共查询到20条相似文献,搜索用时 15 毫秒
1.
P. De Padova J.-P. Ayoub J.-M. Mariot M.C. Richter A.M. Testa B. Olivieri K. Hricovini 《Surface science》2007,601(13):2628-2631
Mn0.06Ge0.94 samples have been grown by molecular-beam epitaxy on Ge(0 0 1)2 × 1. High-resolution transmission electron microscopy shows the coexistence of an ordered diluted Mn0.06Ge0.94 film and of nanoscopic crystallites, which were identified as Mn5Ge3 by electron diffraction. The magnetic properties of the Mn0.06Ge0.94 samples show a superposition of a paramagnetic behavior, due to the interaction of Mn atoms diluted in the Ge host, and a ferromagnetic behavior attributed to the Mn5Ge3 crystallites dispersed into the films. The Mn L2,3 X-ray absorption spectra of the Mn0.06Ge0.94 films exhibit a lineshape typical of metallic Mn, with considerably reduced multiplet structure. 相似文献
2.
In this report, we fabricated a series of Fe3−xCrxO4(0≦x≦2) films by plasma-oxygen-assisted molecular beam epitaxy (MBE) and did structural and electrical characterizations of these films. These films show textured single phase quality and the lattice parameters are consistent with those of the bulk at low Cr composition (x<0.9). However, the lattice parameters show severe deviation from the bulk value in the intermediate region of 0.9≦x≦1.5 and no diffraction can be resolved at x∼2. These discrepancies may be attributed to the cation distributions and the instability of spinal structure as Cr concentration becomes dominant. The resistivity presents a typical Arrhenius temperature dependence with ρ=ρ0 exp (Ep/kBT) indicating that the transport is due to a hopping mechanism. The prefactor ρ0 increases in Fe3−xCrxO4, at smaller x but tends to level out for x>1, suggesting that Cr3+ ions may start to replace Fe3+ ions at the A site in the high x region. The activation energy of electrical hopping gradually increases at low Cr concentration but abruptly rises to ∼110 meV at x>0.9, suggesting a crossover from electron-hopping mediated transport to a thermally activated band gap excitation. 相似文献
3.
By using the first-principles calculation, we study the structural, magnetic, and electronic properties of the SrFeAsF compound and its Co-doped counterpart SrFe1 − xCoxAsF (x=0.125). It is shown that the competition of the nearest and next-nearest neighbor exchange coupling J1 and J2 between Fe ions gives rise to a frustrated striped antiferromagnetic order in SrFeAsF and an accompanied lattice distortion, while for the Co-doped case, both J1 and J2 decrease significantly as well as the lattice distortion, and thus the antiferromagnetic order is suppressed greatly. This is further confirmed by the electronic structure calculation that the density of states at the Fermi level increases with Co doping as well as the itinerancy of Fe d electron. 相似文献
4.
We have grown MnxGe1−x films (x=0, 0.06, 0.1) on Si (001) substrates by magnetron cosputtering, and have explored the resulting structural, morphological, electrical and magnetic properties. X-ray diffraction results show there is no secondary phase except Ge in the Mn0.06Ge0.94 film while new phase appears in the Mn0.1Ge0.9 film. Nanocrystals are formed in the Mn0.06Ge0.94 film, determined by field-emission scanning electron microscopy. Hall measurement indicates that the Mn0.06Ge0.94 film is p-type semiconductor and hole carrier concentration is 6.07×1019 cm−3 while the MnxGe1−x films with x=0 has n-type carriers. The field dependence of magnetization was measured using alternating gradient magnetometer, and it has been indicated that the Mn0.06Ge0.94 film is ferromagnetic at room temperature. 相似文献
5.
The electronic and optical properties of the direct band gap alloys SnxGe1 − x (x = 0.000, 0.042, 0.083, 0.125, 0.167, and 0.208) have been studied by using the generalized gradient approximation in the framework of the density functional theory. The calculated lattice constants obey Vergard's law. The band structures show that the alloys have direct band gap and the band gaps can be tunable by Sn contents. The optical properties of the SnxGe1 − x alloys with the physical quantities such as the complex dielectric function, the energy-loss function and the static dielectric constant, respectively, are shown to support the potential application of infrared devices in the future. 相似文献
6.
