I'm trying to understand superparamagentism. There is an experimental medical treatment that uses the superparamagnetism properties of nanoparticle-sized iron oxide particles. Injected into a cancer tumour, when the person is placed in a rapidly alternating magnetic field, the iron oxide particles heat - effectively burning the tissue into which they are injected. As far as I understand, when an iron oxide particle is sufficiently small, it acts as a single magnetic domain. And as the particle gets smaller, it's Curie temperature decreases (have I got that right?) to something approaching room temperature - giving it the properties of a superparamagnet. Quite what this means in terms of iron oxide (which I presume is acting like a paramagnet) and why placing it in an alternating magnetic field will cause it to heat, I do not understand. Can anyone make sense of this?