Sandwich-Shell Structure in Grain Boundary Diffused (Ce,Y,La)–Fe–B Magnet

Grain boundary diffusion (GBD) process improved the coercivity and the thermal stability of magnets by the core-shell-type reaction phases formed between the Nd
₂
Fe
₁₄
B matrix grains and heavy rare-earth. Sintered (Ce-Y-La)-Fe-B magnet GBD processed at 940 °C for 10 h with TbHx source was prepared. Sandwich structure with (Ce,Y)
₂
Fe
₁₄
B, (Tb,Ce,Y)
₂
Fe
₁₄
B, and (Ce,Tb,Y)
₂
Fe
₁₄
B shells was formed around the Y-rich core in the GBD processed matrix grains. Formation mechanism of the sandwich-shell core structure was proposed and discussed.