Mn-doped Compounds Research Articles

TB-mBJ for doping concentration effects on magneto-optical properties in [formula omitted] spintronics materials

An investigation for electronic, magnetic, and optical properties of Mn-doped ZnSnAs2 compound performed using advanced computational methods. Using spin-polarized density functional theory (DFT) calculations with local orbital linearized augmented plane wave (lo-LAPW) method and Tran–Blaha’s modified Becke–Johnson (TB-mBJ) functional, Mn-doped n-type chalcopyrite semiconductor ZnMnxSn(1−x)As2, studied within varying Mn doping concentration range 0≤x≤0.5. Doping of Mn to Sn site in pure ZnSnAs2 creates a strong spin effect, which makes it useful spintronic materials. We observed with increase the Mn concentration in ZnSnAs2, energy bandgap changes while the magnetic strength of the unit cell remains unchanged, showing stability of system’s magnetism. Optical properties of the Mn doped ZnSnAs2 compounds analysed in term of dielectric function, absorption spectra, and refractive index. Optical properties show, compound is optically low active in the Infrared (IR) region and more active in visible and ultraviolet (UV) region. The electronic and optical properties of Mn-doped ZnSnAs2, offer potential technological advancements in semiconductor device design technology and engineering.

Enhanced thermoelectric performance of CuSbSe2 via Mn doping

Ternary chalcostibite CuSbSe2 compound is known for low thermal conductivity. However, the poor electrical properties severely limit its thermoelectric performance. In this study, the Mn-doped CuSb1-xMnxSe2 (x = 0–0.04) samples were synthesized by vacuum melting with spark plasma sintering, and their thermoelectric properties were characterized. The results indicate that the impurity phase Cu3SbSe3 will be generated when Mn content x > 0.02, and the carrier concentration and mobility were optimized significantly for the Mn-doped compounds, thus enhancing the electrical transport performance. In terms of results, the PF increases from 1.3 × 102 to 2.18 × 102 µW m−1 K−2 at 673 K. Point defects and the second phase enhance phonon scattering and lead to a lower lattice thermal conductivity for CuSb1-xMnxSe2 compounds, the κl decreases from 0.39 to 0.26 W m−1 K−1 at 673 K. As a consequence, a maximum figure of merit ZT of ∼0.53 was achieved at 673 K for CuSb0.97Mn0.03Se2, which is 140 % higher than the intrinsic CuSbSe2.

Intrinsic thermal stability enhancement in n-type Mg3Sb2 thermoelectrics toward practical applications

Mg3Sb2-based Zintl compounds show great promise for thermoelectric power generation due to their favorable properties, such as high thermoelectric performance over a wide range of temperatures, low cost, and mechanical robustness. However, their practical application is severely impeded by the low thermal stability induced by significant Mg loss at elevated temperatures. Here, with the goal to intrinsically enhance the thermal stability of Mg3Sb2-based materials, a strategy of Mn doping at the Mg site is investigated and is found to be effective. In addition to having a high average zT, Mn-doped Mg3Sb1.5Bi0.5 exhibits negligible variation in electrical performance throughout a 40-hour continuous electrical properties measurement at 673 K. Microstructure and composition analyses verify the high structural stability of the Mn-doped sample following the long-term in situ measurement. Density functional theory (DFT) calculations show that the enhanced thermal stability of the Mn-doped compound results from the stronger bonding between Mn and Mg atoms in comparison to the Mg-Mg bonds, which can significantly suppress the formation of Mg vacancies. This study demonstrates a novel approach to the development of reliable thermoelectric materials with both a high zT and intrinsically improved thermal stability for applications.

