AVS 45th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Thursday Sessions
       Session MI-ThA

Paper MI-ThA4
Systematic Measurement of Exchange Coupling Across the Periodic Chart of 3-d Transition Elements to Understand Magnetization In Ferromagnetic Mn Alloys@footnote 1@

Thursday, November 5, 1998, 3:00 pm, Room 324/325

Session: Structure & Magnetism of Surfaces & Interfaces
Presenter: W.L. O'Brien, University of Wisconsin, Madison
Authors: W.L. O'Brien, University of Wisconsin, Madison
S. Banerjee, University of Wisconsin, Milwaukee
B.P. Tonner, University of Wisconsin, Milwaukee
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Ultrathin films of Mn alloyed with Fe, Co and Ni have magnetic properties quite distinct from their bulk counterparts with same composition. Even the sign of exchange coupling in the ultrathin films are opposite to those of bulk alloys. For example, Mn impurities in bulk Fe are ferromagnetic with the magnetization of Mn parallel to the Fe magnetization, while we find that ultrathin alloys of the same composition are ferrimagnetic with an antiparallel coupling between Mn and Fe. Bulk Mn-Co alloys with dilute Mn concentration are ferrimagnetic with antiparallel coupling between Mn and Co whereas ultrathin films of same composition have the magnetization of Mn parallel to the Co. Finally, bulk 1:1 MnNi is an antiferromagnet, while the ultrathin alloys of same composition are ferromagnetic with Mn magnetization parallel to the Ni magnetization. To explore how widespread are these substantial differences in the magnetic phase diagrams of the ultrathin films, as compared to bulk, we performed a systematic measurement of the magnetic coupling for V, Cr, Mn, Fe, Co and Ni overlayers to Fe, Co and Ni substrates. The sign of the exchange coupling can be summarized by a simple electron counting rule. In this analysis of the periodic chart, we do not find parallel magnetic coupling when the sum of the formal atomic number of d electrons per atom (overlayer plus substrate) is less than 12. Considering this d=12 rule, Mn is located in a special position in the periodic table near the transition region between parallel and antiparallel coupling with Fe, Co and Ni. This rule works both for atomically clean surfaces, and surfaces modified by chemisorption. @FootnoteText@ @footnote 1@Work supported by the National Science Foundation, DMR, and performed at the Wisconsin Synchrotron Radiation Center.