- 标题
- 摘要
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- 实验方案
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Raising the Operating Temperature of (Ga,Mn)As/GaAs Spin Light Emitting Diodes by Applying Post-Growth Treatment
摘要： Spin light emitting diodes (spin-LEDs) containing (Ga,Mn)As ferromagnetic layers are fabricated based on InGaAs/GaAs heterostructures and studied. We achieve increases in the operating temperatures of our spin-LEDs by subjecting the surface of the structures, prior to depositing an ohmic metal contact, to pulsed laser annealing. The fabricated devices produce circularly polarized electroluminescence when placed in an external magnetic field. The temperatures at which circularly polarized electroluminescence is still observed is raised from 30 K for unprocessed structure to 110 K for laser-annealed structures. The observed effect is linked to an increase in the Curie temperature of the (Ga,Mn)As layer as a result of laser impact.
关键词： ferromagnetic layers,circularly polarized electroluminescence,Curie temperature,Mn)As,pulsed laser annealing,Spin light emitting diodes,(Ga
更新于2025-09-10 09:29:36
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Time resolved imaging of the non-linear bullet mode within an injection-locked nano-contact spin Hall nano-oscillator
摘要： Time-resolved scanning Kerr microscopy (TRSKM) has been used to image precessional magnetization dynamics excited by a DC current within a nano-contact (NC) spin Hall nano-oscillator (SHNO). Injection of a radio frequency (RF) current was used to phase lock the SHNO to TRSKM. The out of plane magnetization was detected by means of the polar magneto optical Kerr effect (MOKE). However, longitudinal MOKE images were dominated by an artifact arising from the edges of the Au NCs. Time resolved imaging revealed the simultaneous excitation of a non-linear 'bullet' mode at the centre of the device, once the DC current exceeded a threshold value, and ferromagnetic resonance (FMR) induced by the RF current. However, the FMR response observed for sub-critical DC current values exhibits an amplitude minimum at the centre, which is attributed to spreading of the RF spin current due to the reactance of the device structure. This FMR response can be subtracted to yield images of the bullet mode. As the DC current is increased above threshold, the bullet mode appears to increase in size, suggesting increased translational motion. The reduced spatial overlap of the bullet and FMR modes, and this putative translational motion, may impede the injection locking and contribute to the reduced locking range observed within NC-SHNO devices. This illustrates a more general need to control the geometry of an injection-locked oscillator so that the autonomous dynamics of the oscillator exhibit strong spatial overlap with those resulting from the injected signal.
关键词： nano-contact spin Hall nano-oscillator,Time-resolved scanning Kerr microscopy,bullet mode,injection locking,ferromagnetic resonance
更新于2025-09-10 09:29:36
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Molecular adsorption and strain-induced ferromagnetic semiconductor-metal transition in half-hydrogenated germanene
摘要： Very recently, half-hydrogenated germanene has been achieved in an experiment. In this paper, we investigate the effects of tetracyanoquinodimethane (TCNQ) molecular adsorption and strain on the electronic properties of half-hydrogenated germanene through first-principles. As an electron-acceptor molecule, TCNQ is exploited to non-covalently functionalize the half-hydrogenated germanene. However, this physical adsorption induces a ferromagnetic semiconductor–metal transition in half-hydrogenated germanene due to charge transfer from the substrate to the TCNQ molecule. More importantly, the superstructure of half-hydrogenated germanene/TCNQ is extremely sensitive to biaxial tensile strain. Under the biaxial tensile strain of 0.25%, the ferromagnetic semiconductor–metal transition induced by molecular adsorption can surprisingly be overturned. Meanwhile, a strong p-type doping is exhibited. Remarkably, it would return from a ferromagnetic semiconductor to a metal again when the biaxial tensile strain increases to 1.5%. Our analysis based on the structural and electronic properties of half-hydrogenated germanene/TCNQ indicates that such metal–semiconductor–metal transition in half-hydrogenated germanene/TCNQ under biaxial tensile strain may originate from the strong local deformation, resulting in the energy of the valence band maximum decreasing below or increasing above the Fermi level.
