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The texture in magnets made from NdFeB anisotropic HDDR powders was examined using an inverse pole figure and [006] pole figure. Unlike anisotropic magnets made by hot deformation, the magnets produced in the present study did not show a strong preferred orientation. The [006] pole figure of these magnets shows a weak [006] texture in contrast to that observed for the anisotropic magnets made by the hot deformation process. TEM studies carried out on these samples indicate that they contain some grains which have grown bigger than the adjacent small grains. Alignment of flakes with large grains in an applied magnetic field makes these magnets made from HDDR powders anisotropic.

The annealing behavior of amorphous terfenol-D thin films is examined in this work. Amorphous thin films were prepared by DC magnetron sputter deposition from alloy targets. Differential scanning calorimetry of these films was performed in the temperature range 100-800/spl deg/C. Based on DSC data annealing experiments were performed at 400, 550, 575, 600 and 650/spl deg/C. X-ray diffraction shows RFe/sub 2/ phase is formed when samples are annealed at 575-600/spl deg/C. Other phases observed are Fe and rare earth oxide.

This research is focused on (1) design of novel nanocomposite structures for high energy-product permanent magnets, (2) design of enhanced high-temperature Co-based alloys by compound-alloy modifications, and (3) development of enhanced hard and soft magnets via novel processing methods including mechanical alloying, cluster-assembled materials, and rolling techniques. Model nanocomposite hard-soft combinations have been developed with energy products of about 50 MGOe and coercivities of about 40 kOe. A theoretical understanding has been achieved of the structural characteristics needed to produce high energy products in the exchange-coupled nanocomposites. A variety of 2:17, 1:7, 5:17 and modified compounds have been investigated both experimentally and theoretical. It has been shown that transition-metal additions such as Ti, Cu, and Zr, are capable of stabilizing the disordered hexagonal Sm(CoM)7 phase with beneficial increases in anisotropy. Considerable development work on processing methods has been performed in this period.

The effect of quench rate on nanostructure and magnetic properties of PrCo5 alloy has been investigated. The increase of quench rate through wheel speed in melt spinning suppresses the formation of the secondary Pr2Co17 and Pr5Co19 phases with low magnetocrystalline anisotropy field and refines the nanostructure. This significantly improves the coercivity, remanence, and energy product. For example, increasing the wheel speed from 30 m/s to 70 m/s increases the coercivity and energy product from 3.2 kOe and 4.0 MGOe to 10.3 kOe and 13.7 MGOe, respectively. The magnetic hardening mechanism appears to be a mixture of reversed-domain-nucleation and domain-wall-pinning. The temperature coefficient of coercivity for the 70 m/s sample is −0.16%/K from 300 to 700 K, which is better than that of sintered SmCo5 magnets. Low temperature coefficients of coercivity and remanence indicate that rapidly quenched PrCo5 ribbons may be suitable for bonded magnets with high operation temperature.

The effect of Mo addition on phase composition and nanostructure of nanocrystalline Zr16Co84−xMox (x = 0–2.0) melt spun at 55 m/s has been investigated. All the ribbons consist mainly of a hard magnetic Zr2Co11 phase with rhombohedral crystal structure but also contain minor amounts of soft-magnetic phases. The increase in cell volume on alloying suggests that Mo mainly enters the rhombohedral Zr2Co11 structure and occupies the Co site. Mo addition promotes the formation of the hard magnetic phase and increases its volume fraction. The mean grain size of the hard magnetic phase remains almost unchanged with the increase of Mo content. But the average grain size of the soft magnetic phase decreases from about 200 nm to 50 nm. This promotes the exchange coupling of the hard and soft magnetic phases and thus leads to a significant increase in coercivity and isotropic energy product, from 0.6 kOe and 0.5 MGOe for x = 0 to 2.9 kOe and 4.2 MGOe for x = 1.5.

