共查询到20条相似文献,搜索用时 15 毫秒
1.
Ferromagnetic Ga1−xMnxAs layers (where x≈4.7–5.5%) were grown on (1 0 0) GaAs substrates by molecular beam epitaxy. These p-type (Ga,Mn)As films were revealed to have a ferromagnetic structure and ferromagnetism is observed up to a Curie temperature of 318 K, which is ascribed to the presence of MnAs secondary magnetic phases within the film. It is highly likely that the phase segregation occurs due to the high Mn cell temperature around 890–920 °C, as it is well established that GaMnAs is unstable at such a high temperature. The MnAs precipitate in the samples with x≈4.7–5.5% has a Curie temperature Tc≈318 K, which was characterized from field-cooled and zero-field-cooled magnetization curves. 相似文献
2.
J.L. Harris L.V. Shapoval L.H. Strauss 《Journal of magnetism and magnetic materials》2009,321(8):1072-1076
Polycrystalline samples of the II-V-diluted magnetic semiconductor Cd1−xMnxSb (x=0.05-0.20) were synthesized. Standard high temperature ceramic methods under an inert atmosphere were utilized for sample fabrication. Structural characterization was done using X-ray diffractometry (XRD), which indicated that a simple substitution of Mn for Cd is probably not occurring. Hysteresis, ac susceptibility, dc magnetization, and spontaneous magnetization measurements were performed for Cd0.90Mn0.10Sb. The hysteresis data indicated the presence of a ferromagnetic component. Ferromagnetism in the Cd0.90Mn0.10Sb system is likely due to two sources: Mn spins in small Mn-rich regions and a small amount of MnSb in a minority phase. Analysis of the spontaneous magnetization as a function of temperature for Cd0.90Mn0.10Sb yielded the value 0.172 for the critical exponent β. In MnSb, β was found to have the value 0.379, which is close to the theoretical value for 3D-Heisenberg systems. Thus, in Cd0.90Mn0.10Sb, the ferromagnetism is not of the 3D-Heisenberg type; rather, it is closer to 2D Ising behavior, indicating reduced effective dimensionality. 相似文献
3.
(Ga1−xMnx)N thin films grown on GaN buffer layers by using molecular beam epitaxy were investigated with the goal of producing diluted magnetic semiconductors (DMSs) with band-edge exciton transitions for applications in optomagnetic devices. The magnetization curve as a function of the magnetic field at 5 K indicated that ferromagnetism existed in the (Ga1−xMnx)N thin films, and the magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature of the (Ga1−xMnx)N thin film was above room temperature. Photoluminescence and photoluminescence excitation spectra showed that band-edge exciton transitions in (Ga1−xMnx)N thin films appeared. These results indicate that the (Ga1−xMnx)N DMSs with a magnetic single phase hold promise for potential applications in spin optoelectronic devices in the blue region of the spectrum. 相似文献
4.
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
5.
(Ga1−xMnx)N/GaN digital ferromagnetic heterostructures (DFHs) and (Ga1−xMnx)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 (Ga1−xMnx)N/GaN DFHs decreased with increasing Mn mole fraction and that the saturation magnetic moment and the coercive field in the (Ga1−xMnx)N/GaN DFHs were much larger than those in (Ga1−xMnx)N thin films. These results indicate that the (Ga1−xMnx)N/GaN DFHs hold promise for potential applications in spintronic devices. 相似文献
6.
Sang Soo Yu Ki Hak Kim Young Eon Ihm Dojin Kim Hyojin Kim Soon Ku Hong Chang Soo Kim Hyun Ryu Sangjun Oh 《Journal of magnetism and magnetic materials》2006
Si1−xMnx (x?0.22) thin films were grown by using a thermal evaporator, and their magnetic and electrical properties were investigated. The Si1−xMnx semiconductors are amorphous when Mn concentration is 9.0 at% and less. The electrical resistivities of amorphous Si1−xMnx (x?0.09) semiconductor thin films are in the range of 9.86–6.59×10−4 Ω cm at room temperature and decrease with increasing Mn concentration. The amorphous Si1−xMnx (x?0.09) semiconductor thin films are p-type and hole densities are 3.73×1018–1.33×1022 cm−3 at room temperature. Low temperature magnetization characteristics reveal that amorphous Si1−xMnx (x?0.09) semiconductor thin films are paramagnetic. 相似文献
7.
Nanocrystalline spinel ferrite thin films of CoxFe3−xO4 (x=0.3, 0.5, 0.8, and 1.0) have been prepared by RF sputtering on quartz substrate without a buffer layer at room temperature and annealed at the temperature range from 200 to 600 °C in air. The as-sputtered films exhibit the preferred orientation and the high magnetization and coercivity. After annealing, the preferred orientations become poor, but the magnetization and coercivity increase. The sample with a magnetization of 455 emu/cm3, a coercivity of 2.8 kOe, a remanence ratio of 0.72, and a maximum energy product of 2.4 MGOe has been obtained. The influence of Co ions and annealing temperature on the magnetic properties has been discussed. 相似文献
8.
