Spin Injection from Ferromagnetic Metal Directly into Non-Magnetic Semiconductor under Different Injection Currents

For ferromagnetic metal （FM）/semiconductor （SO） structure with ohmic contact, the effect of carrier polarization in the semiconductor combined with drift part of injection current on current polarization is investigated. Based on the general model we established here, spin injection efficiency under different injection current levels is calculated. Under a reasonable high injection current, current polarization in the semiconductor is actually much larger than that predicted by the conductivity mismatch model because the effect of carrier polarization is enhanced by the increasing drift current. An appreciable current polarization of 1% could be achieved for the FM/SC structure via ohmic contact, which means that efficient spin injection from FM into SC via ohmic contact is possible. The reported dependence of current polarization on temperature is verified quantitatively. To achieve even larger spin injection efficiency, a gradient doping semiconductor is suggested to enhance the drift current effect.     

Tunable Spin Hall Magnetoresistance in All-Antiferromagnetic Heterostructures

We investigate the spin Hall magnetoresistance （SMR） in all-antiferromagnetic heterostructuresα-Fe₂O₃/Cr₂O₃with Pt contacts.When the temperature is ultralow （<50 K）,the spin current generated in the Pt layer cannot be transmitted through Cr₂O₃ （t=4 nm）,and the SMR is near zero.Meanwhile,when the temperature is higher than the spin fluctuation temperature T_F （≈50 K） of Cr₂O₃ and lower than its Né...     

Spin-Polarized Carriers Injection from Ferromagnetic Metal into Organic Semiconductor

Charge carriers in organic semiconductor are different from that oftraditional inorganic semiconductor. Based on three-current model,considering electrical field effect, we present a theoretical model todiscuss spin-polarized injection from ferromagnetic electrode into organicsemiconductor by analyzing electrochemical potential both in ferromagneticelectrode and organic semiconductors. The calculated result of this modelshows effects of electrode's spin polarization, equilibrium value ofpolarons ratio, interfacial conductance, bulk conductivity of materials andelectrical field. It is found that we could get decent spin polarizationwith common ferromagnetic electrode by increasing equilibrium value ofpolarons ratio. We also find that large and matched bulk conductivity oforganic semiconductor and electrode, small spin-dependent interfacialconductance, and enough large electrical field are critical factors forincreasing spin polarization.     

Spin-Polarized Carriers Injection from Ferromagnetic Metal into Organic Semiconductor

Charge carriers in organic semiconductor are different from that of traditional inorganic semiconductor. Based on three-current model, considering electrical field effect, we present a theoretical model to discuss spin-polarized injection from ferromagnetic electrode into organic semiconductor by analyzing electrochemical potential both in ferromagnetic electrode and organic semiconductors. The calculated result of this model shows effects of electrode＇s spin polarization, equilibrium value of polarons ratio, interracial conductance, bulk conductivity of materials and electrical field. It is found that we could get decent spin polarization with common ferromagnetic electrode by increasing equilibrium value of polarons ratio. We also find that large and matched bulk conductivity of organic semiconductor and electrode, small spin-dependent interracial conductance, and enough large electrical field are critical factors for increasing spin polarization.     

Large Magnetoresistance Based on Double Spin Filter Tunnel Barriers

We propose and theoretically analyse a double magnetic tunnel device that takes advantages of the spin filter effect. Two magnetic tunnel barriers are formed by different spin filters which have different barrier heights. The magnetoresistance of the device is low （high） when the magnetic moments of the two spin filters are parallel （antiparallel）. We present a theoretical calculation of the magnetoresistance based on electric tunnel effect. In addition, the effect of the difference barrier heights and exchange splitting energies between the two spin filters are also analysed in detail. The numerical results show that the spin filter in this configuration gives a magnetoresistance larger than that with standard magnetic tunnel junctions.     

Spin Kinetics in Low-Dimensional Semiconductor Systems

Spin kinetics in low-dimensional semiconductor systems was investigated spectroscopically. In the structures, owing to the quantum confinement, the degeneracy of the heavy-hole (HH) and light-hole valence bands was removed. Semiconductor systems were pumped for governing transitions from the HH valence band to the conduction band for the generation of the conduction-band-electron spins, and a maximum ～80% initial spin polarization was obtained in the systems at liquid helium temperature. Distinct spin oscillations and polarization decay were also observed. Spin kinetics of the drifting electrons was studied as a function of the external magnetic field as well as that of the system temperature in the exact Voigt configuration.     

