Morphology evolution and enhanced magnetostriction of (Fe_0.81Ga_0.19)_99.9Tb_0.1 crystals prepared by liquid metal cooling Bridgman directional solidification

Previously the magnetostriction of FeGa alloys was enhanced in melt spun ribbons due to the solid solution of trace rare earth elements. Unfortunately, applications of the ribbons are limited. Here, (Fe_0.81Ga_0.19)_99.9Tb_0.1 crystals were prepared by liquid metal cooling Bridgman directional solidification over the wide withdraw rate range of 7.2–18000 mm/h. With the increasing withdraw rate, an evolution from<001>-oriented single crystals possessing cellular morphology, to<001>-oriented polycrystals possessing dendritic morphology, and then to randomly-oriented polycrystals was observed. Simultaneously, the solid solution of trace Tb element was promoted, which was evidenced by the decrease of the Tb-rich precipitates and the strengthened magnetocrytalline anisotropy energy. As a result, the magnetostriction effect was significantly enhanced. Large magnetostriction of 390 ppm, which was 30% higher than that of binary Fe_0.81Ga_0.19 crystal, was realized in the<001>-oriented (Fe_0.81Ga_0.19)_99.9Tb_0.1 crystal grown at a withdraw rate of 3600 mm/h.