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A solid-state phase transformation (SSPT) is observed in nanocrystalline [Sm.sub.2][Fe.sub.17][C.sub.x], x=0-1 ([Th.sub.2][Zn.sub.17]-type carbides) prepared by both ball milling and rapid solidification. Upon annealing at 800 [degrees] C the [Sm.sub.2][Fe.sub.14]C ([Nd.sub.2][Fe.sub.14]B-type) phase is formed for x [greater than or equal to] 0.3. For x between 0.3 and 1.0, the [Sm.sub.2][Fe.sub.17][C.sub.y] (y [similar to] 0.3) and [Sm.sub.2][Fe.sub.14]C phases co-exist. The process of the SSPT to [Sm.sub.2][Fe.sub.14] is faster in finer-grain samples. The annealing time required for a complete transformation varies from 15 min for a sample with an average grain size of 40 nm to 28 h for a 200 nm grain size sample. These results suggest that the SSPT is made accessible by reducing the grain sizes. Studies on [Nd.sub.2][Fe.sub.17][C.sub.1.0] show that certain [Nd.sub.2][Fe.sub.14]C powders synthesized through SSPT contain highly anisotropic particles, suggesting a promising technique to produce anisotropic [Nd.sub.2][Fe.sub.14]B-type permanent magnets.

Samarium cobalt nanoparticles were prepared by ball milling under argon, both with and without a surfactant. X-ray diffraction indicated a single Sm[Co.sub.5] phase, with an average size of 25 nm from Debye-Scherrer analysis of the peak widths, but a broad size distribution based on TEM. SQUID magnetometry yielded the coercivity as a function of temperature between 4 and 300 K. Large coercivities ([H.sub.c] = 2.1 T at 10 K) were observed in the bare particles, but the values were significantly reduced ([H.sub.c] = 0.12 T at 5 K) for those coated with surfactant, indicating probable surface oxidation.

We examine the low frequency BH loop and complex permeability spectra of multilayer permalloy films laser processed to define samples consisting of stripes perpendicular and parallel to the as-deposited easy axis. For stripes defined perpendicular to the easy axis, it is found for films of thickness [greater than or equal to] 0.745 [[micro]meter] that the demagnetizing field, which is a function of groove depth and stripe width, is able to reorient the easy and hard axes from the initial orientation resulting in a permeability spectra dependent upon groove depth. For relatively thick spacer layers, 45 nm, laser definition of stripes perpendicular to the easy axis induces the different magnetic layers to switch independently. For thinner films the easy and hard axes do not re-orient, but the independent switching of the layers is seen for the thicker spacer layer films. For stripes defined parallel to the easy axis the anisotropy of the sample increases with groove depth, resulting in a decrease in measured permeability.

The effects of [Co.sub.79][Cr.sub.21] undercoats and nucleating layers on the coercive force, anisotropy field, and 5 MHz to 100 MHz complex permeability spectra of magnetically soft, [Ni.sub.81][Fe.sub.19] thin films rf sputtered onto glass substrates are investigated. While very thin layers of hcp oriented [Co.sub.79][Cr.sub.21] [approximately equal to] 5 nm, do not affect the coercive force of the NiFe layer, they do increase the measured anisotropy. Thicker CoCr layers increase both the coercive force and anisotropy field. The 5 nm layers of [Co.sub.79][Cr.sub.21] act to increase the magnitude of the [Mu][prime] spectra, [Mu] = [Mu][prime] - j[Mu][double prime], while decreasing the [Mu][double prime] spectra; thicker layers of CoCr reduce both [Mu][prime] and [Mu][double prime].

The alloys with chemical compositions of [Nd.sub.16][Fe.sub.76-x] [B.sub.8][Zr.sub.x] (x = 0, 0.1) have been HDDR processed, and the magnetic properties and anisotropy of the HDDR material have been characterised by means of VSM measurements using a magnetically aligned sample. Anisotropy of the HDDR powder material has been evaluated by comparing the remanence values of the aligned sample measured along the aligning direction and the direction perpendicular to it. It has been found that the intrinsic coercivity of the HDDR powder strongly depends on the particle size of the powder. As the particle size decreases, the intrinsic coercivity decreases radically, and this is explained in terms of structural damage induced in the particle during mechanical milling. It has also been found that the degree of alignment representing the anisotropy of the HDDR powder is enhanced with decreasing particle size. Some degree of alignment has also been observed in the HDDR material obtained from the Zr-free Nd-Fe-B-type alloy, and this may possibly be attributed to either incomplete disproportionation, excess grain growth of the recombined grains or the presence of very fine particles as a result of milling.

Thin films of [Nd.sub.2][Fe.sub.14]B ([approximately]30-60 nm) were grown with c-axis texture bY means of molecular beam epitaxy. A two-phase structure is observed in both the x-ray diffraction and the hysteresis loops, due to an interfacial reaction during the initial growth. Coercivities are 1-2 T at 20 K, and the anisotropy fields are bulk-like. Microstructural analysis by atomic and magnetic force microscopies reveal lateral grain sizes of [similar to]200 nm, which could explain the hard magnetic properties.

