Mn 3d Electrons Research Articles

Tuning the magnetic properties of nonmagnetic monolayer Mo2C by doping and adsorption

For purpose of probing doping and adsorption induced ferromagnetism in nonmagnetic behavior of Mo2C monolayer, the electronic and magnetic properties of a transition metal atom (TM = V, Cr, Mn, Fe, Co, Ni) doped/adsorbed in/on Mo2C monolayer are researched by first principles methods. Firstly, both pristine and TM-doped/adsorbed in/on Mo2C monolayer show the metallic character. For Mn/Co-doped Mo2C monolayer, they present ferromagnetism with the total magnetic moments of 0.656 μB and 0.722 μB, which mainly come from the 3d electrons of Mn and Co sites. Moreover, the Cr/Mn/Fe/Co atom adsorption on Mo2C monolayer exhibit spin-polarized character. The exchange splitting in the d shell is discovered in Cr/Mn/Fe/Co-adsorbed onto monolayer Mo2C. Finally, the positive value of MAE for Co-doped and Cr/Mn/Co-adsorbed Mo2C systems indicates an out-of-plane easy axis, whereas the negative MAE value for Mn-doped Mo2C monolayer and Fe adsorption on Mo2C monolayer implies the easy axis in the surface.

Possible Heavy-Fermion State in \(\mathcal{P}\mathcal{T}\)-Symmetric Antiferromagnet CeMnSi

The magnetic properties of CeMnSi with a tetragonal crystal structure were investigated for the first time using single crystals. CeMnSi exhibits an antiferromagnetic (AFM) ordering of Mn-3d electrons at TN = 242 K, whereas Ce-4f electrons remain paramagnetic down to the lowest temperature with the following characteristic behaviors: a moderately enhanced Sommerfeld coefficient, a steep decrease in electrical resistivity at low temperatures, and an almost temperature-independent magnetic susceptibility at low temperatures despite a Curie–Weiss increase at high temperatures. From these results, we propose that a noble correlated electron state is realized even in the Mn-AFM ordered state and is protected by the space–time (\(\mathcal{P}\mathcal{T}\)) inversion symmetry inherent in the Mn-AFM ordering. We also show systematic changes in the lattice parameters of RTSi (R = rare-earth elements, T = Mn, Fe, and Co), providing the basis for understanding the unique electronic properties of CeTSi.

Formal Valence, Charge Distribution, and Chemical Bond in a Compound with a High Oxidation State: KMnO4

KMnO4 has unusual formal manganese oxidation state Mn+7 that seems puzzling: the energy of creating such ion (119 eV) is much greater than the energy of chemical bonds (up to ~10 eV). We have used the Wannier functions formalism to analyze the distribution of Mn-3d electrons and O-2p electrons for empty electronic states in the {text{MnO}}_{4}^{ - } complex and have found that, while formally one has {{d}^{0}} configuration for manganese ion in this compound, in reality only about one-half of the hole density described by these Wannier functions corresponding to this configuration belongs to d-electrons, while the other half is spread over surrounding oxygen atoms. This corresponds much more to Mn+7 state than to Mn+2, because the calculated total number of d‑electrons is equal to 5.25. Our analysis has also sown nearly perfect covalent type of chemical bond within the {text{MnO}}_{4}^{ - } complex with negligible contribution of the ionic part.

Photoferroic prospective of multiferroic HoMnO3 compound, evaluated on the base of the DFT study of its magnetic, electronic, and optical properties

In this work, non-collinear spin density functional theory based all-electron full-potential linearized augmented plane wave electronic structure method have been employed to study magnetic, electronic, and optical properties of multiferroic HoMnO3 compound in order to evaluate its potential to be used in photovoltaic applications. Exchange and correlation effects of the Ho 4f- and Mn 3d-electrons were treated on the base of the local spin density approximation including effective Hubbard (Ueff) correction. We concluded that the ground state magnetic structure should be described by Γ3 irreducible representation of the P63cm space group, for both the Mn and the Ho magnetic sub-lattices. The calculated indirect and direct band gaps, corresponding to the transition from the O 2p-to the Mn 3d-states, are found to be 1.25 eV and 1.4 eV, respectively, in very good agreement with the experimental findings. Calculated dielectric tensor spectra are found to be in satisfactory agreement with the experiment as well. On the base of these results, we investigated photoferroic properties of the HoMnO3 by calculating its absorption coefficient spectrum and the effective mass tensor of the photogenerated electrons and holes. By comparing results with those of isostructural LuMnO3 and the YMnO3 multiferroics, we concluded that the HoMnO3 exhibits similar photoferroic properties, a fact that classifies it as a material suitable for photovoltaic applications.

