Remanent Magnetization Of Particles Research Articles

Multi-domain structures in spheroidal Co nanoparticles

The structure of multi-domain micromagnetic states in hcp cobalt nanoparticles of spheroidal shape has been studied using numerical simulation in the range of diameters 20–200 nm. The single-domain diameters of the particles are determined depending on their aspect ratio. The complicated vortex structure of domain walls for two- and three-domain micromagnetic configurations is investigated. It has been shown that three domain states are actually strongly deformed two vortex states. In hcp cobalt particles of sufficiently large sizes two types of three-domain micromagnetic states with close total energies have been obtained. They differ in different magnetization directions of the exchange cores of the vortex domain walls. The remanent magnetization of particles has been calculated for two- and three-domain micromagnetic states. The single-domain diameters of fcc cobalt nanoparticles with cubic type of magnetic anisotropy were also calculated.

A reexamination of the performance of demagnetizing coils on finely ground natural magnetite

Since the last period of intensive study of the demagnetization process for magnetite during the 1950s, our understanding of the physical basis of the magnetism of small particles has increasing exponentially. In light of this improved understanding, the demagnetization process, particularly as applied to finely ground particles of natural magnetite, was reexamined. Magnetometer measurements showed that the coercivity and remanent magnetization increase markedly as the particle size decreases below 10 μm. Although industry-standard 60-Hz demagnetizing coils reduced the remanent magnetization of these particles to a significant extent, the particles remained strongly magnetized, forming magnetic agglomerates of 100 particles or more under quiescent conditions. Although in previous work with high-coercivity synthetic magnetite, it had been found that increasing the strength and frequency of the applied field gave improved demagnetization, applying the same conditions to finely ground natural magnetite gave no significant improvement. The sizable remanent magnetization of the fine natural magnetite particles after all known demagnetization processes is a fundamental property related to the limited number of magnetic domains in each particle. Whether these particles behave as individual particles or as larger agglomerates in any particular unit operation depends upon the amount of shear stress to which the particles are subjected.