| Tb-Dy-Fe giant magnetostrictive alloys, which possess high magnetostriction and low magnetocrystalline anisotropy at room temperature, have been applied widely in many fields. Considerable efforts have been carried out to improve the intrinsic magnetic properties and application performance through substituting the Rare earth, transition metals or doping small atoms.In the present study, Tb0.3Dy0.7Fe2, Tb0.36Dy0.64(Fe1-xCox)2 (x≤0.30) and Tb0.36Dy0.64(Fe0.85Co0.15)2-yBy(y≤0.15) alloys have been prepared by vacuum arc-melting. The effects of Co and B substitutions on the magnetic and magnetostrictive properties of Tb0.36Dy0.64Fe2 alloys were investigated by X-ray diffraction, SQUID, Mossbauer spectra, SEM and so on. The main results are summarized as follows:The Mossbauer spectrum of Tb0.36Dy0.64(Fe1-xCox)2 (x≤0.30) alloys were composed of two six-line subspectra with area ratio 1:3, indicating that the easy magnetization direction (EMD) of each sample lied along <111> at room temperature. It was found that the hyperfine field Hhf increased with increasing Co content, indicating the increase of iron momentμFe. With increasing Co content, the central shift CS first decreased and then increased due to the effects of both electron transfer and volume effect. The absolute values of both QS(Ⅰ) and QS(Ⅱ) increased with increasing Co content, which indicates the increase of electric field gradient of the nucleus. The composition dependences of the magnetic transition temperature and magnetization were consistent with the variation of hyperfine parameters, which can be ascribed to the 3d electrons transfer between Fe and Co atoms.Crystal structure and magnetic properties of magnetostrictive alloys Tb0.36Dy0.64(Fe0.85Co0.15)2-yBy(y≤0.15) have been investigated. The matrix of these compounds kept a cubic MgCu2-type structure, possessing giant magnetostriction at room temperature. Lattice parameter a of the Laves phase decreased to reach a minimum at y = 0.10, then increased with increasing boron content. The introduction of boron effectively increased both Curie temperature TC and spin reorientation temperature Tr, which is ascribed to the enhancement of the exchange interaction of 3d sublattice. The Mossbauer spectrum for all samples can be fitted by two sextets with area ratio of about 1:3, showing that the easy magnetization direction (EMD) lies along <111> direction at room temperature. The mean hyperfine field Hhf increased with boron content, indicating that iron momentμFe is enhanced. Although the addition of B enlarged the magnetocrystalline anisotropy constant K1, the composition dependence of the ratioλ/K1 for Tb0.36Dy0.64(Fe0.85Co0.15)2-yBy (y≤0.15), however, reached a maximum value at y = 0. 05 under high magnetic fields.
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