Thermal-expansion anomalies and spontaneous magnetostriction of Lu2Fe17−xSix intermetallic compounds

The thermal expansion of Lu2Fe17−xSix solid solutions has been measured by X-ray powder diffraction. The magnetic ordering in all compounds within the homogeneity range (x⩽3.4) is accompanied by a large spontaneous volume magnetostriction, distributed anisotropically over the principal axes of the hexagonal crystal structure. The volume effect ωs in the ground state reaches 14.7×10−3 in Lu2Fe17 and decreases monotonously to 8.9×10−3 for x=3.4, following the reduction of magnetic moment. Despite a still large ωs, the Invar behavior observed in Lu2Fe17 changes to a positive thermal expansion for x>1 due to an increasing Curie temperature.