ELEMENTS-STRATEGIC RESEARCH TOWARD NEW PERMANENT MAGNETS

More than thirty years have elapsed since the invention of the Nd-Fe-B permanent magnet and we are still searching for new materials that can be considered as candidates on which the next generation permanent magnets may be developed. New magnets must be clearly benchmarked with respect to not only magnetic performance of today’s best Nd-Fe-B magnets but also elements sustainability. Elements Strategy Initiative Center for Magnetic Materials (ESICMM) started in 2012 as a ten-year project under the MEXT’s Elements Strategy Initiative. ESICMM is focused on the development of high-performance permanent magnet materials that may meat such clearly benchmarked requirements. One of the most critical subjects is to develop atomistic understanding of coercivity mechanism of permanent magnets since coercivity sensitively depends on atomic defects and arrangements at interfaces of macroscopic crystal grains. For this purpose, atomistic microstructural characterizations, ab-initio simulations of interfacial structures, and finite element micromagnetic simulations are to be closely combined. Construction of data base and simulation algorithms of thermodynamics and kinetics of structural formation in relevant alloy systems is another highly focused area of investigation in ESICMM. Recent topics relevant to development toward Dy-free Nd-Fe-B include characterization of intergranular film-like phase with soft X-ray MCD, grain-boundary diffusion (or infiltration) process using low-melting temperature Nd-rich alloys, small-angle neutron diffraction analysis of the infiltrated magnets, large-scale first-principles of the atomic structure near interfaces, equilibrium experiments and thermodynamic assessments of sub-phases, and on. The search for new compounds with superior intrinsic magnetic parameters arrived at synthesis of NdFe12N. Issues for the future investigations will also be discussed.