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The dose dependence of the exchange bias field and magnetoresistance by 10 keV-He ion bombardment in an applied magnetic field were investigated for Co/Cu/Co/FeMn top spin valves. The exchange bias field H[sub eb] of the pinned Co layer can be enhanced, reversed, and reduced similarly to an exchange biased bilayer system. Additionally, upon ion bombardment, the free Co layer couples increasingly strong to the pinned Co layer until they act magnetically as one single pinned layer. The magnetoresistance decreases exponentially with increasing ion dose, caused by a higher sheet resistance due to increasing defect density and increasing coupling between the free and the pinned ferromagnetic layer. A phenomenological model is extended to describe the ion bombardment-induced changes of H[sub eb] of ferromagnet/antiferromagnet exchange biased bilayers by including saturation effects. This model is compared to available experimental data. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Low RA MgO magnetic tunnel junctions prepared at Singulus (Ta 3/CuN 30/Ta 5/PtMn 20/CoFe 2.5/Ru 0.7/CoFeB 3/MgO 1.2/CoFeB 3/Ta 5 (thickness in nanometers) were microfabricated at INESC-MN. The junctions were patterned into micron-sized sensors (5–20 μm2) with controlled shape anisotropy (aspect ratio ranging from 2 to 20). A small external longitudinal bias field (15–30 Oe) was further used to improve sensor linearity. The MgO junctions have a resistance-area product of 150 Ω μm2 and a maximum tunnel magnetoresistance of 130%. Noise measurements were done in linearized sensors, from dc to 500 kHz. The magnetic and nonmagnetic contributions to the 1/f noise were determined. From the data fitting, Hooge parameters of ∼2.20×10-9 μm2 were obtained for the nonmagnetic 1/f noise. Analysis of direct experimental data revealed the possibility to detect variations of magnetic fields in the order of 10-10 T/Hz0.5 with these MgO junctions, demonstrating their potential for ultralow-field detection. [ABSTRACT FROM AUTHOR]

We investigate the spin-dependent Seebeck coefficient and the tunneling magneto thermopower (TMTP) of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJ) in the presence of thermal gradients across the MTJ. The thermo power voltage VTP across the MTJ is found to scale linearly with the heating power and reveals similar field dependence as the tunnel magnetoresistance (TMR). Based on calibration measurements and finite element simulations of the heat flux, the thermal gradient and large spin-dependent Seebeck coefficients of the order of (240 ± 110) μV/K are derived. From additional measurements on MTJs after dielectric breakdown, a TMR up to 90% and Seebeck coefficients up to 650 μV/K can be derived. [ABSTRACT FROM AUTHOR]

We study tunneling magnetothermopower (TMTP) in CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars. Thermal gradients across the junctions are generated by an electric heater line. Thermopower voltages up to a few tens of µV between the top and bottom contact of the nanopillars are measured which scale linearly with the applied heating power and hence the thermal gradient. The thermopower signal varies by up to 10 µV upon reversal of the relative magnetic configuration of the two CoFeB layers from parallel to antiparallel. This signal change corresponds to a large spin-dependent Seebeck coefficient of the order of 100 µV/K and a large TMTP change of the tunnel junction of up to 90%. [ABSTRACT FROM AUTHOR]