Sujeet Chaudhary Kanwal Preet Bhatti S.C. Kashyap 《Journal of magnetism and magnetic materials》2009,321(8):966-970
In the present paper, the preliminary investigations of a series of ZnO thin films co-doped with indium and cobalt with an objective to elucidate the correlation, if any, between the carrier concentration and the induced room temperature ferromagnetism (RTFM), are presented. The single-phasic (Zn99.5In0.5)1−xCoxO thin films are deposited by spray pyrolysis. The substitution of Zn2+ by Co2+ has been established by optical transmission analysis of these films. The films are ferromagnetic at room temperature; and the magnetization has higher value for indium and cobalt co-doped thin film as compared with Zn090Co0.1O thin film (having no indium). 相似文献
9.
We synthesized the Mn-doped Mg(In2−xMnx)O4 oxides with 0.03?x?0.55 using a solid-state reaction method. The X-ray diffraction patterns of the samples were in a good agreement with that of a distorted orthorhombic spinel phase. Their lattice parameters and unit-cell volumes decrease with x due to the substitution of the smaller Mn3+ ions to the larger In3+ ions. The undoped MgIn2O4 oxide presents diamagnetic signals for 5 K?T?300 K. The M(H) at T=300 K reveals a fairly negative-sloped linear relationship. Neither magnetic hysteresis nor saturation behavior was observed in this parent sample. For the Mn-doped samples, however, positive magnetization were observed between 5 and 300 K even if the x value is as low as 0.03. The mass susceptibility enhances with Mn content and it reaches the highest value of 1.4×10−3 emu/g Oe (at T=300 K) at x=0.45. Furthermore, the Mn-doped oxides with x=0.06 and 0.2, respectively, exhibit nonlinear magnetization curves and small hysteretic loops in low magnetic fields. Susceptibilities of the Mn-doped samples are much higher than those of MnO2, Mn2O3 oxides, and Mn metals. These results show that the oxides have potential to be magnetic semiconductors. 相似文献
10.
G.V. Lashkarev V.I. Sichkovskyi V.E. Slynko T. Story W. Knoff 《Journal of magnetism and magnetic materials》2009,321(11):1782-1784
It is expected that joint existence of ferromagnetic properties and ferroelectric structural phase transition in diluted magnetic semiconductors IV-VI leads to new possibilities of these materials. Temperature of ferroelectric transition for such crystals can be tuned by the change of Sn/Ge ratio. Magnetic susceptibility, Hall effect, resistivity and thermoelectric power of Ge1−x−ySnxMnyTe single crystals grown by Bridgeman method (x=0.083-0.115; y=0.025-0.124) were investigated within 4.2-300 K. An existence of FM ordering at TC∼50 K probably due to indirect exchange interaction between Mn ions via degenerated hole gas was revealed. A divergence of magnetic moment temperature dependences at T?TC in field-cooled and zero-field-cooled regimes is obliged to magnetic clusters which are responsible for superparamagnetism at T>TC≈Tf (freezing temperature) and become ferromagnetic at TC arranging spin glass state at T<Tf≈TC. Phase transition of ferroelectric type at T≈46 K was revealed. Anomalous Hall effect which allows to determine magnetic moment was observed. 相似文献
11.
The magnetic and magnetoresistive properties of spinel-type Zn1−xCoxFe2O4 (x=0, 0.2 and 0.4) ferrites are extensively investigated in this study. A large negative magnetoresistance (MR) effect is observed in Zn1−xCoxFe2O4 ferrites of spinel structure. These materials are either ferrimagnetic or paramagnetic at room temperature, and show a spin-(cluster) glass transition at low temperatures, depending on the chemical compositions. The MR curves as a function of magnetic fields, MR(H), are parabolic at all temperatures for paramagnetic polycrystalline ZnFe2O4. The MR for ZnFe2O4 at 110 K in the presence of 9 T applied magnetic field is 30%. On the other hand, MR(H) are linear for x=0.2 and 0.4 ferrimagnetic Zn1−xCoxFe2O4 samples up to 9 T. The MR effect is independent of the sintering temperatures, and can be explained with the help of the spin-dependent scattering and the Yafet–Kittel angle of Zn1−xCoxFe2O4 mixed ferrites. 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.
Sang Soo Yu Kyung Hee Han Young Eon Ihm Dojin Kim Hyojin Kim Chang Soo Kim Hyun Ryu Sangjun Oh 《Journal of magnetism and magnetic materials》2006
Amorphous Ge1−xCrx thin films are deposited on (1 0 0)Si by using a thermal evaporator. Amorphous phase is obtained when Cr concentration is lower than 30.7 at%. The electrical resistivities are 1.89×10−3–0.96×102 Ω cm at 300 K, and decrease with Cr concentration. The Ge1−xCrx thin films are p-type. The hole concentrations are 5×1016–7×1021 cm−3 at 300 K, and increase with Cr concentration. Magnetizations are 7.60–1.57 emu/cm3 at 5 K in the applied field of 2 T. The magnetizations decrease with Cr concentration and temperature. Magnetization characteristics show that the Ge1−xCrx thin films are paramagnetic. 相似文献
14.
