An earlier theory of the exchange coupling between two ferromagnets separated by a nonmagnetic transition metal spacer was based on size quantization of the electron energies in the spacer. It is now generalized to include the effect of hybridization between the conduction and d bands both in the ferromagnet and in the spacer. The new theory thus unifies the approach based on coupling via d electrons, valid for transition metal spacers, with RKKY-type theories for noble and simple metals which rely on coupling via conduction electrons. The theory is applied to calculate the period and strength of the long-period oscillatory coupling in (001) CO/Cu trilayer.

The origin of oscillatory interlayer coupling via Cu is explored in sputtered Co/Cu Multilayers by varying the hole concentration in the copper layers by doping with elements of different valence. Detailed studies were carried out for a series of Cu-Ni alloys. The oscillation period of pure Cu is observed to increase monotonically with increasing Ni concentration and is almost doubled for 40 atomic % Ni. The increase in oscillation period can be accounted for by considering changes in the topology of (he Fermi surface of the alloy resulting from the change in band Tilling.

The Magnetoresistive properties of sputtered Ni8.1Fe1.9/Ag Multilayers have been investigated as a function of both Ag and NiFe layer thicknesses and thermal treatments. For the virgin sample, the Magnetoresistance (MR) ratio at room temperature goes through a maximum of 17% for a Ag thickness of about 11 A. In addition, the R (H) curve is found to be perfectly linear and reversible. Contrary to the MR ratio, the saturation field is observed to decrease continuously as the Ag thickness increases, leading to an increasing slope of the R (H) curves. Upon annealing, we observe both an increase of the MR ratio and a decrease of the saturation field, leading to a three fold increase of the MR slope for annealing temperatures of 280°C. Such a behavior appears to be highly dependent on the layer thicknesses.

The Magnetoresistance (MR), Magnetic properties, and crystal structure of dc magnetron sputtered CO/Ag periodic multilayers have been investigated. The Co layer thickness was fixed at -30 Å while the thickness of the Ag layer was systematically varied. ‘Giant’ magnetoresistance was observed. The MR ratio has been found to decline monotonically with increasing Ag thickness in the range 30 Å to 107 Å. Although the maximum room temperature MR ratio is a Modest 4.78%, a more technologically significant measurement of field sensitivity (MR ratio/FWHM of the MR vs. H peak) is a promising 0.1%/Oe at its best. The effect of the number of bilayer units has also been examined and no substantial differences were noted between multilayers containing 8, 9, and 10 bilayer units. Coercivities as determined by both magnetometer and the splitting of the MR peaks are in agreement and increase from 25 to 38 Oe with increasing Ag thickness. Evidence for antiferromagnetic coupling is apparent in the hysteresis loops. High angle X-ray diffractometry (HXRD) in the θ-2θ mode revealed a strong Ag (111) texture in the film, with satellite peaks indicating a layered structure. Low angle XRD (LXRD) also yielded broad superlattice peaks in all samples at least to the second order.

The giant magnetoresistance effect in antiferromagnetically coupled Fe/Cr Multilayers has been attributed to spin dependent scattering at the interfaces between the constituents. One possible source of this spin dependent scattering is chromium impurities in the iron layers due to intermixing at the interfaces. Annealing the films can promote the diffusion of the components, increasing the impurity concentration and therefore the Magnetoresistance. For this study Fe/Cr Multilayers were annealed at several temperatures and for several durations. Annealing at moderate temperatures (∼ 350°C) increases the Magnetoresistance, while higher temperature anneals (∼ 600°C) cause the magnetoresistance to disappear completely. Long anneals at 330°C (> 100 hours) also reduce the Magnetoresistance. VSM Measurements indicate that the antiferromagnetic coupling is reduced in the annealed samples but show no evidence of Magnetically “dead” alloy layers. Low angle X-ray diffraction indicates that the structural effect of annealing is very subtle in comparison to the significant magnetic effect.

X-ray photoelectron spectroscopy (XPS) has been used to investigate grain boundary diffusion of Cu and Cr through 1000 Å thick Co films in the temperature range of 325°C to 400°C. Grain boundary diffusivities were determined by modeling the accumulation of Cu or Cr on Co surfaces as a function of time at fixed annealing temperature. The grain boundary diffusivity of Cu through Co is characterized by a diffusion coefficient, D0gb, of 2 × 104 cm2/sec and an activation energy, Ea,gb, of 2.4 eV. Similarly, Cr grain boundary diffusion through Co thin films occurs with a diffusion coefficient, Do,gb, of 6 × 10-2cm2/sec and an activation energy, Ea,gb of 1.8 eV. The Co film microstructure has been investigated before and after annealing by x-ray diffraction and transmission electron Microscopy. Extensive grain growth and texturing of the film occurred during annealing for Co deposited on a Cu underlayer. In contrast, the microstructure of Co deposited on a Cr underlayer remained relatively unchanged upon annealing. Magnetometer Measurements have shown that increased in-plane coercivity Hc, reduced remanence squareness S, and reduced coercive squareness S* result from grain boundary diffusion of Cu and Cr into the Co films.

