Pd-rich Co-Pd alloy films are well known to exhibit perpendicular anisotropy. In this study, Co35Pd65 films were made by the vapor deposition method. The thickness of the films ranged from 80 to 2000 Å. Following measurements were carried out on each film sample: the impurities and alloy compositions were checked by Auger depth profile analysis (AES), the surface topology was mapped out by an atomic force microscope (AFM), the structural analysis was done by using the X-ray diffractometer (XRD), and the magnetic properties, such as magnetic anisotropy and saturation magnetization, were measured by a SQUID magnetometer and/or a MOKE (using the longitudinal or polar effect) apparatus. Magnetic quantities, such as the out-of-plane (either hard or easy axis) squareness ratio Mr/Ms, saturation magnetization Ms, and anisotropy energy Ku, are closely related to the structural properties, such as the degree of (111) texture, grain size D, mode of growth (nucleation texture or growth texture), and impurities in films. The emphasis is placed on the thickness dependence of these quantities, and the interrelationship among them.

As a probe of the short range chemical and topological order, NMR is useful for structural investigations of magnetic multilayers (interface structure and composition, bulk phases and defects, strains). The magnetic character of the raw data makes it also possible to study local magnetic properties of these composite systems, and to correlate them with local structural features. The hyperfine field is the first output of an NMR experiment which gives a direct insight on the local magnetization in ferromagnets. NMR is also sensitive to the restoring torque exerted on the electronic moment by the local magnetic anisotropy and/or exchange and dipolar couplings. Combined with the fact that the various parts of a sample (atomic planes involved in the interfaces, bulk phases and bulk defects) can be discriminated in the spectra, the magnetic information contained in the data allows to probe quantitatively or, at least, to place on a relative scale, the different magnetic responses of the different parts of a sample. We present here the relevant results which we have obtained in the course of our investigations of Co based multilayers and spin valves (interface magnetic profiles, inhomogeneities of magnetic anisotropy and of magnetic coupling).

Unusual magnetic behaviours occur in thin Fe films grown on Ir(100) by Molecular Beam Epitaxy. Four different magnetic sites are actually observed in these layers by Conversion Electron Mössbauer Spectrometry. The magnetic relaxation phenomena found in the strained FCC structure together with spin wave softening observed in the strained BCC structure point to small magnetic correlations along the growth direction.

We report on the integration of the predicted half-metallic (100% spin-polarized) ferromagnetic Heusler alloy NiMnSb into NiMnSb/Cu and NiMnSb/Ag multilayer structures, and on their magnetic, microstructural and magnetotransport properties. The NiMnSb layer thickness was fixed at 30Å and those of Cu and Ag were varied from 5 to 60Å. The multilayers were characterized using x-ray diffraction (XRD), four-wire resistivity measurements, atomic force microscopy, SQUID magnetometry and magnetotransport measurements. Moderate substrate temperatures (250°C) are shown to be sufficient to produce stochiometric Clb-structured NiMnSb. XRD data confirm that the NiMnSb ultra-thin layers retain their crystalline quality and texture. SQUID measurements shows that the bulk saturation magnetization (∼740 emu/cm3) is maintained and that it is strongly sensitive to interlayer diffusion and roughness. AFM studies show that the surface roughness, which can be as low as 4Å, depends on the choice of spacer layer, layer thickness and substrate temperature. The relationship between the measured magnetoresistance, NiMnSb crystalline quality, magnetic properties and interfacial roughness are discussed.

Tb03.Dy0.7Fe2 (known as Terfenol-D) thin films have been epitaxially grown for the first time with [110] as the growth direction. X-Ray diffraction measurements evidence that the films are strained compared to the bulk alloy. Mössbauer spectroscopy and Kerr rotation measurements show that the easy magnetization direction varies from <116> at 4.2 K to around <133> at 300 K. This variation is different from the bulk case (for which the magnetization is along <100> at 4.2 K and along <111> at room temperature). This effect can be qualitatively understood if we consider the influence of the strains induced by epitaxy on the various energy terms which govern the direction of magnetization.

Pseudomorphic Fe(110) films, deposited on W(110) at room temperature, with a mean thickness of 1.5 monolayers. are composed of double layer islands with a diameter of the order of 10 nm on a monolayer sea. The double layer islands are ferromagnetic (superparamagnetic) below 500 K, the monolayer sea becomes ferromagnetic below 222 K. Magnetic anisotropy is uniaxial in both components. The easy axis is perpendicular to the film plane in the double layer islands and within the film plane (along [110]) in the monolayer sea. The perpendicular anisotropy in the double layer islands apparently is caused by the pseudomorphic strain. The lateral scale for the anisotropy switching roughly coincides with the exchange lengths in both media. The strength of the exchange interaction between double layer islands rapidly increases when the monolayer sea becomes ferromagnetic.

