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Fine cobalt and silver powders have been ball-milled to yield a granular solid of composition [Co.sub.30][Ag.sub.70] in the form of coarse powder. The material is an intimate mixture of grains of fcc Co in a silver matrix. The cobalt is in the single-domain size range, and the samples exhibit coercivity (0.07 T at 296 K) and unusual thermomagnetic effects, including field-induced unidirectional anisotropy. There is a large, isotropic negative magnetoresistance, which exceeds 10% at 4.2 K.

Size effects in two-phase Boolean magnets composed of an aligned hard phase and a soft phase with high magnetization are investigated. In 'overcritical' magnets, where the size of the soft regions is larger than the Blochwall width [[Delta].sub.h] of the hard phase, the energy product is reduced compared to the corresponding 'undercritical' magnets with small soft regions, where theoretical energy products as high as 1 MJ/[m.sup.3] have been predicted. Nevertheless, the theoretical energy product only gradually drops with increasing size of the soft regions, and it may still exceed the theoretical energy product 516 kJ/[m.sup.3] of [Nd.sub.2][Fe.sub.14]B.

Non-equilibrium nitrogenation of transition-metal rich rare-earth intermetallics can be used to increase the nitrogen content beyond its equilibrium concentration. For example, nitrogenation of [Sm.sub.2][Fe.sub.17] using ammonia yields volume expansions up to 8.3 vol %, which correspond to a composition [Sm.sub.2][Fe.sub.17][N.sub.x] with x [approximately equal to] 4. This effect is related to catalytic action at the metal surface where ammonia is decomposed into nitrogen and hydrogen, with nitrogen absorption on a site where it is weakly bound, as an intermediate step. For overloaded [Sm.sub.2][Fe.sub.17][N.sub.x] with x > 3 the net reaction energy [U.sub.o] = 5 [+ or -] 10 kJ/mole indicates a nearly temperature-independent occupation of the non-9e sites.

Exchange hardning of nanostructured two-phase systems composed of an aligned hard phase and a soft phase with high magnetization is investigated using a micromagnetic approach which accounts for interactions between the soft regions. For Sm2Fe17N3 (2.5 nm)/Fe65Co35(9nm) multilayers an energy product as high as 1 MJ/m cube (120 MGOe) is predicted, with a rare-earth content of only 5wt%. Giant energy products may also be achieved in suitable cellular and disordered structures.

A lattice gas model was used to characterize interstitial modification of the rare-earth intermetallic compound R2Fe17Zx, R=Y,Sm and Z=N,C,B,Si and S. The results showed that solid-state reaction was the most promising method for introducing metalloids into intermetallic lattices. Solid-state reaction can be used at temperatures where hydrocarbon gases would destroy the lattice and features a large entropy of the gas.

The crystal field in the nitrogenated intermetallic compounds Sm2Fe17N3-delta and Sm(Fe11Ti)N1-delta was analyzed. The results showed that the intrinsic crystal field contribution per nitrogen atom was approximately at the same level in both intermetallics. This observation indicated that nitrogen provided a common mechanism of crystal field modification in both compounds. It was shown that charge penetration had negligible effects in the case of the local interstitial but was important in the polarization of non-4f orbitals.

The characteristics of Co/Pd multilayered thin films produced by pulsed laser deposition were investigated. The results showed that the material featured a (111) texture with diffraction patterns typical of a modulated period structure. At low field regimes, magnetoresistance was highly anisotropic and varied by -2% in the transverse configuration and +1% in the longitudinal configuration.

The role played by Zn in the formation of Zn-Fe phases in Sm2Fe17Nx permanent magnets was investigated using x-ray analysis and differential scanning calorimetry. The results showed that the coercivity of the magnet can be enhanced by heat treatment subsequent to the formation of the paramagnetic phase. An observed dip in the demagnetization curve indicated the possible presence of an additional paramagnetic phase.

Coercivity and nucleation fields for three-dimensional inhomogeneities in Sm2Fe17Ny permanent magnets were investigated. The results showed that linearized micromagnetic formulations can be used for calculating the nucleation fields. The lowest eigenvalue of the linearized problem yields the nucleation field. However, it was shown that nonlinear equations must be solved to achieve more realistic coercivity values.

Several model calculations are conducted to explain the different effects of nanostructuring on the magnetic entropy of the magnetic compounds and thin-film nanostructures. Most of the entropy of the compounds is shown to be localized near the grain boundaries.

