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Spintronics relies on the ability to transport and use the spin properties of an electron rather than its charge. We describe a spin ratchet at the single-electron level that produces spin currents with no net bias or charge transport. Our device is based on the ground-state energetics of a single-electron transistor comprising a superconducting island connected to normal leads via tunnel barriers with different resistances that break spatial symmetry. We demonstrate spin transport and quantify the spin ratchet efficiency by using ferromagnetic leads with known spin polarization. Our results are modeled theoretically and provide a robust route to the generation and manipulation of pure spin currents. 10.1126/science.1196228

The doping of charge carriers into the Cu[O.sub.2] planes of copper oxide Mott insulators causes a gradual destruction of antiferromagnetism and the emergence of high-temperature superconductivity. Optimal superconductivity is achieved at a doping concentration p beyond which further increases in doping cause a weakening and eventual disappearance of superconductivity. A potential explanation for this demise is that ferromagnetic fluctuations compete with superconductivity in the overdoped regime. In this case, a ferromagnetic phase at very low temperatures is predicted to exist beyond the doping concentration at which superconductivity disappears. Here we report on a direct examination of this scenario in overdoped [La.sub.2-x][Sr.sub.x]Cu[O.sub.4] using the technique of muon spin relaxation. We detect the onset of static magnetic moments of electronic origin at low temperature in the heavily overdoped non-superconducting region. However, the magnetism does not exist in a commensurate long-range ordered state. Instead it appears as a dilute concentration of static magnetic moments. This finding places severe restrictions on the form of ferromagnetism that may exist in the overdoped regime. Although an extrinsic impurity cannot be absolutely ruled out as the source of the magnetism that does occur, the results presented here lend support to electronic band calculations that predict the occurrence of weak localized ferromagnetism at high doping. doi/ 10.1073/pnas.1007079107

We describe an analytical system for in situ measurement of the charge that develops by contact electrification when a ferromagnetic sphere rolls on the surface of a polymer. This system makes it possible to survey the ability of polymeric surfaces to charge by contact electrification. Because the measurement of charge using this tool does not require physical contact of the charged sphere with the measuring electrode, it also enables the kinetics of charging to be examined. The research has focused on the contact charging of spheres having a core-and-shell geometry (a common core of ferromagnetic steel, and a variable shell of thin films of metals, or metals with surface oxides) rolling on the surface of polymeric slabs; it has generated an internally consistent set of data that include the polarity and magnitude of charging for a homologous series of polymers that differ chemically in the pendant group on a polyethylene backbone.

In order to correlate giant magnetoresistance with changes in magnetic domain structure, we have studied lithographically-defined spin-valve elements in-situ by Lorentz transmission electron microscopy, whilst simultaneously passing a controlled current through the clement and applying a magnetic field. For a given current, the changes in magnetic domain structure can thus be correlated with changes in the resistance of the film. Spin valve structures with MnFe and MnNi pinning layers were examined and the technique proved particularly useful in identifying regions of the spin valve corrupted by corrosion of the pinning layer.

We introduce here a novel technique specifically designed to measure the thermoelectrical properties of nanoscale ferromagnetic wires, prepared by electrodeposition in nanoporous membranes. The conditions of measurements have been determined through experiments performed on uniform Co and Cu wires made in different kinds of membranes at different temperatures, from 300 K down to 70 K. We then investigated the magnetic field dependence of Co-Cu multilayer nanowires in the current-perpendicular-to-plane geometry: the relation between the giant magnetoresistance and the magnetothermopower demonstrated the efficiency of this experimental technique. Index Terms--Ferromagnetic nanostructures, magnetic fields, thermopower.