关键词： ferromagnetic semiconductor–metal transition,p-type doping,half-hydrogenated germanene,TCNQ molecular adsorption,biaxial tensile strain
更新于2025-09-10 09:29:36
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Coherent control of femtosecond spin current investigated by polarization dependent terahertz emission spectroscopy in ferromagnetic heterostructures
摘要： Approaches towards highly-efficient generation of controllable ellipitical ferromagnetic nano-heterostructures are demonstrated. The mechanism for the coherent control of femtosecond spin current in ferromagnetic heterostructures are discussed.
关键词： coherent control,ferromagnetic heterostructures,terahertz emission spectroscopy,femtosecond spin current
更新于2025-09-09 09:28:46
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The Study of Features of Formation and Properties of A3B5 Semiconductors Highly Doped with Iron
摘要： Layers of InAs, InSb, and GaSb semiconductors highly doped with iron during their growth by the method of pulsed laser deposition are studied experimentally. The best temperatures for layer formation on GaAs (100) substrates are: 250°C (InSb : Fe), 300°C (InAs : Fe), and 350°C (GaSb : Fe). At high Fe concentration (over 10 at %) the layers display ferromagnetic properties expressed in emergence of a hysteresis curve within the magnetic field dependences of the Hall resistance, negative magnetoresistance, and in some cases, ferromagnetic-type magnetization at measurements at room temperature. The atoms of iron do not change the type of layer conductivity; InAs : Fe and InSb : Fe layers possess n-type conductivity, and GaSb : Fe layers display p-type conductivity due to their intrinsic point defects.
关键词： Hall effect,A3B5 semiconductors,ferromagnetic properties,magnetoresistance,iron doping,pulsed laser deposition
更新于2025-09-09 09:28:46
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Electronic Structures and Ferromagnetic Properties of 3d (Cr)-Doped BaSe Barium Selenide
摘要： In this study, we have employed the first-principle methods based on spin-polarized density functional theory to investigate the structural parameters, the electronic structures, and the half-metallic ferromagnetic behavior of chromium (Cr)-doped barium selenide (BaSe) such as Ba1 ? xCrxSe at concentrations x = 0.25, 0.5, and 0.75. The exchange and correlation potential is described by the generalized gradient approximation of Wu and Cohen (GGA-WC). The calculated structural parameters of BaSe are in good agreement with theoretical data. Our findings reveal that the p-d exchange coupling is ferromagnetic for Ba0.75Cr0.25Se and Ba0.5Cr0.5S, but it becomes anti-ferromagnetic for Ba0.25Cr0.75S. The electronic structures exhibit that the Ba1 ? xCrxSe materials for all concentrations are half-metallic ferromagnets with spin polarization of 100% and total magnetic moment per Cr atom of 4 μB. Therefore, the Ba1 ? xCrxSe compounds are suitable candidates for possible spintronics applications.
关键词： DFT,Cr-doped BaSe,Half-metallic ferromagnetic,Electronic structures
更新于2025-09-09 09:28:46
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An Inverted Magnetron Operating in HiPIMS Mode
摘要： An ionized physical vapor deposition technique for thin ferromagnetic films is proposed. The technique is based on high power impulse magnetron sputtering (HiPIMS) with positive discharge polarity. A gapped-target was employed as the cathode of the magnetron. By applying positive HiPIMS pulses to the anode, sputtered particles inside the magnetron source were ionized and extracted through the gap. Using a discharge current with a peak of about 13 A, an ion flux in the order of 1021 m?2s?1 was obtained at a distance of 45 mm from the magnetron. In addition, deposition rates of up to 1.1 ?/s for nickel films were achieved using a 30 Hz repetition rate and 300 μs pulse width.
