Papers by Keyword: Spin Injection

Abstract: To obtain a larger spin signal for use in graphene-based spintronic devices, the spin injection efficiency needs to be enhanced. Previously researchers can increase the efficiency by inserting a tunnel barrier such as Al₂O₃ or MgO between ferromagnet and graphene. However, the key value in spin transport is still very low because of the conductance mismatch as well as the limit to fabricate a high-quality tunnel barrier at the junction surface. Here we use a highly spin-polarized ferromagnetic material—Heusler alloy Co₂MnGe as a substitutional scheme without the tunnel barrier. The spin injection efficiency of our Co₂MnGe (111)/graphene junction can be as high as 73% which is much higher than 1% of ferromagnet/graphene or 30% of ferromagnet/oxide/graphene using first-principles study. The large spin polarization can be explicated by analyzing the transmission spectrum at the nonequilibrium state.

Abstract: The authors have been investigated structural, magnetic and electrical transport properties for CFAS/n-GaAs junctions. From cross sectional TEM image, RHEED and XRD patternz of thin CFAS films, CFAS films found to be grown epitaxially on GaAs, and shown L2₁-ordered structure for the films with substrate temperature (T_CFAS) of 300°C and 400°C. It is hard to find some additional phase around the interface between CFAS and GaAs. Magnetic moment (and magnetic anisotropy energy) of CFAS increased (and decreased) with increasing T_CFAS up to 300°C and decreased (and increased) at T_CFAS of 400°C, respectively. The asymmetry of current (J)-voltage (V) curve for the junction with T_CFAS =300°C was found to be larger than those for other junctions. It was found there is the relation between T_CFAS dependence of spin signal obtained by three terminal Hanle or four terminal non-local measurement and that of magnetic moment, magnetic anisotropy field or asymmetry of J-V curve.

Abstract: Spin injection mechanisms for radiation and detection of terahertz waves based on magnetic nano junction are considered. High efficiency of terahertz radiation is theoretically explained and the method of the detection of this radiation is offered. The device of the spin injected terahertz radiators is presented.

Abstract: Longitudinal resistivity in strong parallel magnetic fields up to B = 14 Tesla was measured in Si-MOSFET with a narrow slot (90nm) in the upper metallic gate that allows to apply different gate voltage across the slot and, therefore, to control the electron density n₁ and n₂ in two parts of the sample independently. The experimental scheme allows us to pass through the source-drain channel relatively large DC current (I_DC), while the dynamic resistance was measured using a standard lock-in technique with small AC current. It was shown that the sample resistance is asymmetric with respect to the direction of DC current. The asymmetry increases with increase of magnetic field, DC current, and difference between n₁ and n₂. Results are interpreted in terms of a current-induced spin accumulation or depletion near the slot, as described by a spin drift-diffusion equation. The effect on the sample resistance is due to the positive magnetoresistance of Si-MOSFETs in parallel magnetic fields.

Abstract: The emergence of spintronics (spin-based electronics), which exploits electronic charge as well as the spin degree of freedom to store/process data has already seen some of its fundamental results turned into actual devices during the last decade. Information encoded in spins persists even when the device is switched off; it can be manipulated with and without using magnetic fields and can be written using little energy. Eventually, spintronics aims at spin control of electrical properties (I-V characteristics), contrary to the common process of controlling the magnetization (spins) via application of electrical field. In the meantime, another revolution in electronics appears to be unfolding, with the evolution of Molecular Spintronics which aims at manipulating spins and charges in electronic devices containing one or more molecules, because a long spin lifetime is expected from the very small spin-orbit coupling in organic semiconductors. This futuristic area is fascinating because it promises the integration of memory and logic functions,

Abstract: The spin-dependent electronical conductivity of polarons is studied in the spin polarized organic semiconductor .It is found that the spin dependence of the electronical conductivity is induced by the spin polarization of the organic semiconductor, for the spin polarization makes the up-spin and the down-spin polarons have different density, which generates the spin-dependent electronocal conductivity. The spin-dependent electrical conductivity can be directly affected by the match level of conductivities s₀/s_f at the interface of the FM/OSE. Moreover, the current spin polarization in the organic semiconductor can be strengthened by the electric-field in the low-electric-field region .

Abstract: The electronic structures of Co-based Heusler alloys with nonstoichiometric atomic compositions as well as those at the interface of semiconductor junctions are investigated using first principles band calculations. It is shown that the electronic structure of a Co-based Heusler alloy is half-metallic, even for nonstoichiometric but Co-rich compositions, whereas the half-metallicity is lost for Co-poor compositions. It is also shown that magnetic moments at the interface of Co2MnSi/ Si junctions are sensitive to the growth direction and interface structure of the junctions. Efficient spin-injection into Si can be achieved by using a (111)-oriented Co-rich Heusler alloy and controlling the layer-by-layer stacking sequence at the interface.

Abstract: We consider a metamagnetic phase transition of itinerant electrons in the metamagnetic- ferromagnetic metal junction. The current flow between a ferromagnetic metal and a metamagnetic metal produces the non-equilibrium spin imbalance acting as an effective magnetic field and initiating the first-order type transition from low- to high-magnetization states of the metamagnet in the vicinity of the ferromagnet. We show that the current dependence of the length of high-magnetization state region diverges at some threshold value, due to nonequilibrium shift, generated in a contact between the high and low magnetization states of the metamagnetic metal.

Abstract: We have investigated the magnetic effect on the electrical properties of Al and Ni electrode based organic light-emitting devices (OLEDs). The Ni electrode-based OLEDs were compared to Al-based OLEDs in terms of their applied magnetic fields (0.3 T). We found that for current density-voltage on Al and Ni electrodes for OLEDs, Ni electrodes can be applied to OLEDs. The value of magneto-impedance or the resistance ratio decreased in comparison to situations with the absence of a magnetic field. The magneto-impedance or resistance effect indicated that the spin polarization was preserved through the organic layer. We found that the frequency response of magneto-impedance decreased the external magnetic field at room temperature. Electrical characterizations of the OLEDs with spin-polarized electrodes indicated the applicability of the ferromagnetic electrodes to organic light-emitting devices.

Abstract: The spin transport in a lateral spin-injection device with an FeCo/Si/FeCo junction has been investigated. Magnetoresistance (MR) signals were found to appear at low magnetic fields in the range 4 – 300 K. This is attributable to the switching of the magnetization of the two ferromagnetic contacts in the device for certain magnetic fields over which the magnetization in one contact is aligned antiparallel to that in the other. Our results suggest that the spin-polarized electrons are injected from the first contact and, after propagating through the bulk Si, are collected by the second contact.