Theoretical studies predict that the light magnetic doping of Dirac semimetals leads to the occurrence of extraordinary properties and quantum states, including the Weyl semimetal, axionic insulator, topological superconductor, and others. However, thespecific materials that can exhibit these phenomena, as well as the characteristic concentrations of magnetic atoms are still unknown. In this work, the ab initio study of the electronic and magnetic properties of the Cd 3 As 2 Dirac semimetal doped isoelectronically with Mn atoms at concentrations of 4, 6, and 8% has been carried out. In the analysis of the results, the main focus has been on the break of the spatial and time symmetry in the alloys, the behavior of the electron spectrum near the top of the Dirac cone, and spin ordering processes in Mn atoms. The results obtained have been compared with the previous theoretical and experimental data and, based on these results, a detailed picture of the effect of isoelectronic magnetic doping on the properties of the Cd 3 As 2 Dirac semimetal has been presented.

The magnetic doping of Dirac semimetals breaks their time-reversal symmetry thus giving rise to anomalous transport phenomena promising for applications. While the Dirac cone (DC) manifestations were observed in the electron transport of (Cd1_ xCrx)3As2 alloys up to x = 0.06, their mechanism remains challenging. To address this challenge, we performed DFT calculations of the (Cd0.96Cr0.04)3As2 alloy with the non-magnetic (NM), ferromagnetic (FM), and antiferromagnetic (AFM) spin orders. It was found that the NM state is unstable, while the FM state has the lowest energy. The band structure analysis revealed that Cr 3d states are distributed in energy not uniformly, but with Cr-free windows, in which the Dirac spectrum can survive. The only exception is the Dirac point vicinity, where a narrow gap is formed. Outside the window, the DC band strongly hybridizes with the Cr 3d states and disappears. Near EF, such a Cr-free window with the DC band exists only in the FM down arrow state and is absent in the NM, FM up arrow, and AFM states. The Fermi surface of FM (Cd1_ xCrx)3As2 has two parts: the DC down arrow sheet with the velocity vF approximate to 1 center dot 106 m/s and several sheets with low vF, originating from Cr 3d up arrow states. As an example of transport properties, the dc conductivity of FM (Cd1_ xCrx)3As2 was estimated. We found that at T -> 0 K the DC down arrow electrons have a very large transport lifetime and therefore dominate in the conductivity. In this dominance, the role of the Cr-free window is double: it ensures the DC down arrow surviving and greatly reduces an admixture of Cr 3d down arrow orbitals to DC down arrow states, so suppressing the scattering of DC down arrow electrons by doped Cr atoms. This mechanism looks rather general and may be applied to the design of magnetic topological alloys.

Theoretical studies predict that the low magnetic doping of the Dirac semimetals (DS) leads to the appearance in them of unusual quantum states and properties: the states of Weil semimetals, axionic insulator, topological superconductor and so on. However the specific materials in which these phenomena can be observed, as well as the characteristic concentrations of magnetic atoms are still unknown. In the present work, an ab initio study of the electronic and magnetic properties of the DS Cd3As2 doped isoelectronically with Mn atoms at concentrations of 4, 6, and 8% was performed. When analyzing the results, the main attention is paid to breaking spatial and time reversal symmetry in alloys, the behavior of the electronic structure near the top of the Dirac cone, and the processes of spin ordering in Mn atoms. The results obtained are compared with earlier theoretical and experimental studies, and on their basis a detailed picture of the effect of isoelectronic magnetic doping on the properties of the DS Cd3As2 is given.

Doping by Mn breaks the time-reversal and crystal symmetry of Cd3As2, splits Dirac cones and changes band structure. We study these changes using both DFT calculations and magnetotransport measurements. Our band structure of Cd3As2 is confirmed by calculations of dielectric tensor and reflectivity consistent with an experiment. Calculations take into account the n-carrier density of Cd3As2 samples similar to 1.10(18) cm(-3) which shifts the Fermi level by epsilon(F) similar to 50 meV. The Mn-doping of Cd3As2 is simulated with the Cd46Mn2As32 cell for 9 configurations of Mn atoms. Our simulation shows the preference for antiferromagnetic spin order and tendency towards Mn clustering. Doping by Mn causes transition of Cd3As2 into a trivial topological state with a gap of E-g approximate to 40 meV. Our experimental studies of (Cd1-xMnx)(3)As-2 show that a negative sign of magneto-conductivity is observed at x = 0 and 0.017, but changes to a positive one at x = 0.033 . We argue, this sign change is closely connected with the gap opening and is basically controlled by the ratio E-g/epsilon(F). (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The electronic and optical spectra of the Bi3Se2 topological insulator digitally doped with V, Cr, Mn, Fe, and Co atoms are calculated using density functional theory. It is shown that the introduction of magnetic atoms into separate delta layers (one per 2–9 Bi2Se3 quintuple layers) multiply enhances magnetic effects. A special emphasis is put on Mn doping, which gives rise to the ferromagnetic spin ordering. The sensitivity of the spin order to the concentration and location of magnetic atoms is revealed. The study of an analytical model describing the resonant scattering of electrons in Bi2Se3 by atomic layers of transition metals also suggests the existence of spin-polarized states within the Bi2Se3 band gap. Our ab initio calculations show that transitions between the nested branches of the electronic spectrum, which exist near the Fermi level, are responsible for features of the optical conductivity at -ω ≈ 0.15−0.3eV, the infrared plasmon, and the Kerr angle θK > 12° in the infrared spectral range.

