Microstructure and magnetostriction of Fe 1− xTb x alloys prepared by solid-state synthesis

Abstract

Fe 1− x Tb x was mechanically alloyed over a range of compositions 0.1< x<0.9. Based on X-ray diffraction measurements, a complete diagram of the resulting phases was drawn as a function of alloying time and composition. Depending on the composition, the microstructure of the as-milled powder is nanocrystalline or amorphous, with solubility ranges differing from those observed in the thermodynamically equilibrium structures. Terbium is soluble in the iron lattice with 0< x<0.33. A single-phase amorphous structure was isolated with x=0.33, and a single-phase Laves Fe 2Tb structure with 0.4< x<0.5. At higher terbium concentrations, a mixture of Fe 2Tb and terbium was obtained. The magnetic properties of the mechanically alloyed binary Fe 2Tb were studied in more detail. The mechanically alloyed binary Fe 2Tb powders were cold compacted and annealed. The highest magnetostriction was measured after annealing the samples at 500°C, resulting in a crystal size of 7–8 nm. Without an external load, the saturation magnetostriction λ s for the nanocrystalline Fe 2Tb was measured to be 1225×10 −6. This is 30% higher than that of the zone-melted coarse-grained Terfenol-D with the composition of Fe 2Tb 0.3Dy 0.7. When a constant magnetic field was applied perpendicular to the primary driving magnetic field, the saturation magnetostriction λ s of the nanocrystalline Fe 2Tb sample was measured to be 1582×10 −6. This value is 80% higher than the magnetostriction in unstressed zone-melted Terfenol-D.