Study On Structure And Magnetic Properties Of Rare Earth Transition Metal Intermetallic Compounds

The new class of R(rare earth)-T(transition metal) intermetallics namely,R3(Fe,M)₂₉ (R =Ce, Pr,Nd, Sm, Gd, Tb,Dy, Y; M =Ti,V,Cr,Mn,Mo,Nb,W ) are of current interest in the field of permanent magnet materials. Based on the study on R-T permanent-magnet material Nd₃(Fe,Ti)₂₉, this thesis deals with a study of the structural and magnetic properties as well as the the magnetocrystalline anisotropy. Below, the main experimental results and conclusions are summarized:1. A rare-earth-transition metal intermetallic compound is a candidate for excellent permanent materials when it fulfills the following conditions: it must has a large spontaneous magnetization, a strong uniaxial magnetocrystalline anisotropy and a high magnetic ordering temperature . Since the R3(Fe,M)₂₉ phase is an intermediate phase between the ThMn12 and Th2Zn17-type structures, production of the single R3(Fe,M)₂₉ is difficulty and time consuming. For example,the Nd₃(Fe,Ti)₂₉ phase is usually produced by annealing of Nd–Fe–Ti alloy ingots at a high temperature of 1373K for a long period of 72–130h. The annealed Nd–Fe–Ti alloy still contains a small amount ofα-Fe phase. We study the structure and magnetic properties of Nd–Fe–Ti alloy abtained by annealing of Nd–Fe–Ti ribbons produced by the melt-spinning technique. The XRD patterns and thermomagnetic curves show that the melt-spinning ribbons and the alloys annealed at a low temperature contain a large amount of Nd2(Fe,Ti)17 phase together withα-Fe phase. Substitution of Ti for Fe does not lead to a change of crystal structure, all alloys are in Th2Zn17-type structures. With increasing Ti content Curie temperature TC decrease monotonously . The Tc decrease from 503K to 483K for as-spun ribbons and 493K to 463K for 873K annealed alloys, respectively. Substitution of Ti for Fe may reduce the amount of magnetic ion, therefore the Tc decrease monotonously.2. In order to improve the intrinsic magnetic properties of Nd₃(Fe,Ti)₂₉ type compounds, such as saturation, magnetization, Curie temperature, and magnetocrystalline, anisotropy, in addition to formation of nitrides of these compounds, ion substitution is also an effective method. Recently some investigations of substitution of Co for Fe have been carried out. It has been found that substitution of Co for Fe leads to a transition of magnetocrystalline anisotropy compounds. From basal plane to uniaxial in Gd₃( Fe,Co) 25Cr4. In this thesis we study on substitution of Co for Fe in Nd₃(Fe,Ti)₂₉ alloys produced by melt-spinning technique. XRD patterns and thermomagnetic curves show that the melt-spinning ribbons contain a large amount of Nd2(Fe,Ti)17 phase together withα-Fe phase. Substitution of Co for Fe does not lead to a change of crystal structure, all alloys are in Th2Zn17-type structures. It is worth noting that the saturation magnetization increases monotonically with Co concentra tion. But due to the smaller atomic radius of the Co atom compared wit Fe, TC of Nd₃Fe27.6-xCoxTi1.4 compounds increases strongly with increasing Co content. It is 453K when x=0 and in increase to 675K when x=6.0.3. In order to find out the effect that Gd substitute Nd in Nd₃(Fe, Ti)₂₉ compound, we investigate the structure and magnetic properties of (Nd1-xGdx)Fe27.31Ti1.69 compounds by XRD and magnetic measurements. All compounds with x in the range of x≤0.6 crystallize in Nd₃(Fe, Ti)₂₉-type structure. Substitution of Gd for Nd leads to a contraction of unit-cell volume. That's because the smaller atomic radius of the Gd atom compared wit Nd .The Curie temperature Tc of (Nd_1-xGd_x)Fe_27.31Ti_1.69 compounds increases monotonically with increasing Gd content. We think it's due to the Gd-Gd exhange interaction. Saturation magnetization Ms and spin reorientation temperature Tsr of(Nd_1-xGd_x)Fe_27.31Ti_1.69 compounds decrease with increasing Gd content. As temperature falls from room temperature to 5K, a spin reorientation from easy plane to the easy cone occurs for (Nd_1-xGd_x)Fe_27.31Ti_1.69 compounds.4. To find out the change of magnetocrystalline anisotropy for Er substitute Nd in Nd₃(Fe, Ti)₂₉ , (Nd_1-xEr_x)Fe_27.31Ti_1.69 compounds were investigated by XRD and VSM and magnetic measurements. Substitution of Er for Nd does not lead to a change of crystal structure, All compounds with x in the range of x≤0.5 crystallize in Nd₃(Fe, Ti)₂₉-type structure. As temperature decreases from room temperature to 5K, a spin reorientation from easy plane to the easy cone occurs for (Nd_1-xEr_x)Fe_27.31Ti_1.69 compounds.