Spin-dependent tunneling junctions with hard magnetic layer pinning

Abstract

We have fabricated ferromagnet-insulator-ferromagnet tunnel junctions with Co and NiFe electrodes, where the Co electrodes are pinned with a hard magnetic Co81Pt19 alloy layer. This approach gives a coercivity of about 300 Oe for the Co layer, while that of the NiFe is about 80 Oe, so we obtain antiparallel magnetization over a wide field range. The Al2O3 tunneling barrier layers were formed by in situ plasma oxidation of elemental Al layers with thicknesses from 10 to 25 Å. For the junctions, we find room temperature magnetoresistance ratios as high as 13% and nonlinear current–voltage curves that are well fit by the Simmons tunneling theory. Depth profiling x-ray photoelectron spectroscopy of oxidized Al barrier layers on Co underlayers reveals a stoichiometry of nearly Al2O3.

Ignition and reaction mechanism of Co–Al and Nb–Al intermetallic compounds prepared by combustion synthesis

“…Ni-Al is the most investigated system. Fewer studies have been devoted to the synthesis and characterization of other promising aluminides, such as the intermetallics in the Nb-Al [4][5][6][7][8] and Co-Al [9][10][11][12][13] systems.…”

Temperature dependence of the magnetization reversal in Co(fcc)–BN–Co(poly hcp) structures

“…Most researchers in this field use different magnetic materials for the two electrodes and/or the shape anisotropy to create the two different coercivities 3 or they use an antiferromagnetic layer to pin one of the ferromagnetic layers. 4,5 In this article we report results on multilayer structures which were prepared 6 with two magnetic layers with different magnetic properties: a structure consisting of two magnetic layers from the same metal ͑Co͒ but with different crystallographic structure. In addition to the intrinsic difference between these layers, the magnetic behavior, in particular the coercive field of one of the layers, can be significantly modified by the exchange coupling with an adjacent antiferromagnetic layer.…”

Magnetic tunnelling in trilayers with radio-frequency sputtered barrier layers

“…The values of spin polarizations for most ferromagnetic transition metals, measured by spin-dependent tunnelling between a ferromagnet and a superconductor [17] and the expected tunnel magnetoresistance ratios obtained by equation ( 1) are reported in table 1. Parkin et al [11] and Bobo et al [18] have already reported that excessive plasma oxidation of 10-20 Å thick Al layers would lead to a decrease or the disappearance of tunnelling magnetoresistance. Bobo et al also report the oxygen presence in Co underlayers by XPS depth profiling.…”