High performance ferrite magnets - From the perspective of powder technology

Abstract

Coercivity in hexa-ferrite magnets originates in the magnetic behavior of so-called "single domain particles" with uniaxial magneto-crystalline anisotropy. The critical diameter, below which a single domain is stable, is estimated at around 1 micrometer (10 −6 m) for M-type Sr-ferrite, which means that control of grain size to under a micron is significant for achieving high coercivity. For this reason studies were performed on a process for obtaining submicron powder and sintered grains, as well as on techniques for obtaining high orientation under magnetic fields when using submicron powder. For analytical purposes, Particle size distribution, magnetic properties, and lattice defects of Sr-ferrite particles were investigated to explain the observed behavior.