Abstract
The magnetic properties of 5 commercially available magnetic microsphere samples are tested and compared with those stated by their manufacturers. A suspension of magnetic, iron oxide nanoparticles is studied for comparison. Two of the microsphere samples have magnetic properties which do not support the manufacturer's claims of superparamagnetism. The remaining 3 microsphere samples as well as the nanoparticle suspension are superparamagnetic or ferromagnetic as claimed by the manufacturers. Field cooled and zero field cooled magnetisations indicate that the non-superparamagnetic microsphere samples contain blocked magnetic particles at room temperature. This observation is supported by the open hysteresis loops of the room temperature, field dependent magnetisation measurement. There is a significant paramagnetic component in the superparamagnetic microspheres. This is also present to a lesser extent in a nanoparticle suspension.