Diamagnetism

Diamagnetism is one of the manifestations of magnetism in matter: diamagnets magnetized in an external magnetic field so that the magnetic field is proportional slowing in its interior to the strength of the applied magnetic field and diamagnetic materials accordingly have a tendency to migrate out an inhomogeneous magnetic field.

The proportionality of field weakening is the magnetic permeability ĩr - and is determined at diamagnets <1 (see paramagnetism ) (or the magnetic susceptibility ĩr 1).

In physics, all materials with negative magnetic susceptibility and without magnetic order are classified as diamagnetic. The most diamagnetic elements under normal conditions are bismuth and carbon.

History

Sebald Justinus Brugmans 1778 observed that certain materials are repelled by magnetic fields. The term " diamagnetism ", however, is by Michael Faraday. He coined it in 1845 when he realized that all materials in nature have a shape of a diamagnetic response to an external magnetic field.

Model

When an external magnetic field H applied to material, it changes the state of the particles in the atoms of the material so that a magnetic torque is produced which is opposite to the externally applied magnetic field. The induced field B then weakens this external field as the sum of the individual moments of all atoms from the sample. In an inhomogeneous field you have to apply work to move a diamagnetic in regions of higher field strength, since the compensating effects need to be strengthened.

By itself seeks a diamagnetic material in the direction of lower field strength. The actual operations can only be explained by quantum mechanics: The spin of the electron has a magnetic moment and thus produces a field that macroscopically but does not appear due to the Pauli principle and the thermal movements. Magnetic dipoles are induced at the atomic level only by the external field.

Based on these considerations it is clear that any material is diamagnetic. However, because the diamagnetic effects are very small, especially weaker than paramagnetism and orders of magnitude weaker than ferromagnetism, they only occur when such materials to be measured, which are neither para- nor ferromagnetic. We call such substances then as diamagnetic.

Diamagnetic materials have a magnetic susceptibility χ is less than 0 or accordingly a relative permeability less than 1

The susceptibility is only slightly dependent on the temperature, but often highly dependent on the physical state of the crystal system and the direction of the crystal lattice. A large anisotropy is observed for example in pyrolytic graphite deposited (see sortable table ). Compounds of paramagnetic elements, such as aluminum forth herein, may be diamagnetic.

Effects

Superconductors

Superconductors are perfect diamagnetic with the susceptibility -1: they displace the magnetic field lines from their interior ( Meissner effect).

Float

Due to the effect of the removal of a wandering magnetic field it is possible at sufficiently strong magnetic field ( about 15 Tesla in the laboratory), to pass water and even floating creatures. This effect is called diamagnetic levitation also; known were mainly experiments with a floating frog, a spider and various materials ( wooden block). Thus the most convincing simulations of weightlessness are possible under the influence of the gravitational field of the earth.

Pyrolytic graphite is strongly diamagnetic perpendicular to the crystal plane. With a strong neodymium magnets graphite may be held in abeyance.