Magnetic properties of iron clusters in a molecular beam: resolution of a controversy

Magnetic properties of small iron clusters in a supersonic molecular beam are investigated. The magnetization is probed as function of magnetic field, temperature and cluster size. Temperatures are controlled by changing the source temperature (100 K to 500 K) and the expansion conditions. The clusters also may be heated in flight with light from a pulsed laser. Hot clusters are found to be superparamagnetic however cold clusters are not but show strongly reduced magnetization which furthermore is non-linear with the applied field. Experimentally it is found that the anomalies are related to the cluster rotations. We also address a controversy between our earlier findings 1] and those by Bucher et al. 2], and demonstrate that their temperature determinations and consequent conclusions are incorrect.