Co-Cu films of 1000 – 1500 Å thick were produced by means of flash-evaporation technique at 150 K, 400 K, 520 K and 720 K. The Co022Cu078 films produced at 400 K or 520 K exhibit the maximum value of MR of 16.5% at 77 K and 1.5 T. Co-Pt films of 200 Å thick with Pt buffer layers of 200 Å thick were prepared at room temperature (RT) by ultrahigh-vacuum cosputtering. The saturation polar Kerr rotation angles (θk) at RT of CoPt3 film are all larger than those of the Co/Pt multilayered (ML) film of the corresponding composition. The surface morphology, mean grain and magnetic domain sizes, and size distributions of the grains and magnetic domains of the Co alloy films have been investigated by magnetic force microscopy (MFM) and atomic force microscopy (AFM). The results were correlated with those obtained by using MO and optical spectroscopy at both RT and low temperatures (LT) in a spectral ramge of 0.5 – 4.4 eV, and magnetic investigations at both RT and LT including field-dependence measurement of MR. The overall results reflect the changes in the electronic structures and magnetic states of the constituent elements, induced by the structural transformation or correlated with the structures of the films.

We have investigated the soft magnetic properties of new Fe-Cr-Ta-N and Fe-Cr-Hf-N alloy films. Thin films with compositions in the range of Fe-2∼8%Cr-0∼l%Ta (or Hf)-5∼10%N (in atomic %) were prepared by reactive sputtering in a nitrogen-containing atmosphere. The films, most likely nanocrystalline, exhibit excellent soft magnetic properties in the as-deposited condition without any post-deposition heat treatment, e.g., Hc∼l-2 Oe and 4πMs∼15–20 kG. The magnetic properties are highly anisotropie in the film plane as the easy-axis M-H loop is square and the hard-axis loop is linear and closed, with the anisotropy field Ha=20–100 Oe. The films exhibit excellent high frequency behavior even in the GHz frequency range which is attributed to the combination of high 4πMs and relatively high Ha.

J. Mathon has predicted that introducing pseudorandom fluctuations (PRF) in the Co layer thickness could greatly enhance the Current Perpendicular to the Plane (CPP) magnetoresistance (MR) of a Co/Cu superlattice with dimensions comparable to the electron mean-free-path. We have searched for CPP-MR enhancement in sputtered Co/Cu multilayers with Cu layer thicknesses near both the first and second antiferromagnetically coupled peaks in the oscillatory region of the CPP-MR. In both cases, inserting PRF only decreased the CPP-MR.

The interaction of a magnetic (Fe) impurity with the surface of a non-magnetic (Au) semi-infinite host is investigated in terms of fully relativistic spin-polarized first principles calculations. It is shown that the surface induces a magnetic anisotropy on the impurity which is considerably larger than in the bulk. It is also found that the anisotropy constant K(d) is an oscillating function of the distance d between the impurity and the surface with an amplitude which falls as 1/d2 and a period which is determined by the shape of the Fermi Surface of the bulk Au host. However, the question still remains open whether the magnitude of the anisotropy energy is sufficiently large to explain the thickness dependence of the Kondo amplitude B in thin films of dilute FecAu1-c alloys.

Ga1-xMnxAs is a new III-V diluted magnetic semiconductor that can be grown by MBE with Mn concentrations up to x ∼ 0.09. Below a critical temperature Tc, determined by the Mn concentration (about 50 K for x = 0.05) the material becomes ferromagnetic. This is attributed to the magnetic long-range order of Mn-hole complexes, the latter being the result of the strong antiferromagnetic interaction between the holes and Mn 3d spins. Transport and magnetic properties of the Ga1-xMnxAs system are strongly correlated. Above Tc, all samples show transport behaviour characteristic for materials near the metal insulator transition. Below Tc, resistivity decreases as the magnetic ordering sets in. When the magnetisation has reached its saturation value (below ∼ 20 K), variable range hopping is the main transport mechanism. Also, a negative magnetoresistance is observed below Tc.

The role of the sputtering parameters on the properties of thin A12O3 and A1N insulator layers for spin dependent tunneling junctions was studied. A12O3 insulators were prepared by rf sputtering from an A12O3 target in an Ar or Ar-O2 atmosphere and also by plasma oxidation in an O2 atmosphere of a thin Al layer. The thin Al layer was deposited by rf sputtering at room temperature. A1N was prepared by reactive sputtering from an Al target in a Ar-N2 atmosphere. The index of refraction n measured by ellipsometry, was used to optimize the sputtering parameters, and chemical etch rates were used for information on pin-hole density. The aimed values were n=1.75 for A12O3 (corundum structure) and n=2.2 for A1N. For reactively sputtered A12O3, under optimized deposition conditions, n reaches 1.65 for films 300 Å thick. A12O3 thin layers fabricated by plasma oxidation of a thin Al film were also prepared but the oxide layer was too thin for ellipsometry characterization. A1N insulating films show a constant n value of 1.92 from 400 Å down to 60 Å thick films. Rutherford backscattering analysis show that the ratio of Ar to N2 must be less than 1 to avoid O2 incorporation in the film. Junctions of the type glass/buffer/FM/insulator/FM, where FM is either Co or NiFe, were made by contact metal masks with a junction area of 0.25 mm.2 The A12O3 deposited by sputtering from an A12O3 target under conditions expected to give n>1.5 had a magnetoresistance at room temperature MR(RT) of 2.5% with a junction resistance Rj of 2.2 m Ω and by fitting the I-V curve to existing tunneling theory gave an effective barrier thicknesst of 20 Å and a barrier heightΦ of 2.2 eV. These occurred in only one sample (9 junctions) and were not reproducible. The A12O3 insulators prepared by plasma oxidation of a thin Al layer gave a MR(RT)= 4%, tj = 22 Å, Rj=250 k,Ω and Φ =1.4 eV. The A1N insulator with n =1.9 gave a MR(RT)= 1.6 %, t = 20 A, Rj = 4.8 kΦ and barrier height 1.2 eV. In the last two cases junctions with MR at room temperature can be produced with reasonable reproducibility, Al2O3 samples showed a 15–20% increase in MR as the temperature was lowered to 17 K, while AIN junctions show an increase of a factor of 2 in MR at 77 K.

