共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
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
3.
(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
4.
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
5.
ZHANG Bin YAO Shu-De WANG Kun DING Zhi-Bo CHEN Zhi-Tao SU Yue-Yong ZHANG Guo-Yi MA Hong-Ji NIE Rui ZHANG Ya-Wei 《中国物理快报》2006,23(6):1585-1587
The diluted magnetic semiconductor Ga1-xMnxN was achieved by low-pressure metal organic vapour-phase epitaxy (LP-MOVPE). Proton-induced x-ray emission was employed non-destructively, quickly and accurately to determine the Mn-doped content. The magnetic property was measured by a superconducting-quantum-interference-device (SQID) magnetometer. Apparent ferromagnetic hysteresis loops measured at or above room temperature are presented. No ferromagnetic secondary phases were detected by high-resolution x-ray diffraction. The experimental results show that the ferromagnetic signal firstly decreases and then increases with the increasing Mn-doped content from 0.23% to 4.69% and it is the weakest when Mn content is 0.51%. The annealing treatment could make the ferromagnetic property stronger. 相似文献
6.
The interactions in ternary and quaternary Co-based alloy thin films for longitudinal recording media, with different thickness, are studied. The analysis is performed through the measurement of the initial magnetization and ordinary hysteresis curves. The interactions result stronger in quaternary than in ternary alloy films and when the film thickness is smaller. These findings are discussed in relationship with the evolution of the magnetization switching, characterized by a tendency towards a more coherent rotation of the magnetization in single-domain grains of thinnest and quaternary films, owing to the complex structure of these films. The impact of this evolution on the thermal stability of the magnetic properties is also discussed. 相似文献
7.
(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
8.
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
9.
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
10.
Optical and Magnetic Properties of Fe-Doped GaN Diluted Magnetic Semiconductors Prepared by MOCVD Method
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Fe-doped GaN thin films are grown on c-sapphires by metal organic chemical vapour deposition method (MOCVD) Crystalline quality and phase purity are characterized by x-ray diffraction and Raman scattering measurements. There are no detectable second phases formed during growth and no significant degradation in crystalline quality as Fe ions are doped. Fe-related optical transitions are observed in photoluminescence spectra. Magnetic measurements reveal that the films show room-temperature ferromagnetic behaviour. The ferromagnetism may originate from carrier-mediated Fe-doped GaN diluted magnetic semiconductors or nanoscale iron clusters and FeN compounds which we have not detected. 相似文献
11.
Fe50Co50 thin films with thickness of 30 and 4 nm have been produced by rf sputtering on glass substrates, and their surface has been observed with atomic force microscopy (AFM) and magnetic force microscopy (MFM); MFM images reveal a non-null component of the magnetization perpendicular to the film plane. Selected samples have been annealed in vacuum at temperatures of 300 and 350 °C for times between 20 and 120 min, under a static magnetic field of 100 Oe. DC hysteresis loops have been measured with an alternating gradient force magnetometer (AGFM) along the direction of the field applied during annealing and orthogonally to it. Samples with a thickness of 4 nm display lower coercive fields with respect to the 30 nm thick ones. Longer annealing times affect the development of a harder magnetic phase more oriented off the film plane. The field applied during annealing induces a moderate magnetic anisotropy only on 30 nm thick films. 相似文献
12.
Marco Coïsson Franco Vinai Paola Tiberto Federica Celegato 《Journal of magnetism and magnetic materials》2009,321(7):806-809
FeSiB amorphous thin films with thicknesses from 25 to 600 nm have been produced by rf sputtering on Si3N4 substrates. A spin reorientation transition has been observed on the as-prepared samples, as a function of thickness and temperature. Spin reorientation transition is shown to depend on the thermal treatments to which the as-prepared samples have been submitted. Static hysteresis loops obtained as a function of temperature, and magnetic force microscopy images taken at room temperature at the remanence and as a function of an applied magnetic field, have been employed to study the magnetic domain configuration of all the samples, and to see how it is affected by sample thickness, measurement temperature and annealing conditions. 相似文献
13.
Effects of Slight Plastic Deformation on Magnetic Properties and Giant Magnetoimpedance of FeCoCrSiB Amorphous Ribbons
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S. O. Volchkov M. A. Cerdeira V. V. Gubernatorov E. I. Duhan A. P. Potapov V. A. Lukshina 《中国物理快报》2007,24(5):1357-1360
Slight plastic deformation of 0 to 1% by cold rolling is proposed as a treatment which may modify the responses of magnetoimpedance (MI) sensor with an amorphous ribbon used as a sensitive element. The dependence of the magnetic properties of melt spun Fe3Co67Cr3Si15B12 amorphous ribbons and their MI responses in the initial state and after slight plastic deformation on the value of the deformation were comparatively analysed. The shape of the hysteresis loops shows a clear correlation with the value of the deformation. The variations of the total impedance, the real and the imaginary components, are measured for the current intensity of 1.S mA for the frequency of lO MHz. Slight plastic deformation affects both real and imaginary components and allows a control of the shape of the MI curves in a small field in a range usually used in biomedical applications. The proposed deformation treatments can be useful for the construction of the MI sensitive elements with a new type of the responses. 相似文献
14.
