Thermally and field driven magnetization processes in nanometer-scale particle arrays

Nanometer-scale iron particles were fabricated by Scanning Tunneling Microscopy assisted chemical vapor deposition. With this, the particles can precisely be placed at a predetermined position and their dimensions can easily be controlled. The latter enabled us to perform a systematic study of the dependence of thermal activation on the particles' diameter (9-20 nm for the different arrays). Magnetic measurements included Hall magnetometry and variable field MFM. From the temperature dependence of the switching fields of our elongated particles we inferred a thermally activated nucleation-propagation type of magnetization reversal even for the smallest (9 nm) particles. The energy barrier for magnetization reversal in elongated particles is derived, from which dynamic coercivities can be calculated. The impact of thermal activation was found to scale with the particles' cross-section, in agreement with magnetic viscosity measurements.