Magnetism borides

The alloy magnets Nd Fej B and SmCo are prepared by heating the elements at very high temperature. Iron neodynuum boride magnet alloys from Santoku (Molycorp) contain considerable Pr and Dy as well to inhibit corrision and enhance magnetism respectively. 

The crystal structures of the borides of the rare earth metals (M g) are describedand phase equilibria in ternary and higher order systems containing rare earths and B, including information on structures, magnetic and electrical properties as well as low-T phase equilibria, are available. Phase equilibria and crystal structure in binary and ternary systems containing an actinide metal and B are... 

Because they exhibit interplay of magnetic and superconducting properties, the formation and crystal chemistry of MRgMy4B4 compounds have been examined. Ternary rare-earth and actinide (Th, U, Pu)-transition metal borides of the approxi-... 

Most of the known borides are compounds of the rare-earth metals. In these metals magnetic criteria are used to decide how many electrons from each rare-earth atom contribute to the bonding (usually three), and this metallic valence is also reflected in the value of the metallic radius, r, (metallic radii for 12 coordination). Similar behavior appears in the borides of the rare-earth metals and r, becomes a useful indicator for the properties and the relative stabilities of these compounds (Fig. 1). The use of r, as a correlation parameter in discussing the higher borides of other metals is consistent with the observed distribution of these compounds among the five structural types pointed out above the borides of the actinides metals, U, Pu and Am lead to complications that require special comment. 

In the same way the equation for the determination of the specific magnetization of boride FesB was obtained. This phase is formed during the crystallization amorphous alloy Fes2Si2Bi6. As we found the specific magnetization of boride FesB is 192 TllO" cmVm. This value is in 1,5 times greater then the specific magnetization of cementite G-FesC and 1,1 times lower then the specific magnetization of a-iron. 

Nickel of activity comparable to Raney nickel is obtained by reduction of nickel salts, e.g. nickel acetate, with 2 mol of sodium borohydride in an aqueous solution and by washing the precipitate with ethanol [13, 47] Procedure 7, p. 205). Such preparations are designated P-1 or P-2 and can be conveniently prepared in situ in a special apparatus [4] Procedure 2, p. 202). They contain a high percentage of nickel boride, are non-magnetic and non-pyrophoric and can be used for hydrogenations at room temperature and... 

Paramagnetism results from unpaired electrons. As a result, most compounds containing transition, rare-earth, and actinide elements, including oxides, nitrides, carbides, and borides, exhibit paramagnetism. Such ceramics are generally not of importance due to their paramagnetism alone, since they often exhibit other types of magnetism, as well. 

Boron has a particular affinity with rare earth elements, and forms rare earth borides which are of particular interest. The rare earth atoms supply electrons to the boron atomic framework to stabilize and form novel structures, while the shell of f electrons supplies further attractive properties like magnetism. Borides with lower boron content, like the hexaborides RB6 and tetraborides RB4 are well known metallic compounds and have been studied throughout the years, revealing interesting magnetic properties (e.g. Gignoux and Schmitt, 1997). 

The resistivities of the magnetic borides DyB, H0B12, ErB, and TmB, have been carefully measured by Gabani et al. (1999) for good quality crystals with low room temperature resistivities (10-30 p 2 cm) compared to the early work. Near the antiferromagnetic transition temperatures Tn, the resistivities all show small increases in the form of humps and then rapid drops as the temperature is lowered. This behavior can be explained as an initial increase in the resistivity attributed to the appearance of superzone boundaries within the Brillouin zone, followed by a decrease due to a reduction in spin scattering (Taylor and Darby, 1972 Fournier and Gratz, 1993). 

Recently, further detailed investigations have been carried out on the magnetic RB12 compounds and despite the simple structure of the systems, exciting new results are being obtained (e.g. Kohout et al., 2004 Siemensmeyer et al., 2006). Incidentally, it should be noted that the metallic "lower borides" RB4 tetraborides... 

Most of the higher borides described in this work were discovered within the space of 10 years, yet what other new attractive cluster compounds are waiting to be discovered along with their exciting and unexpected magnetic, electrical, and thermal properties ... 

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