Sm-Fe-N and Nd-Fe-B magnets have great potential as high-performance permanent magnet
owing to their excellent intrinsic magnetic properties. However, both these magnets have
limitations in terms of reduction in the magnetic property when it is used for high temperature
(150-180 °C) applications. For example, the reduction in coercivity at higher operating
temperatures (180 °C) exhibited by Nd-Fe-B sintered magnet has been resolved by addition of
Dy through direct alloying. However, due to expensive nature and scarcity of Dy, its use needs
to be minimized.
Conventional sintering of Sm-Fe-N powders into bulk sintered magnet is not possible due to
thermal decomposition of Sm2Fe17N3 phase above 620 °C. The Sm2Fe17N3 loses its magnetic
behaviour by forming soft magnetic α-Fe phase resulting in drastic decrease in magnetic
properties of the sintered magnet. Similarly, low temperature sintering (temperature below 620
°C) of anisotropic powders also has the tendency to form soft magnetic α-Fe phase due to
surface oxidation of its powders. Hence, it is difficult to produce sintered magnet while
retaining its powder properties as it requires exposure to high temperature. Metal bonded
technique has been attracting as potential alternative method to fabricate bonded magnets. Sm-
Ni and Zn-Al low melting eutectic alloys were developed as suitable candidate to address the
above associated problem with Sm-Fe-N in this present work. The prepared Sm-Ni alloy
showed nonmagnetic characteristics which is essential for decoupling the ferromagnetic grains
for either retaining or enhancing the magnetic property. In Zn-Al added sample, it showed
coercivity enhancement from 0.9T to 1.5T at optimum annealing condition.
In addition, Nd-Fe-B sintered magnet is dip coated with DyF3 and the coercivity gets enhanced
to 1.78T from its initial 1.55T range. Microstructural investigation revealed the formation of
core-shell features where shell is responsible for enhancement in the coercivity owing to its
highly anisotropic characteristics.