Coercivity enhancement of Nd−Fe−B thin film magnets by Dy buffer and capping layers

The Dy layer was inserted into the structure of SiO₂/Ti/Nd-Fe-B/Ti as the buffer or capping layer of the Nd-Fe-B layer. The insertions of Dy layers had no significant influence on the film texture with the easy axis mainly perpendicular to the film plane. The film without Dy layer gave the out-of-plane coercivity of 533 kA/m, maximum magnetic energy product (BH)_max of 245 kJ/m³. With a Dy buffer layer, the out-of-plane coercivity and (BH)_max were increased to 1074 kA/m, 291 kJ/m³ respectively. The film with Dy capping layer had a coercivity of 1035 kA/m and (BH)_max of 286 kJ/m³. Microstructure observations showed that the Nd-rich phases were evolved into grain boundaries from triple junctions by a Dy buffer layer deposition, resulting in a well magnetic decoupling of Nd₂Fe₁₄B neighboring grains. Through capping a Dy layer, the environment of grain boundaries had been improved and some Dy diffused into Nd₂Fe₁₄B phases, which contributed to the enhancement of magnetic performance.