Volume 94, Issue 6, 15 September 2003
Index of content:
- MAGNETISM AND SUPERCONDUCTIVITY (PACS 74-76)
94(2003); http://dx.doi.org/10.1063/1.1601313View Description Hide Description
A planar ballistic T-shaped structure with a ring resonator attached is shown to be highly effective in filtering electron spin from an unpolarized source into two output fluxes with opposite and practically pure spin polarizations. The operability of the proposed device relies on the peculiar spin-dependent transmission properties of the T-shaped connector in the presence of Rashba spin–orbit interaction as well as the difference in dynamic phase gain of the two alternative paths around the ring resonator through upper and lower branches for even and odd eigenmodes.
Magnetic coupling in epitaxial TM/MgO/Fe(001) (TM=FeCo, Fe/Co, Fe) macroscopic and microscopic trilayers94(2003); http://dx.doi.org/10.1063/1.1598280View Description Hide Description
Multilayered TM/MgO/Fe (001) heterostructures (TM: FeCo, Co/Fe, and Fe) are grown epitaxially, to study the dependence of the magnetic coupling between the two ferromagneticelectrodes on the insulating MgO barrier width and the lateral dimensions of the structures. The crystal quality is investigated by reflection high-energy electron diffractionin situ at different growth stages of the TM/MgO/Fe(001) heterostructures. Magnetic characterization by superconducting quantum interference device magnetometry (macroscopic structures) and transverse Kerr effect (microscopic structures) shows clearly independent switching of top and bottom electrodes at large (above 20 Å) spacer thicknesses for macroscopic films. This independent switching is also observed on patterned structures. For very thin barriers, decreasing the size of the elements in patterned arrays decreases the number of junctions coupled via pinholes.
94(2003); http://dx.doi.org/10.1063/1.1601291View Description Hide Description
We have investigated the permeability at microwave frequencies of Y-type hexaferrites in zero-magnetic field. The permeability was measured from 0.045 to 10 GHz and it was correlated with multidomain and domain-wall resonances in zero-magnetic field. The basal plane anisotropy field, magnetic remanence, domain-wall thickness δ, and length L of the domain wall were estimated from resonances and permeability data.
94(2003); http://dx.doi.org/10.1063/1.1601689View Description Hide Description
We describe the synthesis, magnetism, and structure of CoPtCrB alloys with Pt concentrations from 10%–43%. The Cr concentration in the alloys was 15%–17% and the B concentration was 9%–11%. The magnetic anisotropy and coercivity increase with increasing Pt up to ≈30%, plateau at ≈35 000 Oe and ≈6000 Oe, respectively, and then decrease. Transmission electron microscopy results show the media form fine isolated grains for all Pt concentrations. X-ray diffraction measurements show that with increasing Pt a face-centered-cubic (fcc) Co-alloy phase is progressively formed at the expense of the hexagonal-close-packed Co-alloy and that this fraction becomes significant for >35% Pt. The formation of the fcc phase likely causes the behavior in the anisotropy. No Pt concentration dependence is observed for the stacking fault density. The x-ray data show that with increasing Pt, the CoPtCrB-alloy lattice parameters exhibit two distinct regions with the slope changing at 16% Pt. The presence of these two regions is discussed.
94(2003); http://dx.doi.org/10.1063/1.1603347View Description Hide Description
We present a detailed analysis of the effect of heat treatments on the microstructure, magnetization, and transport properties of wires produced by the powder-in-tube method. We have used commercial powder with 5 at. % Mgpowder added as an additional source of magnesium and stainless steel as sheath material. We measure the dc transport critical current that can be increased or decreased by more than one order of magnitude as compared with the as-drawn wire, depending on the annealing parameters. We correlate the changes in the critical current with changes in the microstructure, as determined from scanning and transmission electron microscopy analysis. We show through magnetization measurements of short annealed wires that inappropriate annealing conditions result in a deterioration of the connectivity due to the loss of Mg and in inhomogeneous weak-link limited current flow, rendering the critical state model inapplicable. We discuss the optimization of the annealing conditions that strongly improve the connectivity by eliminating most of the microcracks present in the unannealed wires, where excess Mg promotes the recrystallization. The loss of Mg during the heat treatment may be precluded by annealing long wire lengths with a high heating rate.