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1.
(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
2.
Y.H. Kwon C.J. Park T.W. Kim J.Y. Lee B.O. Kim Yong-Hoon Cho 《Solid State Communications》2006,140(1):14-17
The optical properties and the deep levels in bulk Si1−xMnx formed by using an implantation and annealing method were investigated. Transmission electron microscopy, X-ray diffraction, and Hall-effect measurements showed that the annealed bulk Si1−xMnx samples were p-type crystalline semiconductors. The photoluminescence spectra for the annealed bulk Si1−xMnx material showed luminescence peaks corresponding to excitons bound to neutral acceptors and related to dislocations due to the existence of Mn impurities. Deep-level transient spectroscopy results for the annealed bulk Si1−xMnx showed deep levels related to the interstitial and substitutial sites of the Mn+ ions. These results can help improve understanding of the optical properties and the deep levels in annealed bulk Si1−xMnx material. 相似文献
3.
Si1−xMnx diluted magnetic semiconductor (DMS) bulks were formed by using an implantation and annealing method. Energy dispersive X-ray fluorescence, transmission electron microscopy (TEM), and double-crystal rocking X-ray diffraction (DCRXD) measurements showed that the grown materials were Si1−xMnx crystalline bulks. Hall effect measurements showed that annealed Si1−xMnx bulks were p-type semiconductors. The magnetization curve as a function of the magnetic field clearly showed that the ferromagnetism in the annealed Si1−xMnx bulks originated from the interaction between interstitial and substitutional Mn+ ions, which was confirmed by the DCRXD measurements. The magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature was approximately 75 K. The present results can help to improve understanding of the formation mechanism of ferromagnetism in Si1−xMnx DMS bulks. 相似文献
4.
Sang Soo Yu Young Eon Ihm Dojin Kim Sangjun Oh Hyun Ryu 《Solid State Communications》2005,134(9):641-645
Magnetic properties of amorphous Ge1−xMnx thin films were investigated. The thin films were grown at 373 K on (100) Si wafers by using a thermal evaporator. Growth rate was ∼35 nm/min and average film thickness was around 500 nm. The electrical resistivities of Ge1−xMnx thin films are 5.0×10−4∼100 Ω cm at room temperature and decrease with increasing Mn concentration. Low temperature magnetization characteristics and magnetic hysteresis loops measured at various temperatures show that the amorphous Ge1−xMnx thin films are ferromagnetic but the ferromagnetic magnetizations are changing gradually into paramagnetic as increasing temperature. Curie temperature and saturation magnetization vary with Mn concentration. Curie temperature of the deposited films is 80-160 K, and saturation magnetization is 35-100 emu/cc at 5 K. Hall effect measurement at room temperature shows the amorphous Ge1−xMnx thin films have p-type carrier and hole densities are in the range from 7×1017 to 2×1022 cm−3. 相似文献
5.
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
6.
The magneto-transport properties of ferromagnetic Ga1−xMnxAs epilayers with Mn mole fractions in the range of x≈2.2-4.4% were investigated through Hall effect measurements. The magnetic field-dependent Hall mobility for a metallic sample with x≈2.2% in the temperature range of T=0-300 K was analyzed by magnetic field-dependent mobility model including an activation energy of Mn acceptor level. This model provides outstanding fits to the measured data up to T=300 K. It was found that the acceptor levels with activation energies of 112 meV at B=0 Oe decreased to 99 meV at B=5 kOe in the ferromagnetic region. The decrease in acceptor activation energy was due to the spin splitting of the Mn acceptor level in the ferromagnetic region, and was responsible for increase in carrier concentration. 相似文献
7.
We report on the ferromagnetic characteristics of Zn1−xMnxO films (x=0.1-0.3) prepared by the sol-gel method on silicon substrates using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and superconducting quantum interference device (SQUID) magnetometry at various temperatures. Magnetic measurement show that the Curie temperature (TC) and the coercive field (HC) were ∼39 K and ∼2100 Oe for the film of x=0.2, respectively. EDS and TEM measurements indicate that Mn content at the interface is significantly higher than that at the center of the Zn0.8Mn0.2O film showing the ratio, Zn:Mn:O≅1:12:15. This experimental evidence suggests that ferromagnetic precipitates containing manganese oxide may be responsible for the observed ferromagnetic behavior of the film. 相似文献
8.
Li0.5Fe2.5−xMnxO4 (0≦x≦1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, ferric nitrate, manganese nitrate and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Mn-substituted lithium ferrite powders. The resultant powders annealed at 650 °C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that the Mn content were strongly influenced the magnetic properties and Curie temperature of Mn-substituted lithium ferrite powder. As for sintered Li0.5Fe2.5−xMnxO4 specimens, substituting an appropriate amount of Mn for Fe in the Li0.5Fe2.5−xMnxO4 specimens markedly improved the complex permeability and loss tangent. 相似文献
9.
