Spontaneous magnetostriction in R2Fe14B (R=Y, Nd, Gd, Tb, Er)

Thermal expansion anomalies of R2Fe14B (R=Y, Nd, Gd, Tb, Er) stoichiometric compounds were studied by X-ray diffraction with high-energy synchrotron radiation using a Debye-Scherrer geometry in temperature range of ∼10-1000 K. A large invar effect with a corresponding large temperature dependence of lattice parameters ∼10-15 K above their Curie temperatures (Tc) are observed. The a-axes show a larger invar effect than the c-axes in all compounds. The spontaneous magnetostrain of the lattices and bonds are calculated. The iron sublattice is shown to dominate the volumetric spontaneous magnetostriction of the compounds and the contribution from the rare-earth sublattice is roughly proportional to the spin magnetic moment of the rare earths. The bond-length changes are consistent with the theoretical spin-density calculation. The average bonds magnetostrain around Fe sites is approximately proportional to their magnetic moments.