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The complete spin polarization of half metallic ferromagnets is destroyed by finite-temperature spin disorders. Polarization declines at finite temperatures due to magnon and phonon effects and hence half-metallic ferromagnetism is limited to zero temperature.

A nucleation-based analytical methodology helps enhance the magnetic strength of aligned two-phase magnets by exchange hardening in nanoscale combinations of a soft-phase and an oriented hard-phase. Breakdown of this high energy magnet occurs in the limit of isotropic magnets having enhanced remanence. The high cost of production of such giant-energy magnets limits their range of application.

The study of the reaction between nitrogen gas and an intermetallic compound with particular reference to Sm2Fe17, treating the Sm2Fe17N(sub y) system as a gas solid solution, shows that there is a large uniaxial strain near the surface of nonuniformly nitrided particles and even in the absence of nitrogen there is core expansion. The reaction of nitrogen atoms with the metal lattice in terms of the net reaction energy U(sub 0) is described by a simple lattice gas models. The equilibrium nitrogen concentration as a function of nitrogenation temperature and gas pressure is calculated.

The gas phase interstitial modification of rare-earth intermetallics is studied. Net reaction energies for nitrogen in Sm2Fe17 and Nd(Fe11Ti) are U0 = - 57 kJ/mole and U0 = - 51 kJ/mole, respectively. The equilibrium nitrogen concentration is calculated as function of temperature and gas pressure using a simple lattice gas model. For nitrogen in Sm2Fe17, refined diffusion parameters D0(N) = 1.02 mm2/s and Ea(N) = 133 kJ/mole, determined by thermopiezic analysis of the initial stage of nitrogen absorption, are used to calculate nitrogen profiles and the time dependence of the mean nitrogen content during nitrogenation. Similiar values are obtained for nitrogen in Nd(Fe11Ti), whereas the activation energies for hydrogen in Sm2Fe17 and Nd(Fe11Ti) are 31 kJ/mole and 45 kJ/mole, respectively. The elastic stress and strain profiles during nitrogenation are calculated. Important results are a large uniaxial strain near the surface of non-uniformly nitrided particles, and core expansion even in the absence of any nitrogen there. Curie temperature and K1 profiles are calculated and suggestions are made regarding the influence of stress on coercivity and disproportionation of the material.

The structural and magnetic properties of substituted [L1.sub.0] compounds are studied. It is shown that ordering has a strong impact on the magnetism of the alloys, particularly on the anisotropy.

Magnon-plasmon interactions are modeled by considering the spin-dependent dielectric response of atom placed in crystalline environment. Magnetic excitations of intra-atomic origin are analyzed which are found to be related to ordinary magnons but involve longitudinal magnetic degrees of freedom and involve much higher energies.

The temperature dependence of the magnetic anisotropy of ferromagnetic materials is analyzed. The findings conclude explain that magnetocrystalline anisotropy is, essentially, a single-ion property by embedding the atom in a metallic or nonmetallic crystalline environment.

Intergranular interactions in nanostructured FePt:Ag thin films and their effect on magnetic hysteresis are investigated. The films, produced by muitilayer deposition plus rapid thermal annealing, consist of FePt nanoparticles embedded in a silver matrix. They are investigated by magnetization measurements and magnetic force microscopy. Analytical model calculations, supported by micromagnetic simulations, are used to elucidate the relation between coercivity, hysteresis-loop slope, and spatial correlations during magnetization reversal. The analytical calculations yield simple expressions for the loop slope and the coercivity as a function of the intergranular exchange. Small intergranular exchange enhances the coercivity, but for strong exchange there is a self-energy cutoff, associated with the onset of cooperative reversal and preventing alpha from becoming negative. Index Terms--Anisotropy, magnetic recording, magnetization reversal.

