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Samarium-cobalt alloys opened the era of the rare-earth permanent magnets, in which the energy density of magnets increased by a factor of ten in the first few decades.

Bulk alloys of Co-substituted Fe 2 TiSi, forming the series Fe 2 Ti 1−x Co x Si (x = 0, 0.25, 0.75 and 1), have been investigated by first-principle density functional calculations.

The authors studied the influence of microstructure and grain size, as well as Curie temperature, on the low-temperature aged Sm(Co0.45Cu0.4Fe0.15)5 alloy in relation to enhanced coercivity. Melt-spinning has been employed in order to achieved a wide range of grain sizes from micro- to nanometer level. XRD and TEM analysis were used to study the structure of as-spun ribbons and SQUID magnetometer was used to determine the magnetic hysteresis parameters. Results showed that the enhanced coercivity of aged ribbons is higher than that one obtained in 1:5 microstructure aged magnets prior to the changes in Curie temperature.

Nanoscale magnetic and nonmagnetic clusters exhibit unique structures and properties, which are strongly depending on their size and distribution. In this study, we have demonstrated the ability of our cluster gun system to fabricate magnetic nanoparticles (Co) with different size and shape, and studied their magnetic and structural and microstructural properties.

In this research, PrFeB-based mechanically milled powders are studied with emphasis on the microstructure peculiarities, phase transformations and their relation with the magnetic properties. X-ray diffraction data of Pr/sub 9/Fe/sub 85/B/sub 6/ and Pr/sub 9/DyFe/sub 76/Co/sub 8/SiB/sub 5/ powders milled for 4 h reveal a structure free of long range crystallographic ordering. Annealing at 400/spl deg/C (27 h), 500/spl deg/C (30 min), and 680/spl deg/C (150 min) is done for the mechanically milled powders. Results show that a well-defined nanophase structure is developed by annealing above 500/spl deg/C. HRTEM micrographs in as-milled powder reveal the presence of bcc (Fe, Co) phase with an average grain size of about 10-15 nm, and an amorphous phase. Annealing the powder at temperatures as high as 400/spl deg/C still does not release the internal stress caused by the energetic collision of the powder particles during milling. The microstructure becomes free of internal stresses and completely crystallizes at 650/spl deg/C.

In this paper, we used Ni substitution for Pt to reduce the transformation temperature of the FePt alloys where FePtNi nanoparticles were fabricated by chemical synthesis. M vs T data showed a blocking temperature at around 35 K, consistent with the tiny size (2-3 nm) of the particles. DSC data indicate a structural transformation from fcc to fct at a temperature about 70/spl deg/C lower in Fe/sub 60/(Pt/sub 0.7/Ni/sub 0.3/)/sub 40/ than in Fe/sub 58/Pt/sub 42/ as confirmed by XRD and hysteresis loop measurements. Mossbauer spectra and relation of coercivity with annealing temperature and time were also presented.

In this paper, cylinders with diameter of /spl sim/0.5" (11-15 mm) were made. Full densities of the hot pressed nanocomposite magnets were achieved even when hot pressed at a low temperature of 700/spl deg/C. The highest density obtained was 7.68 g/cm/sup 3/ for a Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 85/B/sub 6/ magnet hot pressed at 700/spl deg/C with a pressure of 25 kpsi. The coercivity of the hot-pressed magnets was ranging from 0.5 kOe to 6 kOe, depending on the hotness temperature. the highest maximum energy product obtained is 10 MGOe. Comparing with the magnetic properties of the ribbons, the hot pressed magnets demonstrate a relatively low remanence. After the hot press, the density and magnetic properties were characterized and microstructures were observed by transmission electron microscopy (TEM).

In this paper, directional solidification in the presence of a magnetic field to fabricate anisotropic Sm/sub 2/(Co,Cu,Fe,Zr)/sub 17/ magnets was investigated. TEM images and hysteresis loops of directionally solidified bulk magnet were showed.

In this study, we have tried to fabricate FePt nanoparticles with controlled microstructure and magnetic properties by adjusting the sample preparation conditions. The formation of the microstructure is briefly discussed and correlated to magnetic properties of the particles.

Summary form only given. Our recent studies on the effects of composition and processing on the magnetic properties of 2:17 magnets helped us understand their coercivity and the temperature dependence of coercivity H/sub c/(T). Usually composition and processing adjustments lead to the variation of the distribution and amount of Cu at the 1:5 cell boundaries, which then controls the coercivity and its H/sub c/(T). We perform a comprehensive and systematic study to completely reveal the effects of Fe, Cu, Zr and ratio z on the coercivity, especially on the abnormal H/sub c/(T). The latest results will hopefully allow us to fully understand the H/sub c/(T) and the magnetization reversal mechanism.

Summary form only given. In our previous work (IEEE Trans. Mag. vol.36, p.3315, (2000)), we studied the effect of carbon on the formation and magnetic properties of nanocomposite Nd/sub 2/Fe/sub 14/(C,B)//spl alpha/-Fe magnets. In the Nd/sub 10/Fe/sub 82/B/sub 8-x/C/sub x/ (x=0,2,4,5, 6,7) as-spun ribbons for x=0-4 have a majority 2:14:1 phase with some /spl alpha/-Fe, whereas, for larger x the mixture of 2:14:1 phase and /spl alpha/-Fe is obtained only at certain wheel speeds range. Beyond this range, the 2:17 phase and a significant amount of /spl alpha/-Fe were obtained instead, which transform into the tetragonal 2:14:1 phase after annealing. Magnetic measurements showed a slight enhancement of the coercivity (8.7 kOe) for x=2 and then a decrease for larger x. The drop of the coercivity with carbon content can be related to the change in the crystallization behavior and the coarsening of the microstructure. In this work, we study the effect of small substitutions (i.e. Zr, Nb, Cr, Ga, etc.) for iron, in melt-spun Nd/sub 10/Fe/sub 82-x/M/sub x/B/sub 2/C/sub 6/ in order to optimize their microstructure and therefore their magnetic hysteresis properties.

Nd(FeM)/sub 12/ compounds, with M=Mo, Ti, and V, prepared by mechanical alloying were nitrogenated using the gas phase interstitial modification process. The Nd(FeM)/sub 12/ structure has been found to be stable after nitrogenation at around 650 degrees C, but with increased lattice parameters. The change in unit cell volume, delta V/V, is larger in mechanically alloyed powders than in as-cast alloy powders. The change of Curie temperature upon nitrogenation is almost the same delta T/sub c//T/sub c/ approximately=30%, for the three compounds studied. The mechanically alloyed powders and metal-bonded magnets with the ThMn/sub 12/ crystal structure show interesting hard magnetic properties with a coercivity H/sub c/=7-10 kOe. The average grain size of the mechanically alloyed powders with the highest coercivity was shown about 4000 AA. >

Methane and ethane were used to prepare rare-earth transition metal carbides. The structural and magnetic properties of these carbides have been studied. Interstitial carbon atoms expand the unit cell of the R/sub 2/Fe/sub 17/ (R=Y, Ce, Pr, Nd, Sm, Dy, Er) and RFe/sub 10/M/sub 2/ (R=Y, Nd, Sm and M=Mo, V) structures by about 7.5 and 1.5%, respectively. Thus lattice expansion resulted in increases of Curie temperature and spontaneous magnetization. The easy magnetization direction of Sm/sub 2/Fe/sub 17/ is changed from planar to uniaxial with the carbon uptake, while in other R/sub 2/Fe/sub 17/ compounds it remains planar. For RFe/sub 10/M/sub 2/ with R=Y and Nd, a uniaxial anisotropy is observed after carbonation. >