Spin-polarized Electronic Structure Calculations Research Articles

Origins of multi-sublattice magnetism and superexchange interactions in double–double perovskite CaMnCrSbO6

The multi-sublattice magnetism and electronic structure in double–double perovskite compound CaMnCrSbO6 is explored using density functional theory. The bulk magnetization and neutron diffraction suggest a ferrimagnetic order ( TC∼ 49 K) between between Mn2+ and Cr3+ spins. Due to the non-equivalent Mn atoms (labelled as Mn(1) and Mn(2) which have tetrahedral and planar oxygen coordinations, respectively) and the Cr atom in the centre of distorted oxygen octahedron in the unit cell, the exchange interactions are more complex than that expected from a two sublattice magnetic system. The separations between the on-site energies of the d-orbitals of Mn(1), Mn(2) and Cr obtained from Wannier function analysis are in agreement with their expected crystal field splitting. While the DOS obtained from non spin-polarized calculations show a metallic character, starting from Hubbard U = 0 eV the spin-polarized electronic structure calculations yield a ferrimagnetic insulating ground state. The band gap increases with Ueff (U − J), thereby showing a Mott–Hubbard nature of the system. The inclusion of anti-site disorder in the calculations show decrease in band-gap and also reduction in the total magnetic moment. Due to the ∼90∘ superexchange, nearest neighbour exchange constants obtained from DFT are an order of magnitude smaller than those reported for various magnetic perovskite and double-perovskite compounds. The Mn(1)–O–Mn(2) (out of plane and in-plane), Mn(1)–O–Cr and Mn(2)–O–Cr superexchange interactions are found to be anti-ferromagnetic, while the Cr–O–O–Cr super-superexchange is found to be ferromagnetic. The Mn(2)–O–Cr superexchange is weaker than the Mn(1)–O–Cr super-exchange, thus effectively resulting in ferrimagnetism. From a simple 3-site Hubbard model, we derived expressions for the antiferromagnetic superexchange strength JAFM and also for the weaker ferromagnetic JFM . The relative strengths of JAFM for the various superexchange interactions are in agreement with those obtained from DFT. The expression for Cr–O–O–Cr super-superexchange strength ( J~SS ), which has been derived considering a 4-site Hubbard model, predicts a ferromagnetic exchange in agreement with DFT. Finally, our mean field calculations reveal that assuming a set of four magnetic sub-lattices for Mn2+ spins and a single magnetic sublattice for Cr3+ spins yields a much improved T C , while a simple two magnetic sublattice model yields a much higher T C .

Electronic properties of SiC nanoribbon

The electronic properties of zigzag and armchair SiC nanoribbons are studied using a theoretical method. The spin-unrestricted electronic behavior of an armchair and zigzag SiC nanoribbon containing Si and C vacancy in the supercell was investigated. Spin-polarized electronic structure calculations show that armchair SiC nanoribbon was classified as a nonmagnetic semiconductor while zigzag SiC nanoribbon presents a half-metallic electronic structure. Our results suggest that SiC nanoribbon containing point vacancy may be a good candidate for spintronics due to its half-metal properties.

Excitonic effects on the optical spectra of TiB2 nanosheets

Two-dimensional (2D) transition metal borides, have recently attracted tremendous interest and become an emerging class of 2D materials due to their intriguing properties. We report systematic investigation of stability, electronic properties and optical activity of 2D-TiB2 nanosheets using first-principles calculations. By combining elastic and phonon-dispersion calculations, we substantiated the mechanical and dynamic stability of 2D-TiB2 nanosheets. Our results of elastic calculations reveal that addition of an extra layer destroys the auxetic behaviour of monolayer (ML) 2D-TiB2 with significant reduction in the brittleness. Further, based on the spin-polarised electronic structure calculations, we find that a low-dimensional metallic state of ML can be achieved by tuning the distance between the titanium and boron layers. The calculations clearly reveal that metallic nature does not destroys the auxetic behaviour of ML. Subsequently, we investigated the optical response of 2D-TiB2 nanosheets (ML and bilayer (BL)) at the level of density functional theory and many-body perturbation theory. The results obtained by solving Bethe–Salpeter equation (GW+BSE formalism) shows that excitonic effects causes a slight blue-shift in the absorption spectra of the nanosheets with ML being optically active with sharp peaks in infrared (IR) and ultraviolet (UV) regions while BL shows the reduced optical activity across wide range of photon energies spanning the near-IR to UV region. In addition, electronic polarisability of the nanosheet decreases with addition of another layer in ML 2D-TiB2. Further investigation of transition probabilities clearly indicates that the response of ML at Dirac point is tunable by spin–orbital coupling effects which makes these nanosheets promising for spintronic applications. The BL exhibits distinct electronic, and optical properties compared to ML. Our study unravels the structural, elastic, electronic, and optical properties of 2D-TiB2 nanosheets and suggests them as promising candidate for variety of optoelectronic and spintronic applications.

