A rotation of electron spins, above a critical magnetic field, Hc, in an antiferromagnet from parallel to largely perpendicular alignment, relative to an applied magnetic field, Ha, for Ha > Hc.
See also: simultaneous pair transitions
Source:
PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 590 (https://doi.org/10.1351/pac199466030577)