F. Petroff

Large magnetoresistance in tunnel junctions with an iron oxide electrode

We report on the fabrication and properties of (cobalt/alumina/iron oxide) tunnel junctions. We observe magnetoresistance (MR) effects reaching 43% at 4.2 K and 13% at room temperature. This large MR is ascribed to the presence of a Fe3−xO4 (close to half-metallic magnetite) phase identified by electron diffraction. At low temperature, the MR drops sharply when the bias voltage is smaller than 10 mV, which suggests that the magnetoresistance originates from the activation of tunneling channels through spin polarized states below and above the Fermi level in the iron oxide.

Large magnetoresistance in Fe/MgO/FeCo(001) epitaxial tunnel junctions on GaAs(001)

We present tunneling experiments on Fe(001)/MgO(20 A)/FeCo(001) single-crystal epitaxial junctions of high quality grown by sputtering and laser ablation. Tunnel magnetoresistance measurements give 60% at 30 K, to be compared with 13% obtained recently on (001)-oriented Fe/amorphous-Al2O3/FeCo tunnel junctions. This difference demonstrates that the spin polarization of tunneling electrons is not directly related to the density of states of the free metal surface—Fe(001) in this case—but depends on the actual electronic structure of the entire electrode/barrier system.

Magnetic and transport properties of Fe/Cr superlattices (invited)

We describe the magnetic and transport properties of Fe(001)/Cr(001) superlattices grown on GaAs (001) by molecular‐beam epitaxy and characterized by reflection high‐energy electron diffraction (RHEED), Auger spectroscopy, x‐ray diffraction, and electron microscopy. For Cr layers thinner than about 30 A the magnetic behavior reveals strong antiferromagnetic couplings between the Fe layers across the Cr layers. Polarized neutron diffraction experiments confirm the existence of an antiferromagnetic superstructure. We discuss the origin of the antiferromagnetic (AF) coupling. The Fe/Cr superlattices with AF interlayer coupling exhibit a giant magnetoresistance: when an applied field aligns the magnetizations of the Fe layers, the resistivity drops by a factor of 2 for some samples. This giant magnetoresistance can be ascribed to the spin dependence of the electron scattering by interfaces. We compare our results with the predictions of two recent theoretical models.

Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

We study the magnetic properties of spherical Co clusters with diameters between 0.8 nm and 5.2 nm (25\char21{}7000 atoms) prepared by sequential sputtering of Co and

Room temperature spin filtering in epitaxial cobalt-ferrite tunnel barriers

{\mathrm{Al}}_{2}{\mathrm{O}}_{3}.

Magnetoresistance of Fe/Cr superlattices

The particle size distribution has been determined from the equilibrium susceptibility and magnetization data and it is compared with previous structural characterizations. The distribution of activation energies has been independently obtained from a scaling plot of the ac susceptibility. Combining these two distributions we have accurately determined the effective anisotropy constant

Enhanced tunnel magnetoresistance at high bias voltage in double-barrier planar junctions

{K}_{\mathrm{eff}}.

Magnetoresistance in magnetic tunnel junctions grown on flexible organic substrates

We find that

Structural and magnetic properties of Fex–C1−x nanocomposite thin films

{K}_{\mathrm{eff}}

Nanospintronics: when spintronics meets single electron physics

is enhanced with respect to the bulk value and that it is dominated by a strong anisotropy induced at the surface of the clusters. Interactions between the magnetic moments of adjacent layers are shown to increase the effective activation energy barrier for the reversal of the magnetic moments. Finally, this reversal process is shown to proceed classically down to the lowest temperature investigated (1.8 K).