The effects of particle sizes of neodymium iron boron microstructure on the magnetic characteristics

In this work, the magnetic properties of neodymium iron boron (Nd
2
Fe
14
B) powder with different particles sizes are studied using a vibrating sample magnetometer (VSM). The results show that as the particles size decrease, the saturation magnetization (B
s
) and remanent magnetization (B
r
) decrease while coercivity (H
c
) increases to its maximum and subsequently declines towards zero when a particle’s critical radius is reached. In particular, it has been observed when the particle size reduces to the range of 1.0 to 2.0 µm, the B
s
and B
r
of the particles significantly drop to 120.37 Am
²
/kg and 84.38 Am
²
/kg, respectively and its H
c
increases to 0.69 T. Further decrease in size in the mass powder, however causing the H
c
to decline to 0.08 T and the B
s
and B
r
reduce to 99.55 Am
²
/kg and 32.54 Am
²
/kg, respectively as the particle's critical radius is reached. Despite having almost identical average particle sizes, the presence of a notable amount of smaller particles in a particular powder causes the magnetic properties value to shift significantly. The magnetic behavior suggested a superparamagnetic behavior of the smallest NdFeB particles studied.