Nanocrystalline Ti0.75Zr0.25Fe2+x (x = 0-0.4) and Ti0.75−yByZr0.25Fe2.4 (y = 0-0.35) with high saturation magnetization have been fabricated by the melt-spinning technique. Nanocrystalline Ti0.75Zr0.25Fe2+x consists of the hexagonal C14 Laves phase (Ti,Zr)Fe2. Fe addition decreases the lattice parameter a and shrinks the cell volume. The antiferromagnetic Fe-Fe interactions may decrease with the increase of x, leading to a significant enhancement of saturation polarization (Js) and Curie temperature (Tc). The magnetocrystalline anisotropy constant K also increases with increasing x. Excessive Fe addition (x > 0.25) may induce structural disorder which lowers the Js and Tc. Nanocrystalline Ti0.75−yByZr0.25Fe2.4 is composed of hexagonal (Ti,Zr)Fe2 and Fe-rich amorphous phases with relatively high Js. The lattice parameters a, c and cell volume V are almost unchanged with the increase of y for y ≥ 0.16. Simultaneously, the Tc of (Ti,Zr)Fe2 remains unchanged, indicating that B does not enter this lattice but takes part in forming the amorphous phase, in good agreement with the X-ray diffraction results. The volume fraction of the amorphous phase increases with the increase of B content and results in a large enhancement of Js up to 10.8 kG. Further B addition (y > 0.30) decreases Js, possibly due to the decrease of the Js of the amorphous phase.

The effect of chemical order and defect structure on the magnetization process in Sm2Fe17 and Sm2Fe17Nx has been investigated. In Sm2Fe17, chemical disorder results in the development of random anisotropy and a small degree of magnetic hardness. The anisotropy is reduced as long-range order increases. The motion of domain walls in Sm2Fe17Nx is more dependent on the antiphase domain structure than on the amount of long-range order.

The microstructure and chemistry of SmCo2Fe2B melt-spun alloy after multistage annealing was investigated using high resolution transmission electron microscopy (HRTEM) and 3D atom probe tomography. The multistage annealing resulted in an increase in both the coercivity and magnetization. The presence of Sm(Co,Fe)4B (1:4:1) and Sm2(Co,Fe)17Bx (2:17:x) magnetic phases were confirmed using both techniques. Fe2B at a scale of ∼5 nm was found by HRTEM precipitating within the 1:4:1 phase after the second-stage annealing. Ordering within the 2:17:x phase was directly identified both by the presence of antiphase boundaries observed by TEM and the interconnected isocomposition surface network found in 3D atom probe results in addition to radial distribution function analysis. The variations in the local chemistry after the secondary annealing were considered pivotal in improving the magnetic properties.

First-principle calculations are used to investigate the intrinsic magnetic properties of intermetallic alloys of the type XMn, where X is a 4d or 5d element and M is Fe or Co. Emphasis is on the hexagonal C14 Laves-phase 1:2 and 1:5 alloys, the latter crystallizing in the CaCu5 structure. These series are of interest in permanent magnetism from fundamental and practical viewpoints, respectively. In the former, the unit cells form a prototypical motif where a heavy atom with high spin-orbit coupling and magnetocrystalline anisotropy is surrounded by many somewhat smaller M atoms with high magnetization, and the latter are Laves-phase derivatives of renewed interest in permanent magnetism. Our DFT calculations predict magnetic moments, magnetizations and anisotropies, as well as formation energies. The results are analyzed across the 4d and 5d series, especially with respect to hybridization effects between 3d and 4d/5d bands.