Cation exchange route to a Eu(II)-containing tantalum oxide

Traditional synthetic efforts to prepare Eu(II)-containing oxides have principally involved the use of high temperature reactions starting from EuO or a controlled, highly-reducing, atmosphere. Conversely, chimie douce approaches that are more amenable to the targeted syntheses of new, and potentially metastable, Eu(II)-oxides have yet to be explored. Herein, a cation-exchange route to new Eu(II)-containing oxides, e.g., EuTa4-xO11 (x = 0.04), has been discovered and its structure determined by powder X-ray diffraction (Space group P6322 (#182), a = 6.2539(2) Å; c = 12.3417(2) Å). The compound derives from the cation exchange of Na2Ta4O11, via a reaction with EuBr2 at 1173 K, and replacement by half the number of divalent Eu cations. Rietveld refinements show preferential ordering of the Eu cations over one of the two possible cation sites, i.e., Wyckoff site 2d (∼94%; Eu1) versus 2b (∼6%; Eu2). Total energy calculations confirm an energetic preference of the Eu cation in the 2d site. Tantalum vacancies of ∼1% occur within the layer of Eu cations and TaO6 octahedra, and ∼20% partial oxidation of Eu(II) to Eu(III) cations from charge balance considerations. 151Eu Mössbauer spectroscopy measured at 78 K found a Eu(II):Eu(III) ratio of 69:31, with a relatively broad line width of the former signal of Γ = 7.6(2) mm s–1. Also, the temperature-dependent magnetic susceptibility could be fitted to a Curie Weiss expression, giving a μeff = 6.2 μB and θCW = −10 K and confirming a mixture of Eu(II)/Eu(III) cations. The optical bandgap of EuTa4-xO11 was found to be ∼1.5 eV (indirect), significantly redshifted as compared to ∼4.1 eV for Na2Ta4O11. Spin-polarized electronic structure calculations show that this redshift stems from the addition of Eu 4f7 states as a higher-energy valence band. Thus, these results demonstrate a new cation-exchange approach that represents a useful synthetic pathway to new Eu(II)-containing oxides for tunable magnetic and optical properties.

Physical properties of elastically and thermodynamically stable magnetic AcXO3 (X = Cr, Fe) perovskite oxides: a DFT investigation

Spin-polarized calculations of mechanical, electronic structure, phonon, optical and magnetic properties of AcXO3 (X = Cr, Fe) perovskite oxides (POs) has been computed using the full-potential linearized augmented plane wave method. The modified Becke Johnson (mBJ) approximation has been utilized for exchange-correlation potential and implemented in the WIEN2k code. The negative values of formation energy and the positive fRequencies of the phonon modes show the stability of studied perovskite oxides. The mechanical stability is confirmed through the elastic parameters such as shear modulus (G), Bulk modulus (B), Poisson ratio (ν) and Cauchy pressure. The semiconductor nature with an indirect bandgap is observed for both compounds in both spin channels. The computed electron density contour plot describes the bonding nature of both compounds. The magnetic moments are calculated, which show the major involvement of Fe and Cr atoms in the overall magnetism of studied compounds. The optical response is also evaluated, showing the maximum absorption in the ultraviolet region. The overall analysis of the calculated properties shows that the studied oxide perovskites are suitable for spintronic and optoelectronic applications.

Fe3Se4: a possible ferrimagnetic half-metal?

