Papers by Keyword: Spintronics

Abstract: In the summer school of PSD2024, focusing on spin-polarized positron annihilation spectroscopy in materials science, I reported the historical background and its possibility concerning current spintronics field, the basic principles, and prospects. Here, as a memorandum, I mainly summarize the basic principles, which can be relatively well-formulated, with some remarks.

Abstract: Modeling the processes of forming contact regions (interface) of the multilayer niobium-cobalt nanosystem is carried out. The morphology and composition of a multilayer nanosystem interface is investigated. The layer boundaries morphology is shown to depend on the deposition substrate temperature and, largely, is determined by preparing the surface for deposition. The work considers the deposition surface modification by removing its defects. Simulation showed that surface preparation significantly affects the morphology and composition of a multilayer nanosystem interface, depending on the type of deposited atoms and atoms forming the deposition surface.

Abstract: polycrystalline Cu_xY_yO_z are made through solid state reaction. Ferromagnetism is found in this YCuO system at room temperature. The ferromagnetism quite probably originates from Cu₂Y₂O₅ , the Copper Yttrium Oxide. The average magnetic moment per Cu²⁺ is estimated to be 0.04μ_B. Itinerant electron magnetism is a rational explaination for the observed ferromagnetism. The experiment shows that the excessive amount of Cu may lead more defects and further distortion in the lattice and decrease the exchange interaction. This reminds us that the Copper Yttrium Oxide is a substance not only should be avoided in fabricating YBCO superconductors but also should be considered as a potential substance of magnetic semiconductor.

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: Abrupt phase transitions in the structure of ferromagnet/ electroactive polymer/ non-magnetic metal have been found in the number of studies in magnetic field as huge magnetoresistive effects. The sign of magnetoresistance depends on the conductivity state that the polymer has possessed at the beginning of the experiment.The ways of managing of metal/ dielectric phase transition in the polymer layer with the aid of weak external magnetic field are considered. The model of local conversion of charge mobility in the conductive channels is suggested.

Abstract: Literature data on the effective electrical injectors of electron spin for silicon spintronics and stages of the investigation of corresponding magnetic tunnel contacts are reviewed up to 2015 year and a consideration of the current state of the research is given. Different structures for the spin injection, materials and possible applications in silicon spintronics are considered and also possible future research directions are outlined.

Abstract: Spin transport and distribution of spin accumulation in CuPt/Fe heterostructure are numerically investigated, using linearized Levy-Fert model. It was shown that Spin Hall Effect in CuPt layer produces non-equilibrium spin accumulation in adjacent ferromagnetic layer. Spin accumulation vector is not collinear with the direction of magnetization in ferromagnetic layer which leads to the appearance of spin transfer torque. The absolute values and angular dependence of this torque were calculated and it was demonstrated that for the current the values of torques are sufficient for manipulation of magnetization of ferromagnetic layer.

Abstract: We present a brief review of spin torque nanooscillator, which has triggered extensive research interests in the field of nanomagnetism and applied spintronics in recent years. The underlying physical mechanism governing the spin torque nanooscillator is the spin momentum transfer effect, where the angular momentum of itinerant electrons can be passed to localized magnetic moments. The typical device architectures and design of spin torque nanooscillator have been reviewed in this paper, with a particular focus on potential applications of spin torque nanooscillator in the fields of nanotechnology, computing, and biotechnology.Contents of Paper

Abstract: In this paper, we report investigations concerning the fabrication of a diluted Ge (Mn) solution using solid state Mn diffusion, and Mn/Ge reactive diffusion for spintronic applications. The study of Mn diffusion shows that the quasi-totality of the incorporated Mn atoms occupies Ge substitutional sites and probably exhibits two negative elementary charges. The solubility limit of Mn in Ge is comprised between 0.7 and 0.9 % (T  600 °C). We show that substitutional Mn atoms are not ferromagnetic in Ge and consequently that Ge (Mn) diluted magnetic semiconductor can not be produced. Beside the ferromagnetic signal from Mn₅Ge₃, ferromagnetic signals detected in the samples could be always attributed to surface or bulk Mn-Ge clusters. Furthermore, we show that the CMOS Salicide process is potentially applicable to Mn₅Ge₃ nanolayer fabrication on Ge for spintronic applications. During Mn (thin-film)/Ge reaction, Mn₅Ge₃ is the first phase to form, being thermally stable up to 310 °C and exhibiting ferromagnetic properties up to T_C ~ 300 K.

Abstract: This work reports on advances in MRAM cells aiming at sub-nanosecond switching and for sub-20nm technology nodes. Ultrafast precessional spin-transfer switching in elliptical magnetic tunnel junction nanopillars is possible to obtain in samples integrating a perpendicular polarizer and a tunnel junction with in-plane magnetized electrodes. We show that spin transfer torque (STT) switching in less than 500ps can be achieved in these structures with corresponding write energy less than 100fJ. For high density integration and possibly sub-20nm diameter cells the use of a thermally assisted concept for perpendicular anisotropy cells, where the intrinsic heating is used to simultaneously achieve high thermal stability and low current switching.