Current Status of Research and Development toward Permanent Magnets Free from Critical Elements

Abstract

The current status of R&D activities and major results are briefly reviewed, mainly focusing on work reported since about 2010. Developments in and perspectives on less-Dy and Dy-free Nd-(Dy)-Fe-B-type permanent magnets, search and discovery of new hard magnetic materials, progress in the basic understandings of coercivity in hard magnets, and perspectives on anisotropic nanocomposite permanent magnets are overviewed.

Realization of a scanning soft X-ray microscope for magnetic imaging under high magnetic fields

“…A particularly challenging material for magnetic domain observations has been magnetically anisotropic Nd-Fe-B sintered magnets. In these materials, from both physical and metallurgical points of view, magnetic domain observations throughout the entire magnetization process are required to help elucidate the coercivity mechanism (Hirosawa, 2015;Hono & Sepehri-Amin, 2012;Coey, 2012;Gutfleisch et al, 2011). Since the coercivity of commercial Nd-Fe-B sintered magnets is about 1.2 T, it is necessary to apply magnetic fields larger than 3 T in order to saturate the magnetization.…”

Iron Oxide Nanoparticles for Next Generation Gas Sensors

“…The new preparation processes are different from physical and chemical metallurgy technologies, and other conventional methods and approaches. Recently, Prof Satoshi Hirosawa, the leading researcher, has carried out the studies of interesting topics of soft and hard magnetic Febased oxides and alloys via heat treatments with various kinds of specific gases, such as N 2 , H 2 , Ar/H 2 etc at high temperature [90,91], at national Institute for Materials Science (NIMS), Japan. In the wide temperature range from room to about 1000°C, the prepared Fe -based particles with the microscales and good sizes, shapes, and morphologies were proved to be kept in existence of grain and grain boundary structures [78][79][80][81][82][83]87,88].…”

“…In addition to the various kinds of the new Fe-based nanomaterials Figure 11 [89][90][91][92]. The new preparation processes are different from physical and chemical metallurgy technologies, and other conventional methods and approaches.…”

Preparation and characterization of magnetic films of well-dispersed single domain of core–shell α″-Fe16N2/Al2O3 nanoparticles

“…Recent reports have shown that these ferromagnetic NPs with single magnetic domain, by magnetically oriented assembly, will give higher magnetic performance than that of large MNPs with many magnetic domains [5][6][7][8]. However, most of these ferromagnetic NPs with the highest magnetocrystalline anisotropy usually composed of rare-earth elements, such as Nd, Sm, and Dy [8][9][10][11]. Therefore, synthesis of single domain ferromagnetic NPs without rare-earth component and alignment of their magnetic orientation are still become a challenge in the magnet development.…”