Substitutional Mn Atoms Research Articles

Mn Diffusion and Reactive Diffusion in Ge: Spintronic Applications

In this paper, we report investigations concerning the fabrication of a diluted Ge (Mn) solution using solid state Mn diffusion, and Mn/Ge reactive diffusion for spintronic applications. The study of Mn diffusion shows that the quasi-totality of the incorporated Mn atoms occupies Ge substitutional sites and probably exhibits two negative elementary charges. The solubility limit of Mn in Ge is comprised between 0.7 and 0.9 % (T  600 °C). We show that substitutional Mn atoms are not ferromagnetic in Ge and consequently that Ge (Mn) diluted magnetic semiconductor can not be produced. Beside the ferromagnetic signal from Mn5Ge3, ferromagnetic signals detected in the samples could be always attributed to surface or bulk Mn-Ge clusters. Furthermore, we show that the CMOS Salicide process is potentially applicable to Mn5Ge3 nanolayer fabrication on Ge for spintronic applications. During Mn (thin-film)/Ge reaction, Mn5Ge3 is the first phase to form, being thermally stable up to 310 °C and exhibiting ferromagnetic properties up to TC ~ 300 K.

Magnetic Structure of Mn-doped 6H-SiC

We investigated the local magnetic properties of Mn-doped 6H-SiC using ab-initio calculations. The calculation addresses various configurations of Mn single impurity and Mn dimers at substitutional/interstitial sites with and without neighboring Si and C vacancies. The calculations showed that a substitutional Mn atom at either Si or C sites possesses a magnetic moment. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. Our calculations show that antiferromagnetically coupled pair of Mn atoms at Si sites with neighboring C vacancy is magnetically more stable. The calculation also showed that the interstitial sites with C neighbors are more favorable than those with Si and the magnetic moment for Mn at interstitial sites is less compared to that at substitutional sites. The results are used to understand the experimental data obtained on Mn- 6H-SiC for various Mn concentrations.

Synthesis, structural and magnetic behavior of undoped andMn-doped anataseTiO2nanoparticles

Ti1-xMnxO2(x = 0, 0.05) nanoparticles have been synthesized using chemically derived self-propagating combustion reaction method. X-ray diffraction studies demonstrate the formation of anatase phase of TiO2belonging to 141/amd space group in both samples without the formation of any impurity phase. The incorporation of 5 at.% Mn content does not produce any changes in crystal structure which reveals the exact substitution of Mn atoms at Ti sites. Some change in lattice parameters and crystallite size is observed in Mn -doped composition, attributed to the difference in ionic radii. The size of grains obtained using scanning electron micrographs shows the consistent trend with the crystallite size evaluated from X-ray diffraction analysis. Energy dispersive X-ray analysis confirms the incorporation of Mn content in TiO2structure. Ferromagnetic behavior detected only in Mn -doped TiO2composition correspond to the strong Mn d-shell contribution.

Controlled incorporation of Mn in GaAs: Role of surface reconstructions

A combined experimental and theoretical study on the incorporation of Mn in GaAs has been presented. We have successfully controlled the location of Mn atoms at GaAs(001) surfaces by changing the surface atomic geometry. While Mn atoms prefer to substitute Ga sites at a subsurface layer under the As-rich conditions, the incorporation into interstitial sites becomes more favorable as the surface As coverage is decreased. The present results provide a mechanism for the enhanced incorporation of substitutional Mn atoms in GaMnAs under low-temperature (i.e., As-rich) growth conditions.

