Doped Mn Atoms Research Articles

Only the chemical state of Indium changes in Mn-doped In3Sb1Te2 (Mn: 10 at.%) during multi-level resistance changes.

We fabricated and characterized the material with Mn (10 at.%: atomic percent) doped In3Sb1Te2 (MIST) using co-sputtering and synchrotron radiation, respectively. The MIST thin film showed phase-changes at 97 and 320°C, with sheet resistances of ~10 kΩsq (amorphous), ~0.2 kΩsq (first phase-change), and ~10 Ωsq (second phase-change). MIST did not exhibit any chemical separation or increased structural instability during either phase-change, as determined with high-resolution x-ray photoelectron spectroscopy. Chemical state changes were only depended for In without concomitant changes of Sb and Te. Apparently, doped Mn atoms can be induced with movement of only In atoms.

Obtaining half-metallic ferrimagnetism and antiferromagnetism by doping Mn and Fe for DO3-type Heusler compound Cr3Si

The electronic structure, magnetic properties and occupation feature of DO3-type Heusler compounds (Cr1−xMnx)3Si and (Cr1−xFex)3Si (x=n/12, n=0, 2, 4, 6, 8, 10, 12) have been investigated by first principles calculations. The compounds Cr3Si, (Cr1–4/12Mn4/12)3Si, Mn3Si, (Cr1–2/12Fe2/12)3Si, and (Cr1–6/12Fe6/12)3Si are predicted to be half-metallic ferrimagnets. The compound (Cr1–4/12Fe4/12)3Si is predicted to be half-metallic antiferromagnet, which is applicable to spintronic devices due to its zero magnetization. The Fe atoms of (Cr1−xFex)3Si prefer to occupy the (A,C) sites while the Mn atoms of (Cr1−xMnx)3Si tend to occupy the B site, indicating that the occupation of doping atoms is affected strongly by the inter-atom hybridization and the 3d electrons number of doping atoms is not a determining factor. In addition, the results confirm the uniformity rule that the A site is equivalent to C site and the doping atoms prefer to enter the two sublattice uniformly. The more symmetric surroundings of atom coordination in B site in contrast to (A,C) site leads to a typical 3d electronic splitting peaks. The total moment for all the doped compounds (Cr1−xMnx)3Si and (Cr1−xFex)3Si agrees well with the Slater–Pauling rule. The coexisting Cr(B) and Cr(A,C) atoms show antiferromagnetic coupling character for both (Cr1−xMnx)3Si and (Cr1−xFex)3Si. The coexisting doping Mn(B) and Mn(A,C) atoms show antiferromagnetic coupling character for (Cr1−xMnx)3Si while Fe(B) and Fe(A,C) atoms show ferromagnetic coupling character for (Cr1−xFex)3Si.

Structural and magnetic properties of small NinMn clusters

The effects of alloying on the structural and magnetic properties of NinMn (n=1–12) clusters are investigated using all-electron density functional theory. The results reveal that the most stable structures of NinMn (n=1–12) clusters are all similar to those of corresponding Nin+1 clusters. Maximum peaks of second-order energy difference are found at n=3, 5, 8 and 10, indicating that these clusters possess relatively higher stability than their respective neighbors. An enhancement in the magnetic moment is obtained for small binary Ni–Mn clusters compared to that of pure Ni clusters of same size except for Ni10Mn. In addition, the magnetic properties of the doped Mn atom exhibit the magnetic moment surface enhancement effect.

Investigation of microstructure and photoluminescence of Mn and Co co-doped SiC films

Mn and Co co-doped SiC films were fabricated on Si (100) substrates by RF-magnetron sputtering. The lattice structure, composition, chemical valences and photoluminescence of the films were investigated. The lattice structure analysis shows that the films are composed of 3C–SiC and the doped Co atoms form CoSi secondary phase compounds in the films. The analyses of composition and valences display that the doped Mn and Co atoms are in the form of Mn2+ and Co2+ in the films, respectively. The analysis of local structure reveals that the doped Mn substitute for C sites in SiC lattice and no Co or Mn clusters, and Mn- and Co-related compounds except CoSi appear in the films. A violet peak located at 413nm for all the films can be observed in photoluminescence spectra, and the peaks become stronger with the increase of Mn concentration, which should be associated with C clusters.

