious spin-polarization and retain semiconductor character with an indirect bandgap of 0.034 eV and 0.220 eV, respectively, which can be attributed to the strong hybridization between the Fe $d_{xy}$, $d_z^2$ states and $B$, $Np$ orbitals at the $E_F$. Interestingly, the Fe–C co-doped WSe₂ monolayer exhibits a typical non-magnetic semiconductor due to the effective charge compensation between Fe and C atoms, leading to completely symmetrical spin-up and spin-down channel of $a_1$, $a_2$, $a_3$ and $a_4$ states near $E_F$. Moreover, the optical properties of WSe₂ monolayer can be effectively tuned by Fe–NM co-doping, which can attribute to the introduction of impurity state. The excellent magnetic HM, tunable magnetic, optical properties of Fe–NM co-doped WSe₂ monolayers are of great significance for further application in the fields of spintronics, opto-electronics and magneto-optics devices.

We analyze the electronic and magnetic characteristics of the Co₂FeGa Heusler compound and the surface (001) Co₂FeGa with the $L{2}_1$ structure based on first principles calculations. The Co₂FeGa Heusler possesses high Curie temperatures and magnetization, and is therefore the most studied composition for spintronics applications. We examine the influences of (001) surface and relate interactions on the half-metallicity and the magnetic properties with two ideal terminations named Co–Co and Fe–Ga and modified Co– terminated (001) surfaces. We notice that the half-metallicity seen in the bulk Co₂FeGa is destroyed at all terminations, the spin polarization is smaller than that the bulk, the values of the Co–Co, Fe–Ga and Co– terminations are 50%, 27% and 43% respectively, but all surfaces are shown to be metallic due to the surface states staying at the Fermi level despite the confirmed $t_{2g}-e_g$ band splitting caused by the liaison influence. The calculated magnetic moment of these terminations was found for all the subsurface to be close to that of the bulk system and this makes this compound of maximum benefit in the pilot applications of spintronic systems.

By using first-principles calculations, we predict that an in-plane homogenous electrical field can induce half-metallicity in hydrogen-terminated zigzag silicene and germanene nanoribbons (ZSiNRs and ZGeNRs). A dual-gated finite ZSiNR device reveals a nearly perfect spin-filter efficiency (SFE) of up to 99% while a quadruple-gated finite ZSiNR device serves as an effective spin field effect transistor (FET) with an on/off current ratio of over 100 from ab initio quantum transport simulation. This discovery opens up novel prospect of silicene and germanene in spintronics.

We have evaluated the structural and mechanical stability, electronic structure, total spin magnetic moment, and Curie temperature of LaCoTiIn Equiatomic Quaternary Heusler Alloy (EQHA) using first-principles studies. The Generalized Gradient Approximation (GGA) and GGA+U schemes have been used as exchange-correlation functional for the above calculations. From the ground state calculation, LaCoTiIn EQHA with a Type-III structure in the ferromagnetic (FM) state is found to be stable. The electronic structure of LaCoTiIn EQHA depicts half-metallic behavior which has metallic overlap in the spin up ($\uparrow )$ channel and a semiconductor band gap in the other channel. The spin–orbit coupling of LaCoTiIn has a great influence on the band gap of the material. The computed band gap values for the spin down ($\downarrow )$ channel are 0.480 eV and 0.606 eV by using the GGA and GGA+U schemes. The total spin magnetic moment is 1 ${\mu }_B$, according to the Slater–Pauling rule, $M_{\mathrm{\text{Tot}}}$ = ($Z_{\mathrm{\text{Tot}}}$ - 18) ${\mu }_B$. These results obtained can be used as a valuable reference for future research, or they will be used to further motivate the experimental synthesis of the corresponding alloy.

A systematic investigation on magnetism and spin-resolved electronic properties in double perovskite Ca₂CoMoO₆ compound was performed by using the full-potential augmented plane wave plus local orbitals (APW$+lo$) method within the generalized gradient approximation (GGA-PBE) and GGA-PBE$+U$ scheme. The stability of monoclinic phase ($P{2}_1∕n$ #14) relative to the tetragonal ($I4∕m$#87) and cubic ($Fm\bar{3}m$ #225) phase is evaluated. We investigate the effect of Hubbard parameter $U$on the ground-state structural and electronic properties of Ca₂CoMoO₆ compound. We found that the ferromagnetic ground state is the most stable magnetic configuration. The calculated spin-polarized band structures and densities of states indicate that the Ca₂CoMoO₆ compound is half-metallic (HM) and half-semiconductor (HSC) ferromagnetic (FM) semiconductor with a total magnetic moment of 6.0 using GGA-PBE and GGA-PBE$+U$, respectively. The Hubbard $U$ parameter provides better description of the electronic structure. Using the Vampire code, an estimation of exchange couplings and magnetic Curie temperature is calculated. Further, our results regarding the magnetic properties of this compound reveal their ferromagnetic nature. The GGA-PBE$+U$ approach provides better band gap results as compared to GGA-PBE approximation. These results imply that Ca₂CoMoO₆ could be a promising magnetic semiconductor for application in spintronic devices.

Research Highlights

• •Electronic, magnetic, elastic and thermoelectric properties of RbCrC alloy are investigated.
• •Material is half-metallic, ductile and anisotropic in nature.
• •The total magnetic moment (3$\mu$B) obeys the Slater–Pauling rule.
• •The HM RbCrC compound is identified as potential candidate for spintronic applications.
• •ZT calculated values of 0.89 and 0.94 make RbCrC a promising thermoelectric material candidate for use in future devices.