Equiatomic FeAu nanoclusters were produced by inert-gas condensation and embedded in a W matrix. Transmission electron microscopy investigation shows that three kinds of clusters are present: mono-crystalline, polycrystalline, and partially crystalline clusters. It demonstrates that during their formation, the structure of nanoclusters evolves from an amorphous to a crystalline structure. Crystallisation starts at the surface of nanoclusters and currently leads to the formation of poly-crystalline nanoclusters in the end. Most of the investigated objects consist in a duplex amorphous core-crystalline shell structure. Their magnetic properties were investigated by magnetization measurements as a function of magnetic field (hysteresis loops) or temperature (ZFC/FC curves). They show evidence at low temperatures of ferromagnetic and antiferromagnetic states, and ordering as well as superparamagnetism or spin-glass behaviour. Measurements performed after cooling the samples under various applied fields reveal the occurrence of exchange-spring phenomenon, related to the presence of the W matrix, through RKKY coupling between ferromagnetic and antiferromagnetic nanoclusters.

A granular system of FeRh-based nanoprecipitates (∼10–15 nm diameter) embedded in a rapidly solidified copper ribbon matrix was found to transit from a metastable tetragonal L10 (AuCu-1-type) structure to a stable B2 (CsCl-type) structure upon annealing-induced coarsening to ∼94 nm. The hysteretic magnetic transition observed at ∼100 K develops a gradual broadening that accompanies the L10 → B2 crystal structure transition. It is proposed that the Cu matrix influences the structural and magnetic properties of the FeRh-based nanoparticles through interfacial strain and chemical effects. These results emphasize the sensitivity of the magnetostructural response of FeRh to changes in the nanostructural scale, and provide pathways for tailoring the transition.

The effect of quench rate and Zr content on nanostructure and magnetic properties of melt-spun ZrxCo100?x(x?=?16?21) is investigated. High quench rate favours the formation of rhombohedral Zr2Co11, which is the hard phase. The coercivity increases with an increase in quench rate. Zr addition in limited amounts decreases the grain size of magnetic phases, which may promote the effective exchange coupling of soft magnetic phases. Therefore, coercivity and maximum energy product of Zr2Co11-based materials are significantly enhanced. The best magnetic properties,iHc?=?3.0?kOe and (BH)max?=?4.6?MG?Oe, which are the highest reported values among Co?Zr binary alloys, are achieved for x?=?18. The temperature coefficients of coercivity and remanence between 100 and 380?K are ?0.05%?K?1, comparable to those of alnico magnet.

Effects of nanostructuring on the magnetostructural response of the near-equiatomic FeRh phase were investigated in nanocomposite materials synthesized by rapid solidification and subsequent annealing of an alloy of nominal atomic composition (FeRh)5Cu95. Transmission electron microscopy studies confirm attainment of a phase-separated system of nanoscaled (∼10–15 nm diameter) precipitates, consistent with FeRh embedded in a Cu matrix. These nanoprecipitates are crystallographically aligned with the coarse-grained Cu matrix and possess an L10-type (CuAu 1) structure, in contrast to the B2 (CsCl)-type structure of bulk FeRh. It is proposed that the face-centered cubic crystal structure of the Cu matrix serves as a template for the formation and stabilization of the L10 structure in the FeRh nanoprecipitates. Magnetic measurements highlight the existence of multiple magnetic phases in the material exhibiting spin-glass (T ≤ 15 K), ferromagnetic and paramagnetic (T > 20 K) behavior. A thermally hysteretic mag...

Classical crystallographic principles limit allowed rotational symmetries to that of space-filling geometries, such as cubes and hexagons. Space-filling geometries exclude all rotational symmetries except one-, two-, three-, four- and six-fold. It was surprising, and understandably greeted with varying degrees of trepidation, when Shechtman, et al. observed fivefold rotational symmetry (and complete icosahedral symmetry) in a rapidly solidified Al-Mn alloy.1 The sharp diffraction maxima also indicated long-range order, but the order was not periodic but quasiperiodic! The Al-Mn alloy belongs to a new class of alloys, given the name “quasicrystals”, with noncrystallographic rotational symmetries and long-range quasiperiodic order and which have since been reported in over 100 alloy systems.2 This new class of materials, fitting somewhere between amorphous and crystalline materials, has provided new research opportunities in crystallography, physics, chemistry and materials science.

