Characterization of intergranular phase in Nd8Fe86−xNbxB6 (x=0,1,2,3) nanocomposite magnet by Mössbauer spectroscopy

Mössbauer study and nanostructure observation revealed that intergranular phase formed between α-Fe and Nd2Fe14B phase in NdFeNbB alloys plays a significant role on the magnetic properties. The exchange interaction was characterized in term of Henkel Plot (δM plot), and hyperfine field, quardrupole splitting and isomer shift were refined to predict the presence and role of the intergranular phase. By the addition of Nb into Nd8Fe86B6 composition, coercivity was found to increase by 25% due to the grain refinement of both the soft and hard magnetic phases which was decreased from 50 nm of virgin Nd8Fe86B6 to 25 nm in Nd8Fe85Nb1B6 alloys. The role of Nb addition was confirmed to stabilize the Nd2Fe14B lattice preventing from thermal vibration of the corresponding sites at where Fe atoms are substituted by Nb in the Nd2Fe14B lattice. The enhanced coercivity was originated from the exchange hardening of soft and amorphous phases surrounding the hard magnetic Nd2Fe14B crystal.