Half-metallic ferromagnets show 100% spin-polarization at the Fermi level and are ideal candidates for spintronic applications. Despite the extensive research in the field, very few materials have been discovered so far. Here, we present results of electronic band structure calculations based on density functional theory and extensive physical-property measurements for Fe3Se4 revealing signatures of half-metallicity. The spin-polarized electronic band structure calculations predict half-metallic ferrimagnetism for Fe3Se4. The electrical resistivity follows exponentially suppressed electron–magnon scattering mechanism in the low-temperature regime and show a magnetoresistance effect that changes the sign from negative to positive with decreasing temperature around 100 K. Other intriguing observations include the anomalous behavior of Hall resistance below 100 K and an anomalous Hall coefficient that roughly follows the ρ2 behavior.

Correlations and incipient antiferromagnetic order within the linear Mn chains of metallic Ti4MnBi2.

We report measurements on Ti4MnBi2, where a crystal structure involving linear chains of Mn ions suggests one-dimensional magnetic character. The electrical resistivity is metallic, consistent with the results of electronic-structure calculations that find a robust Fermi surface albeit with moderate electronic correlations. A Curie-Weiss fit to the magnetic susceptibility suggests that the Mn moments are in the low-spin S = 1/2 configuration. Neutron diffraction measurements detect weak antiferromagnetic order within the Mn chains, with further evidence for the small staggered moment coming from the entropy associated with the ordering peak in the specific heat as well as from the results of spin-polarized electronic-structure calculations. The antiferromagnetic moments are apparently associated with the and d xy orbitals of Mn while the remaining Mn orbitals are delocalized and nonmagnetic. Strong quantum fluctuations, possibly related to an electronic instability that forms the Mn moment or to the one-dimensional character of Ti4MnBi2, nearly overcome magnetic order.

Half-metallic ferromagnetism in cubic perovskite type NdInO3

ABSTRACT Based on the full-potential linearised augmented plane wave plus local orbitals (FP-L/APW + lo) method within the density functional theory (DFT), the structural, electronic, and magnetic calculations of the cubic oxide perovskite NdInO3 compound have been done under the generalised gradient approximation (GGA). The exchange and correlation (XC) potential is defined as GGA framework in the analyses of structural properties, while both GGA and GGA + U (U is the Hubbard correlation term) approximations are taken to treat the electronic and magnetic properties. It is found that ferromagnetic (FM) configuration is reported as the most stable ground state of the cubic NdInO3 material; however, the equilibrium lattice parameters such as lattice constant (a0 ), bulk modulus (B0 ), its first-pressure derivative (B’), and the minimum of total energy (E0 ) are given in paramagnetic (PM), ferromagnetic (FM), and anti-ferromagnetic (AFM) states. The spin-polarized electronic structure calculations (band structure and density of states) of the cubic oxide perovskite NdInO3 compound verify the half-metallic feature due to the spin-up case which has the metallic nature, whereas the spin-down case presents the semiconducting character. Moreover, the magnetic properties show the integer value of the total magnetic moment for the studied compound (3μB ), where it is manly contributed by Nd atoms with apparition of weak local magnetic moments in non magnetic In and O sites.

Degenerate antiferromagnetic states in spinel oxide LiV2O4**Project supported by the National Key R&D Program of China (Grant Nos. 2017YFA0302903 and 2019YFA0308603), the National Natural Science Foundation of China (Grant Nos. 11774422, 11774424, and 11674374), the CAS Interdisciplinary Innovation Team, the Fundamental Research Funds for the Central Universities, China, and the Research Funds of Renmin University of China (Grant No. 19XNLG13).

The magnetic and electronic properties of spinel oxide LiV2O4 have been systematically studied by using the spin-polarized first-principles electronic structure calculations. We find that a series of magnetic states, in which the ferromagnetic (FM) V4 tetrahedra are linked together through the corner-sharing antiferromagnetic (AFM) V4 tetrahedra, possess degenerate energies lower than those of other spin configurations. The large number of these energetically degenerated states being the magnetic ground state give rise to strong magnetic frustration as well as large magnetic entropy in LiV2O4. The corresponding band structure and density of states of such a typical magnetic state in this series, i.e., the ditetrahedron (DT) AFM state, demonstrate that LiV2O4 is in the vicinity of a metal–insulator transition. Further analysis suggests that the t2g and eg orbitals of the V atoms play different roles in the magnetic exchange interactions. Our calculations are consistent with previous experimental measurements and shed light on understanding the exotic magnetism and the heavy-fermion behavior of LiV2O4.