Several model calculations are conducted to explain the impact of nanostructuring taking place on the various magnetostatic interactions taking place in the permanent magnets. The various mechanisms involved in the nanoscale magnetization processes are also discussed.

Several model and tight-binding calculations are conducted to determine the structural dependence of the magnetocrystalline anisotropy of the various itinerant permanent magnets. The strong oscillations of the anisotropy are shown to be completely tunable by alloying.

Several studies are conducted to explain the permittivity and the permeability of the different Tb-doped and Fe core-shell nanoparticles. The addition of Tb atoms is shown to lead to significant changes in the electromagnetic materials constants and morphology of the nanoparticles.

Several model calculations are conducted to explain the mesoscopic Kondo effect occurring in the different metallic nanoparticles with a magnetic impurity. The magnetic susceptibility of these systems is also determined.

Micromagnetic model calculations are used for examining the magnetism of magnetic surface alloys such as Fe-Pt on Pt(997). The studies have shown that for strong Dzyaloshinski-Moriya (DM) interaction, the zero-field spin structures have changed from uniform to a canted state with a wave vector, and a similar transition has occurred for weak DM interaction when the reverse external field has approached the nucleation field.

The nanostructure and magnetism of [L1.sub.0]-ordered FePt crystallites in matrices of Au and C are examined as a function of the Au and C contents. The magnetic force microscopy images have shown that the slope decrease is accompanied by a reduction in the magnetic correlation length, which is due to the reduced intragranular exchange coupling.

Chromium-doped hydrogenated diamond-like carbon (Cr-DLC) and chromium carbide hydrogenated DLC alloys are prepared by plasma-assisted vapor deposition and examined by x-ray absorption near edge structure spectroscopy and superconducting quantum interference device (SQUID) magnetometry. The heterojunctions have displayed negative magnetoresistance that saturates at than 500 Oe and is suitable for spin-electronics applications.

Model calculations are used for examining the effect of semihard magnetic phases and interphases on the performance of nanostructured two-phase permanent magnets. Very hard nanostructured magnets are created from soft phases with negative but large anisotropy constants.

The growth and magnetism of nanosize Fe clusters on Pt and other metal surfaces are examined. The results have provided ways to control the magnetism of small clusters with the substrate.

The magnetism of ultrasmall Co:CoO core-shell nanoclusters is examined. The proteretic behavior and its particle-size dependence have reflected a subtle interplay between various anisotropies and exchange interactions in the Co and CoO phases and at the Co-CoO interface.

Model calculations are used for examining the magnetization reversal in graded magnetic-recoding media and its effect on the areal density. The results have shown that the write-field reduction has negatively affected the areal density and a trade-off has remained between write field and bit size.

The preparation, structural phase transition and magnetic characterizations of heat-treated monodisperse FePt nanoparticles of 3nm size are described. The results have shown that the transformed 3 nm nanoparticles have a magnetic anisotropy constant that is smaller than those for the bigger particles and the fully ordered [L1.sub.0] bulk phase.

Nanostructured FePt: M (M=C, Ag, Cu) perpendicular magnetic recording media is investigated by numerical simulations and model calculations. The simulations show that intergranular exchange reduces the coercivity of the system, and the magnetization reversal proceeds in a regime between localized nucleation and discrete domain-wall pinning, depending on the intergranular exchange.

A generalized Ruderman-Kittel-Kasuya-Yosida (RKKY) approach is employed to estimate indirect exchange interactions between localized spin in doped magnetic semiconductors. A closed expression with simple geometric interpretation is found in the dilute limit of exchange mediated by two overlapping orbitals.

An attempt is made to examine the structure of micromagnetic energy barriers responsible for slow magnetization processes. Thermally activated slow magnetization processes proceed over energy barriers whose structure is determined by the micromagnetic free energy.

Magnetic properties and L1(sub 0) phase formation of FePt films is investigated by rapid thermal annealing (RTA) and high current-density ion-beam irradiation. The sample prepared by RTA at 550 degree Celsius is found to have (001) texture and strong magnetic perpendicular anisotropy with H(sub c) equal to 6 kOe.

A study of the dependence of magnetic properties in Mn-doped ZnO on sample processing conditions is presented. The ferromagnetism observed at room temperature in the low-temperature-sintered samples is gradually suppressed and finally completely removed, with an increase of annealing temperature.

