Spin-dependent electron tunneling in superconducting vanadium and vanadium-titanium thin films

The tunneling conductance dI/dV of junctions between A1 films and thin superconducting films of V or VTi alloys has been measured in magnetic fields up to 6 T applied parallel to the films. The films have small spin-orbit scattering and show Zeeman splitting of the quasi-particle density of states.     

Study of Co thin films deposited on low-index Cu surfaces by photoemission electron microscopy

The domain structures of Co ultrathin film prepared with μm- and mm-dimension laterally were acquired and compared using X-ray Photoemission Electron Microscope (PEEM). Through depositing the Co film with different thickness on two copper single-crystal surfaces; Cu(1 0 0) and Cu(1 1 0), we report the impacts of thin film lateral dimensions, crystal orientations, and film thickness to the domain structures of Co layer.     

Spin-dependent electron transport in manganite bicrystal junctions

Magnetic bicrystal films and junctions of magnetic La_0.67Sr_0.33MnO₃ (LSMO) and La_0.67Ca_0.33MnO₃ (LCMO) films epitaxially grown on NdGaO₃ substrates with the (110) planes of their two parts misoriented (tilted) at angles of 12°, 22°, 28°, and 38° are investigated. For comparison, bicrystal boundaries with a 90° misorientation of the axes of the NdGaO₃ (110) planes were fabricated. The directions of the axes and the magnetic anisotropy constants of the films on both sides of the boundary are determined by two independent techniques of magnetic resonance spectroscopy. The magnetic misorientation of the axes in the substrate plane has been found to be much smaller than the crystallographic misorientation for tilted bicrystal boundaries, while the crystallographic and magnetic misorientation angles coincide for boundaries with rotation of the axes. An increase in the magnetoresistance and characteristic resistance of bicrystal junctions with increasing misorientation angle was observed experimentally. The magnetoresistance of bicrystal junctions has been calculated by taking into account the uniaxial anisotropy, which has allowed the contributions from the tunneling and anisotropic magnetoresistances to be separated. The largest tunneling magnetoresistance was observed on LCMO bicrystal junctions, in which the characteristic resistance of the boundary is higher than that in LSMO boundaries.     

Spin-dependent transport in a magnetic two-dimensional electron gas

Magneto-transport and magneto-optical probes are used to interrogate spin-dependent transport in magnetic heterostructures wherein a two dimensional electron gas (2DEG) is exchange-coupled to local moments. At low temperatures, the significant s–d exchange-enhanced spin splitting in these “magnetic” 2DEGs is responsible for the observation of unusual transport properties such as a complete spin polarization of the gas at large Landau level filling factors and a pronounced, non-monotonic background magneto-resistance. Magneto-transport measurements of gated samples performed in a parallel field geometry are used to systematically study the variation of the magneto-resistance with sheet concentration, yielding new insights into the dependence of spin transport on the Fermi energy of the majority spin carriers.     

Surface morphology and electron transport correlation in thin iron films

In this work we studied the magnetic, resistive and magnetoresistive properties of thin iron films deposited on vicinal silicon substrates. The film surfaces were characterized by atomic force microscopy which revealed formation of elongated stripes. We show that the morphological anisotropic structure of the films influences significantly both their magnetic and electronic transport.     

Structure and magnetic anisotropy of Co/Cu/Co films

The energy of the magnetic anisotropy of Co/Cu/Co polycrystalline ultradisperse films is investigated as a function of the thickness of copper and cobalt layers. The influence of the structure parameters (the size and distribution of defects, the period and amplitude of roughnesses) on the surface and volume components of the magnetic anisotropy is analyzed. The parameters of the structure inhomogeneities and their distribution over the film surface are determined from two-dimensional Fourier spectra and electron microscope images of the films.     

