The study of magnetism, a fundamental force, has provided many applications in industry and helped us to understand the geology of the Earth. Magnetic nanoparticles have some interesting properties, many of which are yet to be exploited.

Magnetic nanoparticles occur naturally in sediment and align themselves with the Earth's magnetic field. In a process called Detrital Remanant Magnetisation, the moments of these particles freeze at a certain depth. Unearthing these particles and studying their moments can give an indication of how the Earth's magnetic field has changed with time.

In industry, magnetic nanoparticles are used in magnetorheological smart fluids that contain a suspension of magnetic nanoparticles. By applying an external magnetic field to the liquid, its viscosity can be changed, a property exploited in brakes and shock absorbers.

Magnetite nanoparticles are even found inside bacteria that use them as a means of navigation.

To understand the magnetic nanoparticles better, the susceptibility-the degree of magnitisation-of magnetite nanoparticles was investigated.  The particles were put in clay platelets with different ratios. The susceptibility of the samples, measured continuously as the temperature was altered, was used to generate three susceptibility curves. At high temperature, magnetite is superparamagnetic where spins flip with thermal fluctuations but stops at low temperature.

Elizabeth Wann is a Part II in Natural Sciences specialising in Mineral Sciences.