A transition between disordered and ordered arrays of atomic magnetic moments. Where the ordered phase has a net spontaneous magnetization, \(M_{\text{S}}\), the magnetic-ordering temperature is called a @C01444@ temperature, \(T_{\text{C}}\); where the net spontaneous magnetization of the ordered phase remains zero, the ordering temperature is called a Néel temperature, \(T_{\text{N}}\). The temperature at which the two ferromagnetic subarrays of a ferrimagnet just cancel each other is called the compensation point. Materials exhibit @F02349@ behaviour when unpaired electron spins are aligned in parallel, @A00393@ behaviour when the alignment is antiparallel, and @F02344@ 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.
Antiferromagnetic order below \(T_{\text{N}}\) 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.
PAC, 1994, 66, 577. (Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)) on page 585 [Terms] [Paper]