Tag Archives: electromagnetism

Three different types of magnetism

When you think of magnetism the chances are that you’re only thinking of one type of magnetism: ferromagnetism. But there are two other types of magnetism: paramagnetism and diamagnetism, that are less well known.

Ferromagnetism is the only type of magnetism that produces forces large enough to be easily felt, and ferromagnetic materials are the only ones that demonstrate spontaneous magnetism – magnetism outside of an applied magnetic field. The most common ferromagnetic materials are those that contain iron, cobalt and nickel but other elements such as dysprosium and gadolinium and compounds such as chromium oxide and manganese bismide also demonstrate ferromagnetic properties.

Paramagnetic and diamagnetic effects only exist in the presence of an applied magnetic field: paramagnetic materials such as tungsten and aluminium create an attractive force when exposed to magnetic fields and diamagnetic materials such as pyrolytic carbon and mercury create a repulsive one.

A small sheet of pyrolytic carbon levitates above an array of neodymium-iron-boron magnets.

Water is weakly diamagnetic, about forty times less diamagnetic than the pyrolytic carbon shown above, but this is enough that light objects which contain a large amount of water can be levitated if placed in a very strong magnetic field.

This frog was levitated using a 16 tesla Bitter electromagnet at the High Field Magnetic Laboratory at the Radboud University Nijmegen in the Netherlands.

Magnetic levitation

The electric currents used in some Japanese trains are so high that the electromagnetic fields created are strong enough to affect paperclips on board the train.

Watch how the paperclips dance as the train accelerates (uses more electric current) and decelerates (uses less electric current).