Ferromagnetic Ga1−xMnxAs epilayers with Mn mole fraction in the range of x≈2.2-4.4% were grown on semi-insulating (100) GaAs substrates using the molecular beam epitaxy technique. The transport properties of these epilayers were investigated through Hall effect measurements. The measured hole concentration of Ga1−xMnxAs layers varied from 4.4×1019 to 3.4×1019 cm−3 in the range of x≈2.2-4.4% at room temperature. From temperature dependent resisitivity data, the sample with x≈4.4% shows typical behavior for insulator Ga1−xMnxAs and the samples with x≈2.2 and 3.7% show typical behavior for metallic Ga1−xMnxAs. The Hall coefficient for the samples with x≈2.2 and 4.4% was fitted assuming a magnetic susceptibility given by Curie-Weiss law in a paramagnetic region. This model provides good fits to the measured data up to and the Curie temperature Tc was estimated to be 65, 83 K and hole concentration p was estimated to be 5.1×1019, 4.6×1019 cm−3 for the samples with x≈2.2 and 4.4%, respectively, confirming the existence of an anomalous Hall effect for metallic and insulating samples. 相似文献
10.
C.E. Rodríguez Torres F. Golmar L. Errico M. Rentería S. Duhalde 《Applied Surface Science》2007,254(1):365-367
Transparent pure and Cu-doped (2.5, 5 and 10 at.%) anatase TiO2 thin films were grown by pulsed laser deposition technique on LaAlO3 substrates. The samples were structurally characterized by X-ray absorption spectroscopy and X-ray diffraction. The magnetic properties were measured using a SQUID. All films have a FM-like behaviour. In the case of the Cu-doped samples, the magnetic cycles are almost independent of the Cu concentration. Cu atoms are forming CuO and/or substituting Ti in TiO2. The thermal treatment in air promotes the CuO segregation. Since CuO is antiferromagnetic, the magnetic signals present in the films could be assigned to Cu substitutionally replacing cations in TiO2. 相似文献
11.
C.E. Rodríguez Torres L. Errico F. Golmar A.M. Mudarra Navarro A.F. Cabrera S. Duhalde F.H. Sánchez M. Weissmann 《Journal of magnetism and magnetic materials》2007
Transparent pure and Fe-doped SnO2 thin films were grown by pulsed laser deposition technique on LaAlO3 substrates. X-ray diffraction shows that the films are polycrystalline and have the rutile structure. Surprisingly, the pure film presents magnetic-like behavior at room temperature with a saturated magnetization of almost one-third of the doped film (∼3.6 and 11.3 emu/g, respectively) and its magnetization could not be attributed to any impurity phase. Taking into account the magnetic moment measured in the pure film, the effective contribution of the impurity in the doped one can be inferred to be ∼2 μB per Fe atom. A large magnetic moment was also predicted by an ab initio calculation in the doped system, which increases if an oxygen vacancy is present near the Fe impurity. 相似文献
12.
Ferromagnetic Ga1−xMnxAs layers (where x=1.4-3.0%) grown on (1 0 0) GaAs substrates by molecular beam epitaxy were characterized using Raman spectroscopy. As Mn is introduced into GaAs, a marked increase in disorder in the material occurs, as indicated by the growth of the disorder-allowed transverse-optical Raman line. Another important result is that as the Mn concentration in Ga1−xMnxAs increases further beyond ca. 2%, Raman-active coupled-plasmon-longitudinal-optical phonon modes arise, which signals the increasing presence of holes, and thus provides a useful tool for determining their concentration. Using the depletion-layer approach from the Raman spectroscopy data, we determined the carrier concentration for samples with x=2.2% and 3.0% was to be 7.2×1019 and 8.3×1020 cm−3, respectively. 相似文献
13.
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
14.
Polycrystalline Sn1−xMnxO2 (0≤x≤0.05) diluted magnetic semiconductors were prepared by solid-state reaction method and their structural and magnetic properties had been investigated systematically. The three Mn-doped samples (x=0.01, 0.03, 0.05) undergo paramagnetic to ferromagnetic phase transitions upon cooling, but their Curie temperatures are far lower than room temperature. The magnetization cannot be attributed to any identified impurity phase. It is also found that the magnetization increases with increasing Mn doping, while the ratio of the Mn ions contributing to ferromagnetic ordering to the total Mn ions decreases. 相似文献
15.
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
16.
