On conservation of the of crystal lattice symmetry in transition at Curie point in exchange magnets

Abstract

We show that symmetry of the crystal lattice of exchange magnets (containing only 3d magneto-active elements) does not change at the Curie point; only the magnetic symmetry of the crystal is decreasing in the transition point. In the non-exchange magnets (containing only rare-earth magneto-active elements), on the contrary, both the magnetic and crystal-chemical symmetry decrease at the Curie point. There is isotropic magnetic phase in exchange magnets; and their magnetic symmetry is described by color groups of magnetic symmetry of P-type. Non-exchange magnets do not have isotropic phase; their symmetry is described by color groups of magnetic symmetry of Q-type.