AVS 51st International Symposium
    Magnetic Interfaces and Nanostructures Thursday Sessions
       Session MI-ThM

Invited Paper MI-ThM1
Defect Mediated Ferromagnetic Coupling Through an Insulating Barrier Layer@footnote 1@

Thursday, November 18, 2004, 8:20 am, Room 304A

Session: Magnetic Oxides and Half-Metallics
Presenter: P.A. Dowben, University of Nebraska
Authors: P.A. Dowben, University of Nebraska
R.-H. Cheng, Argonne National Laboratory
B. Doudin, University of Nebraska
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Interlayer exchange coupling between two ferromagnetic films, separated by a nonmagnetic non metallic spacer (semiconductor and insulator spacer materials) does occur. This coupling sometimes appears to be distinct from the very low temperature tunneling phenomena between two ferromagnets, through a dielectric spacer layer, as the coupling is sometimes oscillatory. The ferromagnetic coupling between Co and CrO@sub2@, through an insulator (Cr@sub2@O@sub3@) may be rel ated to defect states in the insulating barrier layer.@footnote 2@ In the native Cr@sub2@O@sub3@ surface layer, it appears that at low temperature the conduction band edge electrons are trapped or immobile, and at high temperature there is greater mobili ty. Combined photoemission and inverse photoemission temperature dependent studies confirm the occurrence of a defect mediated blockade energy. It may well be that many defect states are spin polarized, possibly by proximity to the ferromagnetic interface. Other complications exist. The interpretation of junction magneto-resistance results must now assume that ferromagnetic metals will NOT generally form abrupt interfaces with transition metal oxide dielectric barriers. It must be recognized that many met al to metal oxide interfaces involve further oxidation and reduction making such interfaces very heterogeneous, so that nominal CrO@sub2@/Cr@sub2@O@sub3@/Co magnetic junctions are, in fact, more complex multilayers systems akin to a CrO@sub2@/Cr@sub2@O@sub3@/CoO/Co system. @FootnoteText@@footnote 1@ The support of the Office of Naval Research, and the NSF MRSEC (DMR 0213808) are gratefully acknowledged. The authors would like to acknowledge a number of helpful conversations with E. Tsymbal.@footnote 2@ Ruihua Cheng, A.N. Caruso, L. Yuan, S.-H. Liou, and P.A. Dowben, Applied Physics Letters 82 (2003) 1443-1445 .