Effects of the on-site energy on the electronic response of Sr3(Ir1−xMnx)2O7

We investigated the doping and temperature evolutions of the optical response of Sr3(Ir1−xMnx)2O7 single crystals with 0 ≤ x ≤ 0.36 by utilizing infrared spectroscopy. Substitution of 3d transition metal Mn ions into Sr3Ir2O7 is expected to induce an insulator-to-metal transition via the decrease in the magnitude of the spin–orbit coupling and the hole doping. In sharp contrast, our data reveal the resilience of the spin–orbit coupling and the incoherent character of the charge transport. Upon Mn substitution, an incoherent in-gap excitation at about 0.25 eV appeared with the decrease in the strength of the optical transitions between the effective total angular momentum Jeff bands of the Ir ions. The resonance energies of the optical transitions between the Jeff bands which are directly proportional to the magnitude of the spin–orbit coupling hardly varied. In addition to these evolutions of the low-energy response, Mn substitution led to the emergence of a distinct high-energy optical excitation at about 1.2 eV which is larger than the resonance energies of the optical transitions between the Jeff bands. This observation indicates that the Mn 3d states are located away from the Ir 5d states in energy and that the large difference in the on-site energies of the transition metal ions is responsible for the incoherent charge transport and the robustness of the spin–orbit coupling. The effect of Mn substitution was also registered in the temperature dependence of the electronic response. The anomaly in the optical response of the parent compound observed at the antiferromagnetic transition temperature is notably suppressed in the Mn-doped compounds despite the persistence of the long-range antiferromagnetic ordering. The suppression of the spin-charge coupling could be related to charge disproportionation of the Ir ions.

A comprehensive research on new DyCo2Mnx (x = 0.0–1.0) Laves phases

DyCo2Mnx (x = 0.0, 0.2, 0.4, 0.6, and 1.0) compounds were synthesised and found to all be single-phase, isostructural to DyCo2 (MgCu2 Laves phase cubic structure (Fd-3 m) at room temperature). DyCo2Mn exhibits a huge coercivity field HC = 21,170 Oe at 5 K. The magnetic transition at Curie temperature TC, was observed as first order for DyCo2 but second order for the Mn doped compounds. Using Kouvel-Fisher plot, critical isotherm analysis and Arrott-Noaks plot techniques, a detailed critical exponents analysis was carried out on these transitions: critical exponents β ≈ 0.5, γ ≈ 1.0, and δ ≈ 3.0 were derived indicating that all the second-order transitions belong exhibit long-range magnetic interactions during the magnetic transitions. High-resolution synchrotron X-ray measurements confirm that there are crystal structure transformations sychronised with the magnetic transitions from paramagnetism to ferrimagnetism (PM-FM) at TC in the x = 0.0 and 0.2 cases with crystal structure changing from cubic (Fd-3 m) to tetragonal (I41/amd), However structures remain cubic (Fd-3 m) for x = 0.4, 0.6, and 1.0.

Coexistence of Kondo effect and Weyl semimetallic states in Mn-doped MnxVAl3 compounds

The strong correlation effect in Weyl semimetal is a critical issue in condensed matter physics. Recently, the Kondo effect in Weyl semimetal was theoretically proposed but not yet experimentally realized. Here we suggest a coexistence of the Weyl semimetal and Kondo effect in disordered Mn-doped MnxVAl3. Dilute Mn-doping in type-II Dirac semimetal VAl3 increases the chemical potential so that Dirac point is close to the Fermi energy and lifts band degeneracy, leading to the Weyl semimetal phase transition. We observed a Kondo effect, confirmed by the resistivity minimum at TK = 40 K, and logarithmic increase of electrical resistivity, magnetic susceptibility, and specific heat divided by temperature with a significant Sommerfeld coefficient at low temperature. The angle-resolved magnetoresistance has revealed the negative longitudinal magnetoresistance below Kondo temperature due to chiral anomaly in Mn-doped MnxVAl3. At low temperature below Kondo temperature (T ≤ TK), the exchange interaction by RKKY interaction in MnxVAl3 breaks time-reversal symmetry even in Kondo screening, resulting in the topological phase transition from Dirac to Weyl semimetal. This research shows the coexistence of the Kondo effect and Weyl semimetallic state as well as the temperature-induced topological phase transition.

