The Néel temperature (after Louis Néel , who received the Nobel Prize in Physics for the description in 1970 ) is the temperature above which an antiferromagnetic substance becomes paramagnetic ; the thermal energy here becomes large enough to destroy the magnetic order within the material. The Néel temperature is thus the analogue of the Curie temperature of ferromagnetic substances.
Above, the following applies to the magnetic susceptibility as a function of temperature :
with the material- specific Curie constant
Below , the susceptibility also decreases with decreasing temperature, i. H. at it has reached its maximum.
The Néel temperature of hematite is e.g. B. at 675 ° C.
The derivation takes place from the molecular field theory : d. H. a magnetic moment is considered in the mean magnetic field of its neighbors. As a consequence, the Curies law applies :
the magnetic field constant
the exchange field, whereby the coupling regulates.
So it follows:
and can be identified as.
- Horst Stöcker: Pocket book of physics. 4th edition, Verlag Harry Deutsch, Frankfurt am Main 2000, ISBN 3-8171-1628-4