The Intrinsic Ferromagnetism in a MnO2 Monolayer.

The Mn atom, because of its special electronic configuration of 3d(5)4s(2), has been widely used as a dopant in various two-dimensional (2D) monolayers such as graphene, BN, silicene and transition metal dichalcogenides (TMDs). The distributions of doped Mn atoms in these systems are highly sensitive to the synthesis process and conditions, thus suffering from problems of low solubility and surface clustering. Here we show for the first time that the MnO2 monolayer, synthetized 10 years ago, where Mn ions are individually held at specific sites, exhibits intrinsic ferromagnetism with a Curie temperature of 140 K, comparable to the highest TC value achieved experimentally for Mn-doped GaAs. The well-defined atomic configuration and the intrinsic ferromagnetism of the MnO2 monolayer suggest that it is superior to other magnetic monolayer materials.

Density functional theory study of MnY N (N = 2–13) clusters

We predict that doped Mn atoms can not efficiently improve magnetism of yttrium clusters in most cases, which is different from Mn–Ge, Mn–Bi and Mn–B complexes. The calculated results show that the ground state structures of MnY N clusters favor growth patterns of octahedron structures, with Mn atom occupying the center of yttrium framework at N ≥ 6. There are three minima of the HOMO–LUMO gap with N = 6, 10 and 13 which can be mainly attributed to obvious elevation of energy level of the HOMO. The computed magnetic moment per atom displays size-dependent behavior with oscillational odd–even character. The Mulliken population analysis shows that the doped Mn atom, with antiferromagnetic alignment at N = 5, 9, 11 and 13, tends to reduce the magnetic moment of the system of N ≥ 6. Both structure and chemical bonding are responsible for the variation of magnetism of Mn doped yttrium clusters.

Investigation of structure, magnetic, and transport properties of Mn-doped SiC films

Mn-doped SiC films were fabricated by radio frequency magnetron sputtering technique. The structure, composition, and magnetic and transport properties of the films were investigated. The results show the films have the 3C-SiC crystal structure and the doped Mn atoms in the form of Mn2+ ions substitute for C sites in SiC lattice. All the films are ferromagnetic at 300 K, and the ferromagnetism in films arises from the doped Mn atoms and some extended defects. In addition, the saturation magnetization increases with the Mn-doped concentration increasing. The Mn doping does not change the semiconductor characteristics of the SiC films.

Influence of annealing on the local structure, magnetic and transport properties of Mn-doped SiC films

Mn-doped SiC films are deposited on Si (1 0 0) substrates by the RF-magnetron sputtering technique. The influence of annealing on the local structure, magnetic and transport properties of the films is investigated systematically by x-ray diffraction, x-ray photoelectron spectroscopy, x-ray absorption fine structure, transport and magnetic measurements. The results show that for the as-deposited and 800 °C annealed films, the doped Mn atoms occupy the C sites of the 3C-SiC lattice, only semiconducting behaviour is observed in the whole temperature range and the transport property is governed by Mott variable range hopping behaviour, suggesting that the carriers are strongly localized. After 1200 °C annealing, the majority of Mn atoms form Mn4Si7 secondary phases and a crossover from semiconducting to metallic transport behaviour with transition temperatures occurring at 134 K is detected in the film. Magnetic characterization shows that all the films are ferromagnetic with a Curie temperature of above 300 K and the saturated magnetic moment increases monotonically with increasing annealing temperature. It is speculated that the ferromagnetism of the films is intrinsic and can be ascribed to rely on the percolation of bound magnetic polarons for the as-deposited and 800 °C annealed films. After 1200 °C annealing, the carbon-incorporated Mn4Si7 compounds can be considered to be the origin of ferromagnetism in the film.