First principles calculations of the magnetic properties of PbTi1−xMnxO3

Electronic, optical, and magnetic properties of the Mn-doped PbTiO3 compound were investigated by using density functional theory (DFT). We revealed that this compound has an indirect band gap of 3.01 eV. The calculated complex dielectric functions were in good agreement with the available experimental results. Our calculation demonstrated that Mn substitution changes the nonspin-polarized state of pure PbTiO3 to the spin-polarized state. O and Pb vacancies do not exhibit magnetism. However, Ti vacancies cause magnetism in the crystal, and the calculated magnetic moment was 1.68 µB.

Ab intio investigation of electronic and magnetic properties of Ca1-x TMx Te (TM = V, Cr, and Mn)

The interesting characteristics of spintronics exhibit lower energy consumption, higher density, push up us to find new materials that can be functional for spintronics such as half metallic ferromagnets. Based on density functional theory (DFT) and using full potential linearized augmented plane waves and local orbitals (FP-LAPW + lo) method implemented in Wien2k package, we carried out a study of structural, electronic and magnetic properties of CaTe doped with V, Cr, and Mn for various concentrations namely x = 0.25, 0.125, and 0.0625. Tran-Blaha-modified Beck-Johnson potential (TB-MBJ) was used to investigate the electronic and magnetic properties. We found that: only Cr-doped compounds are half metallic ferromagnetic materials with 100% spin-polarisation at Fermi level (Ef) and their ferromagnetism stabilization maybe explained by Zener's double exchange mechanism. An integer integrated total magnetic moment per TM atom marked to be 3,4, and 5 in Bohr magneton(μB) for V, Cr, and Mn-doped compounds respectively. We found large half metallic gaps for Cr dopant compounds resulting from the strong p-d hybridization of 5p (Te) and 3d (Cr), which make them promising candidates for spintronic devices and applications.

A systematic study on optoelectronic properties of Mn4+-activated Zr-based hexafluoride red phosphors X2ZrF6 (X = K, Na, Cs): first-principles investigation and prospects for warm-white LEDs applications

The quest for developing energy-efficient and environment-friendly phosphors for lighting devices such as light-emitting diodes (LEDs) is on rise to meet the future energy challenges. In this connection, phosphor-converted white LEDs are promising candidates for the next generation state-of-the-art solid-state lighting technology to substitute the traditional lighting devices such as fluorescent lamps, incandescent lamps, halogen lamps, and backlights for liquid crystal displays. Hereby, we report a systematic analysis on the optoelectronics properties of Zr-based Mn4+-activated phosphors X2ZrF6 (X = K, Na, Cs) for potential optoelectronics and photoluminescence device applications such as LEDs. For the comparative analysis of the first-principles calculations based on full-potential linearized augmented plane wave DFT procedure, we employed spin polarized GGA and GGA + U scheme of exchange and correlation energy potentials. In contrast to parent X2ZrF6 compounds, the band gaps of the Mn-doped X2MnF6 compounds have been lowered considerably. The improvement on band-gap values with GGA + U method reaffirms the famous drawback of GGA-based DFT methods regarding the underestimation of band gaps in highly correlated systems. For the prospects of materials regarding optoelectronics and photoluminescence applications, we first time report a detailed systematic analysis of optical properties such as dielectric functions, energy loss function, reflectivity, absorption coefficient, refractive index and optical conductivity. The materials are weakly photons reflector in IR and visible regions while they are strong photons absorbers in the UV region. In the absence of experimental evidences, indirect evidence of the wide band-gaps of K2ZrF6 and Na2ZrF6 compounds is ascertained via doping of Mn4+ ions. Besides, as all the energy levels of Mn4+ ions are around 4 eV these can also be observed in the experimental absorption spectra.