DFT+U predictions: The effect of oxygen vacancy on the structural, electronic and photocatalytic properties of Mn-doped BiOCl

In order to provide fundamental understanding and guidance for the effective Mn doping BiOCl and enhanced physicochemical properties derived from the interplay between Mn dopant and oxygen defect, the density functional theory (DFT)+U calculations were adopted to evaluate the effects of Mn doping and oxygen vacancy defects on the geometric structure, electronic property, optical absorption, Mulliken charge and effective mass of BiOCl. The suitable theoretical models were built up and their relaxed structural parameters agree well with the experiment values. It is found that both substitutional and interstitial Mn doping BiOCl not only are energetically favorable but also modify band structures to achieve remarkable optical red-shift of BiOCl, and the substitutional Mn-doped BiOCl show better feasible Mn doping behavior due to the beneficial p-type doping characteristic and p–d hybridization between substitutional Mn and adjacent Bi (or O) atoms in the CB (or VBM). The occurrence of oxygen vacancy in BiOCl crystal significantly influences the neighboring Bi 6p states, forming a capture center of photo-excited electrons in the forbidden band, which enhances the efficient mobility of photo-generated carriers and improves the effective separation rate of electron–hole pairs. The better negative formation energy of substitutional Mn-doped BiOCl with oxygen vacancy (BiOCl:VO) demonstrates thermodynamically its favorable structural stability. Besides, the higher relative ratio value for the effective masses of activated holes and electrons in the Mn-doped BiOCl:VO system implies the lower recombination rate of electron–hole pairs. Furthermore, our calculated optical absorption spectra exhibit that the spectral absorption edge of BiOCl is obviously red-shifted and extends to visible, red and infrared light region by the synergistic effect of oxygen vacancy and Mn dopant. Therefore, we theoretically predicted that Mn-doped BiOCl:VO system is expected to become highly promising semiconductor material applied in photocatalytic field for effectively photochemical decomposition of organics or water splitting under the sunlight irradiation.

Ab initio calculations on the effect of Mn substitution in the κ-carbide Fe3AlC

We have performed spin-polarized density functional theory calculations on κ-carbides, (Fe, Mn)3AlC, to investigate both the effect of different exchange-correlation functionals and the effect of Mn substitution. Differently from our previous calculations using the Perdew-Wang functional, Fe2MnAlC is found to be the most stable crystal among crystalline κ-carbides by using the Perdew, Burke, and Ernzerhof functional. Supercell calculations to simulate low Mn concentration show that substitutional Mn atoms hardly interact with each other and suggest that a random alloy model can be applied. The stabilization of Fe2MnAlC and its enhanced magnetization are attributed to the formation of a -Mn-C- linear chain structure.

Mn-doped TiO2 thin films with significantly improved optical and electrical properties

TiO2 thin films with various Mn doping contents were fabricated by reactive magnetron sputtering deposition at 550 °C and their structural, optical and electrical properties were characterized. All films were made of densely packed columnar grains with a fibrous texture along the normal direction of the substrate. The as-deposited structure in the pure TiO2 film consisted of anatase grains with the [1 0 1] texture. Mn incorporation stabilized the rutile phase and induced lattice contraction in the [1 0 0] direction. The texture in the Mn-doped films changed from [1 1 0] to [2 0 0] with increasing Mn content. The incorporation of Mn in the TiO2 lattice introduced intermediate bands into its narrowed forbidden gap, leading to remarkable red-shifts in the optical absorption edges, together with significantly improved electrical conductivity of the thin films. Hall measurement showed that the incorporation of Mn-induced p-type conductivity, with hole mobility in heavily doped TiO2 (∼40% Mn) being about an order higher than electron mobility in single-crystal rutile TiO2. Oxygen vacancies, on the other hand, interacted with substitutional Mn atoms to reduce its effect on optical and electrical properties.

Effects of local relaxation on electronic structure of substitutional Mn atoms in (GaMn)As

We have investigated the effects of local relaxation on the electronic structure of Mn atoms in (GaMn)As and the related properties of this dilute magnetic semiconductor (DMS). The nearest neighbours of the substitutional Mn atom have been considered for relaxed and non-relaxed conditions, while the other atoms have been left unaffected by the Mn impurity. Gallium Arsenide (GaAs), when doped with Mn atoms in a small concentration, becomes ferromagnetic retaining its semiconductor properties and it also acquires half metallic character. These characteristics of this DMS are vital for spintronic applications. We have implemented the scheme of pseudopotential method within the density functional formalism to calculate the electronic structure of (GaMn)As and computed the total density of states and partial density of states under the supercell scheme for unrelaxed and relaxed nearest neighbours of the substitutional Mn atom. We have also discussed a more realistic approach to calculate the local magnetic moment in this kind of systems. At the end, we have discussed the relevance of the present research work in the spintronic applications.