Mössbauer parameters of Fe57 substituents in the topological insulator Bi2Se3

$^{57}$Fe M\"ossbauer spectroscopy can probe several \emph{local} structural, electronic and magnetic properties of Fe-containing systems. However, to establish a direct relationship between these properties and a system's geometric structure, the experimental M\"ossbauer parameters need to be analyzed \emph{via} electronic structure calculations. Herein, structural, electronic and magnetic effects of iron substituents in the topological insulator $Bi_2Se_3$, as uniquely probed by $^{57}$Fe M\"ossbauer spectroscopy, have been determined \emph{via} spin-polarized electronic structure calculations. The iron ion substituents, of \emph{nominal} Fe$^{3+}(S = 5/2)$ oxidation and spin state, are unequivocally shown to substitute Bi$^{3+}$ sites in epitaxial $Bi_2Se_3$ thin-films used for M\"ossbauer measurements. Concomitant with iron substitution, \emph{localized} structural rearrangements take place whereby the longer Bi-Se bonds of the native system are replaced by significantly shorter Fe-Se counterparts in the Fe-containing system. The resulting distorted-octahedral environment about substituent iron ions gives rise to characteristic M\"ossbauer parameters ($\delta_{Fe} \approx$ 0.51 mm/s, $\Delta E_{Q} \approx$ 0.20 mm/s) which have been calculated in excellent agreement with measured values for Fe-doped $Bi_2Se_3$ thin films. Consistent with a substituent Fe$^{3+}$ ion's \emph{nominal} high-spin electronic configuration ($t_{2g}^{\uparrow \uparrow \uparrow} e_g^{\uparrow \uparrow}$), an Fe-centered spin density has been established which, nevertheless, extends towards neighboring Se atoms \emph{via} direct Fe-Se bonding and concomitant Fe(d)-Se(p) hybridization.

Effect of Structure on the Electronic, Magnetic and Thermal Properties of Cubic Fe2MnxNi1−xSi Heusler Alloys

The concentration dependence of the phase stability, half-metallicity, thermal and magnetic properties of Fe2MnxNi1−xSi (0 ≤ x ≤ 1) Heusler alloys in two structures, Cu2MnAl (Fm3m) and Hg2TiCu (F43m), were investigated at the ab initio level using density functional theory. The exchange–correlation term was assessed using local spin density (LSDA) and generalized gradient approximation (GGA) along with Hubbard-U (U) corrections. Spin-polarized electronic band structure calculations for Fe2MnxNi1−xSi (0 ≤ x ≤ 1) alloys in their Cu2MnAl- and Hg2TiCu-structure have been carried out. These results indicate that the Hg2CuTi-type structure is more stable than the Cu2MnAl-type structure with increasing Mn content, from x = 0 to 0.25 using LSDA. No significant differences were observed using LSDA + U over GGA. The full Heusler compounds Fe2MnxNi1−xSi (0 ≤ x ≤ 1) are half metals in the Cu2MnAl-type structure for x = 0.75 and x = 1, and behave like a metal in the CuHg2Ti-type. The minority bands exhibit a band gap of about 0.11 (0.56) eV for Fe2Mn0.75Ni0.25Si using GGA (LSDA + U). Using the GGA scheme, the obtained band energy was smaller than that obtained by using the LSDA + U approach. These results clearly show that the lattice parameter, bulk modulus and total magnetic moment vary quadratically with Mn doping. The main contribution to the total magnetic moment comes from Mn or Fe atoms in B sites in both types of structures. The total magnetic moment of Fe2MnxNi1−xSi (0 ≤ x ≤ 1) alloys is typically in the range of 2–3 μB in the Cu2MnAl-Type and 3–4 μB in Hg2TiCu-Type per formula unit and consists of an average of 2 μB per Mn atom and less than 1 μB per Fe atom in the Cu2MnAl-Type, and an average of 2 μB per Mn atom and around 1 μB per Fe atom in the B site Hg2TiCu-Type. Using the quasi-harmonic Debye model, the concentration and temperature effects on the unit cell volume, thermal expansion coefficient, bulk modulus, the Debye temperature and heat capacity, for Fe2MnxNi1−xSi (0 ≤ x ≤ 1) Heusler alloys are investigated and analysed.