Investigation of microstructures and optical properties in Mn-doped SiC films

Mn-doped SiC films were prepared on Si(100) substrates by RF-magnetron sputtering technique. The microstructures and composition of films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The XRD results show that the Mn-doped SiC films form a 3C–SiC crystal structure and some doped Mn atoms occupy the C sites of SiC lattice. The XPS results suggest that there exist SiC, CC and SiMn bonds in the films, but the signal of SiC bond decreases and that of CC bond increases with the increase of Mn concentration. The Mn K-edge XANES and EXAFS measurements show that the majority of Mn atoms form Mn4Si7 secondary phase compounds and the existence of Mn metal and MnO can be safely excluded. Then the photoluminescence (PL) properties of films are observed at room temperature. The origin of 413-nm PL peak is associated with C cluster centers, which obviously correlates with the Mn-doped concentration.

Magnetic behavior of Mn-doped GaN (11¯00) film from first-principles calculations

Using first principles calculations based on spin-polarized density functional theory, the magnetic behavior of Mn-doped GaN (11¯00) film is studied. The doping Mn atoms have an attractive pair interaction. Our results give the ground state with antiferromagnetic coupling for Mn-doped GaN (11¯00) film when the nearest neighbor Ga atoms on the surface layer are replaced by Mn atoms, which is contrary to the ferromagnetic coupling when Mn is doped in the bulk GaN. However, in-plane tension and hole doping can switch the magnetic ordering from antiferromagnetism to ferromagnetism, which is important for application in semiconductor spintronics.

X-Ray Absorption Spectroscopy and X-Ray Magnetic Circular Dichroism Studies of Transition-Metal-Codoped ZnO Nano-Particles

We report on x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies of the paramagnetic (Mn,Co)-co-doped ZnO and ferromagnetic (Fe,Co)-co-doped ZnO nano-particles. Both the surface-sensitive total-electron-yield mode and the bulk-sensitive total-fluorescence-yield mode have been employed to extract the valence and spin states of the surface and inner core regions of the nano-particles. XAS spectra reveal that significant part of the doped Mn and Co atoms are found in the trivalent and tetravalent state in particular in the surface region while majority of Fe atoms are found in the trivalent state both in the inner core region and surface region. The XMCD spectra show that the Fe$^{3+}$ ions in the surface region give rise to the ferromagnetism while both the Co and Mn ions in the surface region show only paramagnetic behaviors. The transition-metal atoms in the inner core region do not show magnetic signals, meaning that they are antiferromagnetically coupled. The present result combined with the previous results on transition-metal-doped ZnO nano-particles and nano-wires suggest that doped holes, probably due to Zn vacancy formation at the surfaces of the nano-particles and nano-wires, rather than doped electrons are involved in the occurrence of ferromagnetism in these systems.

Molecular and electronic structures of Mn-doped tris-8-hydroxyquinolinate gallium: DFT calculation and experiment

Molecular and electronic structures of Mn-doped tris-8-hydroxyquinolinate gallium (Gaq 3) were investigated by first-principle density-functional theory (DFT) calculations and Fourier transform-infrared spectroscopy (FTIR) and photoluminescence (PL) spectra measurements. Calculation results show that the lowest unoccupied molecular orbital (LUMO) sets reside mainly on N 2, N 3 p states, as well as on the p states of their third-nearest-neighbor C atoms. The doped Mn atoms prefer to be located at the ligand center. The electrons deplete from the Mn atom and accumulate mainly on the C, N atoms within the pyridyl ring of ligand A. The magnetic moment is mainly localized around the d orbital of Mn atom and the 2p states of C and N atoms on pyridyl ring are also spin polarized due to the hybridization with Mn 3d states. The positive charged Mn ions lead to an electron trap site in the energy gap and a red luminescence appears in PL spectra, which may be related to the MLCT excited states.