An ordered L10 structure has been formed in near-stoichiometric Fe-Au alloy nanoparticles. The L10 structure with a = 0.367 nm and c = 0.360 nm was observed in nanoclusters with diameters below 10 nm after slow cooling from 600 °C. The stable L10 structure formed from a parent fcc solid solution phase observed in the as-formed clusters. The fcc phase has a lattice parameter of 0.417 nm, significantly expanded compared to both Au and γ-Fe. The saturation magnetization and coercivity of both fcc and L10 structures were much lower than expected considering Fe dilution effects suggesting competing ferromagnetic and anti-ferromagnetic ordering.

Some nontrivial aspects of the magnetic and structural characterization of hard-magnetic nanoparticles are investigated. Dilute ensembles are well-described by mean-field theory, although there is an asymmetry between exchange and magnetostatic interaction fields. Corrections to the mean-field approximation are caused by cooperative effects and have the character of Onsager reaction fields, which are much stronger in micromagnetism than in atomic-scale magnetism. The slow dynamics of zero-field-cooled (ZFC) magnetization curves is strongly affected by the particles′ magnetic anisotropy, which reduces the corresponding energy-barrier height from 25 to 19.1 kBT.

[sup 27]Al and [sup 63,65]Cu NMR is reported for powdered stable Al-Cu-Fe and Al-Cu-Ru icosahedral quasicrystals and crystalline approximants, and for an Al-Pd-Mn single-grain quasicrystal. [sup 27]Al NQR spectra at 4.2 K were observed in Al-Cu-Fe and Al-Cu-Ru samples. From quadrupole-perturbed NMR spectra at different magnetic fields, and from zero-field NQR spectra, a wide distribution of local electric-field gradient (EFG) tensor components and principal-axis-system orientations was found at the Al site. A model EFG calculation based on a 1/1 Al-Cu-Fe approximant successfully explained the observed NQR spectra. The average local gradient is largely determined by the [ital p]-electron wave function at the Al site, while the width of the distribution is due to EFG lattice contribution. Comparison of [sup 63]Cu and [sup 27]Al NMR shows the EFG distribution at the two sites is similar, but the electronic contribution to the EFG is considerably smaller at the Cu site, in agreement with a more [ital s]-type wave function of the conduction electrons. Overall spread of EFG values is well reproduced by calculation based on the approximant. However, the experimental spectra indicate a much larger number of nonequivalent sites when compared with the simulated NQR spectra based on the 1/1 approximant. Themore » short-range, local chemical order is well represented by the approximant, but differences in coordination must be included at intermediate range in the quasicrystal. Measured [sup 27]Al Knight shift, magnetic susceptibility, and nuclear spin-lattice relaxation time as a function of temperature indicate reduced density of states at the Fermi level by a factor of 7 or 8 from the value in Al metal, consistent with the notion of a pseudogap for these quasicrystals. No differences in measured parameters were detected as a function of composition of the quasicrystalline alloys.« less

Nanoparticles of YCo2, YCo3, and YCo5 are produced by cluster-deposition and investigated bothstructurally and magnetically. The nanoparticles have sizes of less than 10 nm and aresuperparamagnetic at 300 K, irrespective of stoichiometry. As-produced nanoparticles exhibitdisordered structures with magnetic properties differing from those of the bulk particles.The temperature-dependent magnetization curves of the nanoparticles reveal blocking temperatures from 110 to 250 K, depending on stoichiometry. The magnetic anisotropy constant K1 of disordered YCo5 nanoparticles of 7.8 nm in size is 3.5 × 106 ergs/cm3, higher than those of thedisordered YCo2 (8.9 × 105 ergs/cm3) and YCo3 (1.0 × 106 ergs/cm3) nanoparticles.

