Dy-Free Nd-Fe-B Based Permanent Magnets

Nd$_{2}$Fe$_{14}$B based permanent magnets are the current state of the art for high performance magnets. The prototype crystallize in the $P$4$_{2}$ \textit{/ mnm} tetragonal crystal structure, where the Nd atoms occupy the \textit{4f} and \textit{4g }sites, Fe atoms occupy six different atomic sites (\textit{16k}$_{1}$, \textit{16k}$_{2}$, \textit{8j}$_{1}$, \textit{8j}$_{2}$, \textit{4e}, \textit{4c}), and B occupies only the \textit{4g} site. The leading contribution to the magnetocrystalline anisotropy in Nd$_{2}$Fe$_{14}$B energy comes from the Nd ions, which strongly prefer a $c$-axis alignment at ambient temperature. Nd$_{2}$Fe$_{14}$B permanent magnet has excellent magnetic properties at room temperature but has poor high temperature properties (T\textgreater 400 K). A small amount of Dy (up to 10{\%}) is substituted for Nd in Nd$_{2}$Fe$_{14}$B to increase the high temperature performance. Although Dy containing Nd$_{2}$Fe$_{14}$B magnets are desired for high temperature applications, the high price and limited supply of Dy urges the development of Dy-free permanent magnets. Here, we discuss the magnetic properties of several Dy-free Nd-Fe-B based nanostructured magnets and propose alternatives for Dy-based Nd$_{2}$Fe$_{14}$B permanent magnets for high temperature applications such as electric drive motors and wind turbines. This work was supported by the U.S.DOE, ARPA-E, Rare Earth Alternatives in Critical Technologies for Energy (REACT). The research was performed at the Ames Laboratory which is operated for the U.S. DOE by Iowa State University under contract {\#}DE-AC02-07CH11358.