A.W. Rushforth K. Výborný K.W. Edmonds C.T. Foxon A.C. Irvine K. Olejník Jairo Sinova B.L. Gallagher 《Journal of magnetism and magnetic materials》2009,321(8):1001-1008
We present details of our experimental and theoretical study of the components of the anisotropic magnetoresistance (AMR) in (Ga,Mn)As. We develop experimental methods to yield directly the non-crystalline and crystalline AMR components which are then independently analysed. These methods are used to explore the unusual phenomenology of the AMR in ultra thin (5 nm) (Ga,Mn)As layers and to demonstrate how the components of the AMR can be engineered through lithography induced local lattice relaxations. We expand on our previous [A.W. Rushforth, et al., Phys. Rev. Lett. 99 (2007) 147207] theoretical analysis and numerical calculations to present a simplified analytical model for the origin of the non-crystalline AMR. We find that the sign of the non-crystalline AMR is determined by the form of the spin-orbit coupling in the host band and by the relative strengths of the non-magnetic and magnetic contributions to the impurity potential. 相似文献
15.
We report the optical and magnetic properties of laser-deposited Zn1−xCoxO (x=0.06-0.3) thin films with no intentional electrical carrier doping. The analysis of the high-temperature magnetization data provides an unambiguous evidence that antiferromagnetic superexchange interaction is the dominant mechanism of the exchange coupling between Co ions in Zn1−xCoxO alloy, yielding the value of the effective exchange integral J1/kB to be about −27 K. The low-temperature magnetization data reveals a spin glass transition in Zn1−xCoxO alloy for the Co content x>0.15, giving the value of the spin freezing temperature Tf to be ∼8 and ∼12 K for x=0.2 and 0.25, respectively. Optical spectra analysis shows a linear increase of the band gap Eg with the increase of the Co content following Eg=3.231+1.144x eV. 相似文献
16.
B. Pandey S. Ghosh P. Srivastava D.K. Avasthi D. Kabiraj J.C. Pivin 《Journal of magnetism and magnetic materials》2008
We report synthesis of a transparent magnetic semiconductor by incorporating Ni in zinc oxide (ZnO) matrix. ZnO and nickel-doped zinc oxide (ZnO:Ni) thin films (∼60 nm) are prepared by fast atom beam (FAB) sputtering. Both undoped and doped films show the presence of ZnO phase only. The Ni concentration (in at%) as determined by energy dispersive X-ray (EDX) technique is ∼12±2%. Magnetisation measurement using a SQUID magnetometer shows that the Ni-doped films are ferromagnetic, having coercivity (Hc) values 192, 310 and 100 Oe and saturation magnetization (Ms) values of 6.22, 5.32 and 4.73 emu/g at 5, 15 and 300 K, respectively. The Ni-doped film is transparent (>80%) across visible wavelength range. Resistivity of the ZnO:Ni film is ∼2.5×10−3 Ω cm, which is almost two orders of magnitude lower than the resistivity (∼4.5×10−1 Ω cm) of its undoped counterpart. Impurity d-band splitting is considered to be the cause of increase in conductivity. Interaction between free charges generated by doping and localized d spins of Ni is discussed as the reason for ferromagnetism in the ZnO:Ni film. 相似文献
17.
The structural stability and magnetic properties of Co-doped or -adsorbed polar-ZnO surface systems are investigated using first-principles calculations. It is found that Co ions energetically prefer to substitute for Zn in the outermost layer of both Zn- and O-terminated surfaces. Substitutional Co ions are antiferromagnetically coupled at ideal ZnO surfaces, which indicates additional defects or strain played a critical role in the reported ferromagnetism of ZnO : Co system. In addition, it is found that the adsorbed Co ions are preferred to ferromagnetic coupling, which may provide a new approach for spin injection of a ZnO film. 相似文献
18.
Gaurav Shukla 《Applied Physics A: Materials Science & Processing》2009,97(1):115-118
In this paper, we report on pulsed laser deposition of n-type Cu-doped ZnO thin films on c-plane sapphire substrates at 700°C.
XRD and HRTEM were employed to study the epitaxial growth relationship between the Zn1−x
Cu
x
O film and sapphire substrate. Absorption measurements showed excitonic nature of the thin films and a decrease in the bandgap
energy with increased Cu concentration was observed. Such as-deposited films showed room temperature ferromagnetism with Curie
temperature (T
c
) at around 320 K. The moment per Cu atom decreases as the Cu concentration increases. The largest magnetic moment about 0.81μ
B
/Cu atom was observed for Zn0.95Cu0.05O thin films. The presence of any magnetic second phase was ruled out and the ferromagnetism was attributed to Cu ions substituted
directly into the ZnO lattice. 相似文献
19.
Structural and magnetic properties of Fe-doped anatase TiO2 films fabricated by sol-gel spin coating are investigated. X-ray diffraction measurements reveal that Fe^3+ ions are incorporated into the TiO2 lattice. No ferromagnetism-related secondary phases and magnetic nanopaxticles are observed in the films. The presence of electron paramagnetic resonance signals at 9- 2.0 supports oxygen vacancies and/or defects generated in the films after annealing in vacuum. Magnetic measurements indicate that Fe-doped anatase TiO2 films are ferromagnetic at room temperature. These observations suggest that oxygen vacancies and/or defects axe energetically favorable for the long range Fe^3+-Fe^3+ ferromagnetic coupling in Fe-doped anatase TiO2 films. 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