Magnetism
Introduction
Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. All materials are influenced to some extent by a magnetic field. The strongest effect is on ferromagnetic materials, which are strongly attracted to magnetic fields and can be magnetized to become permanent magnets, producing a magnetic field themselves.
History of Magnetism
The history of magnetism dates back to ancient times. The ancient Greeks, for instance, were aware of the peculiar properties of lodestone, a naturally magnetized mineral. The word magnet was adopted in Middle English from Latin magnetum, which in turn is derived from Greek "magnítis líthos" meaning "Magnesian stone", a type of iron ore from Magnesia, a region in the ancient Greek region of Thessaly.
Fundamental Concepts of Magnetism
Magnetism is fundamentally caused by two sources. First, electric currents, which are the motion of electric charges, produce magnetic fields. This is the principle behind electromagnets. Second, many elementary particles have a property called spin, which can be thought of as the particle spinning around an axis. This spin gives rise to a magnetic moment, which can produce a magnetic field.
Types of Magnetism
There are several types of magnetism, including ferromagnetism, paramagnetism, diamagnetism, and antiferromagnetism, among others.
Ferromagnetism
Ferromagnetism is the basic mechanism by which certain materials form permanent magnets. This means the compound can either be permanently magnetic or it can be magnetized by an external magnetic field. The term refers to the fact that the magnetic moments in the material are able to align themselves even when there is no external magnetic field present.
Paramagnetism
Paramagnetism refers to materials like aluminum or platinum which become magnetized in a magnetic field but their magnetism disappears when the field is removed. Paramagnetic materials have a small, positive susceptibility to magnetic fields. These materials are slightly attracted by a magnetic field and the material does not retain the magnetic properties when the external field is removed.
Diamagnetism
Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. It is the result of changes in the orbital motion of electrons due to the external magnetic field. Diamagnetic materials, like water, or copper, lead and carbon, have a permeability less than 1.
Antiferromagnetism
Antiferromagnetism is a phenomenon in which the magnetic moments of atoms or ions in a compound are ordered in a regular pattern with neighboring spins pointing in opposite directions. This is, the spins cancel out and the substance is not magnetic.
Magnetic Fields and Forces
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. A permanent magnet's magnetic field pulls on ferromagnetic materials and attracts or repels other magnets.
Applications of Magnetism
Magnetism has numerous applications in modern life. These include the design and functioning of electrical appliances and machinery, such as the electric generator and the electric motor, as well as in the storage of data in computers and credit cards. Magnetic resonance imaging (MRI) uses a strong magnetic field to image the body.