Strong d–d electron interaction inducing ferromagnetism in Mn-doped LiNbO 3

Mn-doped LiNbO 3 was prepared by ion beam implantation with Mn content of 1 to 5 at.%. The samples were ferromagnetic. The maximum atomic magnetic moment was 5.83 μ B/Mn for the samples with Mn content of 3 at.% in the implanted layer. Structure characterization using X-ray absorption near edge structure determined that the Mn atoms substituted principally the Li atoms in the LiNbO 3 lattice. The magnetic mechanism was understood with the aid of electronic structure calculation using local density approximations plus U method. The calculated results demonstrated that the Mn:LiNbO 3 with Mn atom on the Li site is half-metallic ferromagnetic. The calculated magnetic moment per cell agreed well with the experimental results. Spin splitting of the d-states occurred for both the Mn dopant and the Nb atoms. The doped Mn atom interacts strongly with its neighboring Nb atoms. This strong d–d electron interaction can work at long range through the whole crystalline cell.

Distribution of doped Mn at the Σ3 (1 1 2) grain boundary in Ge

Using first-principles density functional theory method, we have investigated the distribution and magnetism of doped Mn atoms in the vicinity of the Σ3 (1 1 2) grain boundary in Ge. We find that at low concentration, the substitutional sites are energetically favorable over the interstitial ones for Mn. The binding energy of Mn varies with lattice sites in the boundary region, and hence a non-uniform distribution of Mn nears the boundary. However, the average of their segregation energy is quite small, thus no remarkable grain boundary segregation of Mn is predicted. Due to volume expansion at the grain boundary, the spin polarization of Mn is slightly enhanced. Overall, we find that the magnetism of Mn-doped Ge is not sensitively dependent on the grain structure.

Cosputtered Mn-doped Si thin films studied by x-ray spectroscopy

Substitutionally doped Si1−xMnx thin films were fabricated by a magnetron cosputtering method at a low growth temperature. X-ray absorption fine structure (XAFS) and x-ray diffraction (XRD) techniques were used to investigate the structures of the Si1−xMnx thin films. The XRD results exhibit that no secondary phases such as metallic Mn or Mn–Si compound can be detected. The detailed analysis of the extended XAFS together with the x-ray absorption near-edge structure spectra at the Mn K-edge unambiguously reveals that the doped Mn atoms are incorporated into the Si matrix and substitute for the Si sites in the Si lattice. The results clearly indicate that the Mn occupations in silicon thin films are quite sensitive to the growth conditions and the postannealing treatment.

Structural and Chemical Characterization of Mn Doped GaN Nanowires by X-ray Absorption Spectroscopy

We report on structural chemical state of doped Mn atoms in single crylstalline Mn doped GaN nanowires by X-ray absorption spectroscopy. Anomalous X-ray scattering and K-edge X-ray absorption fine structure measurement make it clear that Mn atoms substitute the Ga sites and they largely take part in the wurtzite network of host GaN. X-ray absorption and X-ray magnetic circular dichroism spectra at Mn L(2,3)-edges show that doped Mn has local magnetic moment and the electronic configuration of the doped Mn is mainly 3d(5) component. The structural and chemical states of the doped Mn atoms imply that they ascribe to the observed ferromagnetism in these diluted magnetic semiconductor nanowires.

Built-in electric field assisted spin injection in Cr and Mnδ-layer doped AlN/GaN(0001) heterostructures from first principles

