Amorphous Magnetic Materials

Amorphous ferromagnetic Co-Au films were first produced by vapor deposition on substrates cooled to liquid nitrogen temperature, but stimulus for expanded effort in this direction resulted from the development of techniques for rapidly quenching alloys from the liquid state to produce metastable phases. These techniques are referred to as splat cooling. Magnetic and Mossbauer studies of (Pd, - tMj8oSi2o alloys, where M = Fe, Co, or Ni, and of Fe-rich Fe-P-C alloys, and magnetic and 

X-ray studies of Mn-P-C alloys show that magnetic ordering temperatures are lower than the crystalline counterparts, usually multiphase, and that the magnetic behavior of these amorphous metals is largely due to the presence of atomic clusters rich in magnetic atoms. 

Amorphous rare-earth transition-metal alloys have recently been prepared and the net exchange interaction will depend on whether the R-ion is light or heavy, just as occurs in the crystalline R-transition-metal alloys and insulators.  

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For a two-sublattice antiferromagnet, one simply has two coupled single-ion equations such as Equation (15) that are simultaneously solved selfconsistently for the two sublattice average moments. A p-sublattice material gives rise to p coupled equations and presents no special difficulty. The MFT method has been generalized to random, disordered, and amorphous magnetic materials by Rancourt et al. (1993). 

Fujimori, H., Yoshimoto, H. Masumoto, T. (1981). Anomalous eddy current loss and amorphous magnetic materials with low core loss. Journal of Applied Physics, 52,1893-8. 

Kirby et al. (1994) developed a simple model vdiich is particularly useful for describing magnetization reversal in amorphous magnetic materials and multilayers with strong perpendicular anisotropy. They assumed that magnetization reversal in the uniform thin film occurs locally by thermal activation over the anisobropy barrier. They divided the sample into identical small volumes (cells) V, assumed fliat reversal occurred by coherent rotation, and proposed that the energy of the yth volume could be written as... 

Soft magnetic materials are characterized by high permeabiUty and low coercivity. There are sis principal groups of commercially important soft magnetic materials iron and low carbon steels, iron—siUcon alloys, iron—aluminum and iron—aluminum—silicon alloys, nickel—iron alloys, iron-cobalt alloys, and ferrites. In addition, iron-boron-based amorphous soft magnetic alloys are commercially available. Some have properties similar to the best grades of the permalloys whereas others exhibit core losses substantially below those of the oriented siUcon steels. Table 1 summarizes the properties of some of these materials. 

Nanoscale thin films and multilayers, nanocrystalline magnetic materials, granular films, and amorphous alloys have attracted much attention in the last few decades, in the field of basic research as well as in the broader field of materials science. Such... 

The topics of surfaces and sintering will be new to most students. The short chapter on bonding and the chapters on amorphous materials and liquid crystals introduce new concepts. These are followed by treatment of molecular morphology. The final chapters are on magnetic materials, porous and novel materials, and the shape memory. 

Abstract The focus of this chapter is primarily directed towards nanocrystalline soft magnetic materials prepared by crystallization of amorphous precursors. The key elements involved in the development of this class of materials are three-fold (i) theoretical models for magnetic softness in nanostructures (ii) nanostructure-property relationships and (iii) nanostructural formation mechanisms. This chapter surveys recent research on these three areas with emphasis placed on the principles underlying alloy design in soft magnetic nanostructures. 

Figure 5. Relation between saturation magnetostriction and saturation magnetization for amorphous [41] and nanocrystalline [1, 39, 40] soft magnetic materials.

If the sonolysis is done in the presence of a support or porous host, then colloidal metal particles are formed. These powders have a surface area over a hundred times greater than powders commercially available and are amorphous. Such materials are generally considered for catalytic reactions and not for magnetic applications. 

Ferchmin AR, Kobe S (1983) Amorphous Magnetism and Metallic Magnetic Materials— Digest. North-Holland Publishing Company, New York... 

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