Equiatomic MnAu clusters with average sizes of 4 and 10 nm are produced by inert-gas condensation. As-produced clusters are used to form both dense cluster films and films with clusters embedded in a W matrix with a cluster volume fraction of 25%. Both structure and magnetism are size-dependent. Structural analysis of the 10 nm clusters indicate a distorted tetragonal body-centered cubic structure with lattice parameters a = 0.315 and c = 0.329 nm. The 4 nm clusters have a partially ordered tetragonal L10 structure with lattice parameters a = 0.410 nm and c = 0.395 nm. Magnetic properties of the clusters show evidence at low temperatures of mixed ferromagnetic and antiferromagnetic interactions and ordering as well as paramagnetic spins. Saturation moments are as large as 0.54 µB per average Mn atom. The results are compared with earlier theoretical calculations on bulk MnAu.

Developing texture in nanocrystalline permanent magnet alloys is of significant importance. Directional annealing is shown to produce texture in the permanent magnet alloy (Sm12Co88)99Nb1. Melt spinning produced isotropic grain structures of the hard magnetic metastable SmCo7 phase, with grain sizes of ∼300 nm. Conventional annealing of melt-spun (Sm12Co88)99Nb1 alloy produced Sm2Co17 phase with random crystallographic orientation. Directional annealing of melt-spun (Sm12Co88)99Nb1 alloy, with appropriate combinations of annealing temperature and translational velocity, produced Sm2Co17 phase with (0 0 0 6) in-plane texture, as determined by x-ray diffraction analysis and magnetic measurements. The magnetization results show out-of-plane remanence higher than the in-plane remanence resulting in the degree of ‘magnetic’ texture in the order of 25–40%. Coercivity values above 2 kOe were maintained. The texture development via directional annealing while minimizing exposure to elevated temperatures provides a new route to anisotropic high-energy permanent magnets.

The effect of nanostructuring on magnetostatic interactions in permanent magnets is investigated by model calculations. Emphasis is on the energy product as a function of packing fraction of the magnetic phase, of the magnet’s macroscopic shape, and of the nanoscale feature size. The main difference between nanostructured and macroscopic magnetic bodies, namely, the transition between coherent and incoherent reversal, has a far-reaching impact on demagnetizing field and energy product. For small magnet sizes, the energy product is substantially enlarged, up to μ0Ms2/4 for soft magnetic materials, but this effect is difficult to exploit in real devices. In bulk magnets, the energy product depends on the packing fraction f of the soft phase and exhibits a maximum μ0Ms2/12 for f=2/3. Nanoscale magnetization processes involve demagnetizing factors different from the macroscopic ones used to determine the optimum shape of permanent magnets. Confusion of these two types of demagnetizing fields yields unphysical mechanisms, such as hysteresis-loop overskewing and the addition of self-interaction fields to the external field.

Alloys around the Sm–Co eutectic composition provide an opportunity to form two-phase nanocomposite permanent magnets consisting of nanoscale Co fibers embedded in Sm2Co17.While ternary alloying elements may refine the scale of the structure, they may also disrupt the eutectic growth and lead to the formation of primary Co. Thus, microstructural selection maps were constructed for conventionally solidified Sm–Co–V alloys. It was found that V additions enlarged the primary Sm2Co17-forming region and, at (Sm0.09Co0.91)97V3, resulted in a eutectic structure. Upon rapid solidification, this alloy was determined to have a coercivity of 5 kOe with a high remanent ratio. However, the V addition reduced the magnetization, which limited the energy product to 4.3 MG Oe. The rapidly solidified structure consisted of primary SmCo7 dendrites along with an intergranular Co region, suggesting that eutectic structure formation is skewed by underlying metastable phase relationships.

Rapidly solidified Ni54Fe27−2xGa19+2x (x=0, 1, 2, 3, and 4) ferromagnetic shape memory alloys were made by melt-spinning with variation of Fe and Ga contents to report on the martensitic phase transformation, microstructures, and magnetic properties. Rapid solidification produced pure L21 phase by preventing the formation of γ-phase. To study the effect of heat treatment on the phase transitions, microstructures, and the magnetic properties, the melt-spun ribbons were partly heat treated at different temperatures of 800, 900, 1000, 1100, and 1200 K with holding times of 5, 10, and 15 min followed by either water quenching or air cooling. The microstructures of the as-spun ribbons as revealed by electron microscopy studies exhibited a gradual transition from cellular to dendritic structure with increasing Ga concentration and with the presence of some internal martensitic twin bands at higher Ga content. The ribbons exhibited very low coercivity with high saturation magnetization, as high as ∼87 emu/g (dec...

