Magnetostrictive Properties In (Pr,Nd)-modulated Laves Compounds

The C15 Laves phase RFe₂ magnetostrictive compounds have been widely applied in sonar transducer,sensors and actuators,because of their large magnetostriction and low magnetocrystalline anisotropy at room temperature.Terfenol-D(Tb_0.27Dy_0.73Fe₂)possess a giant mgnetostriction?1200 ppm at 80KA/m?.However,Terfenol-D,which known as “Black Gold”,mainly contains expensive heavy rare earths,i.e.Tb and Dy,restricting its widespread application.According to the calculation of a single ion model,PrFe₂ and NdFe₂ should have large magnetostriction constant at absolute zero.What's more,Pr and Nd are much cheaper than Tb and Dy.So it is interesting to develop magnetostrictive materials based on light rare earth Pr and Nd.In this thesis,we have systematically investigated(Tb_0.2Pr_0.8)_xDy_1-xFe_1.93,Tb_xDy_0.2-xNd_0.8Fe_1.93 magnetostrictive compounds.We also investigated Tb_0.15Dy_0.05Nd_0.8Fe_1.93 compounds through rapid quenching by melt-spinning method.The main results of this thesis are as following:1.Ambient-pressure and high-pressure synthesis of magnetostrictive(Tb_0.2Pr_0.8)_xDy_1-xFe_1.93 alloys.Tb_xDy_1-xFe_1,93 compounds with 80 at.% Pr substitution for Td have been fabricated by arcmelting and subsequently ambient-pressure annealing.The crystal structure,magnetic properties and magnetostriction of(Tb_0.2Pr_0.8)_xDy_1-xFe_1.93?0?x?0.5?alloys have been investigated.The pure cubic MgCu2-type structure can't be achieved when the Pr content exceeds about 20 at.% in the rare-earth.Then,high-Pr content(Tb_0.2Pr_0.8)_xDy_1-xFe_1.93?0.3?x?1.0?cubic Laves phase alloys with MgCu2-type structure were prepared by high-pressure annealing.The step-scanned XRD?440?reflection peaks,magnetization and magnetostriction have been investigated,which prove(Tb_0.2Pr_0.8)_xDy_1-xFe_1.93?0.3?x?1.0?alloys is an anisotropic compensation system.The anisotropy point is close to x=0.8,where the easy magnetization direction?EMD?of the compound change.When x=0.6,the compound magnetostriction is the minimum,it is accord with the trend of the saturation magnetization.2.Spin-structure phase diagram and magnetostriction in Tb_xDy_0.2-xNd_0.8Fe_1.93 alloys.High-Nd content Tb_xDy_0.2-xNd_0.8Fe_1.93?0?x?0.2?cubic Laves phase alloys with MgCu2-type structure were prepared by high-pressure synthesis.The spin configuration diagram accompanied with different crystal structures was constructed through the analysis of M?ssbauer effect,temperature dependence of ac.Initial susceptibility xac?T?,magnetostrictive behavior.The structure goes through tetragonal ? orthorhombic ? rhombohedral,which enriches the spinstructure phase diagram of magnetostrictive materials.It is found the magnetostriction peaks at x=0.15.The saturation magnetostriction?720ppm?of Tb_0.15Dy_0.05Nd_0.8Fe_1.93 is much larger than that of Ho-doped Tb0.2Dy0.22Ho0.58 compound?530ppm?.3.Structure and magnetic properties of melt-spun Tb_0.15Dy_0.05Nd_0.8Fe_1.93 compoundAs Tb_xDy_0.2-xNd_0.8Fe_1.93 alloys synthesized under high-pressure,we intend to develop high-Nd content Tb_0.15Dy_0.05Nd_0.8Fe_1.93 cubic Laves phase alloys with MgCu2-type structure by melt-spinning and subsequent low-temperature annealing.We find that wheel speed and annealing temperature have a great influence on the structure and magnetic properties of Tb_0.15Dy_0.05Nd_0.8Fe_1.93 alloys.Improving the wheel speed and the annealing temperature can enhance the saturation magnetization?MS?and reduce the coercive force?iHc?.The ribbons with single Laves phase were obtained at a wheel of 45m/s and subsequent low annealing temperature?773 K?,and a large magnetostriction can be achieved.In comparison with high-pressure method,the method of melt-spinning technique is a more economic and more convenient way to develop high-Nd content magnetostrictive compound.