Magnetic and magnetoresistive properties of magnetic thin films deposited on periodically structured substrates have been studied. By using a thermodynamical heat treatment, we activate the step bunching phenomenon on vicinal Si(111) substrates misoriented towards [112] which results in a laterally modulated surface with a period around 0.1 μm. Epitaxial magnetic thin films deposited on these substrates exhibit an in-plane uniaxial anisotropy and a specific magnetoresistive behavior which characterizes the magnetization reversal process. In this contribution, we demonstrate that these properties can also be observed in non-epitaxial structures grown either by molecular beam epitaxy or by sputtering. In particular, magnetotransport measurements show that by varying parameters such as the nature of the magnetic metal, the layer thickness or the strength of the induced anisotropy, we can modulate the interplay between the anisotropy and the exchange stiffness, and, consequently, observe gradual magnetization reversal behaviors between a Stoner-Wohlfarth uniform mode and a non-uniform mode.

We present the results of calculations of the magnetic order in Fe/Cr systems with a mono-atomic step at the interface. The study of such a systems is of particular interest since it is believed that topological defects play an essential role in the exchange coupling mechanism in Fe/Cr multilayered systems. We show that assuming only collinear magnetism, an interfacial step creates a very extended magnetic defect in the Cr layer. On the other hand, when the local magnetic moments are allowed to rotate, the magnetic defect is very localized near the step and the presence of the step induces a non-collinear coupling between the Fe layers in Fe/Cr superlattices.

The perpendicular magnetic anisotropy in Fe/Cu thin film over- and interlayers is investigated in terms of the fully relativistic spin-polarized band theory. The formation of the ground state is addressed and a layer-resolved analysis of the magnetic anisotropy energies for the Fe/Cu(100) and the Cu/Fe/Cu(100) system is presented both for ferromagnetic and anti-ferromagnetic cases.

Micron size particulate arrays of amorphous R-Co (R = Sm and Gd) alloys with a thickness of 200 nm were fabricated on top of a 20 nm thick Nb film by means of e-beam lithography and sputter deposition. The arrays consist of 2 × 2 μm2 square particles with a spatial periodicity of 4 μm along an edge of the square. Interesting oscillations due to the fluxoid quantization were observed both in the transition lines and the magnetization curves of the underlying Nb film. The superconducting state of the Nb film was found to be modulated by stray fields of the square magnetic particles.

Sub-micron size ferromagnetic Fe wires were also prepared in order to investigate the magnetoresistance effect associated with pinning and depinning processes of a magnetic domain wall confined in the wire. Low temperature transport, Lorentz microscopy and electron holography measurements demonstrated a clear change in resistivity associated with the depinning of a pinned single domain wall.

Thickness dependence of the magneto-optical Kerr effects (MOKE) in ultrathin ferromagnetic films, antiferromagnetic films and nonmagnetic films were measured carefully employing wedge shaped samples at room temperature. The oscillations of the polar Kerr ellipticiry with respect to the film thickness and its energy dependence were observed for the Fe and Au ultrathin films, and revealed a formation of spin-polarized quantum well states both in the bcc-Fe (100) layers and the fcc-Au(001) layers.

On the other hand, bcc-Cr (100) ultrathin layers grown on 3ML of Fe(100) layer showed about 2ML period oscillation of the polar MOKE for the photon energy in between 2.25 and 3.75eV, indicating an existence of a long range antiferromagnetic order. The Cr film also showed energy dependent oscillation peaks for the very thin region (d<10ML). The longitudinal MOKE were measured also for Cr samples, and revealed 2ML period oscillation. The mechanism of the MOKE oscillations is discussed from the view points of quantum size effects and the antiferromagnetic order.

The <Atomic Saw> method has been successfully used to cut a Fe thin film, epitaxially grown onto a (001) MgO substrate, into stripes (widths ranging from 1 μm to 100 nm) and boxes (lateral sizes ranging from 1 μm to 3 μm). A structural analysis of these magnetic structures by atomic force microscopy has shown that their geometries are controlled by the plastic strain. A magnetooptical study of the Fe stripes has revealed a surprising uniaxial magnetic anisotropy with an in-plane easy axis perpendicular to the stripes. This strong anisotropy can be explained by an anisotropie relaxation of the misfit between the starting Fe film and the MgO substrate, induced by the cutting into stripes. Magnetooptical experiments on boxes have revealed that the initial cubic symmetry is recovered since, in this case, the relaxation is similar in perpendicular directions. They have also proved that their magnetization reversal is governed by nucleation phenomena.

A new processing technique was developed to synthesize metal-ceramic films containing nano-sized Ni or Co particles embedded in a MgO matrix. Sol-gel solutions were spun on different substrates with varying coefficients of thermal expansion, oxidized by heating in air and reduced to form a metal-ceramic two phase mixture. This method allows the generation of perpendicular magnetic anisotropy by use of residual stresses arising from a coefficient of thermal expansion difference between the film and substrate. Magneto-optical measurements show that the films can have relatively large Kerr and Faraday rotations, and that the metal particles have sufficient vertical magnetic anisotropy to support perpendicular magnetization. The magneto-optical properties of the films are related to the metal particle size, film thickness and substrate choice.

