共查询到20条相似文献,搜索用时 15 毫秒
1.
E.S. Mushailov P.D. Kim I.A. Turpanov G.V. Bondarenko S.E. Mishina 《Journal of magnetism and magnetic materials》2006
Magnetic Co1−xCux alloys in the form of single-crystal and polycrystalline films were grown under strongly non-equilibrium conditions using magnetron and triode sputtering techniques. It was found that these alloys could be obtained not only in the expected face-centered cubic structure, but also in a tetragonal phase, undetected earlier for present alloys. Results comparing some structural, magnetic and electric properties of these two phases are also presented here. 相似文献
2.
J.Q. Li 《Solid State Communications》2004,129(7):431-435
Electron paramagnetic resonance on La2/3−xYxCa1/3MnO3 in the paramagnetic (PM) regime is presented for 0≤x≤0.133. The resonance linewidth (ΔHpp) decreases with cooling, reaches the minimum at Tmin, and then anomalously increases with further cooling toward Tc. Our analysis on ΔHpp(T) below Tmin shows that the anomalous PM behavior below Tmin is due to the appearance of a ferromagnetic (FM) phase within the PM matrix caused by the applied magnetic fields. The correlation between the anomalous PM and the colossal magnetoresistance is discussed. We argue that both are caused by the phase segregation in which the compound is phase-separated into a mixture of FM and PM regions. 相似文献
3.
Alka V. Deshmukh S.M. Yusuf N.P. Lalla 《Journal of magnetism and magnetic materials》2010,322(5):536-1217
Present study reports the detailed structural and magnetic, as well as chemical analysis of polycrystalline Zn1−xMnxO (where x=0, 0.005, 0.01, 0.03, 0.05 and 0.1) samples synthesized by the high-temperature solid state reaction route. X-ray diffraction studies reveal the presence of secondary phase for higher Mn-doping concentrations (x≥0.03). Secondary phase formation having spinel structure is confirmed and reported as an evidence for the first time using transmission electron microscopy study. Chemical investigations using X-ray photoelectron spectroscopy showed the presence of Mn in two valence states. From the observed results we are of the opinion that Zn2+ ions, mainly present at or near grain boundaries, diffuse into manganese oxide to form a stable spinel phase ZnxMn3−xO4 at or near the grain boundaries of ZnO/Zn1−xMnxO. Magnetization measurements did not show any magnetic transition down to 5 K. 相似文献
4.
Cd1−xZnxS (0?x?0.5) nanocrystals have been synthesized using a simple chemical precipitation method. Morphological and crystallographic analyses have been done using transmission electron microscope (TEM) and X-ray diffraction (XRD). Room temperature energy and time resolved photoluminescence spectra of these synthesized nanophosphors have been studied using xenon lamp spectroflourometer and high peak power, pulsed N2-laser excitation, respectively. Photoluminescence spectra are composed of broad peaks ranging from green to red region of the visible spectrum. Important optical parameters: excited state lifetime, trap-depth and decay constant values have been calculated from recorded luminescence decay curves. These nanophosphors show typical lifetime shortening and high quantum yield with increasing concentration of Zn. 相似文献
5.
Younghun Hwang Sunglae ChoHyekyeong Kim Youngho Um 《Journal of magnetism and magnetic materials》2006
We have investigated the magnetic and electrical transport properties of Si1−xMnx single crystals grown by the vertical Bridgman method. The alloys with Mn concentrations up to x=0.64 have weak ferromagnetic ordering around TC∼30 K. However, Si0.25Mn0.75 alloys show weak ferromagnetic ordering at 70 K and antiferromagnetic ordering at 104 K, which is confirmed by magnetization and electrical transport studies. 相似文献
6.
Concentration-driven reorientation phase transitions in ultrathin magnetic films of FeCo alloy have been studied. It is established that, in addition to the easy-axis and easy-plane phases, a spatially inhomogeneous phase (domain structure), a canted phase, and also an “in-plane easy-axis” phase can exist in the system. The realization of the last phase is associated with the competition between the single-ion anisotropy and the magnetoelastic interaction. The critical values of Co concentration corresponding to the phase transitions are evaluated, the types of phase transitions are determined, and the phase diagrams are constructed. 相似文献
7.
Magnetoresistive La0.67−yYyBa0.33MnO3/LaAlO3 thin films were prepared by the sol-gel spin-coating method. Our resistivity and the electron spin resonance (ESR) measurements indicate that the main factor determining the metal-insulator transition temperature Tm is the cation disorder represented by the cation radii variance σ2, and that ferromagnetic insulating regions coexist in the ferromagnetic metallic phase. In the paramagnetic phase, the dissociation energy of spin clusters and the polaron hopping energy obtained from the ESR intensity and linewidth also displayed a prominent dependence on σ2. Polaron localization due to Jahn-Teller distortions appears to be responsible simultaneously for the decrease in the ferromagnetic order and for the increase in the orbital order. 相似文献
8.