High-coercivity CoPt magnetic force microscope tips have been modified by focused ion beam milling to improve the resolution of magnetic domain images. The magnetic materials around the apex have been removed, leaving a 30-nm diameter magnetic particle at the tip end. Due to the smaller amount of magnetic material, the stray field from this new tip is significantly reduced, and the spatial resolution of the magnetic domain images is improved. The tip is used to obtain high-resolution domain images of a CoCrPt-Si[O.sub.2]/Ru perpendicular recording medium with linear recording densities from 800 to 1000 kfci. Magnetic patterns of 900 kfci, corresponding to a bit size of 28 nm, are well resolved. From the analysis of the power spectrum of the track profiles for these images, a spatial resolution as good as 11 nm under ambient conditions with a commercial magnetic force microscope is achieved. Index Terms--Domain images, focused ion beam technology, magnetic force microscopy, magnetic recording.

Electron microscopy, x-ray diffraction and superconducting quantum interference device magnetometry are used for examining the FePt and Fe3O4 nanotubes produced by hydrogen reduction in nanochannels of porous alumina templates. Fe3O4 tubes are formed by a thermally decomposed Fe nitrate solution at 250 degrees C that is reduced in hydrogen for 2.5 h at the same temperature.

The magnetic properties and switching behavior of anisotropic magnetic nanodots are examined. A strong interdot interaction is observed in dot separations of less than 50 nm resulting in a probable controlled switching of neighboring dots.

Linear muffin-tin orbital calculations were used to examine the electronic band structure of ordered equiatomic compounds of 3d transition elements (Mn, Fe, Co, Ni) with nonmagnetic 4d and 5d elements (Rh, Pd, Pt, Ir). Mn spins in a given plane prefer to align antiferromagnetically as indicated by the pronounced negative exchange interactions between four Mn-Mn first nearest pairs, J(sub 11) observed in all Mn compounds.

The temperature dependence of the magnetocrystalline anisotropy of PtCo and its atomic origin are investigated by first-principle and model calculations. The Pt spin moment necessary to realize the leading 5d anisotropy contribution is due to neighboring Co atoms. At finite temperatures, Co spin disorder strongly reduces the Pt moment and the anisotropy. This is in contrast to the situation encountered in 3d and 3d-4f magnets, where the atomic magnetic moments remain largely conserved, even above the Curie temperature. A consequence of the L[1.sub.0] mechanism is that the [K.sub.1] (T) curve of exhibits a negative curvature, in contrast to the unfavorable positive curvature for rare-earth transition-metal magnets. Index Terms--Anisotropy, finite-temperature magnetism, inteatomic exchange, L[1.sub.0] magnets, permanent magnets, PtCo.

The Curie temperature of rare-earth Co intermetallics is investigated by self-consistent spin-polarized electronic-structure calculations on Y--Co compounds. The total exchange interaction of a given site with all other sites ([J.sub.o) is calculated by the linear-muffin-tin-orbital method using the local force theorem and employed to obtain mean-field Curie-temperature estimates. The theoretical predictions for Y[Co.sub.3], Y[Co.sub.5], and [Y.sub.2][Co.sub.17] are in fair agreement with the experimental Curie temperatures. For Y[Co.sub.5], the variation of exchange interactions ([J.sub.ij]) with distance is analyzed, and it is discussed how the presence of nonequivalent cobalt sites affects the Curie temperature of the compounds. Index Terms--Curie temperature, exchange interactions, magnetic moment, permanent magnets, rare-earth cobalt intermetallics, Y[Co.sub.5].

Research into cooperative and noncooperative magnetization processes in magnetic nanostructures is presented. It is found that the Preisach model overestimates the coercivity. In general, cooperative effects are strongest for narrow switching-field distribution.

Research into the magnetism of antimony overlayers on a ferromagnetic substrate is presented. This approach produces a layer-specific analysis of the spin polarization. The relatively long range of the Sb spin polarization is attributable to the semimetallic nature of the Sb overlayer.

The net Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between well-separated spin distributions can be mapped onto a RKKY interaction between two point-like effective moments. In 4f metals and alloys, the RKKY interaction gives rise to a magnetoelectric two-ion anisotropy.

A study was conducted to analyze the effects of the shape of the energy landscape on the magnetic viscosity. The evolution of a quantum-mechanical system was characterized by the time-dependent Schrodinger equation. Experimental results indicated that the activation energy related to thermally activated hopping changes the magnetic viscosity by minimizing the attempt-frequency prefactor.

