Mn 3d States Research Articles

Hydrostatic-pressure-dependent electronic and optical properties of tungstate MnWO4: A first-principles study

The dependence of electronic structure and optical properties of tungstate MnWO4 on hydrostatic pressure is presented using the first-principles method based on density functional theory. The calculation results show that the energy band gap of MnWO4 decreases along three different stages with pressure increasing, from which it is deduced that the material will transform into the metal state at about 134.7 Gpa. Meanwhile, the crystal structure of MnWO4 also undergoes three different stages. Besides, it is found that the energy range of Mn 3d states and O 2s states expand gradually with pressure as well the peak of them reduce accordingly. In addition, the results show that the peaks’ position in the imaginary part of dielectric function and the absorption band edge of MnWO4 are also influenced by the external pressure.

First principles study on ferromagnetism of diluted magnetic semiconductor Li(Zn, Mn)N

Based on the first-principles calculations, the ferromagnetic origin and magnetic mechanisms of the Li(Zn, Mn)N system were investigated. The systems with different concentrations of magnetic moments and carriers were established. Compared with the Li16+y(Zn15Mn)N16 systems, the Li16+y(Zn14Mn2)N16 systems are more stable. Different from the Li15(Zn14Mn2)N16 system, Li16(Zn14Mn2)N16 and Li18(Zn14Mn2)N16 systems are anti-ferromagnetic semiconductors; the ferromagnetic state of the Li17(Zn14Mn2)N16 system is the preferred state. The spin magnetic moments mostly originated from Mn-3d states strongly hybridized with the N-2p and Li-2s states around the Fermi level. The ferromagnetic mechanism can be explained by the Mn-N-Mn chain with the p-d hybridization.

Electrical resistivity, magnetism and electronic structure of the intermetallic 3d/4f Laves phase compounds ErNi2Mnx

The non-stoichiometric intermetallic compounds RENi2Mnx (RE = rare earth) with the cubic MgCu2-type structure display a large variety of magnetic properties which is due to a complex interplay between the degrees of freedom of the 3d and 4f electrons and their interactions. We performed a comprehensive study of the electrical resistivity, magnetic properties and the electronic structure of ErNi2Mnx (x =0, 0.25, 0.5, 0.75, 1, 1.25) compounds by employing a suitable set of complementary experimental approaches. We find an increase in electrical resistance compared to ErNi2 upon Mn doping, the residual resistivity ratio decreases with increasing manganese content. The Curie temperature exhibits a sharp increase to around 50 K for Mn concentrations x ≥ 0.5, whereas the saturation magnetization decreases with growing Mn content x ≥ 0.5. Valence band X-ray photoelectron spectroscopy reveals an increasing intensity of Mn 3d states near Fermi energy in dependence of Mn concentration and Curie temperature. Resonant photoelectron spectroscopy of ErNi2Mn0.75 reveals that the photoemission decay channels dominate the valence band spectra across the Er N5 and Mn L3 X-ray absorption maxima, whereas the L3VV Auger dictates the resonant valence band spectra close to and at the Ni L3 X-ray absorption edge.

Electronic structures and optical properties of Mn-doped LiCaN new diluted magnetic semiconductors

Using the first-principle density functional theory based on the full potential linearized augmented plane wave method, the geometric structures of new diluted magnetic semiconductor Li1± y (Ca1− x Mn x )N ( x =0, 0.125; y =0, 0.125) were optimized. The electronic structures and optical properties were calculated and discussed in detail. The results show that the magnetic and electrical properties of the doped system can be separately regulated by Mn doping and Li off-stoichiometry. When Mn doped in the system, the electrons of the Mn 3d split into triply degenerate t 2g and double degenerate e g energy levels. Meanwhile, the Mn 3d states hybridize with Ca 4s and N 2p states, leads to the systems display half-metallic ferromagnetism. In Li excess and insufficient compounds, the band gaps and magnetic moments decrease, while the Curie temperature and electrical conductivity increase, and they exhibit 100% spin injection. In addition, the half-metallicity of Li insufficient system enhances significantly. In Li excess compound, Jahn-Teller effect leads to the highest Curie temperature and the lowest formation energy. Comparing optical properties indicates that the imaginary part of dielectric function, complex refractive index function, optical absorption function and the imaginary part of photoconductivity are all affected by Li stoichiometry. The energy loss functions of the doped systems show obvious blue-shift effect and much stronger plasma resonant frequency, and the oscillating range of plasma is wider in Li excess and insufficient compounds.