Spin-dependent transport properties of debrominated tetrabromopolyaromatic with Cu or Co doping embedded between zigzag graphene nanoribbon electrodes

Using density functional theory combined with non-equilibrium Green's function method, we investigate the spin-dependent transport properties of debrominated tetrabromopolyaromatic (D-TBPA) molecules embedded between zigzag graphene nanoribbon electrodes, and the effects of copper and cobalt side doping have also been considered. Our results show that the copper doping can insert new energy levels around the Fermi Level and keep spin degeneration of band structure, the cobalt doping can also induce spin splitting. The results on spin transport properties of D-TBPAs embedded into zigzag graphene nanoribbon electrodes show that these systems exist spin filtering and negative differential resistance behaviors. Corresponding physical mechanism on the spin-dependent transport property has been revealed according to the frontier molecular orbital characteristics.     

Magnetoresistance in epitaxial [NiFe/Cu/Co(/Cu)] films

Epitaxial [NiFe/Cu/Co(/Cu)] films have been grown on Si(100)/Cu substrates using an ultrahigh vacuum evaporation method. Magnetoresistance (MR) and magnetization were measured at room temperature with maximum applied field, 40 kA/m. The (100) oriented [NiFe(3 nm)/Cu(6 nm)/Co(3 nm)/Cu(6 nm)] × 10 multilayers showed a sharply peaked MR curve (when the external field was applied along [011] direction) due to magnetization rotation of free NiFe layers separated from Co layers with thick Cu layers. Furthermore the interposition of a Ag layer in the Cu layer reduced the couplings between ferromagnetic layers and improved the sensitivity of the [NiFe/Cu/Co(/Cu)] film. Si(100)/Cu(5 nm)/[Co(3 nm)/Cu(2.4 nm)/Ag(0.2 nm)/Cu(2.4 nm)/NiFe(3 nm)/Cu(2.4 nm)/Ag(0.2 nm)/Cu(2.4 nm)] × 10 multilayers showed a resistivity change of about 8.2% per kA/m (12 Oe).     

Spin-dependent transport in films composed of Co clusters and C $_{\mathsf{60}}$ fullerenes

Granular films of Co-cluster/C₆₀ mixtures have been prepared by the co-deposition of well defined Co clusters (mean diameter 4.5 nm) and C₆₀ fullerenes onto a cold ( 35 K) substrate. Films having a Co cluster volume fraction show a resistivity , typical for tunneling with a Coulomb barrier. The tunneling magnetoresistance (TMR) has a value of TMR ( % for and is decreasing by almost one order of magnitude going to . We explain this unusual decrease of the TMR with increasing as caused by electron-doping of the C₆₀ fullerenes due to the known charge transfer process occurring between transition metal surface and C₆₀. Increasing electron doping may lead to an increasing probability for spin-flip processes within the tunneling barrier, resulting in a decrease of the TMR.Received: 17 March 2004, Published online: 3 August 2004PACS: 75.47.-m Magnetotransport phenomena; materials for magnetotransport - 73.40.Gk Tunneling - 73.40.Rw Metal-insulator-metal structures     

Spin-dependent resonant tunneling through quantum-well states in magnetic metallic thin films

Quantum-well (QW) states in nonmagnetic metal films between magnetic layers are known to be important in spin-dependent transport, but QW states in magnetic films remains elusive. Here we identify the conditions for resonant tunneling through QW states in magnetic films and report first principles calculations of Fe/MgO/FeO/Fe/Cr and Co/MgO/Fe/Cr. We show that, at resonance, the current increases by 1 to 2 orders of magnitude. The tunneling magnetoresistance ratio is much larger than in simple spin tunnel junctions and is positive (negative) for majority- (minority-) spin resonances, with a large asymmetry between positive and negative biases. The results can serve as a basis for novel spintronic devices.     

Magnetic anisotropy of Co/Cu/Co films with indirect exchange coupling

The effect of isothermal annealing on the magnetic anisotropy, bilinear and biquadratic exchange coupling energies, and domain structure of Co/Cu/Co trilayer fiilms with d_Co=6 nm and d_Cu=1.0 and 2.1 nm prepared by magnetron sputtering has been studied. It is shown that, under isothermal annealing, the biquadratic coupling energy decreases by more than an order of magnitude in films with d_Cu=1.0 nm and increases in films with d_Cu=2.1 nm. The fourth-order magnetic anisotropy is shown to be related to the existence of biquadratic exchange energy.     