How different are Te clusters—a first-principles study

Density functional theory-based electronic structure calculations are carried out to obtain the geometries corresponding to the lowest three energy values for Tey (y = 2 − 20) clusters. A comparison of the stability from binding energy curve of these clusters with exchange-correlation energy functional approximated within the local density approximation (LDA), generalized gradient approximation (GGA) and hybrid functional (PBE0) indicates the structures to be most stable within the LDA, and these results are also found to be closer to those obtained from the experiments. A transition from two-dimensional to three-dimensional structures is observed at y = 5. Clusters form arm-chair and crown-like structures for small sizes and ring-like geometries for larger sizes. Partial charge density and eigenvalue spectrum reveal that there is no s-p hybridization and the highest occupied states are mostly π non-bonding orbitals. Clusters with even number of atoms show a charge distribution approximately uniformly localized around each atom similar to the σs anti-bonding orbital in Te2. Comparative study of the structural and electronic properties of small Tey clusters (y = 2 − 8), with corresponding isoelectronic sulphur and selenium clusters, predicts sulphur clusters to be most stable and Te clusters to be least stable. Bond lengths increase while bond angles decrease in going from S → Se → Te but the shapes of the geometric structures are more or less the same. Following the work of Ghosh et al. (J Phys Chem C 112:983–989, 2008) on Te helical structures and Pal et al. (Sci Rep 3:2051-1-7, 2013) on Se helical chains, we have carried out spin-polarized electronic structure calculations for helical chains of Tey (y = 3 − 8). Interestingly, we have found that Te helical chains also reveal a behaviour similar to that predicted for Se chains by Pal et al.

Enhancing the magnetic moment of ferrimagnetic NiCo2O4 via ion irradiation driven oxygen vacancies

Ion irradiation has emerged as a powerful tool for the efficient control of uniaxial lattice expansion to fine tune and modulate the otherwise inaccessible complex correlated phases in oxide thin-films. We report the fine tuning of the magnetic moment, ferromagnetic-paramagnetic and metal-insulator transition temperatures in the NiCo2O4 inverse-spinel oxide by creating oxygen deficiencies, employing high energy He-ion irradiation. Tailoring of oxygen vacancies and consequently a uniaxial lattice expansion in the out-of-plane direction drives the system toward the increase of the magnetic moment by two-times in magnitude. The magnetic moment increases with the He-ion irradiation fluence up to 2.5 × 1016/cm2. Our results are corroborated well by spin-polarized electronic structure calculations with density functional theory and X-ray absorption spectroscopic data, which show peak-height change and energy shift of Co-L2,3 and Ni-L2,3 edges driven by the oxygen vacancies. These results demonstrate a new pathway of tailoring oxygen vacancies via He-ion irradiation, useful for designing new functionalities in other complex oxide thin-films.

Electronic structure and optical properties of GdNi2Mnx compounds

The electronic structure and optical properties of GdNi2Mnx compounds (x = 0, 0.4, 0.6) were investigated. Spin-polarized electronic structure calculations were performed in the approximation of local electron spin density corrected for strong electron correlations using the LSDA+U method. The changes in the magnetic moments and exchange interactions in GdNi2Mnx (x = 0, 0.4, 0.6) governing the increase in the Curie temperature with manganese concentration were determined. The optical constants of the compounds were measured by the ellipsometric method in the wide spectral range of 0.22–15 μm. The peculiarities of the evolution of the frequency dependences of optical conductivity with a change in the manganese content were revealed. Based on the calculated densities of electron states, the behavior of these dispersion curves in the region of interband absorption of light was discussed. The concentration dependences of several electronic characteristics were determined.

