Effect of magnetoelastic interaction on the thermal expansion of the trigonal crystal FeBO3

• Consistent approach to the interpretation of thermal expansion in magnetic crystals is developed. • FeBO 3 – a trigonal antiferromagnet with weak ferromagnetism – is used as a model object. • Different character of the thermal expansion above and below the magnetic ordering temperature is described taking into account magnetostrictive deformations. • A model based on the symmetry of the crystal and its domain structure is put forward. • The temperature dependences of magnetoelastic constants over a wide temperature range and the hitherto unknown constants are determined. Iron borate FeBO 3 – a trigonal antiferromagnet with weak ferromagnetism – was used as a model object for experimental and theoretical studies of thermal expansion. X-ray diffraction analysis indicated that the character of the thermal expansion changes significantly when passing through the Néel point. In the magnetically ordered state below the phase transition temperature, the thermal changes in the crystal lattice parameters are additionally affected by magnetostrictive deformations. A theoretical model was developed that allows interpreting experimental data and determining the magnetoelastic constants using X-ray diffraction analysis. Temperature dependences of some of the magnetoelastic constants of iron borate were determined, and the hitherto unknown constants were found. These data are essential to describe various phenomena associated with magnetoelastic interactions in magnetically ordered materials.