Three sets of exchange spring magnetic films and multilayers with different characteristics and well-defined uniaxial anisotropy have been studied by magnetization and ferromagnetic resonance (FMR) techniques. It was found that the exchange spring behavior is strongly influenced by the thickness of the individual layers. In FMR measurements, two or more modes can be observed. These modes are related only to the soft phase and the different resonance fields arise from the different anisotropy of the soft layers. It was also observed that the effective demagnetization field is larger in multilayers than in single films, suggesting the presence of an additional easy plane anisotropy. Index Terms--Exchange spring magnet, ferromagnetic resonance, magnetic thin films, materials for microactuators.

The structural and magnetic properties of Ni and Co films electrodeposited directly onto (001) and (011) n-GaAs have been studied. Both Ni and Co films grown on (011) n-GaAs are found to show a well-defined uniaxial anisotropy. Anisotropy fields of ~ 1000 Oe are found for Ni films, larger than would be expected from simple crystal anisotropy. Films grown on (001) n-GaAs show a small but definite anisotropy which is found to be very dependent on pH. Index Terms--Electrodeposition, epitaxy, ferromagnetic films, magnetic anisotropy, spintronics.

The temperature-dependent magnetic anisotropies of [Fe.sub.n]/[V.sub.m](001) superlattices on MgO(001) were determined by Ferromagnetic Resonance (FMR). The Fe-layer thickness n ranges between 2 and 4 atomic layers. The shape anisotropy dominates, and the easy-axis of the magnetization of the samples is always in the film plane. The second-order out-of-plane magnetic anisotropy is mainly determined by magnetoelastic effects due to the in-plane lattice expansion of the Fe. The fourth order in-plane anisotropy presents a strong temperature dependence as a result of the competition between a volume part favoring the Fe-[100] and a surface part favoring the Fe-[110] in-plane direction. A very small step-induced in-plane uniaxial anisotropy reveals the existence of very-large atomically-flat terraces. This information, in combination with the observation of very narrow FMR-linewidths, indicates the excellent structural quality of our samples. Index Terms - Coherency strains, ferromagnetic resonance, magnetic anisotropy, superlattices.

The magnetoresistance (MR) associated with domain boundaries has been investigated in microfabricated bcc Fe (0.65 to 20 [micro]m linewidth) wires with controlled stripe domains. Domain configurations have been characterized using MFM. MR measurements as a function of field angle, temperature and domain configuration are used to estimate MR contributions due to resistivity anisotropy and domain walls. Evidence is presented that domain boundaries enhance the conductivity in such microstructures over a broad range of temperatures (1.5 K to 80 K). Index Terms - Domain Walls, Fe, MR.

The polycrystalline FeNi/Ag/CoNi asymmetric trilayer films were prepared by the UHV magnetron sputtering on silicon. In plane magnetization measurements showed double-step hysteresis loops. Magnetoresistance (MR) measurements revealed giant magnetoresistance effect with magnitudes in 0.15-0.29% range at room temperature. The saturation magnetizations and the interaction between layers were studied by ferromagnetic resonance and revealed an undistinguishably weak interlayer coupling from out-of-plane geometry of measurements. The MR data are interpreted based on the incomplete domain alignment model for polycrystalline magnetic films. Index Terms - FMR, GMR, magnetic films, magnetization

Non-propagating surface resonance modes have been observed on epitaxial W/Ni/W and W/Ni films. These modes are excited when the surface of the W buffer layer exhibits some roughness. The resonance fields of the modes are independent of the thickness of the Ni, the modes exhibit exceptionally small linewidths and very weak intensities. The results are interpreted using the model of surface spin waves, related to the variations of the exchange constant near the interfaces. Index Terms - epitaxy, highly localized surface modes, interface roughness, Ni thin film.

Two measurement method based on reversible magnetization rotations, have been used to determine interfacial exchange energy (IEE) magnitude between ferromagnetic and antiferromagnetic (F/AF) layers. Anisotropic magnetoresistance determined the rotations of the magnetization away from the unidirectional easy axis, and the second method used measurements of ac susceptibility.