First-principles study on half-metallic ferromagnetism of half-Heusler alloys VLiBi and CrLiBi

The hypothetical half-Heusler alloys VLiBi and CrLiBi containing only one transition metal element are constructed. The electronic structure and magnetic properties of VLiBi and CrLiBi are investigated by using the first-principles full-potential linearized augmented plane wave method based on density functional theory. The spin-polarized calculations of electronic structure for the half-Heusler alloys VLiBi and CrLiBi are performed. The calculation results reveal that VLiBi and CrLiBi are half-metallic ferromagnets with the half-metallic gaps of 0.25 eV and 0.46 eV and the total magnetic moments of 3.00 μB and 4.00 μB per formula unit, respectively. The total magnetic moments mainly originate from the magnetic moment on V or Cr atom. Li and Bi have small atomic magnetic moments, where the atomic magnetic moment of Bi is negative. The mean field approximation method is used to estimate the Curie temperatures of the alloys. The calculated results show that the values of Curie temperature for VLiBi and CrLiBi are 1401 K and 1551 K, respectively. To study the robustness of the half-metallicity with the change of lattice constant, the electronic structures of VLiBi and CrLiBi are also calculated under their lattice constant changing from-10% to +10% relative to the equilibrium lattice constant. It is found that the VLiBi and CrLiBi can maintain their half-metallicity and retain their total magnetic moments of 3.00 μB and 4.00 μB per formula unit even when their lattice constants change from-5.6% to 10.0% and from-6.9% to 10.0%, respectively. To discuss the effect of strongly correlated interaction on the half-metallicity, the electronic structure of VLiBi and CrLiBi are calculated by the LDA+U method with U for V-3d and Cr-3d orbital. The calculation results indicate that VLiBi and CrLiBi can keep their half-metallicity and integer total magnetic moments of 3.00 μB and 4.00 μB when the value of U reaches to 5 eV. Also, the electronic structure of VLiBi and CrLiBi are recalculated by the GGA+SOC method. The calculated results show that 1) there are some spin-down bands crossing the Fermi level, 2) the spin polarizations of VLiBi and CrLiBi at the Fermi level are 98.8% and 94.3%, respectively, and 3) total magnetic moments of VLiBi and CrLiBi are 3.03 μB and 4.04 μB per formula unit, respectively. The spin-orbit coupling has a weak effect on the half-metallic of half-Heusler alloy VLiBi and the spin polarization is still high for the half-Heusler alloy CrLiBi. The half-Heusler alloys VLiBi and CrLiBi may be useful in spintronics and other applications.

Polar Intermetallics Pr5 Co2 Ge3 and Pr7 Co2 Ge4 with Planar Hydrocarbon-Like Metal Clusters.

Planar hydrocarbon-like metal clusters may foster new insights linking organic molecules with conjugated π-π bonding interactions and inorganic structures in terms of their bonding characteristics. However, such clusters are uncommon in polar intermetallics. Herein, we report two polar intermetallic phases, Pr5 Co2 Ge3 and Pr7 Co2 Ge4 , both of which feature such planar metal clusters, namely, ethylene-like [Co2 Ge4 ] clusters plus the concatenated forms and polyacene-like [Co2 Ge2 ]n ribbons in Pr5 Co2 Ge3 , and 1,2,4,5-tetramethylbenzene-like [Co4 Ge6 ] cluster in Pr7 Co2 Ge4 . Just as in the related planar organic structures, these metal-metalloid species are dominated by covalent bonding interactions. Both compounds magnetically order at low temperature with net ferromagnetic components: Pr5 Co2 Ge3 through a series of transitions below 150 K and Pr7 Co2 Ge4 through a single ferromagnetic transition at 19 K. Spin-polarized electronic structure calculations for Pr7 Co2 Ge4 reveal strong spin-orbit coupling within Pr and considerable magnetic contributions from Co atoms. This work suggests that similar structural chemistry can emerge for other rare-earth/late-transition-metal/main-group systems.