We report the observation of excellent hard magnetic properties on purely single phase ErCo7−xCux compounds with x=0.3, 0.5, 0.8 and 1. Cu substitution leads to a decrease in the saturation magnetization, but enhances the uniaxial anisotropy in this system. The large anisotropy field (∼100 kOe) is attributed to the Er and the Co sublattices. Domain wall pinning effect seems to play a crucial role in determining the temperature and field dependences of magnetization in these compounds. The hard magnetic properties obtained at room temperature (RT) are comparable to the best results obtained in other RCo7 based materials. 相似文献
9.
Stoichiometric BaxSr1−xTiO3 ceramics (x=0.7, 0.8, and 0.9) have been prepared by solid-state reaction method. It has been observed in our experiments that the photoluminescence (PL) spectra in such samples at room temperature were centered around 800 nm; the results have been found to differ from observations in current literature. An explanation of this phenomenon was given, and the origin of such photoluminescence is ascribed to certain defects existing in these compounds, such as oxygen vacancies. 相似文献
10.
J. Deisenhofer H.-A. Krug von NiddaA. Loidl E.V. Sampathkumaran 《Solid State Communications》2003,125(6):327-331
We report electron-spin resonance (ESR) measurements in polycrystalline samples of (Gd1−xYx)2PdSi3. We observe the onset of a broadening of the linewidth and of a decrease of the resonance field at approximately twice the Néel temperature in the paramagnetic state. This characteristic temperature coincides with the electrical resistivity minimum. The high-temperature behavior of the linewidth is governed by a strong bottleneck effect. 相似文献
11.
Shuang Qiao Denglu Hou Yanyan Wei Weixia Gao Yuchan Hu Congmian Zhen Guide Tang 《Journal of magnetism and magnetic materials》2009,321(16):2446-2450
MnxGe1−x thin films were prepared by magnetron sputtering with a substrate temperature of 673 K and subsequently annealed at 873 K. The X-ray diffraction (XRD) measurements showed that all samples had a single Ge cubic structure. No films showed clear magnetic domain structure under a magnetic force microscope (MFM). Atom force microscope (AFM) measurements showed that the films had an uniform particle size distribution, and a columnar growth pattern. X-ray photoelectron spectroscopy (XPS) measurements indicated that the valences of both Mn and Ge atoms increase with the Mn concentration. The resistance decreased with increasing temperature, suggesting that the films were typical semiconductors. Magnetic measurements carried out using a Physical Property Measurement System (PPMS) showed that all samples exhibited ferromagnetism at room temperature. There was a small concentration of Mn11Ge8 in the films, but the ferromagnetism was mainly induced by Mn substitution for Ge site. 相似文献
12.
S. Taniguchi N. Fukuoka Y. Nagata Y. Noro 《Journal of magnetism and magnetic materials》2009,321(19):3335-3341
Epitaxial thin films of CaRu1−xMxO3 (M=Ti, Mn) were fabricated on a (0 0 1)-SrTiO3 substrate by spin-coat method using organometallic solutions (metal alkoxides). Results of X-ray diffraction and transmission electron microscopy indicate that the epitaxial films were grown pseudomorphically so as to align the [0 0 l] axis of the CaRu1−xMxO3 films perpendicular to the (0 0 1) plane of the SrTiO3 substrate. Ferromagnetism and metal-insulator transition are induced by the substitution of transition metal ions. The occurrence of ferromagnetism was explained qualitatively assuming a TiRu6 cluster model for CaRu1−xTixO3 film and a mixed valence model for CaRu1−xMnxO3 film. Ferromagnetism was also observed for layered CaRuO3/CaMnO3 film and CaRuO3/CaMnO3/CaRuO3/CaMnO3 multilayer film and the magnetism was explained by an interfacial exchange interaction model with magnetic Mn3+, Mn4+, and Ru5+ ions. 相似文献
13.
Using full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method, we have investigated the dependence of GaAs clusters with eight atoms on composition. It is found that the ground state structures for Ga-rich and As-rich clusters are cube structures. As the ratio between gallium atoms and arsenic atoms is close to one, structural distortion become increasingly severe, or even the clusters adopt other geometrical configurations as their ground state structures. The energy gap Eg between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO), and the vertical electron affinity show a certain degree of even/odd alternation with cluster composition. Among nine Ga8−nAsn (n=0-8) clusters, only a few of clusters have different energy orders between the ionic and neutral isomers with large binding energy. Some ionic structures would change into other configurations due to severe structural distortion. 相似文献
14.
Based on the pseudopotential scheme, the effect of nitrogen concentration on electronic properties of zinc-blende GaAs1−xNx alloys has been investigated for small amounts of N. The agreement between our calculated electronic band parameters and the available experimental data is generally reasonable. In agreement with recent experiment, we find that the incorporation of a few percent of N in the material of interest reduces substantially the fundamental band-gap energy and narrows the full valence band width. The electron and heavy hole effective masses are found to decrease rapidly when adding a concentration of nitrogen less than 0.005 in GaAs. This may increase the mobility of electrons and heavy holes providing new opportunities regarding the transport properties. The information derived from the present study shows that GaAs1−xNx (0?x?0.05) properties may have an important optoelectronic applications in infrared and mid-infrared spectral regions. 相似文献
15.