Magnetic properties of Mn-implanted 6H-SiC single crystal

The electronic and magnetic structures of Mn-doped 6H-SiC have been investigated using ab initio calculations. Various configurations of Mn sites and vacancy types have been considered. The calculations showed that a substitutional Mn atom at either Si or C sites possesses a magnetic moment. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. The magnetic properties of ferromagnetically and antiferromagnetically coupled pair of Mn atoms in the presence of vacancies have also been explored. Our calculations show that antiferromagnetically coupled pair of Mn atoms at Si sites with neighboring C vacancy is magnetically more stable. Relaxation effects were also studied. The results are correlated to the measured magnetic properties obtained for Mn-implanted 6H-SiC for various Mn concentrations.

Influence of Al on internal friction spectrum of Fe–18Mn–0.6C twinning-induced plasticity steel

The temperature dependence of the damping and the dynamic elastic modulus of Fe–18%Mn–0.6%C twinning-induced plasticity steel with different Al contents were investigated by the impulse excitation internal friction technique. The modulus effect was reduced and the Neel temperature was lowered by the Al addition. The activation energy of the Finkelshtein–Rosin peak increased with Al addition. The Finkelshtein–Rosin peak became broader due to diffusional jumps of the interstitial C with different activation energies resulting from the interaction with substitutional Mn atoms.

Tuning Low-Spin to High-Spin Mn Pairs in 2-D ZnO by Injecting Holes

We have performed an ab initio theoretical investigation of substitutional Mn atoms in planar structures of ZnO, viz., monolayer [(ZnO)1] and bilayer [(ZnO)2] systems. Due to the 2-D quantum confinement effects, in those Mn-doped (ZnO)1 and (ZnO)2 structures, the antiferromagnetic (AFM) coupling between (nearest neighbor) MnZn impurities have been strengthened when compared with the one in ZnO bulk systems. On the other hand, we find that the magnetic state of these systems can be tuned from AFM to FM by adding holes, which can be supplied by a p-type doping or even photoionization processes. Whereas, upon addition of electrons (n-type doping), the system keeps its AFM configuration.

Mn incorporation into the GaAs lattice investigated by hard x-ray photoelectron spectroscopy and diffraction

(Received 22 December 2010; revised manuscript received 31 March 2011; published 15 June 2011) Photoelectron spectroscopy and diffraction have been used to investigate structural changes during the annealing process of Ga1−xMnxAs samples. Hard x-ray radiation helped in observing photoelectron core-level spectra and electron diffraction from the bulk underlying the oxidized surface layer. High electron-energy resolution enabled us to separate the components due to substitutional and interstitial Mn atoms in the intrinsic Mn 2p3/2 photoemission profile, resulting in two peaks at 638.8 and 639.5 eV binding energy, respectively. The peaks display the known characteristic behavior after annealing, that is, an almost complete reduction of the interstitial component and preservation of the substitutional component. In the photoelectron diffraction, a sensitivity of high-energy polar plots to the incorporation sites of photoemitting atoms into the atomic lattice has been shown. As a consequence, the experimental polar plots from substitutional and interstitial Mn atoms, which are supported theoretically, show characteristic features that provide structural information. From the similarities and differences of the polar plots for Mn and Ga, we have confirmed the assignment of components within the intrinsic part of the photoemission Mn 2p3/2 signal suggested by photoelectron spectroscopy.