Ab initio studies of coherent spin transport in Fe-hBN/graphene van der Waals multilayers

This paper presents the results of ab initio studies of the electronic spin inversion and filtering in a ferromagnetic multilayer heterostructure. Spin-polarized electronic structure calculations are performed based on van der Waals density functional theory to give unique insights in to the generation, manipulation and transport of coherent spin conductance. By using an exact theory of the self-consistent ground state of the Fe-hBN/graphene multilayer as a model of the magnetic tunnel junction, hidden asymmetries are unraveled in the spin-resolved charge densities. It is shown that the injection of spin into the graphene/boron nitride tunnel layer from a ferromagnetic contact gives rise to coherent spin current. The projected Fermi surfaces of the up and down spin channels are analyzed to reveal Fermi arc topologies and spin anisotropies. It is also demonstrated that the coherent transport of pure spin-down current in the topological Weyl semimetal phase is robust. The implications of the results on out-of-plane transport of spin polarized conductance in van der Waals multilayer spintronic devices is discussed. The insights derived from this study are expected to open up prospects for further exploration of van der Waals magnetic multilayer heterostructures as a versatile platform for developing materials for Weyltronic applications.

Anti-site-induced diluted magnetism in semiconductive CoFeTiAl alloy

The spin-polarized electronic band structure calculations are carried out to theoretically investigate the effect of anti-site disordering to the electronic band structure and magnetic properties of LiMgPdSb-type CoFeTiAl alloy. We found that the Co–Ti and Fe–Ti antisite disordering can induce the diluted magnetism in CoFeTiAl alloy. Especially, the Fe–Ti antisite disordering can induce a 100% spin polarization at the Fermi level at a certain degree of anti-site disordering. The Co–Fe antisite disordering is easy to occur in CoFeTiAl alloy but has little effect on the semiconductive characteristic and magnetic properties. The Co, Fe and Ti atoms at the anti-site contribute the magnetization in CoFeTiAl alloy. The diluted magnetism in CoFeTiAl alloy can be induced by the anti-site disordering instead of the introduction of magnetic dopant elements.

Oxygen trapped by rare earth tetrahedral clusters in Nd4FeOS6: Crystal structure, electronic structure, and magnetic properties

Single crystals of Nd4FeOS6 were grown from an Fe–S eutectic solution. Single crystal X-ray diffraction analysis revealed a Nd4MnOSe6-type structure (P63mc, a=9.2693(1)Å, c=6.6650(1)Å, V=495.94(1)Å3, Z=2), featuring parallel chains of face-sharing [FeS6×1/2]4− trigonal antiprisms and interlinked [Nd4OS3]4+ cubane-like clusters. Oxygen atoms were found to be trapped by Nd4 clusters in the [Nd4OS3]4+ chains. Structural differences among Nd4MnOSe6-type Nd4FeOS6 and the related La3CuSiS7− and Pr8CoGa3-type structures have been described. Magnetic susceptibility measurements on Nd4FeOS6 suggested the dominance of antiferromagnetic interactions at low temperature, but no magnetic ordering down to 2K was observed. Spin-polarized electronic structure calculations revealed magnetic frustration with dominant antiferromagnetic interactions.

Competition between ferromagnetic and anti-ferromagnetic couplings in Co doped ZnO with vacancies and Ga co-dopants

Spin-polarized first-principles electronic structure and total energy calculations have been performed to better understand the magnetic properties of Co doped ZnO (ZnO:Co) with vacancies and Ga co-dopants. The paramagnetic state of ZnO:Co, in which Co ions lose their magnetic moments, has been found to be unstable. The total energy results show that acceptor-like Zn vacancies and donor-like Ga co-dopants render the anti-ferromagnetic (AFM) and ferromagnetic (FM) states to be more favorable, respectively. With O vacancies, ZnO:Co has been found to be in the weak FM state. These magnetic properties can be understood by the calculated O- and Zn-vacancies and Ga co-dopant induced changes of the electronic structure, which suggest that AFM and FM Co-Co couplings are mediated by O 2p-Co majority (↑)-spin 3d hybridized states in the valence band of ZnO and O-vacancy-derived p states or Ga sp states in the ZnO band gap, respectively. For ZnO:Co with Zn vacancies (Ga co-dopants) the AFM (FM) coupling outweighs the FM (AFM) coupling and results in the AFM (FM) state, while for ZnO:Co with O vacancies, both the FM and AFM couplings are enhanced by similar degrees and result in the weak FM state. This study reveals a competition between FM and AFM couplings in ZnO:Co with vacancies and Ga co-dopants, the detailed balancing between which determines the magnetic properties of these materials.