拓扑绝缘体薄膜生长与栅电压调控输运特性研究

文章讨论了三维拓扑绝缘体制备和输运性质研究方面的进展情况.首先介绍了拓扑绝缘体体材料和薄膜的制备,并介绍了文章作者利用分子束外延方法,在硅表面以及高介电常数材料钛酸锶表面生长高质量拓扑绝缘体Bi2Se3薄膜的工作.然后介绍了拓扑绝缘体输运研究的现状,以及文章作者在栅电压调控拓扑绝缘体外延薄膜的化学势和输运性质方面的研究成果.     

Spin-dependent transport for a two-dimensional electron gas with magnetic barriers

The spin-dependent conductance and magnetoresistance ratio (MRR) for a semiconductor heterostructures consisting of two magnetic barriers with different height and space have been investigated by the transfer-matrix method. It is shown that the splitting of the conductance for parallel and antiparallel magnetization configurations results in tremendous spin-dependent MRR, and the maximal MRRs reach 5300\% and 3800\% for the magnetic barrier spaces W=81.3 and 243.9~nm, respectively. The obtained spin-filtering transport property of nanostructures with magnetic barriers may be useful to magnetic-barrier-based spintronics.     

Spin-dependent transport in organic-ferromagnets

Based on the modified Su-Schrieffer-Heeger model and the non-equilibrium Green's function current formula, the spin polarization of the ferromagnet-electrode connected organic ferromagnet is theoretically studied. The spin polarization can be suppressed by atomic dimerization and be driven by an applied electric field. We investigate the spin polarization from the viewpoint of energy competitions in different interactions under the electric field. In addition, the ferromagnetic electrodes significantly enhance the spin polarization.     

拓扑绝缘体薄膜生长与栅电压调控输运特性研究

文章讨论了三维拓扑绝缘体制备和输运性质研究方面的进展情况.首先介绍了拓扑绝缘体体材料和薄膜的制备,并介绍了文章作者利用分子束外延方法,在硅表面以及高介电常数材料钛酸锶表面生长高质量拓扑绝缘体Bi2Se3薄膜的工作.然后介绍了拓扑绝缘体输运研究的现状,以及文章作者在栅电压调控拓扑绝缘体外延薄膜的化学势和输运性质方面的研究成果.     

Ultrafast electron and magnetization dynamics of thin Ni and Co films on Cu(001) observed by time-resolved SHG

Received: 21 December 1998     

Co与Cu掺杂ZnO薄膜的制备与光致发光研究

采用溶胶-凝胶旋涂法在玻璃衬底上制备了Co, Cu单掺杂及Co,Cu共掺杂ZnO薄膜.用金相显微镜观察了Co与Cu掺杂对ZnO薄膜形貌的影响.X射线衍射（XRD）研究揭示所有ZnO薄膜样品都存在（002）择优取向,在Cu单掺的ZnO薄膜中晶粒尺寸最大.对所有样品的室温光致发光测量都观察到较强的蓝光双峰发射和较弱的绿光发射,其中长波长的蓝光峰和绿光峰都能够通过掺杂进行控制.对不同掺杂源的ZnO薄膜发光性能进行了分析,认为蓝光峰来源于电子由导带底到锌空位能级的跃迁及锌填隙到价带顶的跃迁,绿光峰是由于掺杂造成的 关键词： ZnO薄膜 溶胶-凝胶 Co Cu掺杂 光致发光     

Molecular dynamics simulation of Co thin films growth on Cu(001)

Results of MD simulations of the structure of ultrathin films of Co on Cu(001) are presented. Growth conditions corresponding to vacuum evaporation as well as laser ablation are considered. The dynamics of the growth process and the structure of the as-deposited films are investigated as a function of the kinetic energy of adatoms. The effect of fast interdiffusion due to a high impact energy is observed. Tight-binding potentials in the second-moment approximation are used. Co–Cu interaction parameters are determined from ab-initio electronic structure calculations.