Surface State Induced Ferromagnetism in Co- and Mn-Doped ZnO Surfaces

We studied the magnetic coupling between magnetic atoms at the O-terminated ZnO(0001̅) surface using first-principles total energy calculations. It was found that the substitutional Co and Mn in the O-terminated ZnO(0001̅) surface tend to occupy the outermost cation layer. Different from the magnetic behaviors between substitutional Co and Mn atoms in bulk ZnO, at O-terminated ZnO(0001̅), due to the presence of surface states, the magnetic atoms display ferromagnetic coupling. On the basis of the analysis of electron density of states, n- and p-type doping could enhance the ferromagnetic coupling between Co and Mn atoms at O-terminated ZnO(0001̅), respectively, in good agreement with previous experimental observations. Our results complement the understanding of the origin of ferromagnetism in ZnO-based diluted magnetic semiconductors.

Magnetic interactions of substitutional Mn pairs in GaAs

We employ a kinetic-exchange tight-binding model to calculate the magnetic interaction and anisotropy energies of a pair of substitutional Mn atoms in GaAs as a function of their separation distance and direction. We find that the most energetically stable configuration is usually one in which the spins are ferromagnetically aligned along the vector connecting the Mn atoms. The ferromagnetic configuration is characterized by a splitting of the topmost unoccupied acceptor levels, which is visible in scanning tunneling microscope studies when the pair is close to the surface and is strongly dependent on pair orientation. The largest acceptor splittings occur when the Mn pair is oriented along the $⟨110⟩$ symmetry direction and the smallest when they are oriented along $⟨100⟩$. We show explicitly that the acceptor splitting is not simply related to the effective exchange interaction between the Mn local moments. The exchange interaction constant is instead more directly related to the width of the distribution of all impurity levels---occupied and unoccupied. When the Mn pair is at the (110) GaAs surface, both acceptor splitting and effective exchange interaction are very small except for the smallest possible Mn separation.

Element-specific electronic structure of Mn dopants and ferromagnetism of (Zn,Mn)O thin films

Element-specific electronic structure of (Zn,Mn)O thin films with various Mn concentrations has been investigated using X-ray absorption and emission spectroscopy. According to comparison between the experimental spectra and the density functional theory calculations (partial density of states and exchange interactions for various Mn defect configurations), the substitutional Mn impurities do not induce ferromagnetism in (Zn,Mn)O samples. The ferromagnetic properties can be obtained when defect configurations consisting of both substitutional and interstitial Mn atoms are present. The ferromagnetism in ZnO-based magnetic semiconductors is favored to be Ruderman–Kittel–Kasuya–Yoshida type and the established theoretical model is in a good agreement with the X-ray spectroscopic measurements.

Structural characterization of Mn doped SiC magnetic thin films

Mn-doped SiC magnetic thin films prepared by co-deposited molecular beam epitaxy (MBE) method on Si (111) substrates at 950 ℃ have been investigated by reflection high energy diffraction (RHEED), X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) techniques. RHEED results reveal that the SiC thin films doped with Mn are of the cubic structure. XRD and XANES results show that in the thin films with Mn doping concentrations of 0.5％ and 18％ , almost all the Mn atoms react with Si atoms, forming Mn4Si7 compound embedded in the SiC matrix, and no substitutional or interstitial Mn atoms exist in the SiC lattice. Furthermore, we hold that the ferromagnetism of the Mn doped SiC thin films originates mainly from the Mn4Si7 secondary phase.

X-ray Absorption and Emission Studies of Mn-doped ZnO Thin Films

The electronic structure of Mn-doped ZnO thin films, a dilute magnetic semiconductor (DMS) having possible room temperature (RT) ferromagnetism, synthesized with nominal compositions of Zn1 xMnxO (x = 0.03, 0.05, 0.07, 0.10, and 0.15) by using the spray pyrolysis method are investigated using soft X-ray absorption and emission spectroscopy. The intensity of the pre-edge spectral feature at the O K-edge increases with Mn concentration, which clearly reveals that there is a strong hybridization of Mn ions with the ZnO matrix. The near-edge X-ray absorption fine structure (NEXAFS) measurements at the Mn K- and L3,2-edges show a mixed valence nature for the Mn ions, with Mn 2+ and Mn 3+ /Mn 4+ states, and the Mn 3+ /Mn 4+ states are observed to increase with the Mn-concentration. Mn L2,3 resonant inelastic X-ray scattering (RIXS) measurements show that the excess Mn interstitials appear in the sample and that direct exchange interactions with substitutional Mn atoms may explain the magnetic interaction in Mn-doped ZnO.