Energy difference between the ferromagnetic and antiferromagnetic collinear orderings has been calculated for the uniform and dimer Mn-pair geometries in order to find the ground state distribution of the Mn atoms in InSb (As) hosts. We find the preference of the dimer ferromagnetic configuration of Mn dopants and an importance of optimizing the atomic site positions. The frequency-dependent optical and magneto-optical properties, namely the reflectivity, the electron energy loss spectra, on-and off-diagonal conductivity tensor and the polar Kerr effect, are calculated for comparison with available experimental data. Our calculated MO resonance in In 1-x Mn x Sb (x=1.56%) are found to be in good agreement with corresponding experimental MO spectra. The origin of the large Kerr rotation is discussed.

High-quality ZnO:Co thin films were synthesized on the sapphire (0001) substrates by pulsed laser deposition. XRD result reveals that the Zn1-xCoxO films are of wurtzite-type crystal structure with x up to x = 0.35. The structural, optical and magnetic properties of ZnO:Co thin films are studied by experiments and theoretical calculations. Electronic structure of ZnO:Co with native defects are studied by the first-principles density functional theory. The experimental data and theoretical data have demonstrated quite good agreement. The optical and magneto-optical properties, namely, on-and off-diagonal conductivity tensor and the transversal Kerr effect (TKE), are calculated for comparison with available experimental data. The origin of observed TKE peaks is discussed..

The electronic spectra and relative permittivity of ultrathin (1–3 QL) films of Bi 2 Se 3 topological insulator have been calculated by the density functional theory. The calculated spectra exhibit a characteristic feature: the range of 0.0–0.9 eV below the Fermi level contains two doubly degenerate valence bands (“U-bands”), which are geometrically congruent to low-lying spectral branches in the conduction band. It has been shown that the saturation of optical absorption can result in a significant rearrangement of the electronic structure and properties in the near infrared spectral range in the considered film. In particular, the semiconductor (in the absence of interaction with light) type of conductivity of the film can be changed to the metallic type of conductivity strongly nonlinear in the intensity of light.

This letter presents the first-principles study of a three-dimensional (3D) topological insulator (TI) Bi2Se3 doped with magnetic atoms of 3d-transition metal (TM), Cr or Fe. Calculations are performed within the density functional theory (DFT) and a modified potential of Becke and Johnson (MBJ). Using the MBJ scheme, we show that both systems are semiconductors with a direct gap of 0.21 eV (Bi2Se3:Cr) and 0.27 eV (Bi2Se3:Fe), respectively. The magnetic structures of studied materials are, however, different: Bi2Se3:Cr exhibits a clear ferromagnetic (FM) order, while Bi2Se3:Fe has an antiferromagnetic (AFM) order. In view of the great scientific and practical interest to the 3D FMTI systems, the optical and magneto-optical spectra of Bi2Se3:Cr are calculated.

The results of a comprehensive study of magnetic, magneto-transport and structural properties of nonstoichiometric MnxSi1-x (x ≈ 0.51-0.52) films grown by the Pulsed Laser Deposition (PLD) technique onto Al2O3(0001) single crystal substrates at T = 340°C are present. A highlight of used PLD method is the non-conventional (“shadow”) geometry with Kr as a scattering gas during the sample growth. It is found that the films exhibit high-temperature (HT) ferromagnetism (FM) with the Curie temperature TC ∼ 370 K accompanied by positive sign anomalous Hall effect (AHE); they also reveal the polycrystalline structure with unusual distribution of grains in size and shape. It is established that HT FM order is originated from the bottom interfacial self-organizing nanocrystalline layer. The upper layer adopted columnar structure with the lateral grain size ≥50 nm, possesses low temperature (LT) type of FM order with Tc ≈ 46 K and contributes essentially to the magnetization at T ≤ 50 K. Under these conditions, AHE changes its sign from positive to negative at T ≤ 30K. We attribute observed properties to the synergy of distribution of MnxSi1-x crystallites in size and shape as well as peculiarities of defect-induced FM order in shadow geometry grown polycrystalline MnxSi1-x (x ∼ 0.5) films.

