Structures and magnetic properties of oriented Fe/Au and Fe/Pt nanoparticles on a-Al2O3

Granular thin films of oriented alpha-Fe nanoparticles on a-Al2O3 were fabr icated by electron beam evaporation technique. The process took advantage o f the overgrowth of a-Fe on Au or Pt 'seed' particles epitaxially grown on (100) NaCl substrates, which were later removed in distilled water. The cry stallographic orientation between a-Fe and Au (Pt) nanocrystals was < 100 > (Au(Pt))//< 100 >(Fe) with {010}(Au(Pt))//{011}(Fe). The magnetic coercivit y of the oriented alpha-Fe particles was controllable by particle size and inter-particle distance. Annealing of the a-Al2O3/Fe/Pt films at temperatur es higher than 500 degrees C led to a formation of the ordered L1(0)-FePt p hase. Any one of the three < 100 > axes of the fee parent phase acted as th e tetragonal c-axis of the L1(0) superstructure. Magnetic coercivities of a -Al2O3/Fe/Pt films were found to be largely increased by heat treatment. Th e coercivity of the annealed a-Al2O3/Fe/Pt films reached as high as 3.5 kOe with a squareness of 0.74. It has been shown that magnetic property can be improved by controlling orientation and structure of the magnetic particle s.