A transition between disordered and ordered arrays of atomic magnetic
moments. Where the ordered phase has a net spontaneous magnetization,
,
the magnetic-ordering temperature is called a
Curie
temperature,
;
where the net spontaneous magnetization of
the ordered phase remains zero, the ordering temperature is called a
Néel temperature,
.
The temperature at which the
two ferromagnetic subarrays of a ferrimagnet just cancel each other
is called the compensation point. Materials exhibit
ferromagnetic behaviour when unpaired electron spins
are aligned in parallel,
antiferromagnetic
behaviour when the alignment is antiparallel, and
ferrimagnetic behaviour if the alignment of the spins
is antiparallel with unequal numbers in the two orientations or if
the spins are canted. Therefore, ferromagnetic, ferrimagnetic and
weak ferromagnetic transitions involve a net magnetic moment
change, whereas antiferromagnetic transitions have zero net
magnetic moment change.
Note:
Antiferromagnetic order below
may be complex; for example, canting of spins as in
GdFeO3
,
spiral-spin configuration as may occur in
MnO2
,
and amplitude
modulation, as in some rare-earth
metals.
Source:
PAC, 1994, 66, 577
(Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations
1994))
on page 585