Highly spin-polarized diluted ferromagnetic semiconductors are expected to be widely used as ideal spin injectors. Here, extensive first-principles density-functional theory calculations have been performed to investigate the feasibility of using Cr- and Mn-doped wurtzite polar AlN/GaN0001 heterostructures, with the aim to realize the appealing half-metallic character and, hence, efficient electrical spin injection. To overcome the formation of detrimental embedded clusters, we propose digital -layer doping perpendicular to the growth direction so as to realize enhanced performance at room temperature. The formation energy, electronic and magnetic properties, and the degree of spin polarization for both neutral and charged valence states for various concentrations are studied. Under both metal-rich Al- or Ga-rich and N-rich conditions, Cr and Mn dopants prefer to segregate into the GaN region and reside close to the interface, where dopant incorporation occurs more readily under N-rich conditions. The doped Cr and Mn atoms introduce 3d states in the band gap of the host semiconductor heterostructure. The spin injection channels are constructed via the hybridization between dopant 3d and surrounding host atoms, up to a few monolayers around the interface, where the spin-polarized t2 electrons are injected into AlN without the conductivity mismatch problem. Significantly, for the energetically favorable configurations, the built-in electric field in the AlN/GaN0001 heterointerface serves as a driving force for efficient spin injection through the interface and spin transport in the AlN region. Also importantly, the electronic properties of the heterostructures half metallic, semiconducting, or metallic are found to depend sensitively upon the doping concentration and valence charge states. In general, charged valence states can destroy the ferromagnetic half metallicity for both systems, particularly in n-type materials. These results will be useful with regard to the practical fabrication of desirable heterostructures for optoelectronic and semiconductor spintronic devices.

Small [formula omitted] clusters: Magnetic order and magnetic moment

The effects of a manganese atom on the magnetic order and magnetic moments of Fe n Mn ( n = 1 – 12 ) clusters have been investigated using the all-electron density functional theory. The results reveal that the Fe–Mn couplings in the lowest-energy structures of Fe n Mn ( n = 1 – 12 ) clusters undergo a change from ferromagnetic ordering for the smallest ( n = 1 , 2 ) clusters to ferrimagnetic ordering for the intermediate ( n = 3 – 6 ) clusters. Starting from n = 7 , however, ferromagnetic Fe–Mn couplings completely prevail. The low coordination number of the doped Mn atom results in it having a high spin moment in the Fe–Mn binary clusters, which exhibits a marked magnetic moment surface enhancement effect.

Structural growth sequences and electronic properties of manganese-doped germanium clusters:MnGen (2–15)

The structural growth sequences and electronic properties ofMnGen (n = 2–15) clusters have been investigated using density functional theory (DFT)within the generalized gradient approximation (GGA). An extensive searchof the lowest-energy structures was conducted by considering a number ofstructural isomers for each cluster size. In the ground-state structures ofMnGen clusters, the equilibrium site of the Mn atom gradually moves from the convex, surface to interiorsites as the Ge cluster size varies from 2 to 15. The threshold size for the formation of cagedMnGen and the sealedMn-encapsulated Gen structure is n = 9 and n = 10, respectively. Maximum peaks were observed forMnGen clustersat n = 3, 6, 10, 12 and 14 with the size dependent on the second-order energy difference, implying thatthese clusters are relatively more stable. The electronic structures and magnetic properties ofMnGen inthe ground-state structures are discussed. The doped Mn atom makes the HOMO–LUMO gap of theGen clusters smaller, due to hybridization between the p states of theGe atom and the d states of the Mn atom. Most of the Mn-dopedGen clusters carry a magnetic moment of about1.0 μB, exceptthat MnGe6 andMnGe11 have a magneticmoment of about 3.0 μB. Charge transfer between Mn and Ge was also observed.

Magneto-Transport and Magnetic Properties of Ni-Mn-Ga

We report a detailed investigation of the magneto-transport and magnetic properties of Mn excess Ni-Mn-Ga using the resistivity and magnetization measurements. Magnetoresistance (MR) has been measured in the ferromagnetic state for different compositions in the austenitic, premartensitic and martensitic phases. With Mn doping in Ni2-yMn1+yGa, a decrease in magnetization and MR has been found, since the doped Mn atoms in Ni position are in the antiferromagnetic configuration with the Mn atoms in Mn position. MR for the parent stoichiometric composition Ni2MnGa varies almost linearly with field in the austenitic and pre-martensitic phases, and shows a cusp-like shape in the martensitic phase. This has been explained by the changes in twin and domain structures in the martensitic phase. Hysteresis in the heating and cooling cycles is a characteristic of the first order nature of the martensitic phase transition.