Tuning the magnetic ordering driven by cationic antisite defects in the Li(ZnMn)As system.

The electronic structure and magnetic properties of Li(ZnMn)As with antisite defects have been investigated by using first-principles calculations within the Perdew-Burke-Ernzerhof generalized gradient approximation. The cation antisite defect induced by Zn substitution for As was considered. Mn-3d, As-4p, Zn-4s, and Zn-4p were involved in the formation of d-sp hybrid orbitals, which enhanced the non-localized properties of Mn-3d electrons and provided a channel of Mn(↑)-As(↓)-ZnAs(↓)-Mn(↑) for indirect exchange of electrons between the magnetic ions. The antisite defect of Zn-substituted As belonged to the acceptor doping, rendering the compound p-type characteristics. The existence of the extra free hole carriers regulated the magnetic ordering transition. The ferromagnetic coupling between the Mn magnetic dopants was more favorable in the system with an antisite defect. In this paper, a novel type of dilute magnetic semiconductor with controllable carriers was designed and the mechanism of ferromagnetic coupling was revealed, which provided a theoretical reference for the subsequent studies.

Understanding the effect of Ni and Co doping in magnetic properties of La0.7Ca0.3MnO3: Magnetic Compton spectroscopy and DFT strategies

Magnetic Compton profiles (MCPs) of La0.7Ca0.3Mn0.95(Ni/Co)0.05O3 between 8 and 250 K have been measured using high energy inelastic scattering at SPring-8, Japan. For a quantitative analysis on amendment of magnetic properties, temperature-dependent experimental MCPs are decomposed into constituent profiles related to Mn, Ni/Co and itinerant (diffuse) electrons. Decomposed profiles unambiguously show that Mn-3d electrons are ferromagnetically coupled with Ni/Co ions while itinerant electrons are linked anti-ferromagnetically with Mn-3d and Ni/Co-3d electrons. An annotation of MCP and VSM data depicts that the orbital magnetic moments are anti-ferromagnetically coupled to total spin moments. Variation in magnetic response in undoped and Ni/Co doped perovskites is devoted to formation of mixed valence states of Mn atom. The spin contribution at different sites are found to be in tune with present density functional theory (DFT) based calculations which are thoroughly analyzed on the basis of changes in the eg and t2g states of Mn, Ni/Co caused by Jahn-Teller distortion. Present MCP data and DFT calculations set guidelines to probe the reliable origin to examine magnetic response and half-metallic properties of such manganites.

Study on formation, electronic states evolution and spin polarization transition for MnGa compound under an anisotropic stress

The Formations, stabilities, evolutions of geometries, electronic states together with the spin polarization transitions involved with magnetic properties of the MnGa compound under c axis anisotropic stress are systematically studied within the framework of density functional theory analyzing method. The results show that the anisotropically geometric expansion can be induced under stress. There are five kinds of atomic distances within the compound, with larger distance values for Mn–Mn and Ga–Ga, and smaller distances for Mn–Ga. The induced atomic distance fluctuations are also anisotropic, corresponding to the anisotropic binding strength regulations. The compound under stress is more stable. The s orbital releases electrons, the p and the d orbitals accept electrons for Mn. The s orbital and the d orbital release electrons, the p orbital traps electrons for Ga. The Mn1 and Mn2, Ga1 and Ga2 have diversified configurations under stress. A transition of ionic state of Mn2 is observed. Electrons transfers occur between orbitals and species under stress. The MnGa has anisotropic conductor band structure. The effective mass of conduction band as well as shallow valence band are enhanced under stress. The electronic band experiences a transition from semimetal into metal. The s, p and d electrons form the conduction band and shallow valence band. The d electrons mainly form the deep valence band, too. The localization at −16.8eV of d electrons is weakened under stress. The Mnd electrons get less responsible for the spin state under stress. The Mn1 and Mn2 turn to exhibiting distinctively diverse profiles, the Ga1 and Ga2 turn to exhibiting the same profiles under stress. The Mn shows strong atomic magnetic moment than that of Ga.