A study was conducted to analyze magnetic hardening in SmCo(sub x)-Co multilayers and heat treated nanocomposite films. The films were prepared by dc and rf sputtering. Magnetization loops were determined by an alternating gradient force magnetometer and a superconducting quantum interference device magnetometer. Experimental results indicated that a thick chromium underlayer is needed for magnetic hardening.

The anisotropy of fee (111) Fe/Ni and Fe/Ni/Fe layers is investigated. The films exhibit an oscillating behavior of the preferential magnetization direction depending on whether the surface layer is Ni or Fe. Anisotropy fields are obtained from polar and perpendicular Kerr hysteresis loops and yield a comparatively small perpendicular Fe/Ni interface anisotropy of about 0.15 mJ/[m.sup.2]. The real-space origin of the interface anisotropy is the interlayer hybridization of the yz, zx, and [z.sup.2] orbitals. Index terms - interface anisotropy, ultrathin films, Kerr hysteresis

The diffusion of nitrogen in R(sub2)Fe(sub17) intermetallics by a method that reconciles the solid-solution and immobilization theories of nitrogen diffusion, has been studied. Two-sublattice diffusions may lead to sharp concentration profiles, although the phase structure of the nitride remains unchanged. There is a global relaxation time, that controls the smoothing of concentration gradients.

The crystal-field parameters [A.sub.20] and [A.sub.40] were determined from the magnetocrystalline anisotropy constants [K.sub.1] and [K.sub.2] in a linear approximation for [Sm.sub.2][Fe.sub.17][Z.sub.x] (Z = N, C) compounds. For the materials investigated, the values of [K.sub.1] and [K.sub.2] in a temperature range from 4.2 - 533 K have been obtained by a fit of demagnetization curves. The parameters [A.sub.n0] are calculated in two ways: i) from the [K.sub.i] at zero temperature and ii) from the temperature dependence of the [K.sub.i]. Both methods give equivalent results. The value [Mathematical Expression Omitted] has been obtained which corresponds to an inverse THOMAS-FERMI screening length q [approximately equal to] 2.3 [[Angstrom].sup.-1] calculated within the framework of the screened charge model.

The expansion of magnetic domains in thin films with perpendicular anisotropy is investigated. To determine the domain-wall-velocity as a function of the applied magnetic field a selfconsistent magnetic-viscosity approach is used. The main predictions of the theory are a linear behaviour in the limit of moderately strong fields, a quasi-exponential behaviour for fields close to the propagation field, and a negative velocity for very small and negative fields. The predictions of the theory are compatible with domain-wall investigations on Au/Co/Au sandwiches.

Elastic and magnetic properties of ultrathin iron films on tungsten(110) are investigated. In situ film stress measurements during growth show stress values of 25 GPa per deposited monolayer. Our experiments indicate that the tremendous film stress triggers the formation of a misfit dislocation network at a coverage of 1.5 monolayers. The effect of the film stress and its spatial variation on the magnetic behavior are discussed. We find an high coercivity of order 0.3 T for 1.5 monolayer thick films. A model is presented that explains the high coercivity in terms of strong domain wall pinning.

The magnetism of sesquilayer bcc iron films on W(110) is investigated. Coercivity data and theoretical calculations indicate that the freezing of the magnetization at low temperatures reflects exchange-dominated domain-wall pinning rather than superparamagnetic spin-glass behaviour.

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 impact of interstitial nitrogen on the phase transition and the magnetocalroic effect observed in the Mn(As,Si) systems. The Curie temperature of the systems is shown to increase with nitrogen atoms and decrease with silicon addition.

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.

The studies related to optical, structural, and magnetic properties of two substantially different cobalt nanostructure thin films deposited at an oblique angle of incidence of 85 degree away from the substrate normal are reported. The results from comparison between an achiral columnar thin film grown without substrate rotation and a chiral nanocoil sculptured thin film by glancing angle deposition with substrate rotation are also presented.

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.