We have used polarized neutron reflectivity to prove the existence of oscillatory coupling in MBE-grown Co/Cu (111) superlattices. For a sample of composition [3.4 nm Co/2.0 nm Cu]10, we find that only a small fraction of the sample volume exhibits coherent antiferromagnetic order, with the structure of the remainder of the film being attributable to ferromagnetic domains and small disordered structures.

In-situ recording of ultra-thin film growth by Low Energy Electron Microscopy (LEEM) results in accurate determinations of monolayer metal deposition rates for difficult to calibrate deposition geometries. Deposition rates and growth features were determined for Cu and Co on W (110) allowing for thickness control at the submonolayer level. Also, the transparencies of non-Magnetic overlayers of Pd (111) and Cu (111) to very low energy spin polarized electrons were compared and qualitatively explained by band structure considerations. Cu (111) is much more transparent than Pd (111) so that magnetic domain structures can be observed through at least 4 nmof Cu (111). This suggests the use of Cu (111) and other metals of suitable band structure as protective layers for surface magnetic studies.

Magnetic circular dichroism in the Fe 2p x-ray absorption is observed in multilayers of (Fe9.5Å/Pt9.5Å)92. The Magnetization and helicity are both in the plane of this multilayer which is prepared by magnetron sputter deposition. This sample is part of a study to examine magnetization in the ternary multilayer system of FeCo/Pt. Lattice and layer pair spacings are measured using x-ray scattering. The atomic concentration profiles of the multilayer films are characterized using Auger electron spectroscopy coupled with depth profiling. Conventional and high resolution transmission electron microscopy are used to examine the thin film, growth morphology and atomic structure.

A study has been made of the magnetic properties of epitaxial 6 Monolayer (ML) fcc-Fe films on Cu (100) with various thicknesses of epitaxial Cu deposited on top of the Fe. It was found that the magnetic properties undergo striking changes as a function of the Cu thickness. The easy axis of magnetization goes from being in-plane for the bare Fe to perpendicular upon the deposition of 1 ML Cu. Concurrently there is a dramatic decrease in the Kerr signal intensity at saturation. Upon depositing a second ML of Cu the Kerr signal intensity more than doubles, and the easy axis remains perpendicular. For Cu overlayers of 3 ML to 10 ML the Kerr signal intensity at saturation gradually diminishes to below the level of detectability, as if the Fe were nonmagnetic. A superlattice consisting of 60 ML Cu/ (6 ML 57Fe/10 ML Cu)×5/Cu (100) was fabricated and studied at room temperature by conversion electron Mòssbauer spectroscopy. The results confirmed that the Fe is indeed nonmagnetic. The four inner Fe layers of the 6 ML film have the same isomer shift as bulk fcc-Fe in precipitates in Cu, and the two boundary Fe layers exhibit an asymmetric quadrupole doublet.

The stable structure of cobalt is hexagonal closed packed (hep), but cobalt can be stabilized in the face centered cubic structure (fee) by epitaxy on Cu (100). These films are ferromagnetic with [110] in plane easy axis. The Magnetic anisotropies of these films strongly depend on their structure, and in particular to the possible deviation from the isotropie fee structure. We have studied these films by surface EXAF.S. By recording the spectra both in normal incidence and in grazing incidence we have shown that the Co/Cu (100) films have a face centered tetragonal structure: the mean nearest neighbour distance parallel to the surface is 2.55 Å (same value as in bulk copper) and the interlayer bonds length is 2.50 Å (same value as in bulk cobalt). We conclude that the films are in perfect epitaxy on copper (100) with a contraction of the lattice parameter perpendicular to the surface of 4%. A constant tetragonalization is observed for films of 2 to 15 Monolayers.

We present a comparative in situ RHEED and Polar Magneto-optic Kerr Effect study of the first stages of the growth of a Au overlayer on top of a (111) Co ultrathin film. Drastic behaviours are evidenced on the RHEED diagram, Magnetic anisotropy and coercive force, around 1,5 ML of Au coverage.