J.-S. Kang G. Kim S.S. Lee S. Choi S. Cho S.W. Han H.J. Shin B.I. Min 《Journal of magnetism and magnetic materials》2006
The spatial concentration distribution and local electronic structure of ferromagnetic Ge1−xTx (T=Cr, Mn, Fe) DMS single crystals have been investigated by using scanning photoelectron microscopy (SPEM), X-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). It is found that doped T ions in Ge1−xTx crystals are chemically phase-separated, suggesting that the observed ferromagnetism arises from the phase-separated T-rich phases in Ge1−xTx. 相似文献
16.
Ahmad Yazdani 《Journal of magnetism and magnetic materials》2009,321(24):3990-3996
In this paper it is demonstrated that the second phase transition of Gd2In intermetallic compound gets eliminated by diluting Gd2−x(LaY)xIn at a critical composition of x=0.5. The exchange coupling for intra-cluster interactions is estimated in the correlation ranges of 3.3 Å<RC<3.6 Å (anisotropic source) and for inter-cluster interactions in the ranges of RC>4 Å where the correlation length is defined as . The sign and strength of the exchange coupling are identified by the eigenvalues λ(k) and are obtained from zeros of the 4×4 matrix of JijRR′ along the three directions of the reciprocal lattice for each dilution (x=0.25, 0.5, 0.75, 1). The transition temperature is calculated using the minimum eigenvalue λmin (k=0, π) which agrees with the experiment. Magnetic field and temperature dependence of the magnetization and electrical resistivity measurements show that: (i) Elimination of the AFM phase is caused by breaking of some FM short-range exchange couplings, and (ii) Conduction electrons order antiferromagnetically at low temperatures and ferromagnetically at high temperatures. 相似文献
17.
SrBi2−xPrxNb2O9 (x=0, 0.04 and 0.2) ceramics were prepared by a solid state reaction method. X-ray diffraction analysis indicated that single-phase layered perovskite structure ferroelectrics were obtained. A relaxor behavior of frequency dispersion was observed among Pr-doped SrBi2Nb2O9. The degree of frequency dispersion ΔT increased from 0 for x=0-7 °C for x=0.2, and the extent of relaxor behavior γ increased from 0.94 for x=0-1.45 for x=0.2. The substitution of Pr ions for Bi3+ ions in the Bi2O2 layers resulted in a shift of the Curie point to lower temperatures and a decrease in remanent polarization. In addition, the coercive field 2Ec reduced from 110 kV/cm for an undoped specimen to 90 kV/cm for x=0.2. 相似文献
18.
Using first-principles total energy calculations within the full-potential linearized augmented plane wave (FP-LAPW) method, we have investigated the structural, electronic and thermodynamic properties of potassium halides (KClxBr1−x, KClxI1−x and KBrxI1−x), with x concentrations varying from 0% up to 100%. The effect of composition on lattice constants, bulk modulus, band gap and dielectric function was investigated. Deviations of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the three alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and coworkers. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing ΔHm as well as the phase diagram. 相似文献
19.
I. Dincer Y. Elerman E. Duman A. Elmali H. Ehrenberg H. Fuess 《Journal of magnetism and magnetic materials》2007
We have studied the effects of Co substitution for Mn on the structure and magnetic properties of the HoMn6−xCoxSn6 compounds (0?x?0.25) with HfFe6Ge6-type structure (space group P6/mmm) by X-ray powder diffraction and magnetization measurements. A monotonic decrease of the lattice parameters a and c is observed with increasing Co content. While the compounds with x=0 and 0.05 exhibit ferrimagnetism in the whole temperature range, the compounds with 0.1?x?0.15 show ferrimagnetism, helimagnetism and re-entrant ferrimagnetism with decreasing temperature. For the compounds with x=0 and 0.05, the spin reorientation temperature is observed. A metamagnetic transition from helimagnetic magnetic ordering to ferrimagnetism is observed for the compounds with x=0.1 and 0.2. The results are summarized in the HoMn6−xCoxSn6 magnetic phase diagram. 相似文献
20.
Yasumitsu Matsuo Yasuhito Tanaka Junko Hatori Seiichiro Ikehata 《Solid State Communications》2005,134(5):361-365
We have investigated the origin of the change in proton activity in the phase transition at TII-III (=369 K) in Cs3H(SeO4)2 from the viewpoint of its ferroelasticity by using 1H NMR and X-ray measurements. It is found that the second moment of the 1H NMR absorption line rapidly decreases at TII-III with increasing temperature. From this result, we conclude that the hopping motion of a proton, which is the precursor motion in the superprotonic phase, becomes more active above TII-III. This result is consistent with the fact that the electrical conductivity in phase II is larger than that in phase III. Furthermore, it is also found that the spontaneous strain decreases abruptly at TII-III. From these results, it is deduced that the decrease in the spontaneous strain at TII-III causes the increase in the proton activity at TII-III. In addition, it is deduced that the increase in proton activity and the decrease in the spontaneous strain at TII-III are closely related with the appearance of the superprotonic phase transition at TI-II (=456 K). 相似文献