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Magnetoresistive sensors using a tunnel magnetoresistance (TMR) spin valve structure with CoFe and CoFeB free layer (FL) are investigated. Lateral dimension, thickness, and magnetic properties of the circular-shaped FL energetically favor the nucleation of a magnetic vortex. In the vortex configuration, the sensors show the expected hysteresis-free transfer curve. Distinct differences between CoFe and CoFeB in the vortex typical parameters are observed. The experimental results are compared to micromagnetic simulations. Influence of saturation magnetization ${M}_{s}$ on the vortex transfer curve is studied in order to reproduce the experimental data. However, only by adjusting ${M}_{s}$ iteratively the experimental data cannot be fully reproduced: The vortex annihilation ( ${H}_{\mathrm {an}}$ ) in CoFeB occurs at smaller fields than simulated. On the other hand, the change in TMR signal at ${H}_{\mathrm {an}}$ is significantly smaller in the experiment for CoFe. Discrepancies are most pronounced at ${H}_{\mathrm {an}}$ . This investigation focuses on the magnetic and electric properties at the edge of the FL structure. Reduction in ${H}_{\mathrm {an}}$ can be explained for 1.1 $\mu \text{m}$ FL diameters by introducing a magnetically disturbed edge. Reduced change in TMR signal at ${H}_{\mathrm {an}}$ can be understood by introducing an electrically inactive edge area. The analysis shows that for CoFe and CoFeB different edge inhomogeneity effects are present or edge inhomogeneities have different impacts.

We investigated the structural and magnetic properties of sputter-deposited Mn-Fe-Ga compounds. The crystallinity of the Mn-Fe-Ga thin films was confirmed using X-ray diffraction. X-ray reflection and atomic force microscopy measurements were utilized to investigate the surface properties, roughness, thickness, and density of the deposited Mn-Fe-Ga. Depending on the stoichiometry, as well as the used substrates [SrTiO3 (001) and MgO (001)] or buffer layer (TiN), Mn-Fe-Ga crystallized in the cubic or the tetragonally distorted phase. Anomalous Hall effect and alternating gradient magnetometry measurements confirmed strong perpendicular magnetocrystalline anisotropy. Hard magnetic behavior was reached by tuning the composition. TiN-buffered Mn2.7Fe0.3Ga revealed sharper switching of the magnetization compared with the unbuffered layers.

Magnetic tunnel junctions with Fe1+zCo2-xSi (0 ≤ x ≤ 1)electrodes and MgO barrier were prepared on MgO substrates by magnetron co-sputtering. Maximum tunnel magnetoresistance (TMR) ratios of 262% at 15 K and 159% at room temperature were observed for x = 0.75. Correlations of the annealing temperature dependent atomic ordering and TMR amplitude are discussed. The high TMR for an intermediate stoichiometry is ascribed to the adjustment of the Fermi energy within a minority spin pseudo gap.

Exchange-biased magnetic tunnel junctions with single and double barriers are investigated with respect to the temperature and bias voltage dependence of the tunneling magneto resistance. The single-barrier junctions show a tunneling magnetoresistance ratio of up to 49% at room temperature (72% at 10 K), the double-barrier systems up to 38% (57%), respectively, with three clearly separated magnetic states. The temperature and bias voltage dependence of the double-barrier junctions is explained as a serial connection of two single junctions. Theoretical studies of the tunneling magnetoresistance exhibit that the magnetoresistance ratio can be enhanced by ballistic electrons in double-barrier junctions, but only if the potential of the middle electrode can be shifted.

The signal response of Bangs Laboratories magnetic markers with a mean diameter of 0.86 /spl mu/m on a spiral-shaped giant magnetoresistance sensor with a diameter of 70 /spl mu/m is investigated. The data show a linear dependence of the sensor signal on the surface coverage of the magnetic markers. The detection limit is reached at a coverage of about 5%, which corresponds to about 200 markers distributed across the surface of the sensor. The corresponding molecular binding of the analyte DNA and the magnetic markers show good selectivity and sensitivity.

Co nanocrystals have been prepared via two different chemical preparation routes. Microstructural characterization has. been carried out by conventional and high-resolution transmission electron microscopy. Magnetic characterization reveals that Co nanocrystals with mean particle size distributions about 6 nm are ferromagnetic at room temperature. Superlattices of about 1 /spl mu/m /spl times/ 1 /spl mu/m can be reproduced. For the second preparation route the formation of an /spl epsiv/-Co phase was detected by X-ray diffraction. Whereas the pure Co nanocrystals form domains with a mixture of simple cubic and hexagonal packing, FeCo alloyed nanoparticles form long chain-like structures.