HIGH-FIELD MAGNETOSTRICTION AND MAGNETIC THERMAL-EXPANSION OF RE2FE14B HARD INTERMETALLICS

Thermal expansion measurements on RE2Fe14B (RE = Pr, Nd, Ho, Er and also Y) hard intermetallics are reported. Strong anomalies related to the invar effect below the Curie temperatures are observed, which can be well explained mainly from the strain dependence of the Fe sublattice magnetic moment and exchange interaction. High field magnetostriction measurements, up to 15 T, from 4.2 K up to room temperature have been performed on polycrystalline samples of the series (RE = Pr, Nd, Dy, Ho, Er and also Y), both parallel (lambda(parallel-to)) and perpendicular (lambda(perpendicular-to)) to the applied magnetic field. From them, it is possible to separate out the single-ion crystal field and exchange contributions to the strictions. The complex temperature dependence of the anisotropic magnetostriction, lambda(t), at the highest applied field of 15 T, where lambda(t) = lambda(parallel-to) - lambda(perpendicular-to), represents the symmetry modification of the the RE sublattice, requires the recourse to high order crystal field contributions. In agreement with the spontaneous volume striction, the forced volume one, omega = lambda(parallel-to) + 2lambda(perpendicular-to), which is merely a volume lattice variation without symmetry modification, seems also to be mainly due to the Fe sublattice.