Development of Elongated Particle Magnets

Abstract

The development of permanent magnet materials is briefly reviewed. The present status of fine particle magnets is discussed from the viewpoint of our present understanding and lack of understanding of their behavior. The present methods of preparation and the various theoretical descriptions of the properties of elongated particles are reviewed. New work is presented relating the parameters of preparation to the resulting diameter of the elongated particles prepared by electrolysis into mercury. Rotational hysteresis,coercive force, and coercive force as a function of orientation are reported for particle diameters from 130 A to 305 A. Their behavior is compared to various theoretical descriptions and found to correspond to a noncoherent magnetization reversal mechanism most similar to the chain-of-spheres fanning model rather than the curling, buckling or coherent rotation models. Iron and iron-cobalt alloy particle magnets are described with maximum energy products up to 4.3 and 6.5 million gauss-oe, respectively.

High-Coercivity Fe-Co Nanoparticles Prepared by Pulsed Arc Plasma Deposition

“…411) The coercivity of magnetic materials is known to increase with decreasing particle size, 13) but the coercivity obtained in this study was quite high. The coercivity of the Fe-Co nanoparticles decreased with increasing discharge count, likely due to aggregation and grain growth of the Fe-Co particles.…”

“…13) As FeCo has a high saturation magnetic polarization, several methods have been developed to synthesize Fe-Co nanoparticles. Chemical methods, 48) such as the polyol method 4) and hydrogen reduction method, 5) allow the size and composition of the nanoparticles to be controlled, but it is difficult to prevent aggregation of the particles during the drying process.…”

Microscale magnetic compasses

“…Figure 4B shows magnetization curves for the aligned nano-compasses collected at temperatures of 2, 5, 50 and 300 K and in magnetic fields up to 1 T applied perpendicular to the molecular axis (see the schematic in Figure 4A). These results show that the nano-compasses are ferromagnetic, with coercive fields as high as ∼ 78.5-87.5 mT at 2-50 K, reducing to ∼27.5 mT at room temperature, The grain sizes are controlled in a range of 100-1000 nm where the coercive field is optimally enhanced [37,38], hence the nanocrystalline magnets are magnetically harder than their bulk counterpart.…”

THE MAGNETO-OPTICAL AND MICROSTRUCTURAL PROPERTIES OF CoPt MULTILAYERS GROWN ON Ga2O3 AND ZnO

“…Base on the observations by AFM on the currently studied films, a model of magnetically independent columnar particles [8] may be assumed to rationalize the relation between the coercivity, Hc, and column size, D, as [9] He = 2K _ 4K ~(25kT).~…”