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One of the most critical steps in the realization of high quality tunneling devices is the fabrication of ultrathin oxide layers. This article describes a powerful technique for controlling the oxidation of ultrathin metallic layers. The technique consists of depositing the metallic layer to be oxidized on top of the soft magnetic layer of a bottom spin valve. The oxidation kinetics are then monitored by measuring the current in plane sheet resistance and magnetoresistance. The technique relies on the extreme sensitivity of the magnetoresistance on the degree of specular reflection at the soft magnetic layer/oxide interface. [ABSTRACT FROM AUTHOR]

A first experimental evidence of a significant tunneling magnetoresistance signal of about 5% at 300 K for a magnetic tunnel junction consisting of hard and soft magnetic layers separated by a 2 nm ZnS semiconducting barrier is reported. The samples have been grown by sputtering on Si(111) substrate at room temperature and have the following structure: Fe[sub 6 nm]Cu[sub 30 nm]CoFe[sub 1.8 nm]Ru[sub 0.8 nm]CoFe[sub 3 nm]ZnS[sub x]CoFe[sub 1 nm]Fe[sub 4 nm]Cu[sub 10 nm]Ru[sub 3 nm]. The hard magnetic bottom electrode consists of the artificial antiferromagnetic structure in which the rigidity is ensured by the antiferromagnetic exchange coupling between two FeCo layers through a Ru spacer layer. Barrier impedance scanning microscope (BISM) measurements reveal a good homogeneity of the barrier thickness. Electric transport measurements over square tunnel elements with lateral sizes between 3 and 100 μm, exhibit a typical tunnel current-voltage variations and tunnel res! istance of 2-3 kΩ μm2 with small variations which never exceed a factor of 2, which is in good agreement with the BISM results. This good reproducibility of the junctions is very promising for MRAMs and transistors applications. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work we study properties of very thin insulating Al oxide films, used as barriers in magnetic tunnel junctions. For the small barrier thicknesses required for technological applications (∼10 Å), the presence of pinholes (direct contact between the ferromagnetic metals through the barrier), or oxidation inhomogeneities, are the major factors for vanishing of the tunnel magnetoresistance effect. We have produced and characterized very thin, pinhole-free Al oxide layers, incorporated in magnetic tunnel junctions. The transport properties of the different barriers were analyzed by barrier impedance scanning microscopy and were correlated with the magnetotransport properties of the patterned microsized junctions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetostatic interactions between the soft and the hard magnetic electrodes in magnetic tunnel junctions (MTJs) using artificial ferrimagnets (AFis) are analyzed. We attribute these interactions to the dispersion fields associated to magnetic inhomogeneities arising from domain walls due to local anisotropic ordering. These magnetostatic interactions can be controlled by adjusting the net magnetic moment of the AFi to optimize the magnetotransport response of the MTJ devices.© 2001 American Institute of Physics. Magnetostatic interactions between the soft and the hard magnetic electrodes in magnetic tunnel junctions (MTJs) using artificial ferrimagnets (AFis) are analyzed. We attribute these interactions to the dispersion fields associated to magnetic inhomogeneities arising from domain walls due to local anisotropic ordering. These magnetostatic interactions can be controlled by adjusting the net magnetic moment of the AFi to optimize the magnetotransport respons! e of the MTJ devices.© 2001 American Institute of Physics. Magnetostatic interactions between the soft and the hard magnetic electrodes in magnetic tunnel junctions (MTJs) using artificial ferrimagnets (AFis) are analyzed. We attribute these interactions to the dispersion fields associated to magnetic inhomogeneities arising from domain walls due to local anisotropic ordering. These magnetostatic interactions can be controlled by adjusting the net magnetic moment of the AFi to optimize the magnetotransport response of the MTJ devices.© 2001 American Institute of Physics. Magnetostatic interactions between the soft and the hard magnetic electrodes in magnetic tunnel junctions (MTJs) using artificial ferrimagnets (AFis) are analyzed. We attribute these interactions to the dispersion fields associated to magnetic inhomogeneities arising from domain walls due to local anisotropic ordering. These magnetostatic interactions can be controlled by adjusting the net magnetic! moment of the... [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions have been fabricated, that use Co/Ru/Co and Co/Ru/CoFe artificial ferrimagnet (AFi) systems as hard magnetic electrodes. The ∼22% tunnel magnetoresistance signal obtained, at room temperature, for junctions with Co/Ru/Co was increased to ∼30% by taking advantage of the higher spin polarization of CoFe in contact with the barrier. Along with this improvement, a different reversal behavior for the AFi was obtained. Together with the enhanced thermal stability, up to 350 °C, of the junctions involving the Co/Ru/CoFe system potential use as magnetic sensors is discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work we study phenomena related to the plasma oxidation of thin metallic Al layers, to be used as insulating barriers in magnetic tunnel junctions. We investigate by barrier impedance scanning microscopy how the barrier’s over oxidation influences the local transport characteristics of the oxide layers and the results are correlated with the magnetotransport properties of patterned microsized as-deposited and annealed junctions. Interestingly, the oxygen reservoir existing at the ferromagnetic metal, degenerating the tunnel device, can be utilized for the improvement of the junction’s magnetotransport properties by means of thermal annealing processing. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have fabricated magnetic tunnel junctions that use Co/Ru/Co and Co/Ru/Co[sub 50]Fe[sub 50] artificial ferrimagnet (AFi) systems as hard magnetic electrodes and AlO[sub x] as tunnel barrier. The thermal behavior of the two AFis, incorporated in tunnel junctions, presents dramatic differences, the most remarkable being the much greater thermal stability of the Co/Ru/CoFe system. This stems from the improvement of the interfaces the CoFe alloy forms with its adjacent Ru and AlO[sub x] layers. After successive annealing steps up to 400 °C, junctions incorporating the Co/Ru/CoFe system still present a significant tunnel magnetoresistance signal of nearly 20%, and most importantly, an almost intact magnetic rigidity of the hard magnetic system, being very promising for spin-electronic devices. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]