This work investigates the order-disorder transformations utilizing time-resolved x-ray diffraction at the Advanced Photon Source. The metastable phases that can form during the order-disorder transformations in the Sm–Co intermetallics have the potential to produce materials with enhanced permanent magnetic properties. The high-temperature experiments transformed the disordered alloys with the TbCu7-type structure obtained by rapid solidification into the mixture of the hexagonal and rhombohedral ordered structures at 1375K. The ordering process and the role of the ZrC alloying on the phase formation and ordering transformations were examined. The results showed the formation of shoulders of the fundamental peaks and superlattice peak broadening prior to complete ordering. The lattice parameters expanded linearly up to the onset of ordering, after which an abrupt change of slope was observed. The change in slope suggests a nucleation and growth mechanism for the ordering transformation. The effect of ZrC...

In this paper, we investigate the magnetization reversal in single-phase RE2Fe14B and two-phase α-Fe∕RE2Fe14B with varying nanoscale grain structures and intergranular exchange interactions produced via controlled segregation during crystallization. We show that the loss of coercivity arises because domain-wall processes dominate the magnetic reversal as the exchange interactions increase. Micromagnetic modeling corroborates a transition to strongly cooperative magnetic reversal as the exchange interactions increase. The magnetic reversal is controlled by the growth of interaction domains via discrete domain-wall motion, and the coercivity is intrinsically limited by the presence of interaction domains. To alleviate this problem, we have built an additional length scale into the structure that is below the interaction domain size but above the limit for intergranular exchange interactions to be significant. These “single-interaction domain” structures retain nucleation-type magnetic reversal and high coer...

Highly coercive (Hc up to 37kOe at 300K), high remanent permanent magnets have been achieved by rapid solidification of binary Sm–Co alloys and Sm–Co alloys modified with Nb and C. Rapidly solidified SmCox alloys with x ranging from 5 to 11.5 formed predominantly a solid solution TbCu7-type SmCo7 phase, although hcp Co was observed for x>7.3. A coercivity value of 10kOe was observed for x

Rapid solidification has been utilized to produce a series of Pr–Co alloys between the Pr2Co17 and PrCo5 stoichiometries. In this system, PrCo5 has easy axis magnetization while Pr2Co17 has easy-plane magnetization. Alloys of the form (PrxCo1−x)94Ti3C3 with x ranging from 0.105 corresponding to the Pr2Co17 compound to x=0.167 corresponding to the PrCo5 compound were produced by melt spinning at a tangential wheel speed of 40m∕s. The rapid solidification and alloying additions were found to suppress the formation of the Pr2Co17 ordered phase, leading to the formation of the disordered TbCu7-type structure over a range of Pr∕Co ratios. Hysteresis loops were characterized by a smooth demagnetization curve reflective of single-phase demagnetization. Heat treatment at 800 °C led to the formation of the Pr2Co17 and PrCo5 phases, and the presence of the soft magnetic Pr2Co17 phase drastically decreased the coercivity. The soft magnetic behavior was consistent with in-plane magnetization of the Pr2Co17 structure ...

Isotropic nanocomposite magnetic structures were produced via cluster assembly routes with energy products reaching 18 MG Oe. Gas aggregation produces Fe clusters with an average size less than 10 nm with a very narrow size distribution, and these were embedded in a hard magnetic matrix by cosputtering of FePt. Structures produced were crystallographically isotropic with Fe cluster phase content ranging from 0 to 30 vol %. The coercivity decreased from 13 kOe as Fe cluster content increased. Single-phase-type hysteresis loops indicating excellent exchange coupling at low Fe cluster content give way to a stepped demagnetization loop at an Fe cluster content greater than 20%. The energy product initially increased with Fe cluster content, then decreased.

