Mn Mole Fraction Research Articles

Magnetization and optical bandgap of Cu-Mn vanadate-oxide mixed phase nanostructures

Copper vanadate (CV) and manganese vanadate (MV) exhibit magnetic and optical properties that have drawn the attention. Due to CV polymorphism and phase multiplicity, CV is common to exist as mixed phases. In this study, nanostructures of mixed-phase CVs mixed with MV were synthesized hydrothermally followed by calcination at 400 °C, with Mn mole fractions 0.0, 0.4, 0.6, 1.0. The uncalcined and calcined Mn-Cu vanadates (MCVs) were investigated by XRD, SEM, TEM, FT-IR, EDX, ICP-AES, TGA, DTA, DSC, BET, XPS, and VSM. XRD analysis shows co-existence of multi-phase CVs with MnV2O6 and V oxides. Electron micrographs show nanostructures of multiple morphologies (rods, cubes, sheets, and irregular). As Mn content increased in the MCVs, their thermal stability increased, optical bandgap (Eg) declined from 2.46 to 1.60 eV, and magnetism diverted from the superparamagnetic-like to paramagnetic (Hc from 1362 to 69 G and Mr/Ms from 0.430 to 0.003). Magnetism parameters of calcined MCVs were more labile to Mn content variation compared to the uncalcined MCV counterparts.Graphical

Manganese speciation in Mn-rich CaCO3: A density functional theory study

The manganese content of aragonitic bivalve shells is a potential archival indicator of temporal Mn bioavailability in aquatic environments. The Mn speciation mechanism in biogenic aragonite minerals remains elusive because the analog is challenging to synthesize, and the metastable phase has yet to be fully resolved experimentally. In this study, we performed density functional theory (DFT) computations of hypothetical Mn-doped aragonite to examine its local coordination structure and thermodynamic and electronic properties. Our DFT calculations reproduced the experimental crystal structures and solubility product constants (Ksp) of Mn-doped calcite. The magnetic moment of Mn was close to 5 μB in both Mn-doped calcite and Mn-doped aragonite (Ca1−xMnxCO3). The calculated Ksp of Mn-doped aragonite was higher than that of Mn-doped calcite and increased with Mn content, indicative of the unfavorable coprecipitation of Mn with the aragonite phase. We found that the incorporation of a small mole fraction of Mn into aragonite created significant structural distortion around the Mn site, resulting in mixed coordination numbers of Mn (mainly five and seven). Valence-to-core X-ray emission spectroscopy (XES) measurements are useful in determining the coordination environment of Mn complexes. We calculated theoretical XES spectra, with a 1s core hole in Mn, for Mn-doped calcite and four versions of Mn-doped aragonite. The Boltzmann-averaged spectrum for different coordination numbers in Mn-doped aragonite was akin to an experimental XES spectrum of aragonitic bivalve shells. The energy position of the Kβ2,5 band was calculated to be insensitive to Mn speciation in CaCO3; however, the band intensity was relatively sensitive to Mn speciation. The XES spectrum intensity decreased exponentially with increasing Mn–O distance. This quantitative XES relationship we report can reduce uncertainties in the spectral interpretation due to the absence of an Mn-doped aragonite reference spectrum.

Substrate effects on the structural properties of Cd1-x Mn x Te thin films grown via magnetron Co-sputtering

Cd1-xMnxTe thin films were prepared by co-sputtering CdTe and Mn targets on to a variety of substrates at room temperature. The sputter powers of the CdTe and the Mn targets were fixed at 75 W and 65 W, respectively, and the influences of the substrate on the structural properties of the deposited thin films were investigated. All of the films were polycrystalline in nature, and X-ray diffraction showed that the lattice constant varied between 6.3912 and 6.4518 Ǻ depending on the substrate. The incorporated Mn mole fraction varied between 12.796% and 13.046%; this variation may be attributed to a change in the band-gap. The band-gap energy increased from 1.6767 to 1.6799 eV and the grain size decreased from 133 to 74 nm as the strain increased from 14.12% to 34.12% for the various substrates.

