On conservation of the of crystal lattice symmetry in transition at   Curie point in exchange magnets
  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. 
Khisa Sh. Borlakov and Albert Kh. Borlakov (North Caucasian State   Humanitarian and Technological Academy)
cond-mat.str-el cond-mat.mtrl-sci cond-mat.other