R块外延生长S块与W型铁氧体的永磁特性

W-type ferrite A2+Me22+Fe16O27, which possesses a high saturation magnetization and a large energy of magnetocrystalline anisotropy, have attracted a growing and widespread attention in the past decades due to their vast application prospect and huge potential market value.In this project, we explore a great deal of work on the research of the interactions of Me2+ occupied sites with crystal field effects under the coupling of electronic spin and spin-orbit, in which W-type ferrite has been substituted with multi-ion. The two S blocks, which have 1/2 spinel cell with cubic symmetry, are epitaxially grown on the R block according to its hexagonal symmetry, supper exchange and uniaxial anisotropy. As a result, a permanent magnetic phase (R block + S block) as M-type ferrite is stacked for a match by a soft magnetic phase (S block). We have given undivided attentions to its composition, structure, grain growth, the orientation of magnetic moment distribution and arrangement, single domain structure by some effective control in order to design a novel W-type ferrite with lattice match, which has a large uniaxial anisotropy. By manufacturing highly textured permanent magnets, which are parepred under a temperature gradient technique and an applied field, we resaerch the preferred growth W-type magnet through a polycrystalline material of W-type ferrite and grain boundary doping. With adjusting the crystallographical site occupied with different ions, saturation magnetization, magnetic anisotropy energy and magnet microstructure, it is hoped that the permanent magnet with a high intrinsic coercivity and a large remanence will be discovered. To sum up the points which we have just indicated, this project aims to research into the epitaxial growth of the S block on the R block and permanent magnetic properties of W-type ferrites, in which it not only has rich content of academic research, also has important practical value. Thus, it is expected to achieve a number of innovative research results.

由于W型铁氧体A2+Me22+Fe16O27具有高的饱和磁化强度和大的磁晶各向异性能，其作为永磁材料有着广阔的应用前景和巨大的潜在市场价值。本项目通过对W型铁氧体的离子取代，研究电子自旋和轨道的相互耦合下晶场效应对Me2+占据次晶位的影响。根据R块的六角对称性、超交换作用和单轴各向异性，外延生长具有立方对称的1/2尖晶石晶胞的2个S块。在单胞内，实现永磁相（R+S块）外延生长高饱和磁化强度的软磁相（S块）。通过组成、结构、晶粒优化，对磁矩取向、排布与单畴结构等进行有效的人为控制，以便设计出晶格匹配、单轴各向异性的W型铁氧材料。在一定温度梯度和外加磁场下，研究多晶W型铁氧体材料和晶界掺杂对永磁体的择优生长的影响，以制备出具有高剩磁和高内禀矫顽力的永磁体。因此，本课题提出R块外延生长S块与W型铁氧体的永磁特性的研究，不仅具有丰富的物理内涵，还拥有重要的应用价值，有望取得一些创新性的研究成果。

由于W型铁氧体A2+Me22+Fe16O27具有高的饱和磁化强度和大的磁晶各向异性能，其作为永磁材料有着广阔的应用前景和巨大的潜在市场价值。根据R块的六角对称性、超交换作用和单轴各向异性，外延生长具有立方对称的1/2尖晶石晶胞的2个S块，制备了一些列W型铁氧体A2+Me22+Fe16O27，实现了永磁相（R+S块）外延生长高饱和磁化强度的软磁相（S块），研究了W型铁氧体永磁特性。.在Fe2W型铁氧体中， HA 达到1512 kA· m-1 (19 kOe)，大于BaM的1353 kA· m-1。利用陶瓷法在氮气中制备了W型 BaFe22+Fe163+O27 (1290℃≤ T ≤ 1330℃)系列铁氧体。通过研究与分析发现随温度从1290℃增大到1300℃，剩磁(Br)和最大磁能积[(BH)max]逐渐增大。当剩磁Br最大值达到403mT，磁感应矫顽力（Hcb）和内禀矫顽力（Hcj）最大值分别达到80.75 kA/m和85.54 kA/m，表现出软磁特性。在此实验的基础上，我们用La3+离子取代一部分Sr2+离子，制备了W型Sr1-xLaxFe22+Fe163+O27 (0 ≤ x ≤ 0.15) 铁氧体，并对其微观结构和磁性能进行了系统研究。结果表明，离子取代后W型铁氧体的剩磁(Br)随x增大呈现出先增大后减小的变化趋势，磁感应矫顽力（Hcb）和内禀矫顽力（Hcj）随x增大呈现出先增大后减小的变化趋势。对Sr1−x Lax Zn2 Fe16O27研究发现，当x=0.10时，Br = 414.26 mT, Hcj = 243.78 kA/m, Hcb = 234.69 kA/m ，最大磁能积达到 (BH) max = 31.95 kJ/m3，当x=0.15时，Br = 405.42 mT, Hcj = 265.89 kA/m，Hcb = 257.42 kA/m，最大磁能积达到(BH)max = 31.65 kJ/m3，具有一定的应用价值。.目前，通过离子取代和优化制备条件，如何在R块上外延生长S块，拓展其微波吸收，正日益凸显重要性。研究表明，所有样品在2.0-18.0 GHz的频率下都具有良好的有效吸收性能。还观察到，当Ba1-xCaxCo2Fe16O27的x = 0.40时，微波吸收性随着Ca2+离子的添加而增加，而当在2-15.0GHz的频率范围内x = 0.5