Lattice deformation under the phase transition to helicoidal magnetic structures (the case of europium)

Considerable deformation of the europium monocrystal, when the tetragonal effect occurs in its bcc lattice, which accompanies magnetic ordering of a simple spiral type, is experimentally established. The deformations are shown by the theoretical group analysis to be caused by exchange interaction, being specific for a noncomparable phase and disappearing for a comparable one.