Manipulation of magnetic nanoparticles by the strayfield of magnetically patterned ferromagnetic layers

The manipulation of magnetic particles at the nanometer scale is of great interest for applications in biotechnology. In this work the self-assembly of 12 nm Co nanocrystallites under the influence of magnetic strayfields originating from a magnetically patterned 3 nm thick CoFe layer has been investigated. The magnetic patterning has been carried out by bombardment with 10 keV He ions in an external magnetic field. A controllable accumulation of magnetic nanoparticles has been found at areas of the sample with a head to head orientation of the local magnetization. The force generated by the strayfield of Neel walls without head to head orientation of the magnetization is about ten times weaker and turned out to be just strong enough to attract a relatively small number of nanocrystals. Furthermore, it has been shown that the choice of the procedure to bring the particle solution onto the magnetically patterned sample determines the successful generation of particle arrangements and can be used to tune the number of particles and their coordination within the strayfield. (c) 2007 American Institute of Physics.