The spin-polarized band calculations for the iron nitrides, Fe3N, Fe4N and Fe16N2, have been performed with use of LMTO-ASA Method in the frame of local spin density functional formalism. The results show that the most distant Fe atoms from N have the largest magnetic moment. The central role of the N atom is to bring about the large magnetic moments through the lattice expansion. Concurrently, the N atoms promote an itinerancy of electrons and then in turn prevent the exchange-splitting. This results in an Fe16N2 with the lowest N concentration having the largest magnetic moments. Quantitatively, the obtained magnetic moments are in fair agreements with the experimental results except for Fe16Nr The calculated magnetic moment of Fe6N2 is about 2.4 ΜB/Pε, while the measured value is reported as 3.5 ΜB/FB. The orbital magnetic moment of Fe16N2 is about 0.07 ΜB, which is too small to make up for the difference from the experimental value.

Giant Magnetoresistance (GMR) and soft magnetic properties together with their structural characteristics were investigated for Ni66Fe16Co18/Cu Multilayers. The Multilayers were prepared by the conventional rf sputtering method on glass or Si substrates using various buffer layers including Fe, NiFeCo, NiFe and CoZr. Although Most of the multilayers exhibited (111) preferred orientation, Fe buffered multilayers showed a considerable (200) X-ray diffraction peak at Cu thicknesses around 1 nm and 2.2 nm which corresponded to the peak positions of GMR. By using fee or amorphous underlayers the (200) diffraction intensity decreased while antiferromagnetic coupling strength was much reduced. Cross-sectional transmission electron micrograph revealed that the (100) oriented multilayer was grown on the (100) oriented Fe underlayer. By controlling the crystal orientation and the layer structure, significantly large magnetoresistance ratio of more than 10 % can be achieved in a field as low as 30 Oe.

We present a theoretical study of the combined effect of spin valve and anisotropie magnetoresistance in NiFe/Cu/NiFe layered thin films, using an extended form of the semiclassical Camley and Barnás Model for electron transport. The anisotropie magnetoresistance is treated by introducing spin-dependent anisotropie mean free paths in the NiFe layers. From calculations of both magnetoresistance effects as a function of NiFe and Cu thickness, we discuss the validity of a description of the combined effect in terms of a simple summation of spin valve and anisotropie Magnetoresistance.

Magnetic, Magnetotransport and structural properties of Cu/Co/Cu/NiFe/Femn spin-valve structures were studied before and after sequential annealing in the temperature range 240–360°C. Since no extended interdiffusion is observed, the overall deterioration of the magnetic and magnetoresistive properties of the spin valve is believed to originate from morphological and structural changes. In particular, annealing was found to decrease the magnetoresistive properties of Co as a result of structural changes within the Co layer and at the CO/Cu interface. These changes are accompanied by modifications of the magnetic properties. For annealing temperatures above 240°C, strong grain growth within the Co layer and increasing amount of fee Co explain the increased magnetic hardness of this layer.

We discuss shortly some problems that have been met in recent systematic calculations of the magnetic anisotropy energy (MAE) performed by the present authors as well as in studies of other investigators. As an example, we present MAE for ferromagnetic (001) bilayers with antiferromagnetic inter-plane coupling and for an antiferromagnetic (001) Monolayer. It appears that antiferromagnetism can invoke specific effects and under certain conditions, both MAE and magnetic orbital moment are strongly enhanced.

The ground state spin configuration of antiferromagnetically coupled ferromagnetic thin films is determined by competition between anisotropies, interlayer exchange and the applied magnetic field. It is shown that many details of a ground state spin configuration can be obtained by studying the behavior of the spin wave frequencies as functions of propagation direction and applied field strength. A sensitive dependence on the relative film thicknesses is found for small applied field strengths.

Epitaxial Ni/Cu (001) films grown on Si (001) by Molecular Beam Epitaxy were studied in-situ using the Surface Magneto-optic Kerr Effect (SMOKE) and ex-situ with a Vibrating Sample Magnetometer (VSM). Perpendicular Magnetization is observed for Ni thicknesses 15 Å ≤ h ≤ 60 Å and fully in-plane magnetization for h ≥ 70 Å when the films are characterized in-situ. The reversal in magnetic anisotropy observed in-situ at 60 Å shifts to 125 Å when the films are exposed to air. 100 Å Ni films deposited on Cu1−x-Nix alloy substrates also show a reversal in magnetic anisotropy as x is changed. These results suggest that changes in magnetic anisotropy correlate with misfit strain accommodation.

High resolution Kerr Microscopy has been used to study newly developed Co25Pt75 alloy films with perpendicular magnetic anisotropy. In particular, the dynamics of magnetization reversal processes wase investigated by means of time resolved domain pattern analysis. Domain wall motion dominated magnetization reversal as well as nucleation dominated processes were observed. Magnetic aftereffect phenomena were confirmed by relaxation measurements of magnetic domains. The fractal dimension of the observed domains is correlated to the macroscopic coercivity determined from hysteresis loop Measurements.