AVS 50th International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI+NS-TuA

Paper MI+NS-TuA2
Magnetic Interaction in Assemblies of Nanometer-sized Fe Dots on Cu (111)

Tuesday, November 4, 2003, 2:20 pm, Room 316

Session: Self Assembly and Nanomagnetism
Presenter: M.A. Torija, University of Tennessee, Knoxville
Authors: M.A. Torija, University of Tennessee, Knoxville
J. Pierce, University of Tennessee, Knoxville
J.F. Wendelken, Oak Ridge National Laboratory
E.W. Plummer, University of Tennessee, Knoxville
J. Shen, Oak Ridge National Laboratory
Correspondent: Click to Email
Assemblies of separated iron quantum dots can be prepared on the Cu(111) surface via a buffer-layer-assisted growth process. First, an inert Xe layer is frozen onto a Cu(111) substrate that is held below 30 K. Then, Fe atoms are dosed from a typical evaporation source and form clusters on the Xe layer. Finally, the sample is warmed above 90 K, allowing the buffer layer to evaporate and the formed quantum dots to land on the surface. Scanning tunneling microscopy has shown us that we can control the average spacing and size of the dots by changing the Xe layer thickness and/or the amount of Fe deposited. Surprisingly, the dot arrays show non-zero remanent magnetization that is stable with the passage of time. To distinguish the roles of the magnetic interactions vs. the magnetic anisotropy in stabling the remanent magnetization, measured by SMOKE, we compare the ordering temperature of dot assemblies that have equal size distribution but different density. At fixed dot size distribution, varying the density of the Fe dots from 0.003 to 0.015 leads to an enhancement of ordering temperature from 153 K to 363K. This clearly indicates that magnetic interactions play an important role in stabling the remanent magnetization. Another interesting phenomena that we observed is a spin reorientation induced by the dot size. that for a fixed nominal thickness, the easy axis of magnetization is perpendicular for lower Xe thickness ( small dots), and becomes in-plane for higher Xe thickness ( big dots ). It may be explained by the interplay between surface and bulk anisotropies.