Epitaxial single-crystal thin films of MnxTi1 − xO2 − δ grown on (rutile)TiO2 substrates with pulsed laser deposition: Experiment and theory

Epitaxial rutile-structured single-crystal MnxTi1−xO2−δ films were synthesized on rutile- (110) and -(001) substrates using pulsed laser deposition. The films were characterized by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and aberration-corrected transmission electron microscopy (ACTEM). Under the present conditions, 400°C and PO2=20mTorr, single crystal epitaxial thin films were grown for x=0.13, where x is the nominal average mole fraction of Mn. In fact, arbitrarily thick films could be grown with near invariant Mn/Ti concentration profiles from the substrate/film interface to the film surface. In contrast, at x=0.25, Mn became enriched towards the surface and a secondary nano-scale phase formed which appeared to maintain the basic rutile structure but with enhanced z-contrast in the tunnels, or interstitial sites. Ab initio thermodynamic calculations provided quantitative estimates for the destabilizing effect of expanding the β-MnO2 lattice parameters to those of TiO2-rutile, the stabilizing effect of diluting Mn with increasing Ti concentration, and competing reaction pathways for surface oxide formation.

Synthesis and Piezoelectric Properties of Li, Ca and Mn-codoped BaTiO3 by a Solvothermal Approach

3 at.% Li-doped (Ba1-xCax)(Ti1-yMny)O3 particles with the Ca2+ mole fraction, x, of 0–0.09 and Mn mole fraction, y, of 0 and 0.0005 were synthesized by a solvothermal approach at 200°C. The products consisted of nanoparticles of 50–100 nm in diameter, and did not change very much depending on the amount of Li, Ca and Mn-codoping. The change in relative dielectric constant, Δϵr, in around room temperature decreased by doping Ca2+, and the lowest Δϵr (4.51%) could be realized at x value of 0.03. The mechanical quality factor, Qm, of 3 at.% Li-doped (Ba0.97Ca0.03)(Ti0.9995Mn0.0005)O3 increased to 521, and Δϵr decreased to 1.72%, while the piezoelectric constant, d33 (234pC/N), and electromechanical coupling factor, kp (40.0%), did not change very much compared with 3 at.% Li-doped BaTiO3.

Modeling and optimization of combustion process of 2-propanol over perovskite-type LaMnyCo1−yO3 nanocatalysts by an unreplicated experimental design with mixture–process variables and genetic algorithm methodology

Modeling and optimization of catalytic oxidation of 2-propanol over LaMnyCo1−yO3 nano perovskites was carried out by an unreplicated mixture–process experimental design and genetic algorithm methodologies, respectively. Mixture variables were the components of perovskites in B sites: cobalt and manganese. The process variables were calcination temperature and reaction temperature. An eight term statistical model was proposed to fit the experimental data with determination coefficient of 0.982. The effect of composition and process variables on 2-propanol conversion and interaction of variables was studied by the model. It was found that the activity of nano perovskites increases with a decrease in calcination temperature and an increase in Mn mole fraction in the catalyst. Full conversion of 2-propanol was predicted to occur over LaMn0.65Co0.35O3 at calcination and reaction temperatures of 700 and 273°C, respectively. The structure of nano perovskites was characterized by XRD and FTIR and the morphology was investigated by SEM technique.

Energy Gap Dependence on Mn Content in a Diluted Magnetic Quantum Dot

Positively charged donor exciton binding energy is computed as a function of quantum-dot size within the single band effective mass approximation for different Mn contents in Cd1−xinMnxin Te/Cd1−xoutMnxout Te. The exciton bound polaron is computed for 0 ≤ x ≤ 0.08, on the Mn mole fraction. We determine the energy gap using the mean field approximation and incorporate the exchange interaction between the carrier and the magnetic impurity. The interband emission energy is studied with the height and radius of the cylindrical quantum dot. Valence-band anisotropy is included in our theoretical model using different hole masses in different spatial directions. Spin polaronic shifts as functions of quantum-dot radius and Mn concentration are estimated using the mean field theory. It is found that (i) the energy gap depends on the Mn mole fraction, (ii) it increases linearly with an increase in Mn content, and (iii) the effect is more pronounced for a narrow dot, showing the quantum size effects. Our results are in good agreement with other recently published reports.

