T. L. Wade

Spin-polarized current induced magnetization switch: Is the modulus of the magnetic layer conserved? (invited)

The direct effect of spin-polarized current on magnetization states is studied on various electrodeposited single contacted nanowires (diameter about 60 nm). Three kinds of samples have been studied: (1) Homogeneous Ni nanowires, (2) nanowires composed of both a homogeneous Ni part and a multilayered Co(10 nm)/Cu(10 nm) part, (3) pseudospin-valve pillars Co(30 nm)/Cu(10 nm)/Co(10) electrodeposited in Cu wires. The magnetization reversal due to the current injection is observed in the three cases. The effect is observed with using different experimental protocols, including current activated after-effect measurements. The results obtained suggest that two different mechanisms are able to account for the magnetization reversal: exchange torque and spin transfer. We propose a definition of the two mechanisms based on the conservation or nonconservation of the magnetic moment of the ferromagnetic nanostructure.

Electronic transport of silicon nanowires grown in porous Al2O3 membrane

Electronic transport properties of silicon nanowires grown by chemical vapor deposition, embedded in an insulating alumina nanoporous membrane are studied. Transport measurements were performed from 300to4.2K, which revealed a scaling law of the conductance as a function of the temperature and the dc bias voltage, which the authors interpreted as a Coulomb blockade manifestation. Magnetoconductive measurements at low temperature revealed a positive magnetoconductance which can be well fitted by quasi-one-dimensional (quasi-1D) weak localization theory. These results seem to indicate that electron-electron interactions and quasi-1D effect predominate on the electronic transport properties of these systems.

Anisotropic magnetothermopower : Contribution of interband relaxation

Spin injection in metallic normal/ferromagnetic junctions is investigated taking into account interband relaxation and the consequences in terms of thermoelectric power. On the basis of a generalized two-channel model, it is shown that there is an interface resistance and thermoelectric power contribution due to anisotropic scattering, besides spin accumulation and giant magnetoresistance. The corresponding expression of the thermoelectric power is derived and compared with the expression accounting for the thermoelectric power produced by the giant magnetoresistance. Measurements of anisotropic magnetothermoelectric power are presented in electrodeposited Ni nanowires contacted with Ni, Au, and Cu. It is shown that a thermoelectric power is generated at the interfaces of the nanowire and that the experimental results strongly support the model.

Nanoporous alumina wire templates for surrounding-gate nanowire transistors

Aluminium wires are electrochemically sculptured into bi-directional templates for the templated growth and contacting of nanowires as three terminal devices. The use of this nanostructured template is demonstrated by a ZnO nanowire surrounding-gate field-effect transistor. This bottom-up approach to a 3D nanowire transistor is unique in that it can be almost entirely fabricated in a beaker using aqueous, room temperature electrochemistry. The fabrication procedures and preliminary device characteristics of this new approach to nanowire transistors are shown.

Synthesis and magnetic reversal of bi-conical Ni nanostructures

Microstructure study of pinning sites of highly (0001) textured Sm(Co,Cu)5 thin films grown on Ru underlayer J. Appl. Phys. 111, 07B730 (2012) Spin-torque diode spectrum of ferromagnetically coupled (FeB/CoFe)/Ru/(CoFe/FeB) synthetic free layer J. Appl. Phys. 111, 07C917 (2012) Textured Nd2Fe14B flakes with enhanced coercivity J. Appl. Phys. 111, 07A735 (2012) Influence of Si Co-doping on electrical transport properties of magnesium-doped boron nanoswords Appl. Phys. Lett. 100, 103112 (2012) Additional information on J. Appl. Phys. Journal Homepage: http://jap.aip.org/ Journal Information: Template synthesis in polyethylene terephthalate (PET) membranes has been used to grow hour glass shaped nickel nanowires with a constriction in the range of tens of nanometers at the center. Anisotropic magnetoresistance measurements have been performed on a single nanowire to follow magnetization reversal of the structure. The results are explained via 3D micromagnetic simulations showing the appearance of a complex vortex state close to the constriction whose propagation depends on the angle between the cone axis and the applied field.

Lateral alumina templates for carbon nanotubes and semiconductor nanowires synthesis

We present here, a novel approach for the membrane-based synthesis, also called template synthesis of arrays of nanomaterials with monodispersed geometrical features. The basic principle is to grow or generate the desired material inside the pores of a nanoporous alumina membrane. The pores of are synthesised parallel to the surface of the substrate by performing the anodic oxidation of an aluminium thin film laterally, i.e. parallel to the surface of the substrate, instead of perpendicular as usually done. We obtain highly regular and ordered pore arrays, with a minimum pore size in the range of ~3 to 4 nm, which to the best of our knowledge is the smallest reported to date for anodic alumina membranes. After anodic oxidation, the pores of the lateral alumina membranes have been electrochemically “filled” with Te nanowires. Such porous alumina structures may allow to control the in-plane organisation of arrays of template-grown nanowires and carbon nanotubes for reproducible device fabrication.

Spin transfer by spin injection between both interfaces of a Ni nanowire

Magnetization switching provoked by spin injection is studied in Ni nanowires of various sizes and morphologies. The response of the magnetization to current injection is measured as a function of the amplitude of the current, the temperature, and the symmetry of the interfaces. The efficiency of the response of the magnetization of spin injection is a decreasing function of the temperature, does not depend on the current sign, and occurs only in the case of asymmetric interfaces. It is shown that the switching provoked by spin injection is not affected by the presence of a magnetic domain inside the layer. Some consequences in terms of spin transfer or exchange torque are discussed.

Thermally activated delayed fluorescence evidence in non-bonding transition electron donor-acceptor molecules

The exhibition of thermally activated delayed fluorescence on triazine derivative by the introduction of a nonbonding part is demonstrated. Two molecules containing triazine core as acceptor and carbazole part as donor has been synthesized and characterized. One of these molecules bears an additional nonbonding part by the means of a phenoxy group. The results indicated that the molecule bearing the nonbonding molecular part (phenoxy) exhibit thermally activated delayed fluorescence while not on molecule free of non-bonding group. The results are supported by, photoluminescence, spectral analysis time-resolved fluorescence and time-dependent density functional estimation

Spin-injection-induced magnetization reversal

The usual charge carrier exploited in all electronic devices is the electron (and hole) and possesses hence, associated with its inertial masse, a spin degree of freedom. Manipulating spin-polarized electric current is the role devoted to Spintronics. Investigating the current induced magnetization switching (CIMS), consists in measuring the dynamics of the magnetization due to spin-polarized current injection. It is shown that two different mechanisms are operating. One can be described with a current dependent torque, and the other one is attributed to longitudinal spin-transfer.