关键词： ferromagnetic,ionized physical vapor deposition,HiPIMS,magnetron sputtering,thin films
更新于2025-09-09 09:28:46
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Structural and electrical properties of Gd-doped BiFeO3:BaTiO3 (3:2) multiferroic ceramic materials
摘要： Gadolinium doped BiFeO3:BaTiO3 (3:2) polycrystalline multiferroic ceramics have been prepared by high-temperature solid state reaction technique. X-ray diffraction (XRD) analysis at room temperature of the prepared materials confirmed the formation of the compounds with rhombohedral crystal structure. The average particle size of as prepared samples have been found in the range of 35 nm to 55 nm for different doping concentrations. The average grain size of as prepared samples are less than 100 nm which is confirmed from SEM study. The SEM of annealed compounds showed the uniform distribution of grains and the formation of dense ceramic with average grain size in the order of 4 μm. Dielectric studies of the materials reveals that the dielectric constant ( εr ) and tangent loss (tan δ) decreases with doping concentrations at room temperature. The variation of εr and tan δ with temperature was explained on the basis of Maxwell–Wagner mechanism. The values of grain resistance ( Rb ) and grain capacitance (Cb) were obtained from Nyquist plots for the different doping concentrations at 300 °C. The activation energy ( Ea ) was calculated from the curve of frequency dependent ac conductivity ( σac ) within the range 0.19 eV to 0.45 eV. The remnant polarization of the samples (0.53 μC/cm2) was measured from polarization versus electric field (P–E) hysteresis curves. The ferromagnetic behaviour of the Gd-doped BiFeO3:BaTiO3 (3:2) sample has been studied by SQUID for the lowest doping concentration. The value of remnant magnetization was found 0.0235 emu/g at room temperature.
关键词： multiferroic ceramics,dielectric properties,ferroelectric properties,Gd-doped BiFeO3:BaTiO3,ferromagnetic properties
更新于2025-09-09 09:28:46
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Probing the dielectric, piezoelectric and magnetic behavior of CoFe2O4/BNT-BT0.08 composite thin film fabricated by sol-gel and spin-coating methods
摘要： We investigated in this paper a novel bilayer composite obtained by sol-gel and spin coating of the ferroelectric 0.92Na0.5Bi0.5TiO3–0.08BaTiO3 (abbreviated as BNT-BT0.08) and ferromagnetic CoFe2O4 phases, for miniature low-frequency magnetic sensors and piezoelectric sensors. This heterostructure, deposited on Si-Pt substrate (Si-Pt/CoFe2O4/BNT-BT0.08), was characterized using selected method such as: X-ray diffraction, dielectric spectroscopy, piezoelectric force microscopy, SQUID magnetometry, atomic force microscopy/magnetic force microscopy, and advanced methods of transmission electron microscopy. CoFe2O4/BNT-BT0.08 ferromagnetic–piezoelectric thin films show good magnetization, dielectric constant and piezoelectric response. The results of analyses and measurements reveal that this heterostructure can have applications in high-performance magnetoelectric devices at room temperature.
关键词： ferroelectric,spin coating,ferromagnetic,bilayer composite,magnetoelectric devices,sol-gel
更新于2025-09-09 09:28:46
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摘要： The magnetoresistance of Ni81Fe19 and Co83Gd17 ferromagnetic thin films is measured in Corbino disk geometry, and compared to the magnetoresistance of the same films measured in the Hall-bar geometry. The symmetry of the magnetoresistance profiles is drastically modified by changing the geometry of the sample, i.e., by changing the boundary conditions. These properties are explained in a simple model, showing that the Corbino magnetoresistance is defined by the potentiostatic boundary conditions while the Hall-bar magnetoresistance is defined by galvanostatic boundary conditions.
关键词： boundary conditions,Corbino disk,ferromagnetic thin films,magnetoresistance,Hall-bar geometry
更新于2025-09-09 09:28:46