Photoluminescent and vapochromic properties of the Mn(II)-doped (C6H11NH3)2PbBr4 layered organic–inorganic hybrid perovskite

By a wet-chemistry route we have been able to effectively dope the CHA2PbBr4 compound, a ferroelectric compound with photovoltaic effect, with different amounts of Mn2+ obtaining three pure compounds CHA2Pb1-xMnxBr4 with x = 0.05, 0.07 and 0.11. At room temperature the crystal structure of these new Mn-doped compounds present an orthorhombic symmetric with polar space group Cmc21, as in the case of the undoped compoud (x = 0). Very interestingly, the doped compounds exhibit a broad PL emissions at room temperature, with a maximum around 605 nm and a long PL lifetime (~0.55 ms), whose intensity increases further upon cooling. The observed PL emission is induced from an energy transfer from host semiconductor to the d-orbitals of Mn2+ cation. In addition, we have explored the capability of these materials to act as chemical sensors for volatile organic compounds and report the selective luminescence vapochromic response in this family of compounds. Therefore, the here presented Mn-doped CHA2Pb1-xMnxBr4 compounds belong to the scarce and desirable group of multifunctional materials, where not only ferroelectric and photovoltaic properties can coexist but also photoluminescence and vapochromic properties, rendering them extremely interesting for a large number of potential practical applications.

Magnetic Property of Mn-Doped Monoclinic ZrO2 Compounds

Recently, many theoretical studies have projected that the Mn-doped ZrO2 compounds can exhibit long-range ferromagnetism. This study is to understand the magnetic property of Mn-doped monoclinic zirconia, Zr1−xMnxO2 (x = 0, 0.05, 0.10, 0.15, and 0.20), prepared at equilibrium condition, using solid-state reaction route. The structural property of these samples was studied using X-ray diffraction, and it is observed that all Mn-doped compounds are crystallized into monoclinic symmetry. The magnetic property measurements show that the pure ZrO2 compound exhibit paramagnetic behavior. However, all Mn-doped compounds exhibit ferrimagnetic ordering with a magnetic irreversibility behavior. The magnetic irreversibility in these compounds can be explained in terms of competition between ferrimagnetic and anti-ferromagnetic interactions. The coercivity and the area under hysteresis loop of all Mn-doped compounds are found to increase with the increase of Mn doping. The influence of final sintering temperature on the magnetic property is also studied, and it indicates that the samples prepared at a lower sintering temperature (1200 °C) exhibits better squareness of M-H loop, but with a decreased magnetic moment in comparison to the samples prepared at 1550 °C.

Spin phonon coupling in Mn doped HoFeO3 compounds exhibiting spin reorientation behaviour

An investigation has been carried out on the spin phonon coupling in a series of isostructural polycrystalline orthorhombic (Space group Pnma) compounds HoFe1−XMnXO3 (x ⩽ 0.6) exhibiting spin reorientation below Néel temperature (TN), using magnetization, neutron diffraction, and Raman scattering techniques. Mn doping leads to an anomalous increase in the spin reorientation temperature (TSR), shifting it close to room temperature from TSR ~ 60 K for x = 0 sample, and concomitant lowering of TN. The TSR is absent in samples for x ⩾ 0.5. The magnetic structure undergoes a transition at TSR from Γ4 → Γ1 in the Mn doped compounds as against Γ4 → Γ2 observed in HoFeO3 sample. In the region T < TN an anomalous softening of Raman phonon modes viz., B2g(5) and B3g(3), identified with the stretching motion and breathing mode, respectively, of Fe/Mn–O6 octahedra, is observed in compounds exhibiting spin-reorientation behaviour, indicating a spin-phonon coupling in these compounds. A quadratic correlation between the deviation of phonon frequency and variation of antiferromagnetic moment (Δω M2) is observed in these compounds. The temperature evolution of the M2+ mode obtained from the analysis of neutron diffraction data based on symmetry adapted mode decomposition of the Pnma structure further corroborates the mode softening observation.

Exploration of the structural and optical properties of a red-emitting phosphor K2TiF6:Mn4+**Project supported by the National Natural Science Foundation of China (Grant No. 11574220), Fundamental Research Funds for the Central Universities, China (Grant No. SWU118055), and the Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund (the second phase), China.