Hybridization of electronic states and magnetic properties of self-doped La1−xMnO3+δ (0 ≤ x ≤ 0.15) perovskites: XANES study

Electron structure of self-doped La1−xMnO3+δ perovskites is studied with X-ray absorption spectroscopy by measuring the spectra at manganese L-edges and oxygen K-edge, and analyzing the results for Mn K-edge spectra and magnetization data. The observed change of Curie temperature is explained by the change of level of hybridization of Mn 3d states and the O 2p states, which was manifested by the parallel change of 2p3/2 and 2p1/2 spectra with x and TC.

Electronic structure and magnetic properties of the half-metallic ferrimagnetMn2VAlprobed by soft x-ray spectroscopies

We have studied the electronic structure of ferrimagnetic Mn2VAl single crystal by means of soft X-ray absorption spectroscopy (XAS), X-ray absorption magnetic circular dichroism (XMCD) and resonant soft X-ray inelastic scattering (RIXS). We have successfully observed the XMCD signals for all constitute elements, supporting the spin polarized states at the Fermi level. The Mn $L_{2,3}$ XAS and XMCD spectra are reproduced by the spectral simulation based on density-functional theory (DFT), indicating itinerant character of the Mn 3d states. On the other hand, V $3d$ electrons are rather localized since the ionic model can qualitatively explain the V $L_{2,3}$ XAS and XMCD spectra as well as the local dd excitation revealed by V $L_3$ RIXS.

First-principles study of electronic structures and optical properties of Mn and Cu doped potassium hexatitanate (K2Ti6O13)

Potassium hexatitanate (K2Ti6O13) is a kind of wide band-gap semiconductor material with potential applications in photocatalysis. Unfortunately, it only responds to the short wavelengths of ultraviolet light, which seriously limits the utilization efficiency of solar energy. To extend its response to visible light, a promising strategy is to partly substitute some other transition metals for the Ti element. In this work, the electronic structures and optical properties of Mn-and Cu-doped K2Ti6O13 are systematically investigated by the first-principles calculations with the aid of the CASTEP module in the Materials Studio software package. The PW91 exchange-correlation functional is used with a plane wave basis set up to a 340 eV cutoff. The computational results show that the Mn-and Cu-doped K2Ti6O13 have impurity bands mainly stemming from the mix of Mn or Cu 3d states with Ti 3d states and O 2p states. Compared with the band gap of pristine K2Ti6O13 (2.834 eV), the band gap of Mn-doped one becomes narrow (2.724 eV), and its impurity energy level in the middle of the band gap can be used as a bridge for electronic transitions to facilitate the absorption of visible light. Although the band gap of Cu-doped K2Ti6O13 slightly increases (2.873 eV), it could be greatly narrowed (1.886 eV) when taking into consideration the impurity energy levels closely connected to the valence band. In addition, the impurity energy levels may form a shallow acceptor and suppress the carrier recombination in the Cu-doped K2Ti6O13. As usual, the calculated imaginary part of dielectric function as a function of photon energy shows that the ε2(ω) value is nearly zero for pure K2Ti6O13 when the photon energy is less than 3.5 eV, whereas there are finite values and also some peaks for the Mn-and Cu-doped ones. These peaks may originate from the impurity energy levels, whose occurrence makes the electron excitation occur readily by low photon energy. Thus, the absorption edges in the doped ones can red-shift to the visible-light region with enhancing absorption intensity. Finally, the simulated absorption spectra of the pristine and doped K2Ti6O13 are consistent with their electronic structures, which further confirms the above analysis. All the results show that the Cu-doped K2Ti6O13 exhibits higher visible-light photocatalytic efficiency than the Mn-doped one. The current work demonstrates that the absorption of visible light can be realized by the Mn or Cu doped potassium hexatitanate, with the effect of the latter being better than that of the former. The obtained conclusions are of great significance for understanding and further developing the potential applications of K2Ti6O13 in the field of photocatalysis.

