Borides magnetic properties

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). 

According to the matrix, nanocomposites may be classified into three categories i) Ceramic matrix nanocomposite, ii) metal matrix nanocomposites, and iii) polymer matrix nanocomposite. In the first group of composites the matrix is a ceramic material, i.e., a chemical compoxmd from the group of oxides, nitrides, borides, silicides, etc. In most cases of ceramic-matrix nanocomposites the dispersed phase is a metal, and ideally both components, the metallic one and the ceramic one, are finely dispersed in each other in order to elicit the particular nanoscopic properties. Nanocomposites from these combinations were demonstrated to improve their optical, electrical and magnetic properties [5,4], as well as tribological, corrosion-resistance and other protective properties [6,5]. Thus the safest measure is to carefully choose immiscible metal and... 

Following the discoveries of the excellent magnetic properties of file rare earth transition metal borides, the rare earfli transition metal carbides have also been investigated extensively. For example, an early review and detailed comparative study have been given by Buschow. A more recent review on particular developments has been given for Sm-Fe-C systems, for example. ... 

Ceramics are studied and used for such places that are subject to high temperatures, but many others have a variety of nses. Ceramics is dehned as an inorganic, nonmetallic material processed or consolidated at high temperatnres. Ceramics includes silicates, oxides, carbides, nitrides, snlhdes, and borides of metal or metalloid. The traditional ceramics are mostly silicates as discnssed earlier and nsed as a pot or similar purposes. But today ceramics are pursued as material for high-temperature, electric properties such as ferroelectricity, piezoelectricity, magnetic properties, high mechanical properties, and optical properties. In a word, they are pnrsned as HIGH-TECH material. 

Quaternary boro-nitrides. The well-known magnetic properties of R2T14B ternary borides (T=transition metal) are typified by the neodymium iron compound Nd[2Fei4B, discovered in 1983. Several studies aimed at introducing interstitial nitrogen in the composition of such permanent-magnet materials in order to improve their characteristics, in particular the Curie temperature. 

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. 

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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