In the past, our group has successfully tailored and studied magnetic nanostructures in 2D, 1D and 0D spatial confinement on Cu(111) substrates. We observed a striking collective ferromagnetic long-range order in Fe-nanodots on Cu(111) surface which can be stabilized through the indirect exchange interaction between the nanodots mediated by the substrate. This type of magnetic interaction was expected to have little effect on promoting a global ferromagnetic order in a randomly distributed dot assembly. It is for certain that we need a better understanding and more complete picture of the relative roles of magnetic anisotropy and magnetic interaction (dipolar and indirect exchange interaction, tunneling induced interaction) in the magnetism of reduced dimensionality, in general, and nanodot assemblies, in particular. With this accomplishment in mind, we try to study the collective behavior of interacting magnetic nanoparticles. We propose the following experiment to quantify the relative roles of magnetic anisotropy, dipolar interaction and indirect exchange interaction on the collective magnetic behavior of nanodot assemblies. It consists of three main projects: a) study the role of magnetic anisotropy and dipolar interaction. We used Co dots on TiO2(110) substrate as a prototype. We observed significant perpendicular magnetic anisotropy with perpendicular easy axis for both large and small dot’s density with no sign of hysteresis observed down to 2 K. Since there is no sign of dot-dot interaction or dipolar interaction at the temperature range accessible with the SQUID, we could not use this system to really study the relative role of magnetic anisotropy and the dipolar interaction. b) study the thickness dependence of the substrate that mediates the indirect exchange coupling through ‘quantum well states’. The interaction is observed through the changes in Curie temperature (Tc) of Fe dots as a function of Cu wedge thickness, c) study how the indirect exchange interaction is affected by the dimensional crossover of the surface states from 2D to 1D. The interaction is observed through the changes in the Tc of Fe dots as a function of miscut angle Cu curved substrate. |