Electronic Structure and Visible-Light Absorption of Transition Metals (TM=Cr, Mn, Fe, Co) and Zn-Codoped SrTiO3: a First-Principles Study**Supported by the National Natural Science Foundation of China under Grant No 51474011, the Postdoctoral Science Foundation of China under Grant No 2014M550337, and the Key Technologies R&D Program of Anhui Province of China under Grant No 1604a0802122.

First-principles calculations are performed on the influence of transition metal (TM=Cr, Mn, Fe, Co) as codopants on the electronic structure and visible-light absorption of Zn-doped SrTiO3. The calculated results show that (Zn,Mn)-codoped SrTiO3 requires the smallest formation energy in four codoping systems. The structures of the codoped systems display obvious lattice distortion, inducing a phase transition from cubic to rhombohedral after codoping. Some impurity Cr, Mn and Co 3d states appear below the bottom of conduction band and some Fe 3d states are located above the top of valence band, which leads to a significant narrowing of band gap after transition metal codoping. The enhancement of visible-light absorption are observed in transition metals (TM=Cr, Mn, Fe, Co) and Zn codoped SrTiO3 systems. The prediction calculations suggested that the (Zn,Mn)- and (Zn,Co)-codoped SrTiO3 could be the desirable visible-light photocatalysts.

Electron localization in niobium doped CaMnO3 due to the energy difference of electronic states of Mn and Nb.

The electron localization in Nb-doped CaMnO3 is analyzed in terms of the space and energy distribution of electronic states employing first-principles calculations. The energy difference of Mn 3d states and Nb 4d states makes NbO6 octahedra impede electrical conduction, so the random distribution of Nb in lattices leads to the localization of electrons near the bottom of the conduction bands. Therefore, although more carriers are introduced when Nb-doping content increases, both the electrical conductivity and absolute thermopower decrease in Nb heavy doped CaMnO3. The calculated transport properties agree well with the experimental data, supporting the analysis of localization.

Theoretical study of electronic and optical properties of antiferromagnetic β-MnS using the modified Becke Johnson (mBJ) potential

We have investigated the electronic and optical properties of β-MnS with III-type antiferromagnetic ordering using full potential linearized augmented plane wave (FP-LAPW) method within the framework of the spin-polarized density functional theory as implemented in WIEN2k package. Firstly, it is proven that III-type antiferromagnetic ordering is stable in comparison with others from the total energy calculated using the Perdew-Burke-Ernzerhof (PBE) functional. Then, we study the electronic properties of β-MnS for an energy range from −5 eV to 5 eV using mBJ exchange and PBE semilocal correlation, our calculations show an indirect energy band gap of 2.275 eV and the strong hybridization of Mn-3d states and S-3p state in valence band. Additionally, we also investigate the effect of spin-orbit coupling on the electronic properties, this causes a very slight red-shift in both Mn-3d and S-3p states but no change of energy gap is observed. Finally, the linear optical properties such as absortion coefficient, reflectivity, energy loss function, refractive index, extinction coefficient and optical conductivity have been derived from calculated complex dielectric function for energy from 0 eV to 24 eV considering all the three polarization directions (E//x, E//y and E//z). The obtained results indicate that β-MnS is an optically isotropic material when the energy is small and it becomes anisotropic for high energy.

