Reasearch Of Magnetostrictive Effect For RFe₂-type Compounds

The rare-earth transition-metal(RE-TM) compounds,(Tb1-x Ndx)(Fe0.8Co0.2)2-y and Dy(Ho/Pr)-doped(Tb,Nd)(Fe,Co)1.93, were prepared by arc-melting and subsequent annealing. The epoxy bonded 0-3 type and pseudo 1-3 type Tb1-x Ndx(Fe0.8Co0.2)1.9 composites were also fabricated by curing with and without a magnetic field. The structure, magnetic and magnetostrictive properties were investigated by X-ray diffraction(XRD), vibrating sample magnetometry(VSM), A.C. initial susceptibility, Scanning electron microscopy-energy dispersive X-ray spectroscropy(SEM-EDS) and standard strain gauge techniques.As for the Tb0.4Nd0.6(Fe0.8Co0.2)x and Tb0.3Dy0.6Nd0.1(Fe1-x Cox)1.93 alloy systems, the annealing temperature and the contents of 3d transition-metal were studied, focusing on the formation of the phase structure. The analysis of XRD patterns shows that the proper the annealing temperature and the decrease of 3d transition-metal content can effectively inhibit the emergence of the Pu Ni3-type phase and help to form the single Laves phase in those compounds. In addition, the small amount Co substitution for Fe, in the atom content of ~25 at.%, can enhance the Curie temperature, and subsequently enlarge the temperature scope of application.With the introduction of small amount of Co(~20 at.%), the Tb0.4-x Ndx Dy0.6(Fe0.8Co0.2)1.93, Tbx Nd0.1Ho0.9-x Fe1.93, Tb0.1Ho0.9-x Prx(Fe0.8Co0.2)1.93 compounds are studied for the structure and properties. Based on the A.E. Clark’s theory of magnetic anisotropy compensation, the direct experimental evidence for magnetocrystalline-anisotropy compensation between Tb3+and Nd3+ is obtained, and is found that the critical point of around x = 0.05. The good magnetostrictive properties for the Tb0.35Dy0.6Nd0.05(Fe0.8Co0.2)1.93 compound are achieved, that is, the high polycrystalline saturation magnetostriction λS(~1170 ppm) and the large magnetostriction coefficients(λ111~1600, and λ100~520 ppm) are observed at room temperature. The magnetocrystalline-anisotropy compensation is realized in Tbx Nd0.1Ho0.9-x Fe1.93 alloys. The large polycrystalline saturation magnetostriction is found to be ?S = 585 ppm for x = 0.25, which is near the anisotropy compensation composition. As for the Tb0.1Ho0.9-x Prx Fe2 compounds, the substitution of a small amount of Co for Fe is helpful for the formation of Laves phase with Mg Cu2-type structure, which is supported by the analysis of XRD and SED. The anisotropy compensation between Ho3+ and Pr3+ is realized at room temperature, and the easy magnetization direction(EMD) rotates from <100> to <111> axis with increasing Pr content.As for the Tb1-x Ndx(Fe0.8Co0.2)1.93 system, the alloy was crushed into a particulate form and is successfully fabricated in the epoxy-bonded 0-3 type and pseudo 1-3 type composite rods. The effect of alloy particle volume fraction, magnetostriction coefficient λ111 and λ100, EMD, curing magnetic field, and the bonded type on the structure, magnetostriction and the magnetoelastic properties are studied. The results show that the composite rod has the optimized magnetostrictive properties, when the alloy particle size is around 150-250 μm with the volume ratio ~30 vol.%, and the composite rod formed in 1-3 type configuration cured under the magnetic field of 10 k Oe.