Y.C. Hu W.X. Gao Q. Zhang L. Ma C.M. Zhen G.D. Tang 《Journal of magnetism and magnetic materials》2010,322(24):3902-3906
The local micro-structure as well as the magnetic and transport properties of CrxGe1−x films prepared by means of magnetron sputtering have been investigated. Structural analysis shows that Cr atoms are situated in substitutional sites in the Ge lattice. Electrical transport properties indicate that Cr introduces a shallow acceptor level at 0.016 eV from the valence band implying Cr substituting for Ge. The low temperature ferromagnetism observed in the films is mediated mainly by ferromagnetic superexchange interactions between diluted Cr ions. 相似文献
7.
Weixia Gao Li WangDenglu Hou Yuchan HuQian Zhang Li MaCongmian Zhen 《Applied Surface Science》2011,257(21):8871-8875
Ge1−xMnx (x = 0, 0.013, 0.0226, 0.0339, 0.0565, 0.0678, 0.0904, 0.113) films prepared by magnetron sputtering at 773 K had a Ge cubic structure except for x = 0.1130. Co ion implantation into these films can effectively prevent the formation of a second phase. Both single-doped and co-doped samples were ferromagnetic at room temperature. The d-d exchange interaction between the interstitial Mn (MnT) and the substituted Mn (MnGe) resulted in ferromagnetism in the sputtered films. Since Co ion implantation destroyed the MnT-MnGe-MnT complex, the saturated magnetization decreased. Hall measurements revealed that the Co ion implanted films were n-type semiconductors, and the anomalous Hall Effect (AHE) suggested the ferromagnetism was carrier-mediated in the implanted films. 相似文献
8.
The effect of Cr100−xTix underlayer on orderd-L10 FePt films was investigated. A low-temperature ordering of FePt films could be attained through changing the Ti content of Cr100−xTix underlayer. The ordering temperature of the 30 nm FePt film grown on 20 nm Cr90Ti10 underlayer was reduced to 250 °C which is practical manufacture process temperature. An in-plane coercivity was very high to 6000 Oe and a ratio of remnant magnetization (Mr) to saturation magnetization (Ms) was as large as 0.85. This result indicates that the coercivity obtained at 250 °C by the effect of CrTi underlayer is significantly higher than those obtained at 250-275 °C by the effect of underlayers in other conventional studies. The prominent improvement of the magnetic properties of ordered FePt thin films at low temperature of 250 °C could be understood with considering the strain-induced ordering phase transformation associated with lattice mismatch between Cr underlayer and FePt magnetic layer due to an addition of Ti content. 相似文献
9.
Germanium quantum dots (QDs) were extracted from ultrathin SixGe1−x oxide films using scanning tunneling microscope (STM) tips. The extraction was most efficiently performed at a positive sample bias voltage of +5.0 V. The tunneling current dependence of the extraction efficiency was explained by the electric field evaporation transfer mechanism for positive Ge ions from QDs to STM tips. Ge QDs (∼7 nm) were formed and isolated spatially by extracting the surrounding Ge QDs with an ultrahigh density of >1012 cm−2. Scanning tunneling spectroscopy of the spatially-isolated QDs revealed that QDs with an ultrahigh density are electrically-isolated from the adjacent dots. 相似文献
10.
J.S. Tsay H.W. Chang Y.L. Chiou K.T. Huang W.Y. Chan Y.D. Yao 《Journal of magnetism and magnetic materials》2006
Influences of oxygen exposure on the magnetic properties of Co/Ge(1 1 1) ultrathin films have been investigated by surface magneto-optic Kerr effect technique. As the oxygen exposure increases on Co/Ge(1 1 1) films, their magnetic properties could be modified. As an example for 15 ML Co/Ge(1 1 1) films, the coercivity increases from 730 to 920 Oe and the remanence Kerr intensity is reduced for 500 Langmuir (L) of oxygen exposure. Corresponding compositions analyzed by Auger electron spectroscopy measurement shows that the amount of oxygen on the surface layers increases with increasing the oxygen exposure time. Oxygen distributes on the topmost layers of the film. The adsorbed oxygen influences the electronic density of states of Co and results in the changes of the magnetic properties. Besides, the appearance of O/Co/Ge interface could modify the stress anisotropy, and as a result the coercivity of ultrathin Co/Ge(1 1 1) film is enhanced. 相似文献
11.