First principle investigations of the Pbnm phase BiFeO3, BiFe0.875Mn0.125O3 and Bi0.875X0.125Fe0.875Mn0.125O3 (XBFM) (X = Ce, Gd, Lu)

The structural, magnetic, electronic and optical properties of Pbnm BiFeO[Formula: see text] (BFO), BiFe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (BFM), Bi[Formula: see text]X[Formula: see text]Fe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (XBFM) (X = Ce, Gd, Lu) have been investigated by the first principles within the PBE[Formula: see text]+[Formula: see text]U scheme. It is shown that the dopant Mn in the B sites and Ce (Gd, Lu) in the A sites improves the crystalline quality. The magnetic moments of Bi[Formula: see text]Ce[Formula: see text]Fe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (CBFM) and Bi[Formula: see text]Gd[Formula: see text]Fe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (GBFM) are 10 [Formula: see text] and 16 [Formula: see text] which mainly arises from the strongly localized unpaired 4f electrons of Ce and Gd, 3d electrons of Mn and Fe. While, as BFM, the magnetic moment of Bi[Formula: see text]Lu[Formula: see text]Fe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (LBFM) is 9 [Formula: see text] indicating no effect on the magnetization is made by Lu for its full 4f states. The densities of states of the five systems hint that CBFM is metallic and BFM, GBFM, LBFM are still semiconductors. The metallic properties of CBFM arise from the hybridization between Ce-4f and Mn-3d states which leads the Mn [Formula: see text] states to be split into [Formula: see text] and [Formula: see text] lowering the bottom of the conduction band to cross the Fermi level. Furthermore, we also study the optical properties of Pbnm BiFeO[Formula: see text] (BFO), BiFe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (BFM), Bi[Formula: see text]X[Formula: see text]Fe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (XBFM) (X = Ce, Gd, Lu). In this work, the optical properties including the absorption spectrum, loss function, refractive index and reflectivity spectrum are discussed in detail.

Tuning of structural and optical properties by sintering of multiferroic GdMnO3 precursor

ABSTRACTMultiferroic GdMnO3 was synthesized by the modified sol-gel route. The GdMnO3 precursor were sintered for 2 hours at different temperatures ranging from 300 (GMO300) to 800°C (GMO800). X-ray diffraction pattern shows that the crystallinity improves with sintering temperatures. The Raman data and Fourier transform infrared analysis also support the X-ray diffraction data. UV-Visible spectrum of the sample GMO300 shows absorption peak at 2.39 eV whereas the completely crystallized sample sintered at 800°C (GMO800) shows two absorption bands at 2.25 and 2.56 eV. These bands are attributed to the Mn (d-d) transitions. Higher energy bands at (3.27 and 4.94 eV) of GMO700 and (3.26, 4.40, 4.74 and 5.08 eV) of GMO800 are attributed to the charge transfer transitions from O(2p) to Mn(3d) state. Moreover, the completely crystallized sample (GMO800) exhibits the signature of magneto-dielectric coupling.

Improving the emission of ultrasmall Mn-doped ZnInS quantum dots via Ag-induced trap state energy level

For ultrasmall Mn-doped quantum dots (QDs), the energy transfer of the exciton to the Mn is the key factor for Mn emission. Herein, the Ag-induced electron trap state energy level, which is an intermediate energy level between the conduction band (CB) and 4T1 of Mn, is proposed for improving the energy transfer. After doping the Ag and forming Ag&Mn:ZnInS QDs, most excitons will first be captured by the intermediate energy level and then be transferred to Mn d-states, leading to enhanced photoluminescence (PL) quantum yields (QY) of the QDs from the original 17% (Mn:ZnInS QDs) to 30% (Ag&Mn:ZnInS QDs).

