All substances are magnetic, that is, they are either attracted by a magnetic field (paramagnetic - positive magnetic susceptibility) and concentrate the field or repelled away by one (diamagnetic - negative magnetic susceptibility) and weaken the field. Diamagnetism is a property generated by the cancellation of spins by the pairing up of orbital electrons; all elements have this property, although it is very weak. Bismuth has the highest diamagnetism. Paramagnetism is generated by the un-cancelled spin of any un-paired electrons, and if present, swamps any diamagnetic contribution. Those elements with the highest number of unpaired electrons (usually in the d-orbitals) have the highest paramagnetism. Gadolinium is highly paramagnetic, but below the Curie temperature of just 20░C it becomes ferromagnetic: substances which have infinite magnetic susceptibility at their Curie Temperatures and below which magnetise spontaneously in the absence of an external field. Iron, Cobalt and Nickel are also ferromagnetic, with Curie temperatures of 770░C, 1131░C and 358░C, respectively. Magnetic susceptibility is the factor by which the relative permeability of a substance differs from unity. Paramagnetic susceptibility depends upon the ratio of magnetic to thermal energies, and so is inversely proportional to temperature; Curies law.
Ferromagnetism is due entirely to the effects of paramagnetism, but can only occur when atoms of certain elements gather together en-masse, and is not a property of just one lone single atom. Here, in some paramagnetic substances below their Curie temperature, the un-paired spins of each atom align co-operatively parallel to each other over great distances in the bulk material, forming randomly orientated domains of permanent magnetisation, (but no net magnetic field). [Above the Curie temperature, this cannot happen because the atoms are being continually jostled about and cannot form into domains: the material behaves like a normal paramagnetic substance]. The domains of a ferromagnetic substance can be aligned by an external magnetic field to produce a permanent magnet.