Density and Surface Tension of Liquid Fe-Mn Alloys

The density and surface tension of liquid Fe-Mn alloys were determined by using the sessile drop method at 1823 K (1550 °C). The density of liquid Fe-Mn alloys decreased with increasing Mn content. When the molar volume was plotted with respect to the mole fraction of Mn, a linear relationship was obtained. Consequently, it was found that there is no excess volume in liquid Fe-Mn alloy. The surface tension of liquid Fe-Mn alloys was found to decrease with increasing Mn content. The current experimental data were higher than the reported results but close to the calculated results using Butler’s equation.

Donor exciton binding energy in ZnSe wide bandgap quantum wells

Positive donor exciton binding energy is calculated as a function of well width for a Zn 1− x out Mn x out Se/Zn 1− x in Mn x in Se/Zn 1− x out Mn x out Se quantum well within the single band effective mass approximation for different Mn content. Exciton bound polaron is investigated for 0 ≤ x in ≤ 0.06 , on the Mn mole fraction. We determine the interband emission energy with the mean field approximation invoking the exchange interaction between the carrier and the magnetic impurity. The interband emission energy is computed as a function of well width for different Mn content. The valence band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. It is found that the interband emission energy (i) depends on Mn mole fraction and (ii) increases linearly with an increase of the Mn content and the effect is more pronounced for the narrow well showing the quantum size effects. Also the significant increase in interband emission energy is observed due to spin splitting with Mn ion concentration. The interband emission shows a blue shift of the exciton with an increase of Mn content. Our results are in good agreement with the recent published results.

Energy-gap dependence on the Mn mole fraction and temperature in CdMnTe crystal

We measured the dependence of the energy gap in Bridgman-grown Cd1−xMnxTe crystals, 0≤x≤0.25, on the Mn mole fraction and temperatures from 40 to 300 K. We determined the Mn mole fraction and energy gap, respectively, from electron probe microanalysis and near-infrared Fourier-transform infrared transmission spectra. The energy gap increased linearly with an increase in the Mn content in the crystal and with a decrease in temperature. We formulated new equations from these experimental results, wherein we expressed the energy gap as a function of Mn mole fraction and temperature. Also, we compare our findings with published results.

Thermodynamics of oxygen solutions in iron-nickel, iron-cobalt and iron-manganese melts

The oxygen solubility in Fe-Ni, Fe-Co, and Fe-Ni melts has been calculated. The calculation of oxide phase composition over Fe-Ni, Fe-Co and Fe-Mn melts was carried out at 1873 K. The FeO oxide is mainly contained in the oxide phase of the Fe-Ni system; the NiO content rapidly increases only when the Ni mole fraction is close to unit. In case of the Fe-Co system, the FeO also is contained mainly in the oxide phase and the CoO content rapidly increases as the Co mole fraction increases above 0.8. The MnO oxide is contained mainly in oxide phase of the Fe-Mn system; in this case, when the Mn mole fraction is more than 0.02, the MnO mole fraction in oxide phase is more than 0.9.

Giant Faraday rotation in Cd1–xMnx Te (0 < x < 0.82) crystals

AbstractWe investigated the magneto‐optical properties of diluted magnetic semiconductors Cd1–x Mnx Te crystals grown using a vertical Bridgman method. This material crystallizes in the zinc‐blende structure for values of x < 0.82. The band‐gap energy was depended on Mn mole fraction x linearly and increased with decreasing temperature. The increase of the energy gap with increasing x may be due to a decrease in the lattice constant. Faraday rotation as a function of photon energy with various Mn compositions for CdMnTe in the temperature range of 10–300 K has been measured. The Faraday rotation was increased as the photon energy increased near to that of the fundamental band gap. Verdet constant becomes larger since the effect of the sp ‐d exchange interaction is enhanced as the temperature is lowered. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analysis of magnetic field dependent mobility in ferromagnetic Ga 1− xMn xAs layers