Puneet Sharma R.A. Rocha S.N. Medeiros B. Hallouche A. Paesano Jr. 《Journal of magnetism and magnetic materials》2007
Barium hexaferrite powders with manganese substitution were prepared by mechanosynthesis. The structural and magnetic properties were characterized by X-ray diffractometer and vibration sample magnetometer, respectively. XRD patterns were refined by Rietveld method. Preferential site occupation of manganese ion was investigated by room temperature (RT) Mössbauer measurements. XRD results showed a single-phase barium hexaferrite with some residual hematite. Crystallite size was observed to decrease with substitution amount. Lower saturation magnetization and increased coercivity is observed in substituted samples. RT Mössbauer measurements showed that manganese ions preferentially occupy 12k, 4f2, and 2a sites. 相似文献
15.
Electronic structure calculations were performed for substitutional erbium rare-earth impurity in cubic GaN using density-functional theory calculations within the LSDA+U approach (local spin-density approximation with Hubbard-U corrections). The LSDA+U method is applied to the rare-earth 4f states. The ErxGa1−xN is found to be a semiconductor, where the filled f-states are located in the valence bands and the empty ones above the conduction band edge. The filled and empty f-states are also shown to shift downwards and upwards in the valence and conduction bands, respectively, with increase in the U potentials. 相似文献
16.
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
17.
V.A. Kulbachinskii R.A. Lunin P.V. Gurin B.A. Aronzon A.B. Davydov V.V. Rylkov Yu.A. Danilov O.V. Vikhrova B.N. Zvonkov 《Journal of magnetism and magnetic materials》2006
We report on the transport, magnetotransport and magnetic properties of In0.17Ga0.83As quantum well in GaAs δ-doped by Mn. At low temperatures, the anomalous Hall effect was observed which detects the spin-polarized carriers. Negative magnetoresistance was found at low temperatures, which became positive at high temperature. 相似文献
18.
A series of the double-doping samples La(2+x)/3Sr(1−4x)/3Mn1−xCrxO3 (0?x?0.25) with the Mn3+/Mn4+ ratio fixed at 2:1 have been fabricated. The structural, magnetic, transport properties and Raman spectroscopy have been investigated, and no apparent crystal structure change is introduced by Cr doping up to x=0.25. But the Curie temperature TC and metal-insulator transition temperature TMI are strongly affected by Cr substitution. The room temperature Raman spectra start exhibiting some new features following the increasing concentration of Cr substitutions. Moreover, it is worth noting that the frequency of the A1g phonon mode can also be well correlated with the A-site mismatch effect (σ2), which is influenced mainly by the variety of the Sr content. 相似文献
19.
Zan Yao 《Journal of magnetism and magnetic materials》2009,321(3):203-206
Phase structure and magnetic properties of the as-cast and as-milled/annealed SmCo7−xMox (x=0, 0.1, 0.2, 0.3, 0.4) alloys have been systematically studied. It is found that all the as-cast series alloys are composed of the CaCu5-type and Th2Zn17-type phases. Saturation magnetization of the samples decreases with the Mo content increasing. Intrinsic coercivities (iHc) of no more than 0.06 T are observed in these as-cast samples, due to their rather coarse grain microstructures with an average grain size of 50 μm. The as-milled/annealed SmCo7−xMox powders crystallize in the disordered TbCu7-type (1:7) structure with very fine nanograins, and a minor Co3Mo phase appears in the samples with x=0.1-0.4. High iHc (?0.95 T) are achieved in these samples, with a maximum of 1.26 T located at x=0.2, which can be primarily attributed to strong pinning of the domain wall motion at the nanograin boundaries. The temperature coefficient (β) of the iHc is about −0.22%/°C in the temperature range of 25-400 °C for the as-milled/annealed samples. 相似文献
20.
We have investigated the temperature and composition dependent photoluminescence (PL) spectra in Ga1−xMnxN layers (where x ≈ 0.1-0.8%) grown on sapphire (0 0 0 1) substrates using the plasma-enhanced molecular beam epitaxy technique. The efficient PL is peaked in the red (1.86 eV), yellow (2.34 eV), and blue (3.29 eV) spectral range. The band-gap energy of the Ga1−xMnxN layers decreased with increasing temperature and manganese composition. The band-gap energy of the Ga1−xMnxN layers was modeled by the Varshni equation and the parameters were determined to be α = 2.3 × 10−4, 2.7 × 10−4, 3.4 × 10−4 eV/K and β = 210, 210, and 230 K for the manganese composition x = 0.1%, 0.2%, and 0.8%, respectively. As the Mn concentration in the Ga1−xMnxN layers increased, the temperature dependence of the band-gap energy was clearly reduced. 相似文献