Role of the Fe sublattice on the Invar anomaly in R2Fe14B compounds

Abstract

Thermal expansion anomalies of Nd2Fe14B and Y2Fe14B stoichiometric compounds have been studied by x-ray diffraction with high energy synchrotron radiation using a Debye–Scherrer geometry from room temperature to 1000 K. Y2Fe14B and Nd2Fe14B have similar temperature dependence of lattice parameters and bond distances up to their Curie temperatures Tc. The volumetric spontaneous magnetostriction at room temperature for Nd2Fe14B and Y2Fe14B were determined to be 1.49% and 1.45%, respectively. Among the Fe–Fe bonds, those bonds containing Fe(j2), whose projections are dominantly in the basal plane, have the highest contribution to the Invar effect. These bonds have magnetostrictive strain ranging from 0.4% to 0.8% at room temperature. Above the Curie temperature, Y2Fe14B has an isotropic thermal expansion, while Nd2Fe14B exhibits slightly anisotropic thermal expansion. The iron sublattices dominate the spontaneous volumetric magnetostriction of Y2Fe14B and Nd2Fe14B compounds.