The magneto-transport properties of ferromagnetic Ga 1− x Mn x As epilayers with Mn mole fractions in the range of x≈2.2–4.4% were investigated through Hall effect measurements. The magnetic field-dependent Hall mobility for a metallic sample with x≈2.2% in the temperature range of T=0–300 K was analyzed by magnetic field-dependent mobility model including an activation energy of Mn acceptor level. This model provides outstanding fits to the measured data up to T=300 K. It was found that the acceptor levels with activation energies of 112 meV at B=0 Oe decreased to 99 meV at B=5 kOe in the ferromagnetic region. The decrease in acceptor activation energy was due to the spin splitting of the Mn acceptor level in the ferromagnetic region, and was responsible for increase in carrier concentration.

Ferromagnetic Properties of Mn-Doped III–V Semiconductor Quantum Wells

We investigate magnetic properties of In1−xMnxP and Ga1−xMnxN quantum wells in the mean-field approximation and show the difference between them. In the case of the In1−xMnxP, the dependence of the Curie temperature (Tc) on the hole density exhibits a step-like behavior, reflecting the effect of a two-dimensional Fermi (hole) gas, when the hole–hole exchange interaction is ignored. When we take into account the hole–hole exchange interaction, however, this behavior is broken by the appearance of peaks at the specific two-dimensional carrier densities, and Tc is substantially enhanced in this region. In the case of Ga1−xMnxN, the step-like behavior is obscure, and it appears that Tc increases rather continuously with the increasing two-dimensional (2D) carrier density. This shows very weak step-like behavior compared to other III-Mn-V DMS quantum wells, because the hole effective mass of Ga1−xMnxN is very large, and the large hole effective mass reduces the energy splitting due to the confinement effect. In a multi-heavy-valence-subband model, the Curie temperature of the In1−xMnxP quantum well is about 68 K with 6.5×1012 holes per cm2 and the Mn mole fraction x = 0.05 and the exchange constant Jpd = 0.15 eV nm3. The Curie temperature of the p-type Ga1−xMnxN quantum well can be above room temperature, unless the spin-exchange interaction integral is abnormally small.

Magnetotransport properties of ferromagnetic Ga1−xMnxAs layers on a (100) GaAs substrate

The magnetotransport properties of ferromagnetic Ga1−xMnxAs epilayers with Mn mole fractions in the range of x≈2.2%–4.4% were investigated using Hall effect measurements. The temperature-dependent Hall carrier concentration for a metallic sample with x≈2.2% was analyzed assuming an activation energy from two acceptor levels. It was found that the two acceptor levels with activation energies of 129.4 and 31.6 meV at B=0Oe decreased to 87.6 and 30.7 meV, respectively, at B=5kOe. The decrease in acceptor activation energy from 129.6 to 87.6 meV was due to the spin splitting of the Mn acceptor level in the ferromagnetic region, and was responsible for the increase in carrier concentration. From magnetic-field-dependent Hall resistance data, the Curie temperature was estimated to be TC=60 and 70 K for Ga1−xMnxAs samples with x≈2.2 and x≈4.4%, respectively. The magnetoresistance measurements confirmed that the anomalous Hall effect existed in these samples that showed metallic and insulating behavior, respectively.

Optical Properties of Cd1-xMnxTe Crystals near Fundamental Absorption Edge in Transverse Magnetic Fields

A simple and convenient model is proposed to elucidate the optical characteristics of Cd1−xMnxTe crystals using experimental data on light reflection in magnetic field. The model is based on the quasi-oscillator concept accounting both for the exciton and fundamental absorption edge contributions. The energy dependencies of refraction index and absorption coefficient are presented for Mn mole fraction x = 20% at the magnetic field values up to 5 T.