The spin-resolved electronic structure of the codoped crystals Si < B, V>, Si < B, Cr > and Si < B, Mn>

First, we have evaluated the spin-resolved electronic structure of crystals Si < B, V>, Si < B, Cr > and Si < B, Mn > with the exchange-correlation energy in a form of generalized gradient approximation (GGA-PBE). Next, the strong correlation effects of the V, Cr and Mn 3d electrons have been taken into account by means of the hybrid exchange-correlation functional PBE0. All the calculations have been done for supercells Si30B1V1, Si30B1Cr1, and Si30B1Mn1, modeling the substitutional alloys based on silicon crystal. In the pseudogap materials we are considering here, the Fermi level lies in the valence band. Without taking into account the strong correlations of the 3d electrons of the transition elements, we found the following properties of the materials under study. For the spin up the SiBV has an indirect pseudogap, the SiBCr is a direct gap material, and the SiBMn is an indirect pseudogap material. For the spin down these materials are a direct gap, direct pseudogap and indirect gap materials, respectively. Taking into account the strong correlations of the 3d electrons of the transition elements, we found the following properties of these materials. For the spin up the SiBV and SiBCr are the direct gap materials and SiBMn has an indirect pseudogap. For the spin down the SiBV is a direct pseudogap material, and the SiBCr is an indirect pseudogap compound, and SiBMn has a direct band gap.

First-principles investigations of geometrical and electronic structures of Mn4+ doped A2SiF6 (A= K, Rb, Cs) red phosphors

The first-principle calculations of the structural and electronic properties for a series of the Mn 4+ doped A 2 SiF 6 ( A = K, Rb, Cs) phosphors within a density functional theory are performed to investigate influence of the first cation on the crystal field strength 10 Dq and energy of the Mn 4+ 2 E→ 4 A 2 red emission transition. The structural changes due to an inclusion of the Mn 4+ ions into A 2 SiF 6 hosts are studied in detail here. The obtained results show that the shorter Mn–F bond length leads to higher emission energy of 2 E→ 4 A 2 transition and 10 Dq value. The emission energy for 2 E→ 4 A 2 transition and 10 Dq parameter of the Mn 4+ doped A 2 SiF 6 have been estimated using different functionals, such as conventional electron-electron correlation functional, generalized gradient approximation and local density approximation, the Hubbard type correction, i.e., DFT + U method, to the Mn 3d electrons, to identify most suitable calculating settings for the studied systems. • The first-principle calculations were carried out for Mn 4+ doped A 2 SiF 6 ( A = K, Rb, Cs). • 10 Dq and energy of the Mn 4+ 2 E.→ 4 A 2 red emission transition has been obtained. • Shorter Mn–F bond length leads to higher emission energy of 2 E.→ 4 A 2 transition and 10 Dq value. • Some electron-electron correlation functionals were examined.

Intrinsic ferromagnetic semiconductors in rhombohedral RMnO3 (R = Sc, Y, and Lu) with high critical temperature and large ferroelectric polarization

Ferromagnetic (FM) semiconductors have been recognized as the cornerstone for next-generation highly functional spintronic devices. However, the development in practical applications of FM semiconductors is limited by their low Curie temperatures (T C). Here, on the basis of model analysis, we find that the FM super-exchange couplings in the d 5 − d 3 system can be significantly strengthened by reducing the virtual exchange gap (G ex) between occupied and empty e g orbitals. By first-principle calculations, we predict robust ferromagnetism in three rhombohedral RMnO3 (R = Sc, Y, and Lu) compounds with the T C that is as high as ∼1510 K (YMnO3). The oxygen breathing motions open a band gap and create an unusual Mn2+/Mn4+ charge ordering of the Mn-d electrons, which play an important role in altering the G ex. Interestingly, the rhombohedral RMnO3 compounds are also ferroelectric (FE) with a large spontaneous polarization approaching that of LiNbO3. These results not only deepen the understandings of magnetic couplings in d 5 − d 3 system, but also provide a way to design room-temperature FM–FE multiferroics.

