Synthesis And Magnetostrictive Properties Of High-（Pr,Nd） Content R（FeCo）₂ Laves Compounds

RFe2-type(R = rare earth) magnetostrictive materials with giant magnetostriction have been widely applied in sensors and sonar. As we know, TbFe2 possesses the huge saturation magnetostriction and a large magnetocrystalline anisotropy, therefore, a large magnetostriction can only be obtained at a high magnetic field. Clark et al. proposed RxR’1-xFe2 composition anisotropy compensation system by combining two RFe2 compounds alloys with opposite anisotropy signs and the same magnetostrictive signs, such as Terfenol-D(Tb0.27Dy0.73Fe2). Considering the limitation of the high price of heavy rare earths Tb and Dy, the light rare earth elements, such as Pr and Nd instead of these heavy rare earth elements have been paid more and more attention. According to the theory of single-ion model, the calculated magnetostriction constant of Nd Fe2 is high up to 2000 ppm,Meanwhile, NdFe2 possesses the same of magnetostrictionbut opposite anisotropy signs of K1 with the counterparts of TbFe2. Thus, NdFe2 and TbFe2 can form anisotropy compensation system as TbxNd1-xFe2, likeTbxDy1-xFe2. Ren et al. found that although both DyFe2 and PrFe2 have the positive anisotropy signs of K1, PrxDy1-xFe2 can still be an acceptable anisotropy compensation system as considering the higher anisotropy constant K2 in the frame of single-ion model.The present paper synthesized a series of high-(Pr,Nd) content magnetostrictive materials by both rapid quenching with melt-spinning and high-pressure annealing method. The main points of this paper are as following:1. Structure and magnetic properties of melt-spun Tb0.2Nd0.8(Fe0.8Co0.2)1.9 compoundHigh-Nd content Tb0.2Nd0.8(Fe0.8Co0.2)1.9 cubic Laves compound which could not be prepared by annealing its as-cast ingot was successfully fabricated by melt-spinning and subsequent low-temperature annealing. The effects of wheel speed and annealing temperature on the structure and magnetic properties of Tb0.2Nd0.8(Fe0.8Co0.2)1.9 ribbons are investigated. The ribbons with single cubic Laves phase were obtained at a wheel speed of 40 m/s and subsequent annealing temperature of773 K. The average grain size decreases with the increase of the wheel speed from 10 m/s to 40 m/s.The easy magnetic direction of Tb0.2Nd0.8(Fe0.8Co0.2)1.9 Laves phase lies along <111> at room temperature, which was confirmed by Mossbaure spectra. Meanwhile, the resin-bonded ribbons obtained at a wheel speed of 40 m/s have a magnetostriction of 321 ppm at room temperature. This work demonstrates an alternate way to synthesize the metastable high-Nd content cubic Laves phase magnetostrictive compounds under ambient pressure other than high-pressure annealing.2. Effect of Co substitution on structure and the magnetic properties of melt-spun Tb0.2Nd0.8(Fe1-xCox)1.9(0≤x≤0.4) alloysStructural, magnetic and magnetostrictive properties of Tb0.2Nd0.8(Fe1-xCox)1.9(0≤x≤0.4) alloys have been investigated at room temperature. The matrix of Tb0.2Nd0.8(Fe1-x Cox)1.9 is essentially of a single pseudobinary Laves phase with a cubic MgCu2-type structure for 0.1≤x≤0.4. The lattice parameter decreases linearly with the increase of Co form 7.442 ? to 7.392 ?. The magnetic moment of Tb0.2Nd0.8(Fe1-xCox)1.9 alloys exhibit a maximum near x=0.2, it can be understand within the rigid-model. The Curie temperature were measured increasing with increase of x form 595 K at x=0to 633 K at x=0.2, then decreasing to 555 K at x=0.4. The magnetostriction of resin-bonded ribbons exhibits a peak at x=0.2 under low applied field, the magnetostriction of Tb0.2Nd0.8(Fe0.8Co0.2)1.9measured is 321 ppm at room temperature, this work reveals the effect of the Co content in the synthesis of metastable high-Nd content cubic Laves phase magnetostrictive compounds.3. Synthesis and magnetostrictive properties of Pr1-x Dyx(Fe0.8Co0.2)1.93 cubic Laves compoundsThe structure, magnetic properties and magnetostriction of Pr1-xDyx(Fe0.8Co0.2)1.93(x=0, 0.05, 0.1,0.2, 0.3) compounds were investigated. These compounds, which could not be readily synthesized under ambient pressure, exhibit single cubic Laves phase owing to the method of high-pressure annealing. The Curie temperature increases with increasing x, indicating that the 3d-4f coupling becomes stronger with the addition of Dy element. The saturation magnetization of compounds decreases with increasing x, which can be ascribed to the competition of sublattice magnetization.The easy magnetization direction of the compounds lies along < 111 > with x ≤ 0.05 while lies along< 100 > when x ≥ 0.10. Meanwhile, the low-field magnetostriction λ∥- λ⊥of the compound system peaks at x=0.05 and then decreases with increasing x, which reveals that the composition anisotropy compensation between Pr3+ and Dy3+ might be realized in Pr1-xDyx(Fe0.8Co0.2)1.93 system.Pr0.95Dy0.05(Fe0.8Co0.2)1.93 compound combines a large low-field magnetostriction(648 ppm at 3 kOe)and the merits of low-cost raw materials.