Series of CoxCr1−x thin films have been evaporated under vacuum onto Si (1 0 0) and glass substrates. Chemical composition and interface properties have been studied by modelling Rutherford backscattering spectra (RBS) using SIMNRA programme. Thickness ranges from 17 to 220 nm, and x from 0.80 to 0.88. Simulation of the energy spectra shows an interdiffusion profile in the thickest films, but no diffusion is seen in thinner ones. Microscopic characterizations of the films are done with X-ray diffraction (XRD) measurements. All the samples are polycrystalline, with an hcp structure and show a 〈0 0 0 1〉 preferred orientation. Atomic force microscopies (AFM) reveal very smooth film surfaces. 相似文献
12.
FexNi100−x thin films were produced by galvanostatic electrodeposition on Si (1 0 0), nominal thickness 2800 nm, and x ranging 7-20. The crystalline structure of the sample was determined by X-ray diffraction (XRD). The magnetic properties were investigated by vibration sample magnetometry (VSM) and room temperature 57Fe Mössbauer spectroscopy. Conversion Electron Mössbauer spectroscopy (CEMS) in both film surfaces for the thick self-supported films showed that the magnetic moment direction is in the plane and conventional transmission (MS) that the directions are out of the plane films. The results were interpreted assuming a three-layer model where the external layer has in-plane magnetization and the internal one, out of plane magnetization. 相似文献
13.
The structural, electronic, and optical properties of CdxZn1 − xSe alloys are investigated using the first-principles plane-wave pseudopotential method within the LDA approximations. In particular, the lattice constant, bulk modulus, electronic band structures, density of state, and optical properties such as dielectric functions, refractive index, extinction coefficient and energy loss function are calculated and discussed. Our results agree well with the available data in the literature. 相似文献
14.
Series of CoxCr1−x thin films have been evaporated under vacuum onto Si(1 0 0) and glass substrates. Thickness ranges from 17 to 220 nm, and x from 0.80 to 0.88. Alternating gradient field magnetometer (AGFM) measurements provided saturation magnetization values ranging from 220 to 1200 emu/cm3. Values of squareness exceeding 0.8 have been measured. Coercive field may reach values up to 700 Oe, depending on the percentage of chromium, as well as the substrate nature and the direction of the applied magnetic field. The saturation magnetization value decreases as the Cr content increases. In order to study their dynamical magnetic properties, Brillouin Light Scattering (BLS) measurements have been performed on these samples. Stiffness constant value and anisotropy magnetic field were adjusted to fit the experimental BLS spectra. These results are analyzed and correlated. 相似文献
15.
A series of SmCoAsO1−xFx (with x=0, 0.05, 0.1, and 0.2) samples have been prepared by solid state reactions. X-ray powder diffraction proved that all samples can be indexed as a tetragonal ZrCuSiAs-type structure. A clear shrinkage of the lattice constants a and c with increasing F content indicated that F has been doped into the lattice. The magnetic and transport properties of the samples have been investigated. Parent SmCoAsO compound exhibited complicated magnetism including antiferromagnetism, ferromagnetism, and ferrimagnetism. For the fluorine doped samples, the antiferromagnetic Néel temperatures were almost independent of the F content and metamagnetic transitions were observed below antiferromagnetic Néel temperatures. With increasing F content, high temperature (below 142 K) ferrimagnetic state gradually changed to ferromagnetic state. In the resistivity result, metallic conduction in the region of 2-300 K and Fermi liquid behavior at low temperatures were shown in all samples. Transport properties at applied magnetic fields showed anomalies at low temperatures. 相似文献
16.
Structural, electronic and optical properties as well as structural phase transitions of ternary alloy CdxZn1 − xS have been investigated using the first-principles calculations based on the density functional theory. We found that the crystal structure of CdxZn1 − xS alloys transforms from wurtzite to zinc blende as Cd content of x=0.83. Effect of Cd content on electronic structures of CdxZn1 − xS alloys has been studied. The bandgaps of CdxZn1 − xS alloys with wurtzite and zinc blende structures decrease with the increase of Cd content. Furthermore, dielectric constant and absorption coefficient also have been discussed in detail. 相似文献
17.
