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

Abstract

In this work, the magnetic properties of neodymium iron boron (Nd2Fe14B) 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 (Bs) and remanent magnetization (Br) decrease while coercivity (Hc) 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 Bs and Br of the particles significantly drop to 120.37 Am2/kg and 84.38 Am2/kg, respectively and its Hc increases to 0.69 T. Further decrease in size in the mass powder, however causing the Hc to decline to 0.08 T and the Bs and Br reduce to 99.55 Am2/kg and 32.54 Am2/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.