Thermoelectric Properties of Sm Doped CaMnO&lt;sub&gt;3&lt;/sub&gt; Using Density Functional Theory Method

The electronic structure and thermoelectric properties of CaMnO3 doped with 8% and 17% f block element Sm using first principles calculations and semi-classic Boltzmann theory were presented in this paper. The G-type AFM phase is most stable among five phases for CaMnO3, however, with 8% and 17% Sm doping, these compounds became nonmagnetic phases. CaMnO3 calculated electronic band structure shows an indirect band gap of 0.523 eV, which is underestimated by the density functional theory (DFT) calculations but the band gap explains the semiconducting behavior. However, with 8% and 17% Sm doping, the electronic bandstructure of these compounds exhibit metallic behavior, with Sm and Mn 3d electrons contributing to conduction band, increasing the magnitude of conductivity for doped compounds. All temperature dependence Seebeck coefficient plots show n-typed conduction for all compound with reduced magnitude of Seebeck coefficient for doped compounds. The temperature dependence thermal conductivity plot shows overall thermal conductivity is reduced in Sm doped compound. CaMnO3 with 17% Sm doping exhibit much higher ZT of 0.32 at 800 K showing enhanced thermoelectric properties at high temperature and suitability or high temperature energy conversion devices.

Effects of A-Site cation on the Physical Properties of Quaternary Perovskites AMn3V4O12 (A= Ca, Ce and Sm)

AMn3V4O12 (A = Ca, Ce and Sm) quaternary perovskites are studied in the domain of density functional theory using various potentials. Generalized gradient approximation along with Hubbard U and hybrid density functional schemes are found effective tools for the treatment of these compounds. Changing of A-site cation, affects the physical properties due to the valence distributions Ca+2Mn+23V+44O12, Ce+3Mn+23V+3.754O12 and Sm+3Mn+23V+3.754O12 respectively. Cohesive energy and enthalpy show that these compounds are thermodynamically stable. Electronic and electrical properties reveal the semi-metallic nature of these compounds. It is observed that in these compounds Aʹ-site (Mn) 3d electrons are localized and responsible for the magnetic properties whereas B-site (V) 3d electrons are delocalized, contributed in the electronic behavior. The elastic properties also confirm the stability and demonstrate that these compounds are ductile in nature. DFT as well as post−DFT treatments verify the anti-ferromagnetic nature of these compounds with the dominant Mn+2―O−2―Mn+2 super exchange interactions.

Parasitic Ferromagnetism in Few-Layered Transition-Metal Chalcogenophosphate.

Since the rise of two-dimensional (2D) semiconductors, it seems that electronic devices will soon be upgraded with spintronics, in which the manipulation of spin degree of freedom endows it obvious advantages over conventional charge-based electronics. However, as the most crucial prerequisite for the above-mentioned expectation, 2D semiconductors with adjustable magnetic interaction are still rare, which has greatly hampered the promotion of spintronics. Recently, transition metal phosphates have attracted tremendous interest due to their intrinsic antiferromagnetism and potential applications in spintronics. In the work described herein, parasitic ferromagnetism is achieved for the first time by exfoliating an antiferromagnetic chalcogenophosphate to a few layers. Taking the transition metal chalcogenophosphate Mn2P2S6 as an example, the antiferromagnetic transition at the Néel temperature is completely suppressed, and the magnetic behaviors of the as-obtained few-layered Mn2P2S6 are dominated by parasitic ferromagnetism. We experimentally verify an electron redistribution by which part of the Mn 3d electrons migrate and redistribute on P atoms in few-layered Mn2P2S6 due to the introduced Mn vacancies. The results demonstrated here broaden the tunability of the material's magnetic properties and open up a new strategy to rationally design the magnetic behaviors of 2D semiconductors, which could accelerate the applications of spintronics.

Synthesis, crystal structure, and magnetic properties of oxynitride perovskites SrMn0.2M0.8O2.6N0.4 (M = Nb, Ta).