Semiconductor optoelectronic devices based on GaN and on InGaN or AlGaN alloys and superlattices can operate in a wide range of wavelengths, from far infrared to near ultraviolet region. The efficiency of these devices could be enhanced by shrinking the size and increasing the density of the semiconductor components. Nanostructured materials are natural candidates to fulfill these requirements. Here we use the density functional theory to study the electronic and structural properties of (10,0) GaN, AlN, AlxGa1 − xN nanotubes and GaN/AlxGa1 − xN heterojunctions, 0<x<1. The AlxGa1 − xN nanotubes exhibit direct band gaps for the whole range of Al compositions, with band gaps varying from 3.45 to 4.85 eV, and a negative band gap bowing coefficient of −0.14 eV. The GaN/AlxGa1 − xN nanotube heterojunctions show a type-I band alignment, with the valence band offsets showing a non-linear dependence with the Al content in the nanotube alloy. The results show the possibility of engineering the band gaps and band offsets of these III-nitrides nanotubes by alloying on the cation sites. 相似文献
18.
We have investigated the electronic and magnetic properties of the doped Heusler alloys Co2Cr1−xVxAl(x=0, 0.25, 0.5, 0.75, 1) using first-principles density functional theory within the generalized gradient approximation (GGA) scheme. The calculated results reveal that with increasing V content the lattice parameter slightly increases; both cohesive energy and bulk modulus increase with increasing x. The magnetic moment of the Co(Cr) sites increases with V doping; the total spin moment of these compounds linearly decreases. We also have performed the electronic structure calculations for Co2Cr1−xVxAl with positional disorder of Co-Y(Cr,V)-type and Al-Y(Cr,V)-type. It is found that formation of Al-Y-type disorder in Co2Cr1−xVxAl alloys is more favorable than that of Co-Y-type disorder. Furthermore, we found that Co2Cr1−xVxAl of the L21-type structure have a half-metallic character. And the stability of L21 structure will enhance, however, the Curie temperature decreases as the V concentration increases. The disorder between Cr(V) and Al does not significantly reduce the spin polarization of the alloys Co2Cr1−xVxAl. 相似文献
19.
The electronic structures of Co-based Heusler compounds CoTiAl1−xSix (x=0, 0.25, 0.5, 0.75 and 1) are calculated by first-principles using the full potential linearized augmented plane wave (FP-LAPW) method within GGA and LSDA+U scheme. Particular emphasis was put on the role of the main group elements. In recent years, the GGA calculations of Co2TiAl (x=0) and Co2TiSi (x=1) indicated that they are half-metallic, but the electronic structure of this compound with x=0.25, 0.5 and 0.75 has not been reported yet, neither theoretically nor experimentally. The calculated results reveal that these are half-metallic and exhibit an energy gap in the minority spin state and also show 100% spin polarization. The substitution of Al by Si leads to an increase in the number of valence electrons, with increasing x. Our calculated results clearly show that with the Si doping, the lattice parameter linearly decreases; bulk modulus increases, and the total magnetic moment increases. The calculated energy gap in the minority spin state, using GGA scheme, was smaller than that obtained by using LSDA+U scheme. The outcomes of this research also show that the Co-3d DOS and therefore, the magnetic properties of compounds are dependent on electron concentration of the main group elements and it will affect the degree of p-d orbital occupation. 相似文献
20.
In this paper, we report theoretical investigations of structural, electronic and magnetic properties of ordered dilute ferromagnetic semiconductors Cd1−xFexS with x=0.25, 0.5 and 0.75 in zinc blende (B3) phase using all-electron full-potential linear muffin tin orbital (FP-LMTO) calculations within the density functional theory and the generalized gradient approximation. The analysis of band structures, density of states, total energy, exchange interactions and magnetic moments reveals that both the alloys may exhibit a half-metallic ferromagnetism character. The value of calculated magnetic moment per Fe impurity atom is found to be 4 μB. Moreover, we found that p-d hybridization reduces the local magnetic moment of Fe from its free space charge value of 4 μB and produces small local magnetic moments on Cd and S sites. 相似文献