We have carried out neutron and magnetic studies on [Nd.sub.2][Fe.sub.17-x][T.sub.x] (T=Si, Mn) alloys. The unit cell of the compounds contracts with both Si and Mn substitution. Si atoms avoid the 6c site, prefer the 18h site strongly, fill the 9d site steadily and fill the 18f site only at relatively high Si concentration. Mn atoms avoid the 9d sites but prefer the 6c site strongly, while the 18f site and 18h site fill slowly. The Si site occupancies appear to be dominated by the crystal environment while the Mn site occupancies are dominated by steric considerations. The Curie temperature of the compound [Nd.sub.2][Fe.sub.17] increases significantly with Si substitution but is only affected slightly by the Mn substitution. Although the unit cell contracts with increasing Si concentration, the average length of bonds to the Fe(6c) and the Fe(18f) sites increase slightly at x

Rare-earth-transition-metal thin films are successfully grown by magnetron sputtering onto single-crystal MgO substrates with epitaxial W buffer layers. The use of epitaxial W buffer layers allows oriented single-phase films to be grown. Sm-Co films grown onto W(100), have strong in-plane anisotropy and coercivities exceeding 5 T at 5 K whereas Fe-Sm films have strong perpendicular anisotropy and are magnetically soft.

High-coercivity Sm[Co.sub.x] alloys were prepared by melt spinning. X-ray diffraction data indicate that the alloys exhibit a single phase Sm[Co.sub.5] and [Sm.sub.2][Co.sub.17] structure at x = 5.0 and x = 8.5, respectively. A two-phase structure appears at 5.0 < x < 8.5. The coercivity of the studied alloys increases as the wheel speed is increased up to a maximum value of 40 m/s. The grain sizes of the as-spun alloys were measured to be 0.1-1.0 [[micro]meter]. The high coercivity of the microcomposite alloys can be explained from the unpinning of domain walls at nucleation sites.

[Y.sub.2][Fe.sub.15][T.sub.2]C (T=Al,Ga,Si) crystallize in the rhombohedral [Th.sub.2][Zn.sub.17]-type structure. The refined compositions are in excellent agreement with that of the nominal ones. The site occupancies of the substitutional atoms, (Al, Ga and Si) are found to be similar to those of the corresponding uncarbided compounds and not changed by the C atoms. That is, Al, Ga and Si all profer the 18h site at the present substituent content, which appears to be determined by the site environments since the 18h site has the highest number (3) of rare earth neighbors in the structure. C atoms are found to occupy the octahedral interstitial 9e site (1/2, 0, 0) which has two rare earth neighbors and four Fe/T neighbors, in all three samples. The Curie temperatures have been measured to be 588K, 515K, and 535K for the Ga, Al, and Si samples respectively.

Details of the important parameters for hot pressing isotropic Nd16Fe76B8 HDDR powders are presented. Optimum magnetic properties may be achieved over broad ranges of green compaction pressure and hot pressing temperature, time and pressure. Isotropic HDDR powders with lower Nd-contents (i.e. Nd14Fe79B7 and Nd13Fe80.5B6.5) may also be hot pressed to full density to produce magnets with energy products [approximately]100 kJ/[m.sup.3] and some advantages of hot pressing the lower Nd-content compositions are stated. The cause of the enhanced values of remanence obtained for nominally isotropic hot pressed HDDR magnets is probably due to some alignment induced during hot pressing. The ease of hot pressing HDDR powder suggests this process is commercially viable, particularly as the HDDR powder production process has been estimated to be cheaper than that of the MQ powder.

The magnetic and structural properties of Sm[Co.sub.2][Fe.sub.2]B powders prepared by ball milling, mechanical alloying and melt-spinning have been studied. Sm[Co.sub.2][Fe.sub.2]B powders milled for 5 minutes and then aligned were found to be anisotropic by x-ray diffraction. An optimum coercivity of, Hc = 13.5 kOe, was obtained after milling for 120 minutes corresponding to a particle size in the ranges of 1-6 [[micro]meter]. Mechanically alloyed powders were shown to have the highest coercivity, 16 kOe, after heat-treating at 600 [degrees] C for 30 minutes. The melt-spun samples had a low coercivity due to an unidentified phase possibly with low anisotropy.

Nanocrystalline structures were obtained by a rapid thermal annealing (RTA) process with a heating rate of 600 [degrees] C/min for a soaking time of 2 minutes for melt-spun [Nd.sub.6][Fe.sub.88]-xMx[B.sub.6] amorphous alloys (M = Ti or V, x = 0 [similar to] 5). Exchange coupling interaction between the magnetically hard and soft phases was studied with the [Delta]M plots. Addition of Ti or V to replace iron is effective in increasing remanence ratio, Mr/[M.sub.2T], and energy product of the modified alloys, especially that modified by V, although both saturation magnetization and remanence are decreased due to magnetic dilution. High resolution TEM studies showed that both Ti and V is effective in refining grain size of both hard and soft phases to 20 [similar to] 23 nm compared with 50 [similar to] 52 nm for the x = 0 alloy. The substitution with V results in a decrease in coercivity despite of refined grains.

The relationship between phase transformation and magnetic properties of mechanically alloyed (MA) Sm[Co.sub.7] alloys at different annealing temperatures has been studied. The MA alloy is a mixture of an amorphous phase and a Tb[Cu.sub.7]-type phase, and has low coercivity. Upon annealing, the coercivity initially increases with the amount of Sm[Co.sub.7] phase. Maximum coercivity of 16 kOe has been obtained on single phase Tb[Cu.sub.7]-type Sm[Co.sub.7] compound by annealing at 650 [degrees] C. At higher annealing temperature, coercivity first decreases with the appearance of Ca[Cu.sub.5]-type Sm[Co.sub.5] phase and still further with the formation of [Th.sub.2][Zn.sub.17]-type [Sm.sub.2][Co.sub.17] phase at 800 [degrees] C.

We studied the high temperature decomposition mechanism for the [Fe.sub.17][Sm.sub.2][N.sub.3] phase using several different experimental techniques, as thermomagnetic and thermogravimetric analyses. Our results show that the decomposition occurs in a two step scheme. In the first reaction we have the formation of SmN and a solid solution of nitrogen in iron. In the second step, this solid solution degases, and we observe the evolution of nitrogen over a broad temperature range.