Diamagnetic Levitation
A flat sheet of pyrolytic graphite floats over an array of nine strong neodym magnets (NdFeB). The
magnetization pattern of the magnets is indicated by the white arrows. The diamagnetic substance repels the magnetic field of
a permanent magnet and there by the levitation occurs.
The origin of magnetism lies in the orbital and spin motions of electrons and how the electrons interact with one another.
The best way to introduce the different types of magnetism is to describe how materials respond to magnetic fields. In general, all matter is magnetic but some materials are much more magnetic than others. The main distinction is that in some materials no collective interaction of atomic magnetic moments, will be observed, whereas in other materials a very strong interaction between atomic moments can be observed.
The magnetic behavior of materials can be classified into the following three major groups.,
(1) Diamagnetism (2) Paramagnetism (3) Ferromagnetism.
Diamagnetism : Diamagnetism is a fundamental property of all matter, although it is usually very weak. It is due to the non–cooperative behavior of orbiting electrons when exposed to an applied magnetic field. Diamagnetic substances have atoms with no net magnetic moments (ie., there are no unpaired electrons). However, when exposed to a field, a negative magnetization is produced and thus the susceptibility is negative.
Ferromagnets
The strong and powerful magnets are formed from the ferromagnetic materials. The magnetization will last
longer.
Paramagnetism : This class of materials, some of the atoms or ions in the material have a net magnetic moment due to unpaired electrons in partially filled orbitals. One of the most important atoms with unpaired electrons is iron. However, the individual magnetic moments do not interact magnetically, and like diamagnetism, the magnetization is zero when the field is removed. In the presence of a field, there is now a partial alignment of the atomic magnetic moments in the direction of the field, resulting in a net positive magnetization and positive susceptibility.
Ferromagnetism : Unlike paramagnetic materials, the atomic moments in these materials exhibit
very strong interactions. These interactions are produced by electronic exchange forces and result in a parallel or antiparallel
alignment of atomic moments. Ferromagnetic materials exhibit parallel alignment of moments resulting in large net magnetization
even in the absence of a magnetic field.The elements Fe, Ni, and Co and many of their alloys are typical ferromagnetic materials.
Two distinct characteristics of ferromagnetic materials are their
(1) Spontaneous magnetization and
(2) The existence of magnetic ordering temperature