ESTUDIO TEÓRICO DEL FERROMAGNETISMO DE LA SUPERFICIE m-GaN DOPADA CON Mn

Se realizaron cálculos de primeros principios para estudiar las propiedades estructurales, electrónicas y magnéticas de la superficie m-GaN dopada con manganeso (Mn). Este dopaje generó un momento magnético total de 4 µB debido a la interacción de los estados 2p-N y 3d-Mn. Se encontró que el dopaje de Mn es responsable del 82 % de la magnetización total de la superficie. Además, el dopaje generó cambios estructurales en la superficie y se evidenciaron en las distancias entre las capas atómicas “d12, d23, d34, d45”. La superficie mostró propiedades de metal y semiconductor simultáneamente, estos materiales son llamados “half-metalic”, dependiendo de la polarización del espín. Se determinó la posición sustitucional del dopaje mas estable energéticamente, así mismo se observó que este dopaje generó menos cambios estructurales como lo muestran los porcentajes de cambio en las distancias entre capas atómicas “∆d12, ∆d23, ∆d34, ∆d45”

The electronic and magnetic properties of wurtzite Mn:CdS, Cr:CdS Mn:Cr:CdS: first principles calculations

In this article, density functional theory (DFT) based on generalized gradient approximation (GGA) and GGA+U, U is Hubbard term, is used to study the electronic properties of CdS doped with different dopants (Cr, Mn). The calculations are carried out for Mn-doped CdS, Cr-doped CdS, and co-doping of Mn/Cr in CdS simultaneously. It is found that hopping of electrons is possible with Cr:CdS and Mn:Cr:CdS while Mn:CdS does not allow the hopping of electrons. Moreover, double exchange interactions are observed in Cr:CdS and d-d super-exchange interactions are observed in Mn:CdS. Now the problem becomes interesting when one magnetic ion (Cr) supporting double exchange interactions and another ion (Mn) supporting d-d super-exchange interactions are doped simultaneously in the same system (CdS). The co-doped CdS is more stable even at high Curie temperature due to p-d double exchange interactions and d-d super exchange interactions. Furthermore, the Cr-3d and Mn-3d states present in-between the band gap are responsible for inner shell transitions and hence for optical properties. Therefore, the co-doped system is taken into account to enhance its applications in the field of spintronic and magneto-optical devices.

Hole doping effect on the electronic structure of layered oxypnictide LaOMnAs

Layered oxypnictide LaOMnAs shows an antiferromagnetic insulator-to-ferromagnetic metal transition at room temperature with increasing the defect of LaO layer which induces hole doping into the MnAs layers. In order to reveal the details of the transition, we have performed hard-X-ray photoelectron spectroscopy for the insulating LaOMnAs and metallic (LaO)0.7MnAs. The spectral changes in the valence band, mainly composed of Mn 3d states, Mn 2p core levels, and La 3d core-levels have been observed across the transition. Our results indicated that Mn 3d state was significantly influenced by the defect of LaO layer.

Photocatalytic improvement of Mn-adsorbed g-C3N4

This study employed experimental results and theoretical calculations to investigate Mn-adsorbed g-C3N4 as a potential photocatalyst with high efficiency. Mn was chosen as the incorporating element, because among the 3d transition metals it exhibits the highest binding energy and most suitable band edge positions. The photocatalytic efficiency of Mn-adsorbed g-C3N4 is 3 times higher that of pristine g-C3N4. Although small variations in the phase and surface morphology were observed, which were confirmed to not be the determining factors to improve efficiency. The factors that affect the high photocatalytic efficiency are therefore the electronic structure, optical absorption, and band edge variations after Mn-adsorption. The Mn atoms stably are bonded with N atoms, due to the strong absorption energy and ionic bond. Moreover, reduction of the g-C3N4 band gap after Mn-adsorption results in a red shift of the absorption band edge. The half-filled Mn 3d state introduces impurity states into the forbidden band gap, which will increase the life time of charge carriers. In addition, the up-shifting of band edges of Mn-adsorbed g-C3N4 leads to inhibition of the electron-hole recombination. As a consequence, the photocatalytic efficiency of Mn-adsorbed g-C3N4 is enhanced due to the combination of the aforementioned effects.