We have integrated nanometer-sized ErAs islands in GaAs, resulting in a nano-composite of paramagnetic particles in a semiconductor. Negative giant magnetoresistance of up to four orders of magnitude is observed at low temperatures. We can control the density and size of the ErAs islands, making this an ideal system to investigate transport in magnetic nano-structures.

We demonstrate that it is possible to deposit a wide range of magnetic features, using photoassisted and electron radiation induced selective area organometallic chemical vapor deposition. Large arrays of identical micron to nano scale Ni features were deposited by these methods. Their magnetic properties were studied by alternating gradient force magnetometry as well as magnetic force microscopy. Our morphological and magnetic measurements show that the structures are spatially well defined, and the magnetic properties are related to the structural shapes of the features.

Low temperature magnetization measurements of individual ferromagnetic particles and wires are presented (0.1 < T(K) < 6). The detector was a Nb micro-bridge-DC-SQUID, fabricated using electron-beam lithography. The angular dependence of the switching field could be explained approximatively by simple classical micromagnetic concepts (uniform rotation, curling…). However, dynamical measurements evidenced nucleation and propagation of domain walls, except for the smallest particles of about 20 nm. The variation of the mean switching field distribution (as a function of temperature and field sweeping rate) and of the probabilities of switching (as a function of temperature and the applied field) allowed to study in details the dynamics of magnetization reversal of individual particles. For sub-micron particles, we found that above a crossover temperature of 1K, the mean switching field and the switching probability follow a thermally activated model. For temperatures below IK, the dynamics of magnetization reversal becomes temperature independent which is interpreted in terms of deviations from the Néel-Brown model of magnetization reversal due to surface roughness and oxidazation. Although this crossovei temperature is much too large to be interpreted with current models of quantum tunneling, such an effect cannot be excluded. Measurements performed on ferromagnetic nanoparticles of good quality (single crystalline and with a diameter smaller than 25 nm), allowed us to show for the first time that the magnetization reversal can be described by thermal activation over the anisotropy energy barrier, as originally proposed by Néel. The observation of telegraph noise strengthens these results. Our measurements open the door to the observation of macroscopic quantum tunneling oí the magnetization in an individual particle containing 103-105 spins.

Planar, micron-scale ellipses patterned from 700Å-thick Co films exhibit nearly-complete suppression of hysteresis when magnetized in-plane along their short axes. Using a combination of Magnetic Force Microscopy and Vibrating Sample Magnetometry, we find that the suppression of hysteresis is associated with the continuous deformation of a dipole field configuration. The presence of hysteresis for in-plane, long-axis magnetization is associated with transitions between topologically inequivalent configurations.

Ultrathin epitaxial Co layers grown on Au(111) show strong perpendicular magnetic aniso-tropy resulting in out-of-plane magnetization in thin films. With increasing Co thickness the increasing contribution of the shape anisotropy leads to a reorientation transition of the magnetization which has already been subject of many other studies. In the dynamic in-situ experiments reported here bulk Au(111) is replaced by epitaxially grown Au(111)/W(110). The high time resolution (0.05 ML Co deposition per acquisition cycle) allows to extract several mechanisms which occur during the spin reorientation transition.

We have studied the variation of the structural and magnetic properties of 5-μm thick self-supported Ag/Ni81Fe19 multilayers upon annealing by means of transmission X-ray diffraction and Mössbauer spectroscopy as well as magnetoresistance (MR) and magnetisation measurements.

In the virgin state, X-ray experiments show that both Ag and NiFe are (111) textured; the (220) in plane distances are 1.3 % smaller for Ag and 2 % larger for NiFe than the bulk values. Mässbauer spectra consist of a pure magnetic sextuplet, meaning that no non-magnetic layer is present at interfaces. The hyperfine field at 4.2 K is found only 3 % smaller than the bulk value and the Curie temperature is estimated from both Mossbauer and magnetisation at about 550 K.

Upon annealing, the (220) Ag distance starts increasing above 250°C, whereas the decrease of the (220) NiFe distance starts at a much lower temperature. The densification of the NiFe layers is accompanied by an increase of the Curie temperature, without any effect on the magnetic moment; both this relaxation and the improved structural quality of the layering are responsible for the increase of the MR ratio from 12 % to 16 % after annealing at 240°C. Although the multilayer structure improves up to 320°C, the appearance of localised defects above 250°C leads to a rapid increase of the remanent magnetisation and to a decrease of the MR ratio.

ZnTe/Zn1-xMnxTe superlattices were grown on GaAs (001) substrates by molecular beam epitaxy. The multi-phonon processes including overtones and combinations of optical phonons have been studied by near resonant Raman scattering in the temperature range 13 K to 300 K. The strain arising from lattice mismatch gives rise to a shift in the optical-phonon frequencies. A two-phonon interface mode of superlattice has been observed and identified for the first time. Strain-induced red shifts of exciton energies related to transitions from the conduction subband to the light-hole and heavy-hole subband have been found by photoreflectance measurements. Experimental results agree well with the calculated strain-induced shift in superlattices.