The aim of this work is to investigate the half-metallicity behavior, elastic, thermodynamic and thermoelectric (TE) properties of the Heusler compound RbCrC using the generalized gradient approximation (GGA-PBE96) and the modified Becke–Johnson (mBJ) approach. The electronic band structures and density of states reveal that RbCrC is a half-metallic ferromagnet (HMF). The calculated total magnetic moment of 3$\mu$B follows the Slater–Pauling rule ($M_{\mathrm{\text{tot}}}=Z_{\mathrm{\text{tot}}}-8$). The half-metallicity character can be maintained in the 5.4–7.4 Å lattice constants range and the 0.8–1.2 $c$/$a$ ratio range. Existence of half-metallic ferromagnetism in RbCrC makes it a promising material for practical applications in the spintronic field. Also, the RbCrC exhibits a ductile and anisotropic behavior. The quasi-harmonic Debye model (QHDM) is used to calculate the thermodynamic properties. The BoltzTraP code which is based on semi-classical Boltzmann theory (SCBT) is applied for calculating TE properties. According to the obtained figure of merit values (ZT between 0.89 and 0.94 from 50 K to 800 K), the RbCrC alloy remains a good candidate for thermoelectric applications.

The structural, elastic, electronic and magnetic properties of quaternary OsCrMnSb and IrCrMnSb Heusler alloys are performed employing ab initio electronic structure calculations. It has been identified that the Y_I type is the most stable structure among the three configurations for both OsCrMnSb and IrCrMnSb alloys in the magnetic state. The calculated cubic elastic constants show that these alloys fulfill the mechanical stability criteria. The band structures and density of state calculations reveal the half-metallic (HM) behavior of these alloys with a direct gap, and the half-metallicity is rather originated from the Cr-d states. Results on magnetic properties suggest that OsCrMnSb and IrCrMnSb are HM antiferromagnets. However, the inclusion of spin–orbit coupling affects strongly the IrCrMnSb alloy, losing its HM nature.

The aim purpose of this study is to investigate the structural, elastic, magnetic, electronic properties and half-metallic stability under pressure of ScNiCrZ ($\mathrm{\text{Z}}=\mathrm{\text{Al}}$, Ga and In) quaternary Heusler alloys using full-potential linear muffin-tin orbital (FP-LMTO) method within the gradient generalized approximation (GGA) for exchange, and correlation potential. In order to evaluate the stability of our compounds, the formation energy, and elastic constants have been evaluated. The results showed that our compounds have ferromagnetic ground states and are energetically more stable in type-$\gamma$ configuration. True half-metallic ferromagnetic behavior with 100% spin polarization at Fermi level $E_F$ with high Curie temperature $T_c$, and very interesting bandgap in the minority spin are obtained for the three alloys. The calculated total magnetic moment $M_T$ for all three alloys is consistent with Slater$-$Pauling rule. The half-metallicity is maintained over a wide range of lattice constants making these alloys promising for spintronic, and magneto-electronics applications.

In this paper, we present an ab initio study, based on the density functional theory (DFT) approach and GGA-PBE approximation, of the structural, electronic and magnetic properties of new quaternary Heusler compounds LiX${}^{\prime }$NO (${\mathrm{\text{X}}}^{\prime }=\mathrm{\text{Ba}}$, Ca and Sr). We searched the structural stability of these quaternary Heusler among three different atomic arrangements (type-1, type-2 and type-3) by calculating of the cohesive energy, elastic constant and phonon dispersion. We found that the type-2 structure is the most stable structure in the ferromagnetic phase. The results of the magnetic and electronic properties show that the LiX${}^{\prime }$NO quaternary compound exhibits a half-metallic character with 100% spin polarization at the Fermi level and obey the Slater Pauling rule. It is also divulged that half-metallicity comes mainly from N and O atoms. These theoretical results make these new quaternary alloys as very promising materials for spintronic device.

In this work, we studied doping of pure hafnium disulfide (HfS²) by nonmagnetic atoms C and N. This doping was carried out by the substitution of a host atom S by doping atom C or N. The purpose of this work is to search new half-metallic material for the field of spintronics. This theoretical study is based on density functional theory (DFT) and GGA-PBE approximation. Our calculation revealed that the HfS² binary material doping with carbon and nitrogen induces strong magnetism and predicts new doped materials HfS²-C and HfS²-N. Their magnetic moments are respectively 2${\mu }_B$ and 1${\mu }_B$. The host atoms Hf and the doping atoms induce a strong magnetic moment, while the host atoms S introduce a weak magnetic moment. This magnetism results fundamentally from the coupling between the Hf-5d states and the X-2p states (X = C and N). These two new materials will be promising for the spintronic domain.

One avenue toward next-generation spintronic devices is to develop half-metallic ferromagnets with 100% spin polarization and Curie temperature above room temperature. Half-metallic ferromagnets have unique density of states, where the majority spins are metallic but the minority spins are semiconducting with the Fermi level lying within an energy gap. To date, the half-metallic bandgap has been predominantly estimated using Jullière’s formula in a magnetic tunnel junction or measured by the Andreev reflection at low temperature, both of which are very sensitive to the surface/interface spin polarization. Alternative optical methods such as photoemission have also been employed but with a complicated and expensive setup. In this study, we developed and optimized a new technique to directly measure the half-metallic bandgap by introducing circularly polarized infrared light to excite minority spins. The absorption of the light represents the bandgap under a magnetic field to saturate the magnetization of a sample. This technique can be used to provide simple evaluation of a half-metallic film.