The exploration of the appropriate red phosphor with good luminescence properties is an important issue in the development of current white light-emitting diode (WLED) devices. Transition metal Mn-doped compounds are fascinating luminescent materials. Herein, we performed a systematic theoretical study of the microstructure and optical properties of K2TiF6:Mn4+ using the CALYPSO structure search method in combination with first-principles calculations. We uncovered a novel structure of K2TiF6:Mn4+ with space group P-3m1 symmetry, where the impurity Mn4+ ions are accurately located at the center of the MnF6 octahedra. Based on our developed complete energy matrix diagonalization (CEMD) method, we calculated transition lines for 2Eg → 4A2, 4A2 → 4T2, and 4A2 → 4T2 at 642, nm, 471 nm, and 352 nm, respectively, which are in good agreement with the available experimental data. More remarkably, we also found another transition (4A2 → 2T2) that lies at 380 nm, which should be a promising candidate for laser action.

Investigations on the phase transition of Mn-doped BaTiO3 multifunctional ferroelectric ceramics through Raman, dielectric, and magnetic studies

BaTiO3 (BTO) and BaTi1−xMnxO3 (x = 0.25, 0.50, 0.75 mol%) ceramic materials have been prepared by the sol–gel combustion method. X-ray diffraction (XRD) has been carried out to characterize the phase purity and crystal structure of the prepared compounds, and all XRD patterns suggest tetragonal structure with the phase group of P4mm. The variation in the estimated lattice parameters confirms the incorporation of Mn atoms at Ti site of BTO. Raman spectroscopy studies under various temperatures suggest a phase transition from tetragonal to cubic phase at ~433 K, identified by a distinct Raman mode at 308 cm−1. As Raman modes are getting softened by Mn doping, phase transition temperature of the Mn-doped compounds is significantly decreased from 473 K (x = 0%) to 433 K (x = 0.75%). Dielectric properties such as permittivity and dielectric loss as the function of frequency under various temperatures have two distinct dielectric anomalies (i) at 393 K associated to tetragonal to cubic phase transition and (ii) at 550 K due to oxygen vacancy defect in the samples. Observation of weak ferromagnetism at 2, 300, and 400 K in the M (H) and ZFC-FC curve, suppose its origin due to an intriguing exchange interaction between Mn and oxygen vacancies.

Coexistence of magnetization reversal and exchange bias in Mn-substituted CuCrO2

We systematically studied the magnetization reversal (MR) and exchange bias (EB) properties of Mn-doped CuCrO2 compounds. Single-phase ceramic samples of CuCr1−xMnxO2 (x = 0–0.2) were synthesized with the sol-gel method. Synchrotron radiation X-ray absorption spectroscopy of the Mn 2p, Cr 2p core levels showed that the Cr ion is trivalent and the Mn ion is in a mixed valence state of Mn3+/4+. All the Mn-doped samples, due to the double-exchange interaction between Cr3+–O–Mn3+ and Mn3+–O–Mn4+, showed a ferromagnetic transition in field-cooling magnetization. Interestingly, zero-field-cooling magnetization reversed from positive to negative as temperature decreased below the compensation temperature. The x = 0.05 sample also showed exchange bias. The coexistence of MR and EB in the system can be explained by the competition between ferromagnetic and antiferromagnetic order.

Ab-Initio Investigations of Magnetic Properties and Induced Half-Metallicity in Ga1-xMnxP (x = 0.03, 0.25, 0.5, and 0.75) Alloys.