Silicon (Si) is currently the basis of most of nanodevice technology, therefore ultrathin materials based on Si have the great advantage of easy integration into existing circuitry. First flat silicon nanoparticles have been obtained with perfluorophenyl (PFPh) ligand coating. The size of these particles varied from 15 to 50 nm. Their thickness evaluated with the atomic force microscopy was about 3.3 nm. Based on ab initio DFT calculations we investigate the geometries and electronic structures of free-standing PFPh-stabilized 2D silicon in order to see if such systems have promising electronic and optical properties. We also examined the effect of doping PFPh-stabilized 2D silicon by the Mn atoms.

We present the results of a comprehensive study of magnetic, magneto-transport and structural properties of nonstoichiometric MnxSi1-x (x=0.51-0.52) films grown by the Pulsed Laser Deposition (PLD) technique onto Al2O3(0001) single crystal substrates at T = 340C. A highlight of our PLD method is the using of non-conventional (shadow) geometry with Kr as a scattering gas during the sample growth. It is found that studied films exhibit high-temperature (HT) ferromagnetism (FM) with the Curie temperature TC 370 K accompanied by positive sign anomalous Hall effect (AHE); they also reveal the layered polycrystalline structure with a self-organizing grain size distribution. The HT FM order is originated from the bottom interfacial nanocrystalline layer, while the upper layer possesses the low temperature (LT) type of FM order with TC = 46 K, gives essential contribution to the magnetization below 50 K and is homogeneous on the nanometer size scale. Under these conditions, AHE changes its sign from positive to negative at T < 30 K. We attribute observed properties to the synergy of self-organizing distribution of MnxSi1-x crystallites in size and peculiarities of defect-induced FM order in PLD grown polycrystalline MnxSi1-x (x 0.5) films.

The paper reports on the comprehensive study of properties of nonstoichiometric Si1−xMnx alloys slightly enriched in Mn (x≈0.51–0.55) as compared to the stoichiometric monosilicide MnSi. Mosaic type Si1−xMnx films 55–70nm in thickness were produced by the pulsed laser deposition (PLD) method onto the single crystalline Al2O3 substrates at 340°C. The Curie temperature TC in nonstoichiometric Si1−xMnx (x≈0.52–0.55) films exceeds room temperature, while in their stoichiometric counterpart, MnSi, the TC value does not exceed ≈30К. The consistent data on anomalous Hall effect and transverse Kerr effect prove the global character of ferromagnetic (FM) order caused by magnetic defect formation rather than the presence of FM clusters. Аt Mn content x≤0.55, the magnetization data testify to a good homogeneity in the distribution of magnetic defects without their segregation: variations of the saturation magnetization Ms do not exceed 6% in the temperature range T=10–100К and are well described by the Bloch law. It is also revealed that textured high-quality Si1−xMnx films with x≈0.52 and ТС~300К could be formed by PLD method in the “shadow” geometry (at lower energy of deposited atoms).

Ab initio study is reported on the electronic and magnetic properties of high-pressure-synthesized compounds M GaSb and M Ga2Sb2 (M = Mn, Cr). Based on comparison of obtained results, we discuss trends in the properties of these systems under change of 3d constituent. It is shown that CrGa2Sb2 stands out among the other compounds due to peculiarities of its electronic structure, which lead to very low and anisotropic conductivity. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

X-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectra at the L2,3 edges of Mn in (Ge,Mn) compounds have been measured and are compared to the results of first principles calculation. Early ab initio studies show that the Density Functional Theory (DFT) can very well describe the valence band electronic properties but fails to reproduce a characteristic change of sign in the L3 XMCD spectrum of Mn in Ge3Mn5, which is observed in experiments. In this work we demonstrate that this disagreement is partially related to an underestimation of the exchange splitting of Mn 2p core states within the local density approximation. It is shown that the change in sign experimentally observed is reproduced if the exchange splitting is accurately calculated within the Hartree–Fock approximation, while the final states can be still described by the DFT. This approach is further used to calculate the XMCD in different (Ge,Mn) compounds. It demonstrates that the agreement between experimental and theoretical spectra can be improved by combining state of the art calculations for the core and valence states respectively.

The structural, transport, magnetic, and optical properties of high-pressure-synthesized metastable compounds CrGaSb and CrGa2Sb2 are calculated from first principles. In addition to theoretical results, new X-ray structural measurements of CrGa2Sb2 up to 9 GPa are reported. Both high-pressure phases CrGaSb and CrGa2Sb2 are found to be at the edge between metal and semiconductor, which implies that the standard density functional theory predictions may be misleading. To clarify the situation, a study is conducted whether the results depend significantly on the approximation used for the exchangecorrelation potential. A possible effect of slight nonstoichiometry found in the CrGa2Sb2 samples is also investigated. The calculation results agree with most available experimental data and are internally consistent, which provides the assurance that, as a whole, they give a reliable picture of electronic properties in CrGaSb and CrGa2Sb2. (c) 2012 Wiley Periodicals, Inc.