Magnetic properties also

Chromium—Cobalt—Iron Alloys. In 1971, a family of ductile Cr—Co—Fe permanent-magnet alloys was developed (79). The Cr—Co—Fe alloys are analogous to the Alnicos in metallurgical stmcture and in permanent magnetic properties, but are cold formable at room temperature. Equivalent magnetic properties also can be attained with substantially less Co, thereby offering savings in materials cost. 

Secondly, the electron theory seeks to elucidate the relation between the catalytic and electronic properties of a semiconductor. At the present time we possess a vast amount of experimental material which allows us to infer that the electronic processes taking place in a semiconductor and determining its electrical, optical, and magnetic properties also determine its chemisorptive and catalytic properties. It is the aim of the theory to establish the connection between these two groups of properties. 

Properties Black, semiconducting material. D 4.9. Acicular crystals having strong magnetic properties. Also in powder form. 

Structure factor for small single crystals of C-type rare earth oxides of Y2O3, DyaOs, and H02O3 was investigated from the synchrotron X-radiation point of view [30]. Approximate symmetry in the deformation electron density (Ap) around a rare earth atom with pseudo-octahedral oxygen coordination is similar to the cation geometry. Interactions appeared between heavy rare earth atoms show a pronounced effect on the Ap map. The electron-density symmetry around second rare earth atom is also influenced appreciably by cation-anion interactions and the oxides magnetic properties also reflect this complexity. 

Fe—Co Alloys-. Since Co and Fe are body-centered cubic structures in a nanoparticle, the allied order of both metals is very soft and very suitable to be raw material for nanoparticles. The maximum concentration of Co in the alloy is 35%. This is the saturation concentration of Co. The related magnetic properties also increase with the mixing level (Gubin, 2009). 

Small metal clusters are also of interest because of their importance in catalysis. Despite the fact that small clusters should consist of mostly surface atoms, measurement of the photon ionization threshold for Hg clusters suggest that a transition from van der Waals to metallic properties occurs in the range of 20-70 atoms per cluster [88] and near-bulk magnetic properties are expected for Ni, Pd, and Pt clusters of only 13 atoms [89] Theoretical calculations on Sin and other semiconductors predict that the stmcture reflects the bulk lattice for 1000 atoms but the bulk electronic wave functions are not obtained [90]. Bartell and co-workers [91] study beams of molecular clusters with electron dirfraction and molecular dynamics simulations and find new phases not observed in the bulk. Bulk models appear to be valid for their clusters of several thousand atoms (see Section IX-3). 

Also, novel magnetic properties have been reported in mixed fullerene composites, in which the fullerene is limited... 

Within the periodic Hartree-Fock approach it is possible to incorporate many of the variants that we have discussed, such as LFHF or RHF. Density functional theory can also be used. I his makes it possible to compare the results obtained from these variants. Whilst density functional theory is more widely used for solid-state applications, there are certain types of problem that are currently more amenable to the Hartree-Fock method. Of particular ii. Icvance here are systems containing unpaired electrons, two recent examples being the clci tronic and magnetic properties of nickel oxide and alkaline earth oxides doped with alkali metal ions (Li in CaO) [Dovesi et al. 2000]. 

Substitution for Fe has a drastic effect on intrinsic magnetic properties. Partial substitution by or decreases J) without affecting seriously, resulting in larger and values. Substitution by Ti and Co causes a considerable decrease in K , the uniaxial anisotropy (if j > 0) may even change into planar anisotropy (if < 0). Intermediate magnetic stmctures are also possible. For example, preferred directions on a conical surface around the i -axis are observed for substitution (72). For a few substitutions the value is increased whereas the J) value is hardly affected, eg, substitution of Fe byRu (73) or by Fe compensated by at Ba-sites (65). 

Vanadium—Cobalt-Iron Alloys. V—Co—Fe permanent-magnet alloys also are ductile. A common commercial ahoy, Vicahoy I, has a nominal composition 10 wt % V, 52 wt % Co, and 38 wt % Fe (Table 10). Hard magnetic properties are developed by quenching from 1200°C for conversion to bcc a-phase foUowed by aging at 600°C (precipitation of fee y-phase). The resulting properties are isotropic, with ca kJ/m ... 

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