Structural and photoluminescence properties of thermally evaporated Cd1−xMnxS nano-crystalline films
D. Sreekantha Reddy D. Raja Reddy K.R. Gunasekhar B.K. Reddy 《Solid State Communications》2007,142(8):466-471
Thin films of Cd1−xMnxS (0≤x≤0.5) were formed on glass substrates by resistive vacuum thermal evaporation. All the films were deposited at 300 K and the films were annealed at 373, 473 and 573 K for 1 h in a vacuum of 10−6 mbar. Atomic force microscopy (AFM) studies showed that all the films investigated were in nano-crystalline form with a grain size in the range 36-82 nm. All the films exhibited a wurtzite structure of the host material. The lattice parameters varied linearly with composition following Vegard’s law in the entire composition range. Photoluminescence studies showed that two distinct emission bands were observed for each Cd1−xMnxS compound. One corresponds to internal transition and the other one is due to the transition of Mn2+ ions in interstitial sites or in small ‘Mn’ chalcogenic clusters. 相似文献
17.
Multiple stacked self-assembled (In1−xMnx)As quantum-dot (QD) arrays were grown on GaAs (100) substrates by using molecular-beam epitaxy with a goal of producing (In1−xMnx)As QDs with a semiconductor phase and a high ferromagnetic transition temperature (Tc). Atomic force microscopy, magnetic force microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray fluorescence measurements showed that crystalline multiple stacked (In0.84Mn0.16)As with symmetric single-domain particle were formed on GaAs substrates. Near-field scanning optical spectroscopy spectra at 10 K for the (In0.84Mn0.16)As multiple stacked QDs showed that the band-edge exciton transitions were observed. The magnetization curve as a function of the magnetic field at 5 and 300 K indicated that the multiple stacked (In0.84Mn0.16)As QDs were ferromagnetic, and the magnetization curve as a function of the temperature showed that the Tc was as high as 400 K. These results provide important information on the optical and magnetic properties for enhancing the Tc of (In1−xMnx)As-based nanostructures. 相似文献
18.
We report on the analysis of optical transmittance spectra and the resulting ferromagnetic characteristics of sputtered Zn1−xCoxO films. Zn1−xCoxO films were prepared on (0001)-oriented Al2O3 substrates by the radio-frequency (rf) magnetron co-sputtering method. The XRD results showed that the crystallinity of films was properly maintained up to x=0.30 and no second phase peaks were detected up to x=0.40. The transmittance spectra showed both the increase of the absorption band intensity and the red shift of the absorption peak as well as the band edge with increasing x. We have proved experimentally that these changes depend on Co concentration. These optical properties suggest that sp-d exchange interactions and typical d-d transitions become activated with increasing x, which leads to the enhancement of ferromagnetic properties in Zn1−xCoxO films as shown in the AGM results. Therefore, it is concluded that the ferromagnetism derives from the substitution of Co2+ for Zn2+ without changing the wurtzite structure. 相似文献
19.
Woochul Kim Hee Jae Kang Sam Kyu Noh Jonghan Song Chul Sung Kim 《Journal of magnetism and magnetic materials》2007
The magnetic and structural properties of Fe ion-implanted GaN was investigated by various measurements. XRD results did not show any peaks associated with second phase formation. The magnetization curve at 5 K showed ferromagnetic behavior for 900 °C-annealed sample. In zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements, the irreversibility and a cusp-like behavior of the ZFC curve were observed for 900 °C-annealed sample. These behaviors are typically observed in superparamagnetic or spin glass phase. While the temperature dependence magnetization of 800 °C-annealed sample showed non-Brillouin-like curve and it is not exhibited ferromagnetic hysteresis at 5 K. In XPS measurement, the coexistence of metallic Fe (Fe0) and Fe–N bond (Fe2+ and Fe3+) for Fe 2p core level spectra is observed in as-implanted sample. But 700–900 °C-annealed samples showed only Fe–N bond (Fe2+ and Fe3+) spectra. For Ga 3d core level spectra only Ga–N bonds showed for as implanted with 700–900 °C-annealed samples. From XPS results, it could be explained that magnetic property of our films originated from FeN structures. 相似文献
20.
The structures and magnetocaloric effects of (Gd1−xTbx)Co2 (x=0, 0.25, 0.4, 0.5, 0.6, 0.7, 0.8, and 1) pseudobinary compounds were investigated by X-ray powder diffraction and magnetic properties measurement. The results show that the Tc of the alloy is near room temperature when X=0.6. The magnetic entropy changes of the compounds increase from 1.7 to 3.6 J/kg K with increasing the content of Tb under an applied field up to 2 T. All the compounds exhibit second order magnetic change. As a result, the values of their ΔSM are lower than that of some large magnetocaloric effect materials. 相似文献