Research On Magnetic Properties And Magnetostrictive Properties Of Light Rare Earth RET₂(RE = Pr?Nd?Tb,T = Fe?Ga?Mn?Co) Cubic Laves Phase Alloys

Due to huge magnetostrictive properties,the C15 cubic Laves phase REFe₂(RE=rare earth)alloy is widely applied in sonar transducers,sensors,actuators,etc.Especially,under low temperature conditions,the light rare earth PrFe₂and Tb Fe₂based alloys possess larger magnetostrictive values(PrFe₂-5600 ppm,Tb Fe₂-4400ppm,Nd Fe₂-2000ppm).However,because such alloys also have a large magnetocrystalline anisotropy at low temperatures,it requires a large driving magnetic field to obtain a large magnetostriction value,which greatly limits the application of such alloys.In order to reduce the magnetostriction value of alloys,substituting Fe sites with transition metals so as to achieve large magnetostrictive materials at low fields has become an important way for people to obtain new materials.This paper mainly studies the effects of substituting Fe sites in the PrFe_1.9alloy with transition metals such as Mn and Ga as well as substituting the Fe sites in the Tb Fe₂alloy and the Nd Fe₂alloy with transition metal Co on the alloys'magnetic properties,magnetostrictive properties,and Easy Magnetization Directions(EMD).1.Effect of Ga Substitution on Low-temperature Magnetostrictive Properties of PrFe_1.9AlloysThrough high-pressure annealing,a single MgCu₂cubic Laves phase structure Pr(Gax Fe_1-x)_1.9alloy was successfully prepared.Substituting Fe with Ga can lower the Curie temperature Tc of the alloy.At room temperature,the magnetization of Pr(Ga_xFe_1-x)_1.9alloy is nearly saturated under the applied magnetic field of 8000Oe.Moreover,with the increase of Ga content,the saturation magnetization of the sample also gradually decreases.As the temperature drops from 300 K to 15 K,the alloy's Easy Magnetization Direction(EMD)changes from[111]to[100]at the spin reorientation temperature Tsr,and the addition of Ga enhances the Tsr value.Ga substitution reduces the magnetostriction of high magnetic field(H?8k Oe)and the intrinsic magnetostriction value at low temperature.However,the small amount of Ga doped(x?0.05)can effectively increase the alloy's low magnetic field(H?8k Oe)Magnetostrictive value.2.Effects of Mn Substitution on Low Temperature Structure and Magnetic Properties of the PrFe_1.9AlloyThrough high-pressure annealing,a single MgCu₂cubic Laves phase structure Pr(Mn_xFe_1-x)_1.9alloy was successfully prepared.At room temperature,the magnetization of Pr(Mn_xFe_1-x)_1.9alloy is nearly saturated under the applied magnetic field of H=8000Oe.With the increase of Mn content,the saturation magnetization of the sample also gradually decreases.The research result of Mossbauer spectrum reveals that this alloy'EMD at room temperature is the same as that of the PrFe1.9alloy,which is the(111)direction.It indicates that Mn substitution does not change the alloy's EMD at room temperature.The research of the low temperature magnetic properties on the alloy shows that with the decrease of temperature,the Pr(Mn_xFe_1-x)_1.9(x=0.05)alloy's magnetostriction change curve with temperature(?-T)as well as the change curve of magnetization with temperature(MT Curve)changed abnormally at around 85 K.This is due to the fact that as the temperature decreases,the alloy's EMD decreases with the decrease of the temperature,and changes at T_srfrom(111)to(100).Substituting Fe site in the PrFe1.9 alloy with Mn will cause the increase of the alloy T_sr.3.Research on the Effects of Co Substitution on Low Temperature Structure and Magnetic Properties of the Tb Fe₂Alloyand Nd Fe₂AlloyThrough high pressure annealing,the Tb Fe₂alloy and the Nd Fe₂alloy in the single MgCu₂cubic Laves phase structure were successfully prepared.The research on the magnetic properties of the alloy shows that with the decrease of the temperature,the TbCo₂alloy and Nd Co₂alloy's magnetization strength change curve with the temperature(MT curve)have abnormal changes at around 240 K and 120 K,which is due to the Spin Reorientation(SR)of the alloy at the Curie temperature.Under 15 K,Nd Co₂possesses lower saturation magnetization than that of TbCo₂.However,it possesses smaller magnetocrystalline anisotropy than that of TbCo₂.The XRD precision scanning results reveals that when the temperature range is from130K to 10K,the characteristic peak(222)and the(440)peak of the TbCo₂have a bimodal splitting with the peak shape intensity of 1:1 and 3:1,which indicates that the alloy's EMD is the[111]direction in this temperature range.