Influence of Tb on easy magnetization direction and magnetostriction of ferromagnetic Laves phase GdFe2 compounds

The crystal structure, magnetization, and spontaneous magnetostriction of ferromagnetic Laves phase GdFe2 compound have been investigated. High resolution synchrotron x-ray diffraction (XRD) analysis shows that GdFe2 has a lower cubic symmetry with easy magnetization direction (EMD) along [100] below Curie temperature T-C. The replacement of Gd with a small amount of Tb changes the EMD to [111]. The Curie temperature decreases while the field dependence of the saturation magnetization (M-S) measured in temperature range 5-300 K varies with increasing Tb concentration. Coercivity H-C increases with increasing Tb concentration and decays exponentially as temperature increases. The anisotropy in GdFe2 is so weak that some of the rare-earth substitution plays an important role in determining the easy direction of magnetization in GdFe2. The calculated magnetostrictive constant lambda(100) shows a small value of 37x10(-6). This value agrees well with experimental data 30x10(-6). Under a relatively small magnetic field, GdFe2 exhibits a V-shaped positive magnetostriction curve. When the field is further increased, the crystal exhibits a negative magnetostriction curve. This phenomenon has been discussed in term of magnetic domain switching. Furthermore, magnetostriction increases with increasing Tb concentration. Our work leads to a simple and unified mesoscopic explanation for magnetostriction in ferromagnets. It may also provide insight for developing novel functional materials.