Influence of the TbFe2 crystallization on the magnetic and magnetostrictive properties of (Fe3Ga/TbFe2)n heterostructures

In this work we have investigated (Fe₃Ga/TbFe₂)_n multilayers grown by sputtering at room temperature. These multilayers exhibit a large coercivity associated to the crystalline TbFe₂ Laves phase. To reduce the coercivity it is necessary to control the crystallization of that material. In this work, we focus on the analysis of the properties of the TbFe₂ layers. In the as-grown heterostructures we have found evidence of nanoaggregates in the TbFe₂ layers. The Fe₃Ga thickness and the thermal treatments have an influence on the volume of these nanoprecipitates. In the annealed samples, when increasing the Fe₃Ga thickness we observe a decrease in the nanoaggregate volume and thus in the coercivity. The experimental results indicate that the crystallization of the TbFe₂ depends on the Tb diffusion promoted by the thermal treatment and on the stiffness factor (Y/α) of the Fe₃Ga layer. The magnetostrictive properties are also strongly influenced by the crystallization of the TbFe₂. We have achieved a maximum magnetostriction constant of nearly 550 ppm with a coercive field close to 400 Oe.