Complex perovskites SrMn0.2Nb0.8O2.6N0.4 and SrMn0.2Ta0.8O2.6N0.4 were synthesized; these are rare examples of octahedral Mn2+ in oxynitride perovskites. Joint Rietveld refinement of neutron and X-ray data revealed that SrMn0.2Nb0.8O2.6N0.4 and SrMn0.2Ta0.8O2.6N0.4 had orthorhombic symmetries, in contrast with those of analogous perovskites SrM'0.2M0.8O3-xNx (M' = Li, Na, Mg; M = Nb, Ta), which are all tetragonal. Both SrMn0.2Nb0.8O2.6N0.4 and SrMn0.2Ta0.8O2.6N0.4 exhibited paramagnetic behavior with effective magnetic moments of 5.60μB and 5.94μB, respectively, consistent with a high-spin Mn2+ (d5, S = 5/2) state. The Weiss constants were -24.7 K for SrMn0.2Nb0.8O2.6N0.4 and -15.4 K for SrMn0.2Ta0.8O2.6N0.4, indicating the presence of weak antiferromagnetic spin-spin interactions. The band gaps of SrMn0.2Nb0.8O2.6N0.4 and SrMn0.2Ta0.8O2.6N0.4 were determined to be 1.75 eV and 2.2 eV, respectively, suggesting that the Mn 3d electrons were essentially localized.

First principle study of Mn-doped and vacancy on the magnetism and optical properties of CdS

The generalized gradient approximation method under the framework of spin polarization density functional theory combined with Hubbard U correction is used to study the effects of Mn-doping and vacancy on the magnetic properties and optical properties of CdS. The results show that the system is antiferromagnetic when the two Mn atoms are doped nearest-neighbor, the system has no magnetism when S vacancy. The system has ferromagnetism when Cd vacancy or two Mn-doping next nearest-neighbor, and they have a Curie temperature above room-temperature. The system is also ferromagnetic when doping and vacancy coexist. The magnetic source is the exchange between Mn-3d electrons or the electronic exchange of Mn-3d and unpaired 3s (3p) orbitals of S atoms near the vacancy. Mn single-doped absorption is strong in the visible range, and two Mn-doped systems have better transmission. The calculation of the formation energy shows that the two Mn-doped system is easy to form, but the Cd (S) vacancy are not easy to form experimentally.

Structural, thermodynamic, electronic and mechanical properties of spinel and phonon-harvested AMn2O4 (a: Li, Na, Mg) systems: A First-Principles study

First-principles calculations were carried out to investigate the structural, thermodynamic, electronic, elastic and vibrational properties of LiMn2O4, NaMn2O4 and MgMn2O4 systems at 0 K to mimic their stability trend. We have employed the plane-wave pseudopotential method framed within the density functional theory (DFT) as implemented in the VASP code. The Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional was used with the Hubbard U-correction in the rotationally invariant form to improve the description of the Mn 3d electrons. The calculated equilibrium lattice constants are in good agreement with the available data to within 2%, suggesting the validity of the approach employed. The analysis of the electronic structure showed that the spinel-structured LiMn2O4, NaMn2O4 and MgMn2O4 are half-metallic ferromagnets, due to the absence of the energy band gap around the Fermi level. The elastic constants and phonon dispersion curves suggested mechanical instability on the spinel-structured LiMn2O4, NaMn2O4 and MgMn2O4. Furthermore, all AMn2O4 spinels exhibited a brittle nature dominated by covalent bonding, since the Pugh ratio was less than 1.75. Having discovered that spinels AMn2O4 are mechanically unstable, novel polymorphs were harvested from their respective negative phonon frequencies. First-principles calculations were performed on the phonon-harvested systems and were found to exhibit good thermodynamic and mechanical stability over their spinel counterparts. Moreover, the phonon-harvested polymorphs were predicted to be magnetic semiconductors and ductile.