Pre-edge XANES structure of Mn in (Ga,Mn)As from first principles

Institute of Physics, Academy of Sciences of the Czech Republic, v.v.i., Cukrovarnicka 10, 162 53 Prague 6, Czech Republic * Corresponding author. Tel.: +420-220-318-459; fax: +420-233-343-184; e-mail: gonchar@fzu.cz Received February 20, 2009; accepted May 18, 2009; available on-line November 16, 2009 The X-ray absorption near-edge structure (XANES) at the Mn K-edge in the (Ga,Mn)As magnetic semiconductor was simulated using the full potential linearized augmented plane wave (FLAPW) method including the core-hole effect. The calculations were performed in the supercell scheme for a substitutional and two tetrahedral interstitial Mn sites. The resulting pre-edge absorption structures show sharp distinction between the spectra simulated for the substitutional and interstitial Mn defects, which is determined mainly by the second nearest neighbor ligands. A single feature is obtained for the substitutional Mn impurity, whereas two peaks appear for both types of interstitial defects. An interpretation of the pre-edge features is proposed. (Ga,Mn)As magnetic semiconductor / X-ray absorption near-edge structure / Substitutional / Interstitial / Defects Introduction The Mn-doped GaAs magnetic semiconductors are interesting and promising magnetic materials for potential applications in spin electronics (spintronics). The main motivation behind the preparation and investigation of these materials is the man-made combination of both semiconducting/semimetallic and ferromagnetic properties in one physical system [1-3]. Various configurations of Mn dopants affect the magnetic properties of the (Ga,Mn)As system in different ways. There are several possibilities for a Mn atom to be incorporated in GaAs, and three of them have comparable energy [4] . The substitutional Mn atoms, Mn

Defect-induced ferromagnetism in Mn-dopedCu2O

In an effort to understand the ferromagnetic behaviour ofCu2O-based diluted magnetic semiconductors, the electronic structures of Mn-dopedCu2O sintered samples have been investigated using both experimental and theoretical approaches. MnL2,3 x-ray emission measurements and first-principle calculations reveal that Mn-dopedCu2O sinteredat 650 and 800 °C contains Mn interstitials as well as substitutional Mn atoms, but thedefect configuration depends on the sintering temperature. A reduction ofTC with sintering temperature can be explained by the appearance of an antiferromagneticsuperexchange interaction between substitutional Mn atoms via oxygen.

Mn0.06Ge0.94diluted magnetic semiconductor epitaxially grown on Ge(001): Influence ofMn5Ge3nanoscopic clusters on the electronic and magnetic properties

The structural, electronic, and magnetic properties of the ${\mathrm{Mn}}_{0.06}{\mathrm{Ge}}_{0.94}$ diluted magnetic semiconductor, grown at $520\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ by molecular-beam epitaxy on $\mathrm{Ge}(001)2\ifmmode\times\else\texttimes\fi{}1$, have been investigated. Diluted and highly ordered alloys, containing ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}$ nanocrystals, were grown. The valence band photoelectron spectrum of ${\mathrm{Mn}}_{0.06}{\mathrm{Ge}}_{0.94}$ shows a feature located at $\ensuremath{-}4.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ below the Fermi level, which is the fingerprint of substitutional Mn atoms in the Ge matrix. Magnetization measurements show the presence of a paramagnetic component due to substitutional Mn atoms and of a ferromagneticlike component due to ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}$ nanocrystallites. The Mn ${L}_{2,3}$ x-ray absorption spectrum of this polyphase film shows no marked multiplet structure, but a bandlike character.