Optical absorption spectrum and electronic structure of multiferroic hexagonal YMnO3 compound

Optical absorption (OA) spectrum and electronic structure of the hexagonal YMnO3 compound have been investigated by employment of the first-principles calculations based on density functional theory. The calculations were performed upon the ferroelectric structure of the YMnO3, by testing various approximations of the exchange-correlation effects between the Mn d-electrons and considering two types of magnetic ordering of the Mn sub-lattice: (1) collinear anti-ferromagnetic order of the G-type and (2) non-collinear antiferromagnetic order that correspond to magnetic space group P63. The results demonstrate that satisfactory agreement between the theoretical and the experimental OA spectrum can be achieved only if both non-collinear anti-ferromagnetic order of the Mn spins and strong correlations between the Mn d-electrons are taken into account. The latter is found to be best described by effective Hubbard parameter Ueff = 2.55 eV. The principal features of the OA spectrum are interpreted in terms of calculated electronic structure. It is found that the most important, threshold 1.6 eV OA peak is generated by electron transitions from strongly hybridized occupied Mn d- and its neighboring in-plane O p-states to unoccupied Mn d-states. It is also concluded that the electronic gap (calculated as ∼1.1 eV) should be smaller than the optical one (∼1.6 eV).

First-principles calculation the electronic structure and the optical properties of Mn-decorated g-C3N4 for photocatalytic applications

The electronic structure and the optical properties of Mn-decorated graphitic carbon nitride (g-C3N4) were investigated using the density functional method. The large absorption energy of the Mn atoms on the g-C3N4 surface was found to suppress the clustering of the Mn atoms, which led to a conservation of the photocatalytic activity. The electronic structures of the Mn-decorated g-C3N4 showed that impurity energy levels emerged in the forbidden band of g-C3N4 and that the band edge of g-C3N4 shifted upward to 0.40 eV. In addition, the calculated optical constants showed that the novel photon absorption in the range of visible light originated from electronic transitions from the N 2p states in the upper valence band to impurity Mn 3d states. Moreover, the photon absorption reached a maximum when all sites of triangular N holes were decorated with Mn atoms. Our results provide evidence that the Mn-decorated C3N4 system could be a highly-efficient photocatalyst for solar light due to the extension of the range of photon absorption to include almost all visible light.

Electronic structure of RMn2Si2 (R = Y, La) intermetallics: DFT and XPS studies

The first-principles density functional theory (DFT) calculations of layered RMn2Si2 (R = Y, La) intermetallic compounds with Mn-adjacent layers separated by two Si non-magnetic layers and between them – R-layer (the ThCr2Si2-type structure), are presented. The analysis of the partial and total densities of states (DOS) of both compounds (YMn2Si2 and LaMn2Si2) demonstrates their metallic and magnetic character as well. The noncollinear magnetic ordering with canted moments is found in LaMn2Si2 with moments of 2.99 μB and 0.02 μB for the Mn and the La ions, respectively. In YMn2Si2 the Mn moments form the collinear antiferromagnetic order, and the Y ions are nonmagnetic. Calculated charge density distribution within the cell of RMn2Si2 indicates a covalent bonding between the Mn- and Si-layers of the compound and ionic type of bonding for R ions. It is found that hybridization of the Mn 3d-states with Si 3p-states induces a slight magnetization of Si ions for both compounds. In LaMn2Si2, as compared with YMn2Si2, the MnSi and Mn-R hybridization is weakened as a result of crystal lattice expansion, orbital momentum appearance and spin-orbit interaction influence. Therefore, the Mn d3z2-r2 and dx2-y2 states can participate in the MnMn intra- and interplane interactions, which is likely the reason of formation of the canted magnetic structure. The results of DFT calculations are in agreement with specially performed XPS measurements of YMn2Si2 and LaMn2Si2.