Ab-initio calculations are performed to examine the electronic structures and magnetic properties of spin-polarized Ga1−xMnxP (x = 0.03, 0.25, 0.5, and 0.75) ternary alloys. In order to perceive viable half-metallic (HM) states and unprecedented diluted magnetic semiconductors (DMSs) such as spintronic materials, the full potential linearized augmented plane wave method is utilized within the generalized gradient approximation (GGA). In order to tackle the correlation effects on 3d states of Mn atoms, we also employ the Hubbard U (GGA + U) technique to compute the magnetic properties of an Mn-doped GaP compound. We discuss the emerged global magnetic moments and the robustness of half-metallicity by varying the Mn composition in the GaP compound. Using GGA + U, the results of the density of states demonstrate that the incorporation of Mn develops a half-metallic state in the GaP compound with an engendered band gap at the Fermi level (EF) in the spin–down state. Accordingly, the half-metallic feature is produced through the hybridization of Mn-d and P-p orbitals. However, the half-metallic character is present at a low x composition with the GGA procedure. The produced magnetic state occurs in these materials, which is a consequence of the exchange interactions between the Mn-element and the host GaP system. For the considered alloys, we estimated the X-ray absorption spectra at the K edge of Mn. A thorough clarification of the pre-edge peaks is provided via the results of the theoretical absorption spectra. It is inferred that the valence state of Mn in Ga1−xMnxP alloys is +3. The predicted theoretical determinations surmise that the Mn-incorporated GaP semiconductor could inevitably be employed in spintronic devices.

Electronic structure and magnetism of Mn-doped GaSb for spintronic applications: A DFT study

We have carried out first-principles spin polarized calculations to obtain comprehensive information regarding the structural, magnetic, and electronic properties of the Mn-doped GaSb compound with dopant concentrations: x = 0.062, 0.083, 0.125, 0.25, and 0.50. The plane-wave pseudopotential method was used in order to calculate total energies and electronic structures. It was found that the MnGa substitution is the most stable configuration with a formation energy of ∼1.60 eV/Mn-atom. The calculated density of states shows that the half-metallic ferromagnetism is energetically stable for all dopant concentrations with a total magnetization of about 4.0 μB/Mn-atom. The results indicate that the magnetic ground state originates from the strong hybridization between Mn-d and Sb-p states, which agree with previous studies on Mn-doped wide gap semiconductors. This study gives new clues to the fabrication of diluted magnetic semiconductors.

Ferroic behavior induced by oxygen vacancies in Mn-doped ZnO compounds

Mn-doped ZnO nanoparticles were successfully synthesized through the sol–gel technique. X-ray diffraction results showed that Mn doping did not disturb the hexagonal wurtzite structure of ZnO and no secondary phases were identified. Raman studies indicated the presence of defects in the form of oxygen vacancy clusters created due to Mn doping. Ferromagnetic-like curves were determined at room temperature for the sample with low doping (2% Mn). The results indicate that the observed ferromagnetism at room temperature can essentially be attributed to interactions mediated by magnetic impurities throughout the large number of oxygen vacancies created by Mn ions.

Study of Exchange Bias in Mn-Doped YFeO3 Compound

Single-phase samples of orthorhombic YFe1−xMnxO3 (x = 0 to 0.3) were prepared using solid-state route. Temperature variation of magnetization measurements show antiferromagnetic transition with Neel temperature (TN) in the range of 646 K for x = 0 to 456 K for x = 0.3. Spin canting-induced weak ferromagnetism is observed for T < TN. These materials exhibit an exchange bias behavior as per magnetic hysteresis loop measurement under field-cooled condition. The magnitude of maximum exchange bias field at 413 K is around 1.2 kOe. The observed exchange bias is explained by considering the exchange coupling across the interface of two magnetic phases having a dominant collinear antiferromagnetism and a weak ferromagnetism, respectively.

Synthesis and properties of La0.05Ba0.95Ti1 −xMyO3 (M = Mn, Ce) as anode materials for solid oxide fuel cells

Stoichiometric and sub-stoichiometric lanthanum barium titanates (LBT) of perovskite structure type, substituted or not with Mn and/or Ce at the Ti-site, were prepared by sol–gel route with heat treatment in air. All the compounds display a cubic Pm-3m symmetry, which remains stable in reducing atmosphere. Whereas Mn substitution highly promotes the reducibility of the material, the electrical and electrochemical performance of Mn-doped compounds is decreased with respect to non-doped sub-stoichiometric LBT. In contrast, the electrical conductivity and resistance polarization of Ce-substituted LBT are close to those of non-doped LBT and Ce-substituted LBT appears especially efficient in improving the catalytic properties for methane steam reforming and avoiding carbon formation.