Spin manipulation in Co-doped ZnO

We report the clearly observed tunneling magnetoresistance at 5 K in magnetic tunnel junctions with Co-doped ZnO as a bottom ferromagnetic electrode and Co as a top ferromagnetic electrode prepared by pulsed laser deposition. Spin-polarized electrons were injected from Co-doped ZnO to the crystallized Al2O3 and tunnelled through the amorphous Al2O3 barrier. Our studies demonstrate the spin polarization in Co-doped ZnO and its possible application in future ZnO-based spintronics devices.     

Spin Hall Magnetoresistance and Spin Nernst Magnetothermopower in a Rashba System: Role of the Inverse Spin Galvanic Effect

In ferromagnet/normal‐metal bilayers, the sensitivity of the spin Hall magnetoresistance and the spin Nernst magnetothermopower to the boundary conditions at the interface is of central importance. In general, such boundary conditions can be substantially affected by current‐induced spin polarizations. In order to quantify the role of the latter, we consider a Rashba two‐dimensional electron gas with a ferromagnet attached to one side of the system. The geometry of such a system maximizes the effect of current‐induced spin polarization on the boundary conditions, and the spin Hall magnetoresistance is shown to acquire a non‐trivial and asymmetric dependence on the magnetization direction of the ferromagnet.     

Spin Splitting in Different Semiconductor Quantum Wells

We theoretically investigate the spin splitting in four undoped asymmetric quantum wells in the absence of external electric field and magnetic field. The quantum well geometry dependence of spin splitting is studied with the Rashba and the Dresselhaus spin-orbit coupling included. The results show that the structure of quantum well plays an important role in spin splitting. The Rashba and the Dresselhaus spin splitting in four asymmetric quantum wells are quite different. The origin of the distinction is discussed in this work.     

Effect of Carrier Differences on Spin Polarized Injection into Organic and Inorganic Semiconductors

Spin polarized injection into organic and inorganic semiconductors are studied theoretically from the spin diffusion theory and Ohm＇s law, and the emphases are placed on the effect of the carrier differences on the current spin polarization. The mobility and the spin-flip time of carriers in organic and inorganic semiconductors are different. From the calculation, it is found that current spin polarization at a ferromagnetic/organic interface is higher than that at a ferromagnetic/inorganic interface because of different carriers in them. Effects of the conductivity matching, the spin dependent interracial resistances, and the bulk spin polarization of the ferromagnetic layer on the spin polarized injection are also discussed.     

Semiconductor Lateral Spin Device with Half-Metallic Ferromagnet Electrodes

Physics of the Solid State - In a semiconductor spin device with electrodes formed from the Fe2NbSn half-metallic ferromagnet film, a spin polarization of PS = 4% of electrons injected into the...     

Spin Hall Magnetoresistance in Pt/BiFeO3 Bilayer

Multiferroic materials are general antiferromagnets with negligibly small net magnetization, which strongly limits their magnetoelectric applications in spintronics. Spin Hall magnetoresistance(SMR) is sensitive to the orientation of the Néel vector, which can be applied for the detection of antiferromagnetic states. Here, we apply SMR on the unique room-temperature antiferromagnetic multiferroic material BiFeO₃(BFO). The angular dependence of SMR in a bilayer of epitaxial BFO(001) an...     

Photoluminescence of ZnO and Mn-Doped ZnO Polycrystalline Films Prepared by Plasma Enhanced Chemical Vapour Deposition

ZnO and Mn-doped ZnO polycrystalline films are prepared by plasma enhanced chemical vapour deposition at low temperature （220℃）, and room-temperature photoluminescence of the films is systematically investigated. Analysis from x-ray diffraction reveals that a11 the prepared films exhibit the wurtzite structure of ZnO, and Mndoping does not induce the second phase in the films. X-ray photoelectron spectroscopy confirms the existence of Mn^2＋ ions in the films rather than metalic Mn or Mn^4＋ ions. The emission efficiency of the ZnO film is found to be dependent strongly on the post-treatment and to degrade with increasing temperature either in air or in nitrogen ambient. However, the enhancement of near band edge （NBE） emission is observed after hydrogenation in ammonia plasma, companied with more defect-related emission. Furthermore, the position of NBE shifts towards to high-energy legion with increasing Mn-doped concentration due to Mn incorporation into ZnO lattice.     

