AVS 51st International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI-WeM

Paper MI-WeM5
Ferromagnetic Stability in Fe Nanodot Assemblies on Cu(111) Induced by Indirect Coupling through the Substrate

Wednesday, November 17, 2004, 9:40 am, Room 304A

Session: Magnetic Nanostructures
Presenter: M.A. Torija, Oak Ridge National Laboratory, University of Tennessee, Knoxville
Authors: M.A. Torija, Oak Ridge National Laboratory, University of Tennessee, Knoxville
J.P. Pierce, Oak Ridge National Laboratory, Sandia National Laboratories
Z. Gai, Oak Ridge National Laboratory, Peking University, China
E.W. Plummer, Oak Ridge National Laboratory, University of Tennessee, Knoxville
J. Shen, Oak Ridge National Laboratory
Correspondent: Click to Email
To first order, assemblies of nano-scale magnetic dots are superparamagnetic. In these systems, thermal energy, which causes fluctuation of the dots' magnetic moments, becomes significant enough to overcome the anisotropy energy barrier and randomize their orientation at the so-called blocking temperature. This typically occurs far bellow room temperature. In real nanodots assemblies, it has been generally recognized that the magnetic dipole-dipole interaction can affect the barrier height for flipping the spin of each individual dot as well as the collective magnetic behavior of the dot assembly. In this work, we report collective ferromagnetic behavior in two- dimensional Fe dot assemblies on the Cu(111) surface that persists above room temperature. Our ability to tune the average size and spacing of the dots enables us to investigate the relative contributions of the mechanisms that support this unexpectedly robust magnetic order. Our experimental results and simulations indicate that the high-Tc ferromagnetism cannot be explained by either magnetic anisotropy or dipolar interaction. Direct comparison of the Curie temperatures (Tc) of similar dots prepared on vaious substrates including Cu(100) and Ge(111) allows us to conclude that the observed high-Tc ferromagnetism for Fe dots on Cu(111) is a result of an indirect exchange interaction via the surface states of Cu(111) substrate.