Spin dependent tunnel/spin-valve devices with different pinning structures made by photolithography

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Abstract
Spin dependent tunnel and spin-valve devices were made using rf diode sputtering, with patterning done using standard semiconductor photolithography techniques. In order to tailor the pinning strength of the hard magnetic layers, three types of structures were tried: (1) NiFeCo/spacer/CoFe; (2) NiFeCo/spacer/CoFe/IrMn; and (3) NiFeCo/spacer/CoFe/Ru/CoFe/FeMn, with Al2O3 or Cu as spacers. The magnetoresistance of the spin dependent tunnel devices is up to 24% with a switching field of a few Oe for the free layer of NiFeCo. The saturation fields of the hard layers are a few tens, a few hundreds, and a few thousands of Oe for the three structures, respectively. The first structure is suitable for magnetic memory applications with the hard layer storing the information. The second structure is suitable for magnetic field sensors which must function after relatively high magnetic field excursions. The third structure makes use of the synthetic antiferromagnet of CoFe/Ru/CoFe in addition to the antiferromagnet (FeMn) to achieve the highest pinning field. It also reduces the fringing field to the free layer caused by the pinned layer, due to the flux closure of the two ferromagnetic layers in the synthetic antiferromagnet. This third structure is especially suitable for field sensor applications in environments with excursions of very high magnetic fields between sensing operations.