Revealing angular momentum transfer channels and timescales in the ultrafast demagnetization process of ferromagnetic semiconductors

Ultrafast control of magnetic order by light provides a promising realization for spintronic devices beyond Moore's Law and has stimulated intense research interest in recent years. Yet, despite 2 decades of debates, the key question of how the spin angular momentum flows on the femtosecond timescale remains open. The lack of direct first-principle methods and pictures for such process exacerbates the issue. Here, we unravel the laser-induced demagnetization mechanism of ferromagnetic semiconductor GaMnAs, using an efficient time-dependent density functional theory approach that enables the direct real-time snapshot of the demagnetization process. Our results show a clear spin-transfer trajectory from the localized Mn-d electrons to itinerant carriers within 20 fs, illustrating the dominant role of [Formula: see text] interaction. We find that the total spin of localized electrons and itinerant carriers is not conserved in the presence of spin-orbit coupling (SOC). Immediately after laser excitation, a growing percentage of spin-angular momentum is quickly transferred to the electron orbital via SOC in about 1 ps, then slowly to the lattice via electron-phonon coupling in a few picoseconds, responsible for the 2-stage process observed experimentally. The spin-relaxation time via SOC is about 300 fs for itinerant carriers and about 700 fs for Mn-d electrons. These results provide a quantum-mechanical microscopic picture for the long-standing questions regarding the channels and timescales of spin transfer, as well as the roles of different interactions underlying the GaMnAs demagnetization process.

Magnetic properties and spin momentum densities of Ni excess Ni-Mn-Sn Heusler alloys

Abstract The role of excess Ni in Ni2+xMn1−xSn (x = 0.05, 0.1) Heusler alloys has been reported using temperature dependent magnetic Compton spectroscopy. The experimental Compton profiles from magnetic electrons have been analyzed to quantify the contribution of Mn 3d electrons, Ni sites and sp-electrons in building-up the total spin moments. The experimentally deduced spin momentum densities, total and element-specific spin moments are examined using theoretical investigations within the spin polarized relativistic Korringa-Kohn-Rostoker method. The build-up of spin moments has been explored in terms of total and projected density of states. Site-dependent Ni magnetic moment is also discussed. Heisenberg exchange coupling parameters are also computed to study the change in Ruderman-Kittel-Kasuya-Yosida type exchange interaction on increasing Ni concentration in the Ni-Mn-Sn system.

Schottky specific heat of the lightly Mn-substituted electron-doped SrTiO3

Large changes in the low-temperature specific heat (low-T C) by applying magnetic fields up to 9 Tesla were found in the lightly Mn-substituted electron-doped perovskites Sr1−xLaxTiO3. The changes in the low-T C are qualitatively well explained by the Schottky specific heat (CSch) of localized spins of the Mn 3d electrons in weak internal magnetic fields via itinerant electrons. According to the analysis by using the conventional model, the doped Mn ions are apparently not Mn4+ (S = 3/2) ions, but are Jahn-Teller active Mn3+ (S = 2) ions or mixtures of Mn3+ and Mn2+ ions. However, the actual numbers of localized spins estimated from CSch are about 30% smaller than the expected values. Part of the localized spins of the Mn 3d electrons may disappear due to Kondo coupling with the itinerant electrons, leading to the observed enhancement of the electronic specific heat coefficients.

Electronic properties of [formula omitted]Al20 (R = La, Ce, Yb, Th, U; X = Ti, V, Cr and Mn) cage compounds

Non-spin-polarized electronic structures and Fermi surface properties of RX2Al20 (R = La, Ce, Yb, Th, U; X = Ti, V, Cr, Mn) intermetallic compounds were calculated using the full potential all-electron local orbital (FPLO) approach in the framework of the local density approximation (LDA). Trends of the magnetism are discussed in terms of the characteristics of X-3d bands with a quantitative analysis of the relationship between band electron filling and crystal electric field splitting. Since coordination icosahedra of X-atoms have small trigonal distortion, crystal electric field splits the fivefold degenerate X-3d state into low-energy singlet a1g and two higher-energy doublets eg. In RTi2Al20 and RV2Al20 the population of the related 3d sub-band is not sufficient to cause energetically favorable spin polarization, whereas magnetic instabilities develop in the RCr2Al20 series. Finally, a manifestation of strong repulsive interactions between itinerant Mn-d electrons become most pronounced in ferromagnetic UMn2Al20. The influence of non-magnetic R-f states on magnetic and thermodynamic properties is discussed with special emphasis on the role of the f–p and f–d hybridization. For LaTi2Al20 and LaV2Al20 the calculated quantum oscillation frequencies are in accord with experimental reports.