AVS 51st International Symposium
    Magnetic Interfaces and Nanostructures Friday Sessions
       Session MI-FrM

Paper MI-FrM9
Direct Observation of Nano-Oxide Formation in Spin Valve Multilayers

Friday, November 19, 2004, 11:00 am, Room 304A

Session: Advanced Magnetic Data Storage and Thin Film Processing
Presenter: A.T. McCallum, NIST
Authors: A.T. McCallum, NIST
S.E. Russek, NIST
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The addition of thin oxide layers, that specularity reflect electrons, to spin valve trilayers has been shown to increase the giant magnetoresistance of these structures. Usually the specularity of an oxide is deduced by comparing the resistance and magnetoresistance of samples with and without nano-oxide layers. These comparisons are clouded by sample to sample variations and the fact that adding an oxide changes the growth mode of material deposited on top of the oxide. In-situ conductance measurements allow direct observation of the specularity increase as the oxide forms. One key advantage of this measurement is that on one sample the effects of a range of oxygen exposures are measured. The Co free layer of bottom pinned spin valves was oxidized and the conductance and magnetoconductance were measured. These measurements show that the CoO@sub x@ layers become specular within ~5 monolayers of oxygen exposure. Conductance measurements during the oxidation of relatively thick layers of Co show a specularity increase of at least 0.10. Subsequent oxidation does not change the specularity of the nano-oxide. RHEED patterns taken during the oxidation show the appearance of a new face centered cubic, fcc, 111 lattice with a lattice constant consistent with CoO. The region between these two lattices is probably the region that determines the amount of specularity at that interface with the nano-oxide. A second set of bottom pinned spin valves were made with a 1 nm thick Co@sub 1-x@Fe@sub x@ cap on the free layer. This material was then exposed to oxygen. One nm should be about the amount of metal oxidized. The more Fe that was included in the free layer cap the less the specularity increased with oxygen exposure. The sample with a Co cap had a increase in the magnetoconductance of 0.00020 @ohm@@super -1@ during oxidation. The sample with a pure Fe cap had a decrease in magnetoconductance of 0.00005 @ohm@@super -1@ with oxidation.