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 λ₁₀₀ 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.