The transformation variant of the fcc to fct transformation in FePt thin films was tailored by controlling the stresses in the thin films, thereby allowing selection of in- or out-of-plane c-axis orientation. FePt thin films were deposited at ambient temperature on several substrates with differing coefficients of thermal expansion relative to the FePt, which generated thermal stresses during the ordering heat treatment. X-ray diffraction analysis revealed preferential out-of-plane c-axis orientation for FePt films deposited on substrates with a similar coefficients of thermal expansion, and random orientation for FePt films deposited on substrates with a very low coefficient of thermal expansion, which is consistent with theoretical analysis when considering residual stresses.

Magnequench NdFeB powders having high and low rare earth contents were explosively compacted to obtain cylindrical magnets. The magnetic properties were found to be isotropic and were superior to conventionally consolidated isotropic magnets. The (BH)max was 14.7 MGOe and the remanence was 8.7 kG for the explosively compacted magnet with lower rare earth content. X‐ray diffraction patterns confirm the explosively compacted magnet to be crystalline and the predominant phase to be the 2‐14‐1 phase. Transmission electron microscopy examination showed a microstructure to consist of 20–25 nm size equiaxed grains consistent with the magnetic measurements.

Aluminium-lithium alloys have attracted the interest of aerospace industries for some time now since the use of such alloys reduces the weight of an airframe by roughly ten percent. The production of these alloys, however, requires precise thermal and/or thermomechanical treatments to insure required material properties. Recently, a strong research interest has developed in the use of sensors for monitoring the state of the material during processing and in-service. On Al 2219, combined eddy current (as a measure of electrical conductivity) and hardness measurements were found to be particularly sensitive to the changes occurring during the aging of such alloys. The electrical conductivity, in general, increases with aging. The explanation for this is that the alloying additions in solid solution are very effective in scattering the conduction electrons. As precipitation occurs the resistivity per solute atom decreases, which in turn increases the conductivity. On the other hand, the hardness increases due to precipitation hardening, at least up to peak hardness conditions. Loss of coherency with the matrix and growth of particles reverse the latter trend. In the authors' efforts to characterize the thermal history and the mechanical properties of Al-Li alloy 2090 by NDE techniques, they have noted a strongmore » deviation from the general rule that the conductivity increases with aging. This deviation occurs on samples aged at 200/sup 0/C for extended periods. Noteworthy is the fact that Al 2219 does not show such a conductivity anomaly with aging. In an attempt to understand this phenomenon, Transmission Electron Microscopy (TEM) was used to determine the morphology and crystal structures of the phases present in appropriate samples.« less

Magnetic nanoparticle fluids have numerous biomedical applications, including magnetic imaging, drug delivery, and hyperthermia treatment for cancer. Ideal magnetic nanoparticle fluids have well-separated, biocompatible nanoparticles with a small size distribution that form a stable colloid. We have combined inert-gas condensation, which produces nanoparticles with low polydispersity, with deposition directly into a surfactant-laden fluid to prevent agglomeration. Iron, cobalt, and iron-nitride nanoparticle fluids fabricated using inert-gas condensation have with mean particle sizes from 5–50 nm and remain stable over long periods of time. Iron and cobalt nanoparticles oxidize on exposure to air, with oxidation rates dependent on surfactant type and concentration. Iron-nitride fluids are more oxidation and corrosion resistant, while retaining the same high degree of colloidal stability. Magnetic properties vary depending on the nanoparticle size and material, but can be varied from superparamagnetic to ferromagnetic with coercivities on the order of 1000 Oe. In addition to future biomedical applications, inertgas condensation into fluids offers the opportunity to study interparticle interactions over a broad range of intrinsic materials parameters and interparticle separations.