Enhanced ferromagnetic properties of ZnO: Cu tuned by HPHT

A series of Cu-doped ZnO ceramics were synthesized from pre-prepared Cu-doped ZnO nanocrystals using a cubic anvil high pressure apparatus under various pressure and temperature conditions. The structures, vibrational spectra and magnetic properties were investigated in detail. The results indicated that the enhancement of ferromagnetism had been achieved for the sample tuned by proper pressure and temperature (5 GPa, 500 °C). The ferromagnetism returned again to the primary state once the tuning temperature was raised up to 800 °C. Compared with those of the samples prepared at ambient pressure, the magnetic properties of the samples tuned by HPHT method had been improved greatly.     

Analysis of Acoustic Domain Fluxes in a Piezoelectric Semiconductor n-CdS Measured by Brillouin Scattering Method

Acoustic fluxes constituting an acoustic domain in a piezoelectric semiconducting n-CdS were analyzed by Brillouin scattering method. Obtained results were as follows: 0.8 GHz and 2.0 GHz acoustic fluxes were faster than the sound velocity 1.75 × 10⁵ cm/s. The observed profile of the 2.0 GHz flux agreed fairly well with the simulated one performed numerically by KdV equation. The faster positions of the acoustic domain were formed by lower frequency acoustic fluxes and the slower positions understood by acoustic fluxes around maximum gain frequency generated first in a small signal regime.     

Enhanced photo-induced hydrophilicity of the sol-gel-derived ZnO thin films by Na-doping

Na-doped ZnO thin films with different Na/Zn ratio were prepared by sol-gel method. The microstructure, chemical composition, surface morphology, and wettability of the thin films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and water contact angle apparatus. The relation of wettability and Na/Zn ratio has been studied in detail. The wetting behavior of the thin films can be reversibly switched from hydrophobic to hydrophilic, through alternation of UV illumination and dark storage (or thermal treatment). Photo-induced hydrophilicity of the thin films increases with increasing Na/Zn ratio up to 0.08 and then decreases. The mechanism can be attributed to surface nanostructure and the concentration of Na doping.     

Switching of a Semiconductor Laser with Multi-Detuned Optical Inputs by Controlling Injection Current

The multistability of a Fabry-Perot semiconductor diode laser for an injection current is presented when multi-optical inputs detuned from the cavity-resonant wavelength of a semiconductor laser are injected. m+1 Multi-stable states are shown to be produced in the optical output versus injection current characteristics for m detuned optical inputs. It is shown that optical output can be switched in any one of the optical input wavelengths in a relatively fast response time by applying injection current pulses. Analytical expression based on linear stability analysis is presented to predict the switching time to free oscillating mode, and larger optical input power and detuning are effective to shorten the switching time. The results here are believed to be useful to extend wavelength switching to a scope of electronic manipulation without modulation of optical inputs and can be applicable to actual devices.     

Enhanced photocatalytic activity of Cu-doped ZnO nanorods

Cu-doped ZnO nanorods with different Cu concentrations were synthesized through the vapor transport method. The synthesized nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV–vis spectroscopy. The XRD results revealed that Cu was successfully doped into ZnO lattice. The FE-SEM images showed that the undoped ZnO has needle like morphology whereas Cu-doped ZnO samples have rod like morphology with an average diameter and length of 60–90 nm and 1.5–3 μm respectively. The red shift in band edge absorption peak in UV-vis absorbance spectrum with increasing Cu content also confirm the doping of Cu in ZnO nanorods. The photocatalytic activity of pure and Cu-doped ZnO samples was studied by the photodegradation of resazurin (Rz) dye. Both pure ZnO and the Cu-doped ZnO nanorods effectively removed the Rz in a short time. This photodegradation of Rz followed the pseudo-first-order reaction kinetics. ZnO nanorods with increasing Cu doping exhibit enhanced photocatalytic activity. The pseudo-first-order reaction rate constant for 15 % Cu-doped ZnO is equal to 10.17×10^?2min^?1 about double of that with pure ZnO. The increased photocatalytic activity of Cu-doped ZnO is attributed to intrinsic oxygen vacancies due to high surface to volume ratio in nanorods and extrinsic defect due to Cu doping.