Room-temperature magnetoresistance in CoFeB/STO/CoFeB magnetic tunnel junctions

A series of Co₄₀Fe₄₀B₂₀/SrTiO₃/Co₄₀Fe₄₀B₂₀ magnetic tunnel junctions with a bottom-pinned synthetic antiferromagnet have been prepared by sputtering. Devices optimally annealed at 325 °C exhibit an exchange bias of about 65 mT, and a tunnel magnetoresistance of 2%. The smaller than predicted effect is attributed to the lack of epitaxy between the crystallized CoFeB electrodes and the SrTiO₃ (STO) barrier, due to poor crystal quality of the barrier layer. Unlike MgO, well-crystallized, oriented STO does not grow on amorphous Co₄₀Fe₄₀B₂₀.     

Magnetic structuring of electrodeposits

Metal electrodeposition reflects the pattern of the magnetic field at the cathode surface created by a magnet array. For deposits from paramagnetic cations such as Co2? or Cu2?, the effect is explained in terms of magnetic pressure which modifies the thickness of the diffusion layer, that governs their mass transport. An inverse effect allows deposits to be structured in complementary patterns when a strongly paramagnetic but nonelectroactive cation such as Dy3? is present in the electrolyte, and is related to inhibition of convection of water liberated at the cathode, in the inhomogeneous magnetic field. The magnetic structuring depends on the susceptibility of the electroactive species relative to that of the nonelectroactive background.     

Spin Transport in Multi Wall Carbon Nanotubes with Co Electrodes

The magnetic field dependent transport behaviour of Co contacted multi-wall nanotubes is investigated. A sample with three Co electrodes has been measured by two-channel method with an in-plane magnetic field. When the in-plane magnetic field is perpendicular to the tube, high positive magnetoresistance up to 30% is obtained at low temperature from 3 K to 25K and with field parallel to the tube, negative magnetoresistance up to 15% is observed only from the high resistance junction. The detailed positive and negative magnetoresistance behaviour also changes with temperature.     

Inhomogeneous electrodeposition of copper in a magnetic field

Normally, magnetoconvection driven by the Lorentz force increases the limiting current in the mass-transport limited regime, roughly as the one-third power of the applied magnetic field. Here we show that an applied field can actually diminish the rate of copper electrodeposition at low overpotentials. The effect is related to the formation of a vortex at the leading edge of the flow. Similar, but weaker effects are due to gravity.     

Magnetic nitrides

Nitrogen enters 3d metals and 3d–4f intermetallic compounds as an interstitial provoking a dilation of the lattice. Iron-based alloys are most susceptible to modification by nitrogen, which can turn them from weak to strong ferromagnets. In the 3d–4f compounds it is a major contributor to the crystal field. The influence of nitrogen in BCC, FCC and HCP iron, and then in iron-based intermetallics with 2 : 17, 1 : 12 and 3 : 29 structure types is reviewed. Important issues are the role of nitrogen in enhancing the iron moment and raising the Curie temperature. Progress in processing nitrogen-containing compounds is outlined, and applications of iron nitrides as permanent magnets and as materials for use in magnetic recording are discussed.     

Enhanced corrosion resistance in Nd15Fe77B8 by laser surface amorphization

A thin amorphous layer on a NdFeB ingot produced by surface melting using a KrF excimer laser, and subsequent self-quenching is shown to improve the corrosion resistance properties of the ingot. X-ray diffraction and conversion-electron Mössbauer confirm the amorphous nature of the laser-induced surface layer. Potentiodynamic polarization measurements before and after laser treatment show a shift of Ecorr to a more positive value (ΔEcorr～150 mV) and a reduction in the dissolution current in the passive region. These observations are characteristic of a reduced total corrosion rate.     

Magnetocaloric effect in La0.67Sr0.33MnO3 manganite above room temperature

The La_0.67Sr_0.33MnO₃ composition prepared by sol-gel synthesis was studied by dc magnetization measurements. A large magnetocaloric effect was inferred over a wide range of temperature around the second-order paramagnetic-ferromagnetic transition. The change of magnetic entropy increases monotonically with increasing magnetic field and reaches the value of 5.15 J/kg K at 370 K for Δμ0H=5 T. The corresponding adiabatic temperature change is 3.3 K. The changes in magnetic entropy and the adiabatic temperature are also significant at moderate magnetic fields. The magnetic field induced change of the specific heat varies with temperature and has maximum variation near the paramagnetic-ferromagnetic transition. The obtained results show that La_0.67Sr_0.33MnO₃ could be considered as a potential candidate for magnetic refrigeration applications above room temperature.     

Room temperature magnetism in MB<Subscript>6</Subscript> (M = Ca,Sr, Ba) films grown by pulsed laser deposition

Room temperature magnetism is reported in amorphous MB₆ (M = Ca, Sr, Ba) filmsgrown by pulsed laser deposition; these materials contain no d orf electrons normally associated with magnetic ordering. The magnetismis virtually anhysteretic, isotropic, temperature independent from 4 ? 300 K and saturatesquickly (<0.3 T) with applied field. It is shown that ferromagneticimpurities cannot account for the magnitude of the larger magnetic signals measured. Themagnetism is thought to be due to a defect-based impurity band, which can become spinsplit and result in high temperature Stoner ferromagnetism when the density of states atthe Fermi level is sufficiently high. The magnetic signals correspond to an average filmmagnetization in the range 10 ? 100 kA m^-1, but from analysis of the variationof the magnetic moment with film thickness, it is shown that the magnetism originatesmainly near the interface with the substrate.     

Controlling the demagnetizing field of an in-plane free layer by exchange coupling with a perpendicular multilayer

The demagnetizing field of a Co₅₀Fe₅₀ free layer in an in-planemicron-sized magnetic tunnel junction (MTJ) can be partially compensated by exchangecoupling with a [Co₉₀Fe₁₀/Pt] _N multilayer with perpendicular magnetic anisotropy via a Ru interlayer. The perpendicularanisotropy for N = 5 is optimized for nominal CoFe and Pt thicknessof 0.4 nm and 1.0 nm, respectively. An increase of tunnel magnetoresistance (TMR) from 2%to 75% is observed in MTJs as the free layer thickness, t variesfrom 1.0 nm to 3.0 nm. A phenomenological model is developed to interpret the TMRdependence in terms of the free layer magnetization rotation from in-plane to out-of-planewith decreasing t, a consequence of interlayer exchange coupling with theperpendicular multilayer. We suggest that this strategy could significantly reduce theswitching current density in such MTJs.     

Iron oxide particles in a perfluorosulfonate membrane

Particles of (α-Fe₂O₃ and α-FeOOH have been observed directly in ultrathin (～ 500 Å) sections of Nafion® perfluorosulfonate membranes by transmission electron microscopy, α-Fe₂O₃ is obtained by heating a membrane, previously exchanged with 0.2 M FeCl₃, in an autoclave with water at 150°C. The individual particles are roughly spherical, ～ 100 Å in diameter, but they are grouped together in clusters ranging from a few hundred angströms up to about 1000 Å in size, which are uniformly distributed across the membrane thickness. α-FeOOH is obtained by boiling the membrane in water and exchanging first in 0.2 M FeCl₃ and then in 0.2 M KOH. Well-separated acicular or blade-shaped crystallites up to 1000 Å long and about 100 Å across are observed; they become more numerous towards the membrane surfaces. Amorphous ferric hydroxide, obtained by treating an unboiled membrane in the same way, could not be observed directly.