Magnetism

  • a magnetic quadrupole

    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. magnetism is one aspect of the combined phenomenon of electromagnetism. the most familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. demagnetizing a magnet is also possible. only a few substances are ferromagnetic; the most common ones are iron, cobalt and nickel and their alloys. the prefix ferro- refers to iron, because permanent magnetism was first observed in lodestone, a form of natural iron ore called magnetite, fe3o4.

    all substances exhibit some type of magnetism. ferromagnetism is responsible for most of the effects of magnetism encountered in everyday life, but there are actually several types of magnetism. paramagnetic substances, such as aluminum and oxygen, are weakly attracted to an applied magnetic field; diamagnetic substances, such as copper and carbon, are weakly repelled; while antiferromagnetic materials, such as chromium and spin glasses, have a more complex relationship with a magnetic field. the force of a magnet on paramagnetic, diamagnetic, and antiferromagnetic materials is usually too weak to be felt and can be detected only by laboratory instruments, so in everyday life, these substances are often described as non-magnetic.

    the magnetic state (or magnetic phase) of a material depends on temperature, pressure, and the applied magnetic field. a material may exhibit more than one form of magnetism as these variables change.

    the strength of a magnetic field decreases following an inverse-square law as distance from a (ideal point) magnetic pole increases, and decreases with the inverse of distance from an ideal, infinitely long wire carrying an electric current. many magnetic objects have complex shapes and make complicated magnetic fields; only magnetic dipoles have been observed, but magnetic monopoles have been predicted by some theories.

  • history
  • sources
  • types of magnetism
  • electromagnet
  • magnetism, electricity, and special relativity
  • magnetic fields in a material
  • magnetic force
  • magnetic dipoles
  • units
  • living things
  • quantum-mechanical origin of magnetism
  • see also
  • references
  • further reading
  • bibliography

A magnetic quadrupole

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. Magnetism is one aspect of the combined phenomenon of electromagnetism. The most familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. Demagnetizing a magnet is also possible. Only a few substances are ferromagnetic; the most common ones are iron, cobalt and nickel and their alloys. The prefix ferro- refers to iron, because permanent magnetism was first observed in lodestone, a form of natural iron ore called magnetite, Fe3O4.

All substances exhibit some type of magnetism. Ferromagnetism is responsible for most of the effects of magnetism encountered in everyday life, but there are actually several types of magnetism. Paramagnetic substances, such as aluminum and oxygen, are weakly attracted to an applied magnetic field; diamagnetic substances, such as copper and carbon, are weakly repelled; while antiferromagnetic materials, such as chromium and spin glasses, have a more complex relationship with a magnetic field. The force of a magnet on paramagnetic, diamagnetic, and antiferromagnetic materials is usually too weak to be felt and can be detected only by laboratory instruments, so in everyday life, these substances are often described as non-magnetic.

The magnetic state (or magnetic phase) of a material depends on temperature, pressure, and the applied magnetic field. A material may exhibit more than one form of magnetism as these variables change.

The strength of a magnetic field decreases following an inverse-square law as distance from a (ideal point) magnetic pole increases, and decreases with the inverse of distance from an ideal, infinitely long wire carrying an electric current. Many magnetic objects have complex shapes and make complicated magnetic fields; only magnetic dipoles have been observed, but magnetic monopoles have been predicted by some theories.