I'm seriously revisiting my knowledge on magnetism, and the Curie point has been both enlightening and mystifying. I understand what it does ((ferro)magnetism disappears above it), and have a faint idea how that works. What bothers me is that if (ferro)magnetism stems from the arrangement of electrons in various orbitals (the imbalance in total electron spin), why don't a lot more materials, including basic elements, have a Curie point? What makes the very few ferromagnetic materials so unique?
What bothers me is that if (ferro)magnetism stems from the arrangement of electrons in various orbitals (the imbalance in total electron spin), why don't a lot more materials, including basic elements, have a Curie point? What makes the very few ferromagnetic materials so unique?
Not all materials display magnetism or paramagnetism.
Materials may be classified by their response to externally applied magnetic fields as diamagnetic, paramagnetic, or ferromagnetic. These magnetic responses differ greatly in strength. Diamagnetism is a property of all materials and opposes applied magnetic fields, but is very weak. Paramagnetism, when present, is stronger than diamagnetism and produces magnetization in the direction of the applied field, and proportional to the applied field. Ferromagnetic effects are very large, producing magnetizations sometimes orders of magnitude greater than the applied field and as such are much larger than either diamagnetic or paramagnetic effects.
Ferromagnetic and paramagnetic materials are characterized by the existence of magnetic domains, clusters of molecules/atoms which have a collective magnetic dipole moment because it is an energetically favorable orientation within the cluster. These can be randomly oriented cancelling each other macroscopically, in paramagnets. In ferromagnetic materials the domains are all oriented in a lattice where the dipoles add up. The Curie point is when the kinetic energy due to temperature is large enough to turn ferromagnetic materials to paramagnetic, i.e. disoriented domains.
That is the reason why only ferromagnetic materials have a curie point, because only those lattices have oriented domains which can be dispersed when the temperature is increase above a certain point.