Metal amorphous magnetic metals

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

The magnetic metals were also prepared by a method [25] based on the rapid expansion of supercritical fluid solutions (RESS) coupled with chemical reduction to produce nickel, cobalt, iron, and iron oxide nanopartides of reasonably narrow size distribution. Under the protection of a polymer stabilization agent, the largely amorphous metal nanopartides form stable suspensions in room-temperature solvents. 

In a metallic crystal, the latticework of the atoms is botmd together by a sea of electrons. Each atom—or, more accurately, each nucleus—occupies a position within a crystalline lattice. The electrons, on the other hand, move among all of the available atoms in a series of conduction bands. The net result is that even in an amorphous state metals readily conduct electricity and heat, they are ductile and malleable, and they exhibit the luster seen on metallic surfaces. In the crystalline form, metals can do all of the above and exhibit other properties such as magnetism (which reqtiires ordered crystalline domains), see also Glass Salt. 

The temperature dependence of the resistivity of amorphous non-magnetic metals has been studied by many authors. The most popular theory is still Ziman s theory for the resistivity of liquid metals and several authors have extended this theory to include a dynamic structure factor. Cote and Meisel (1979) used an isotropic Debye spectrum for the phonons to calculate the dynamic structure factor. They obtained a quadratic dependence of the resistivity on temperature at low temperatures. Frobose and Jackie (1977) used both a Debye model and a model of uncorrelated Einstein oscillators in conjunction with a dynamic structure factor to analyse the resistivity. They found that the second model leads to a satisfactory fit for the temperature dependence of the resistivity of CuSn alloys for T 10 K. Ohkawa and Yosida (1977) predict a T ... 

Magnetic properties of amorphous alloys composed of rare earths and non-magnetic metals... 

Ferrer et al. (1978) found excellent agreement between the RAM model description and the high-field magnetization curves obtained by various authors on amorphous alloys in which rare earth elements are combined with non-magnetic metals. Values of the parameters D and obtained by fitting the experimental results obtained by Boucher (1977a,b), Boucher and Barbara (1979) and Ferrer et al. (1978), have been collected in table 3. 

Bellissent, R., Galli, G., Hyeon, T., MigUaido, R, Parette, G., Suslick, K.S. Magnetic and structural properties of amorphous transition metals and alloys. J. Non-Cryst. Solids 205-207, 656-659 (1996)... 

M. Kopcewicz, Mossbauer effect studies of amorphous metals in magnetic radio-fiequency fields. Stmct. Chem. 2, 313-342 (1991)... 

The above treatment assumes a single atomic component system whereas the rare earth transition metal amorphous materials (R-T) are two component and thus three pair correlation functions, G(r), exist, one each for the possible R-R, R-T, and T-T combinations. These are lumped together to produce the observed scattered intensity function, but may be separated by experiments on isotopically substituted alloys which have different neutron scattering amplitudes, or as in the case of Co-P by separating the magnetic components using polarized neutrons (Bletry and Sadoc, 1975). 

All of the heavy lanthanide-transition metal amorphous alloys which are magnetic show antiferromagnetic coupling between the lanthanide and transition metal spins. The Curie temperatures as previously noted, are perturbed significantly from the crystalline values and may be either depressed (J -Fe alloys) or increased (R-Co alloys) due to fluctuations in exchange and anisotropy interactions or band structure effects. The latter has been ascribed by Tao et al. (1974) to explain the anomalous increase in the of R-Co alloys. They suggested a reduced electron transfer from the rare earth conduction bands to the Co d-band in the amorphous state compared to the crystalline. In the case of the RF z alloys the situation is more complex due to the population of both minority and majority spin bands of the Fe. 

It is clear that the field of amorphous alloys and, in particular rare earth-transition metal-aUoys, is one of intense and rapidly expanding interest in magnetism. It has been commented that it is a mistake to delve into amorphous magnetism while one is still far from understanding crystalline magnetic systems, yet the profusion of unique and anomalous phenomena accompanying magnetism in the amorphous state is sure to whet the appetite of many more curious experimentalists and theorists in the future. 

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