The high-field spin structure of magnetic perovskites and related magnetoresistive materials is investigated by model calculations. The noncollinear structure, which contributes to the zero-and finite-temperature spin mixing and reduces the magnetorsistance, is strongly field dependent.

The origin and physical nature anisotropic exchange interactions are investigated. The resulting exchange stiffness is anisotropic, even if the interaction is mediated by an isotropic free electron gas.

The potential use of interacting magnetic nanodots for quantum computing (qubit) operations is investigated by model calculations. The results indicated that maximum operation temperature is proportional to the magnetocrystalline anisotropy of the dot material.

The damping of magnetization processes in nanostructures is investigated by Fokker-Planck-type model calculations and quantum-mechanical considerations based on Fermi's golden rule. In the absence of energy barriers, the problem reduces to a magnetic diffusion equation with a particle-size-dependent diffusivity.

An investigation on the Sm-Co/Co hard/ soft multilayers is presented with varying thickness of soft phase layers. The result suggested that the 1min annealing at 525 degree Celsius retains the layer structure unchanged and the hard phase of Sm-Co forms.

Investigations on the structural and magnetic properties of laminated (Nd, Dy)(Fe, Co, Nb, B)(sub 5.5)/alpha-Fe nanocomposites are conducted. The coercivity is found to increase to 1608 kA/m (20.2 kOe) in thermally processed Nd-Dy-Fe-Co-Nb-B(15 nm)/Fe(4 nm) multilayered nanocomposities.

The fabrication of the L1(sub 0)-ordered clusters, location of the clusters after assembly, and the magnetic properties are studied. A scheme is used to assemble FePt L1(sub 0)-ordered clusters through the use of ordered nanopore templates and an external magnetic field.

The Growth and magnetism of FePt:C composites in nanoscale channels was examined. Small cluster size and high coercivity of 29.0 kOe were found in the FePt clusters synthesized with carbon and heat treated at high temperatures.

Model calculations and micromagentic simulations are used for examining the magnetic ground state and the magnetization reversal of aspherical nanoparticles. No domains are present in the dots at the lower end of the size and thickness range and large particles are multidomain with nearly complete flux closure and complex reversal behavior.

The temperature dependence of the spin polarization of half-metallic ferromagnets is analyzed. A unitary spinor transformation indicates that the corresponding spin mixing goes beyond finite-temperature smearing of the Fermi level, leading to a nonzero density of states in the gap of the insulating spin channel and as a consequence half-metallic ferromagnetism is limited to zero temperature.

The localization behavior of spin waves with k vectors parallel and perpendicular to the wire axis and focus on how imperfections affect the localization behavior is discussed. Due to the small radius of wires, the low-lying modes are of the coherent-rotation type, that is, they do not exhibit any special variation in the plane perpendicular to the wire axis.

CoPt hard magnetic films were produced by loading aqueous solution of CoPt mixture salt into PAF and employing hydrogen reduction at elevated temperature. The AFM images reveal that the pores of PAF substrate are partially covered with CoPt particles.

The spin structure, which is modified by imperfections such as grain boundaries and nanojunctions is discussed. A specific result of the calculations is that the spin-dependent scattering depends on the geometry, size, and material of the boundary or junction and exhibits a size-dependent maximum.

Equivalence of the sweep-rate and magnetic-viscosity dynamics is discussed. The physical reason is that sweep-rate experiments are less effective in probing individual switching events than magnetic-viscosity experiments.

Exchange interactions for nanocrystalline materials consisting of hard magnetic particles embedded in insulating matrix are discussed. The large number of adjacent surface atoms yields an enhancement of the exchange which is linear with the particle radius.

Magnetically alloyed SmCo(sub z) and Sm(Co,Cu,Ti)(sub z) magnets is discussed. Short annealing time produces 1:7 phase with higher crystalline anisotropy, which results in larger coercivity. Mechanically alloyed SmCo(sub z) and Sm(Co,Cu,Ti)(sub z)magnets.

The nanomagnetic behavior of Co-C nanodot arrays investigated by magnetic force microscopy (MFM) and an alternative gradient force magnetometer is presented. The direction of the easy axis is observed directly with MFM by comparing the saturated magnetization state and the remanent, magnetization state.

The solutions of nucleation problems for particles and particle arrays with perpendicular anisotropy are presented. In rings of equidistant dots, interactions between identical particles lead to cooperative effects.