Magnetic alignment by modulated rotating magnetic field as a practical process of three dimensional crystal alignment

Bi-axial grain alignment by modulated rotating magnetic field (MRF) is a candidate of material production process which can be applicable at room temperature. However, to raise MRF into a practical process, one should quantitatively understand requirements for achieving alignment of hard magnetization axis by rotating field. In this review article, rotation speed of MRF and time-dependent viscosity of slurry as two of the requirements are focused on. Orientation degrees of high-critical temperature superconductors' green compacts aligned in MRF were found to be improved with the increase in concentration of butanol added in ethanol-based slurry. This is because time derivative of viscosity of slurry is lowered by the addition of butanol. The author's group has recently developed an equipment that can generate a linear-drive type MRF and, in this review article, attempted to improve an effective rotation speed component in MRF by ingenuity of arrangement of the permanent magnet unit. At the current stage, the effective rotation speed has been successfully increased to be more than 500 rpm. Due to this, the orientation degrees of magnetically aligned powder samples of a high-critical temperature superconductor were also improved. Design of the arranged permanent magnet unit applicable to each substance is important. © 2020 Japan Society of Powder and Powder Metallurgy.