superparamagnetismin
Superparamagnetism is a magnetic phenomenon observed in very small ferromagnetic or ferrimagnetic nanoparticles. When the size of a ferromagnetic material is reduced to the nanoscale, its magnetic behavior can change dramatically. In bulk ferromagnetic materials, the magnetic moments of individual atoms align to form large magnetic domains, resulting in a strong permanent magnetization. However, in superparamagnetic nanoparticles, thermal energy can be sufficient to overcome the energy barrier that keeps the magnetic moments aligned within a single domain. This leads to spontaneous and random fluctuations of the magnetic moment's direction.
The key characteristic of superparamagnetism is that these nanoparticles do not exhibit a permanent magnetic moment