We present results of magnetoresistance measurements on a 50 nm NiO\2.7 nm Co\2.2 nm Cu\3.1 nm Co\2.5 nm Au spin valve performed in vacuum at temperatures up to 400 [degrees] C. Values of [Delta]R/R, R, and coercivities were found to be reversible up to 200 [degrees] C. Irreversible changes in transport properties observed at and above 250 [degrees] C were concurrent with changes in the interlayer coupling. A striking result is that the coercivity of the NiO-coupled Co film remains large for temperatures at and above the Neel temperature of NiO. Evidence is presented for the existence of 'coercivity transfer' between the Co layers.

The magnetic property of supersaturated [Fe.sub.20][Co.sub.30][Cu.sub.50] solid solution, prepared by mechanical alloying, has been investigated by using magnetometry, Mossbauer spectroscopy and inelastic neutron scattering measurements. Magnetization measurement of the alloy could be analysed by ferromagnetism only. However, Mossbauer spectroscopy and inelastic neutron scattering experiment showed that not only ferromagnetic phase but also paramagnetic phase of about 12% coexist in the alloy. Spin wave stiffness constant obtained from the analysis of the temperature dependence of magnetization was similar to the value obtained from analysis of inelastic neutron scattering experiment.

The ferrimagnetic resonance (FMR) linewidth, Enthalpy, and resonant magnetic field of single crystal (Mn Doped) Ba2Zn2Fe12O22 were measured as a function of frequency from 2 to 20 GHz. These measurements were performed utilizing a slot-coplanar device. The linewidth and resonant frequency measurements were found to compare well with those obtained using a standard ferrimagnetic resonance cavity technique and the data was also in agreement with the behavior predicted by Landau-Lifshitz theory with the damping parameter alpha = 0.0014.

Results reveal that all the tris-dithiooxalato compounds, excepting with manganese(sup)II, are ferromagnetic with absolute temperature between 6 and 16 K. The manganese compound is paramagnetic all the way down to 2 K. However, no structural differences are discernible between the ferro- and paramagnetic compounds as indicated by X-ray diffraction analysis.

Ferromagnetic shape memory refers to the behavior of certain alloys that undergo a reversible martensitic transformation and are also ferromagnetic. They undergo the usual shape memory effect by changing temperature, and they can also be made to undergo large changes of shape by applying a magnetic field. Alloys with composition near [Fe.sub.3]Pd undergo a highly reversible FCC to FCT transformation, have high saturation magnetization approximately 2/3 to that of Fe at room temperature, and therefore are good candidates for ferromagnetic shape memory. In this paper, the possibility of inducing a change of shape by rearranging variants of martensite with an applied field is explored. A key measurement for assessing this possibility is the magnetic anisotropy of a single variant of martensite. We measure this property by applying the appropriate stress to a single crystal to completely detwin it. Magnetization curves for the detwinned crystal are measured and the measurements are corrected for shape anisotropy and the stress. These measurements also settle an apparent discrepancy between the easy axis expected on the basis of Density Functional Theory (DFT) calculation with spin (c-axis), and those inferred from magnetomechancial measurements of James and Wuttig (a-axis) [1]. Index Terms--[Fe.sub.70][Pd.sub.30], ferromagnetic, magnetic anisotropy.

We demonstrate the effect of sputter gas pressure and film thickness, d, on the coercivity of Co in Al/Co/Cu sputter-deposited on Si(001). Increased sputter gas pressure produces increased rms roughness and increased O content in our films. The deposited Co thickness at which the onset of ferromagnetism is first observed, [d.sub.c], increases with sputter gas pressure. Above this thickness, d [is greater than] [d.sub.c], the coercivity increases with increasing Co thickness. For film thickness d [much greater than] [d.sub.c], the coercivity is thickness independent. We show that coercivity is directly controllable at technologically relevant thicknesses by regulating sputter-deposition parameters. Index Terms--Cobalt, coercive force, rough surfaces, sputter deposition.