We report on the technique for controlling the microstructure of Nd-rich triple junction and grain boundary phases, which is a key for developing the high-performance Nd-Fe-B permanent magnets. Through a systematic observation on the structural changes in the Nd-rich phases of the Cu-doped magnets during annealing, the structure of meta-stable Nd-oxide required to achieve high coercivity was revealed, and its formation mechanism was clarified. As a result, the annealing process that can stabilize the meta-stable Nd-oxide in the Cu-doped magnets could be developed, thereby improving the coercivity of the magnets further. In addition, by understanding the chemical and structural weak points of the Cu-doped magnets through SEM, EPMA, and HR-TEM analyses, the metal element doping process that can effectively complement the microstructural weakness of Cu-doped magnets could be developed. As a result, the coercivity of Cu-doped magnets was successfully improved with a slight remanence reduction. Based on the results from the current microstructure characterizations, a guideline for developing microstructure control technique on the structure and chemistry of the Nd-rich triple junction and grain boundary phases will be proposed to achieve high coercivity in Nd-Fe-B permanent magnets while minimizing the use of high-cost rare-earth elements.

Nd-Fe-B based permanent magnets are widely used for various applications due to their excellent magnetic properties. However, the increasing demand for Nd-Fe-B based permanent magnet with growth of the eco-friendly vehicle market is accelerating the imbalance between the supply and demand of rare-earth elements such as Dy, Tb, and Nd. For heavy rare earth (HRE)-free or Nd-lean magnets, it is necessary to refine the crystal grains to the single domain size of Nd₂Fe₁₄B phase (~300 nm), and to form the uniform and continuous grain boundaries phase as a non-magnetic phase. The hot-deformed Nd-Fe-B magnet have a very high potential as a HRE-free or Nd-reduced permanent magnet due to its ultra-fine grain size of ~300 nm. In this paper, we introduce overall research and development trend for the hot-deformation process of Nd-Fe-B based permanent magnets to develop the high performance HRE-free or Nd-lean permanent magnets.

Lorentz transmission electron microscopy (TEM) is a powerful tool to investigate magnetic domain structure as well as crystal structure and composition. Various magnetic materials including not only traditional Nd-Fe-B permanent magnet but also topological magnetic configurations such as magnetic skyrmion have received enormous attention from the viewpoint of fundamental science and practical application. Understanding the correlation between magnetic domain, microstructure and physical properties is essential. In this article, several magnetic imaging methods in Lorentz TEM including the Fresnel and Foucault mode, differential phase contrast (DPC), and electron holography techniques. In addition, several examples of magnetic structure observation of magnetic skyrmion and Nd-Fe-B materials are introduced.

This paper deal with the performance analysis of the outer-rotor surface-mounted permanent magnet synchronous motor applied grain-oriented electrical steel (GO). GO is a steel manufactured to facilitate magnetization in the rolling direction of the steel sheet. It has outstanding magnetic properties in the rolling direction. On the other hand, it shows rather low magnetic properties in the transverse direction. In this paper, the GO was applied to stator teeth area with a relatively constant magnetic flux direction. Analysis of the characteristics according to the connection size of the GO and the load, no-load analysis was performed through finite element analysis. As a result of the analysis, the average torque was increased, the torque ripple was decreased, and the efficiency was increased due to the iron loss reduction in the load analysis. In addition, the no-load analysis showed a decrease in total harmonic distortion and cogging torque. Therefore, if the GO is used in an appropriate position in which the magnetic flux direction is considered, it is expected to be applied to various applications to show superior performance.

In this study, iron oxide nanoparticles were synthesized by thermal decomposition method using Fe(acac)₃ and 1- hexadecanol at 330 ℃. TG-DSC is one of the most important characterization techniques to study the Fe₃O₄ nanoparticles generation and growth from reduced mass and endothermal reaction. Analysis of TEM and XRD results yield the average sizes of synthesized spherical magnetite nanoparticles with sizes of 10nm. We could determine the saturation magnetization and coercivity value using the VSM. ZFC and FC curves measured at 100 Oe with the T_B (blocking temperature) was explained to superparamagnetic transition.