Fe-Co Base Magnetostrictive Materials With Laves Phase

Tb1-xNdx(Fe0.8Co0.2)1.93, TbxDy0.9-xNd0.1(Fe0.8Co0.2)1.93and Tb0.2Pr0.8(Fe0.4Co0.6)1.9Bxalloyswere prepared by arc-melting and subsequent annealing. The epoxy bonded0-3type and pseudo1-3type TbxDy0.9-xNd0.1(Fe0.8Co0.2)1.93and Pr(Fe0.4Co0.6)1.93composites were fabricated by curingwith and without a magnetic field. The structure, anisotropy compensation, magnetic properties,and magnetostriction of the alloys and composites were investigated by X-ray diffraction (XRD), avibrating sample magnetometer, A.C. initial susceptibility and a standard strain gauge technique.XRD analysis shows that the Tb1-xNdx(Fe0.8Co0.2)1.93alloys possess predominantly the cubicLaves phase with a MgCu2-type structure for x≤0.6, indicating that Co substitution for Fe tend tostabilize the formation of Laves phase. The lattice parameter of the Laves phase increases withincreasing Nd content and obeys the linear Vegard’s law. The easy direction of magnetization(EMD) is observed toward <111> when0≤x≤0.6, accompanied by a rhombohedral distortionwith large spontaneous magnetostriction coefficients λ111. The saturation magnetization MSatroom temperature (RT) decreases with increasing Nd content when0≤x≤0.5, then increases withfurther increasing x for x≤0.6. The linear anisotropic magnetostriction λa(=λ∥-λ⊥) at RTdecreases initially with increasing x when0≤x≤0.4, then increases with a further increasing xand exhibits a peak in the range of0.4<x <1.0. The anisotropy compensation is realized aroundx=0.60.The easy magnetization direction (EMD) of TbxDy0.9-xNd0.1(Fe0.8Co0.2)1.93alloys at RT rotatesfrom the <100> axis (x≤0.25) to the <111> axis (x≥0.30) with increasing Tb content, subjectedto the anisotropy compensation between Tb3+and Dy3+ions. The analyses of X-ray diffraction,EMD and magnetostriction show that TbxDy0.9-xNd0.1(Fe0.8Co0.2)1.93is an anisotropy compensationsystem and the compensation point is realized around x=0.30. The Laves phase compoundTb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93has a large spontaneous magnetostriction, the coefficient λ111up toabout1600ppm.The alloy particles in1-3type Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93composites lies along the <111>EMD. A good magnetostrictive properties, λ∥and λa(=λ∥-λ⊥) up to around390and650ppm at6kOe, respectively, are obtained for the1-3epoxy/Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93composite with20-vol%alloy particles, which make it a promising candidate for practical applications. The0-3typecomposite of Pr(Fe0.4Co0.6)1.93has a larger magnetostriction than that of1-3type composite, which can be ascribed to the EMD not lying along <111> direction. The result shows the optimum massratio of epoxy resin to powder being5:100.The single Laves phase high Pr-content Tb0.2Pr0.8(Fe0.4Co0.6)1.9Bxcompounds with0.05≤x≤0.15were fabricated successfully by arc-melt and subsequent annealing. The beneficial effects ofpartial boron substitution and the annealing process on the crystal structure, phase stability andmagnetostrictive properties have been investigated. Boron atoms can occupy either thesubstitutional or interstitial site in this alloy system. XRD analysis shows that small amounts ofboron are helpful for the formation of the cubic Laves phase. Partial substitution of boron for ironimproves the magnetostrictive properties of this alloy.