Spontaneous magneto striction and thermal expansibility of TmFeO3 and LuFeO3 rare earth orthoferrites

At low temperatures the TmFeO3 orthoferrite shows a strong spontaneous magn etostriction generated by rare earth Tm atoms. This effect essentially depe nds on the temperature and orientation of the weak ferromagnetism vector of the Fe sublattice and reaches largest values for the directions [100] and [001]. The spin reorientation process in TmFeO3 marks itself mainly in the change of the signs of the linear thermal expansion coefficients in the dir ections mentioned above. Some additional singularities of thermal dependenc ies of expansion coefficients are observed below 20 K, which may be due to a magnetic compensation effect in the investigated orthoferrite. (C) 2001 E lsevier Science B.V. All rights reserved.