Thermal annealing effects on the magnetic properties of (Ga1−xMnx)As thin films grown on GaAs (1 0 0) substrates

Thermal annealing effects on the magnetic properties of (Ga1−xMnx)As with various Mn mole fractions grown on GaAs (100) substrates by using molecular beam epitaxy were investigated. When thermal annealing was performed, the ferromagnetic transition temperature (TC) of the (Ga1−xMnx)As thin films increased. The increase in the TC originated from a decrease in the concentration of the Mn interstitial atoms or from an increase in the uncompensated Mn spin which contributed to the magnitude of the ferromagnetism. These results can help improve the understanding of the effect of thermal annealing on the magnetic properties of (Ga1−xMnx)As thin films grown GaAs substrates.

Optical and magnetic properties of (Ga 1− xMn x)N/GaN digital ferromagnetic heterostructures

(Ga 1− x Mn x )N/GaN digital ferromagnetic heterostructures (DFHs) and (Ga 1− x Mn x )N/GaN grown on GaN buffer layers by using molecular beam epitaxy have been investigated. The photoluminescence (PL) spectra showed band-edge exciton transitions. They also showed peaks corresponding to the neutral donor-bound exciton and the exciton transitions between the conduction band and the Mn acceptor, indicative of the Mn atoms acting as substitution. The magnetization curves as functions of the magnetic field at 5 K indicated that the saturation magnetic moment in the (Ga 1− x Mn x )N/GaN DFHs decreased with increasing Mn mole fraction and that the saturation magnetic moment and the coercive field in the (Ga 1− x Mn x )N/GaN DFHs were much larger than those in (Ga 1− x Mn x )N thin films. These results indicate that the (Ga 1− x Mn x )N/GaN DFHs hold promise for potential applications in spintronic devices.

Dependence of indices of refraction on Mn composition of Zn1−xMnxSe thin films using prism coupler technique

AbstractWe have measured the dependence of the indices of refraction n on alloy composition x of Zn1−xMnxSe films grown by MBE on GaAs (100) substrates for a series of alloy compositions x. The Mn compositions of the films were determined by XRD. A prism coupler technique was used to measure n and thickness of each of the alloy films. On the whole, the indices of refraction n obtained by this method decrease linearly as increasing x showing an inverse relationship with respect to their band gaps, in spite of showing a minimum in the near‐band gap energy in the region of 0 ≤ x ≤ 0.1. We obtained a linear calibration function for n as from the prism coupler technique, which can be used to make an accurate estimate the Mn composition in the Zn1−xMnxSe alloy system if you only measure n. And, the crystalline quality of the Zn1−xMnxSe alloy film was deteriorated showing an exponential dependence of FWHM ratio of alloy layer to GaAs substrate obtained from DCRC as increasing Mn mole fraction. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Hall coefficient investigation of ferromagnetic Ga 1− xMn xAs layers on (100) GaAs substrates

Ferromagnetic Ga 1− x Mn x As epilayers with Mn mole fraction in the range of x≈2.2–4.4% were grown on semi-insulating (100) GaAs substrates using the molecular beam epitaxy technique. The transport properties of these epilayers were investigated through Hall effect measurements. The measured hole concentration of Ga 1− x Mn x As layers varied from 4.4×10 19 to 3.4×10 19 cm −3 in the range of x≈2.2–4.4% at room temperature. From temperature dependent resisitivity data, the sample with x≈4.4% shows typical behavior for insulator Ga 1− x Mn x As and the samples with x≈2.2 and 3.7% show typical behavior for metallic Ga 1− x Mn x As. The Hall coefficient for the samples with x≈2.2 and 4.4% was fitted assuming a magnetic susceptibility given by Curie–Weiss law in a paramagnetic region. This model provides good fits to the measured data up to T=300 K and the Curie temperature T c was estimated to be 65, 83 K and hole concentration p was estimated to be 5.1×10 19, 4.6×10 19 cm −3 for the samples with x≈2.2 and 4.4%, respectively, confirming the existence of an anomalous Hall effect for metallic and insulating samples.