A study of ferromagnetic/ferromagnetic Ni/Co multilayers grown by DC magnetron sputtering with component layer thicknesses between 40 and 5 Å is presented. Structural characterization by small-angle x-ray reflectivity reveals high-quality layered structures with a well-defined composition modulation along the film growth direction. Quantitative interpretation of the superlattice structure parameters, including interface roughness and intermixing, has been performed by modelling the x-ray reflectivity data. Measurements of the magnetotransport properties of these multilayers indicate that the magnetoresistance (MR) effect, Ap ∼ 0.35 μΩ-cm, is roughly constant over the entire compositional range. We attribute the origin of this effect to anisotropie magnetoresistance (AMR). The MR ratio Ap/p, which is as high as 3.0% in a SiO2/(Ni40Å/Co5Å)×6 multilayer with saturation field ∼ 80 Oe, is therefore more strongly dependent on the zero-field resistivity. By fitting a semi-classical model of conduction in multilayers to the resistivity thickness variation, we extracted the mean free paths for conduction in each of the constituent layers as well as the contribution of interfacial scattering in the superlattice structure.

Magnetoresistance (MR) measurements have been performed on two series of Co(3.2 nm)/Ru(x=0.5 to 3 nm)/Co(3.2 nm) and Co(3.2 nm)/Ru(x)/Co.92Ru.08 (3.2 nm) sandwiches prepared by ultra high vacuum evaporation onto mica substrates. At 300 K, all samples of the first series present giant magnetoresistance (GMR) whereas the samples of the second series, and with the same Ru spacer thickness, show an inverse GMR. This inverse GMR is induced by alloying the second Co layer with 8 at% Ru and can be attributed to the change of the scattering coefficients ratio (α) between the two magnetic layers. Indeed, for the first Co layer the scattering coefficient ratio a1 = p↓/↑> 1. However, for the second magnetic layer, alloying Co and Ru may induce an increase of the density of states at the Fermi level for majority spin electrons and as a consequence 0C2 = p↓/↑< 1

The magnetic order of ultra-thin Eu films on Gd(0001) was studied in an element-specific and layer-resolved way using magnetic circular dichroism (MCD) in 4ƒphotoemission (PE). It was found that Eu films up to 2 monolayers (ML) exhibit a high net magnetization parallel to that of the Gd substrate. For Eu coverages exceeding 2 ML, the ferromagnetic alignment of the Eu moments breaks down, except for the Eu interface layer. A comparison of the temperature dependences of the Eu-4/ and Gd-4/ MCD-PE signals for 1-ML-Eu/Gd(0001) with the results of a layer-resolved mean-field calculation results in values for the exchange-coupling constants within the Eu monolayer as well as between Eu and the Gd substrate.

We have observed circular and linear magnetic dichroisms in angle-resolved photoemission spectra of 50-monolayer Gd films grown on Y(0001) and 6-monolayer Fe-Ni alloy films grown on Cu(001). The 4/level of Gd and the Fe 3p level of the Fe-Ni alloy were measured. A different geometry was used for the magnetic circular dichroism than was used to measure the magnetic linear dichroism. The geometries were chosen so that the magnetic circular dichroism is predicted to be closely related to the magnetic linear dichroism for four-fold symmetric Fe-Ni/Cu(001) but not for three-fold symmetric Gd-Y(0001). Experimental results are presented.

In metallic materials, where grain boundaries(GB) are of crucial importance, impurities and alloying elements play an important role in determining their physical and mechanical properties because the behavior of a grain boundary may change drastically with the presence of impurities and alloying elements. For example, in iron and its alloys, including industrially important steels, the intergranular embrittlement is usually associated with segregation of impurities, like P and S, toward the GBs. On the other hand, alloying elements, like Mo and Pd, are helpful for intergranular cohesion in iron, due to either direct cohesion effect or effect upon embrittling potency of other impurities. Understanding the mechanisms of impurity-promoted embrittlement and the consequent cohesion(decohesion) effects is becoming more and more important and remains as a challenge for materials scientists. There have been intensive investigations on these mechanisms for a long time and with the progress in computing techniques in recent years, calculations on more realistic representations of impurity-doped grain boundaries have become possible[1–4].

The anisotropy properties of Ni films on Cu(001) are quite unusual compared to other systems: The magnetization direction of Ni is in-plane for a coverage smaller than a critical thickness of 7 monolayers and out-of-plane for a coverage larger than 7 monolayers. As a first step in the study of this unusual behaviour, we report results of ab-initio calculations of the magnetic order of Ni films on a Cu(001) substrate. The magnetic moments are computed by means of the real-space Tight-Binding LMTO method allowing non-collinear magnetic moments and including spin-orbit coupling to account for magnetic anisotropy effects. As the number of Ni layers is increased, we discuss the stability of the system with a magnetization in-plane or out-of-plane.

Magnetic Fe/Ni multilayers, investigated by Magnetic Force Microscopy (MFM), show a stripe domains structure in which the magnetization is oriented in the film plane. This structure is attributed to the equilibrium configuration between competing in-plane anisotropy of the Ni layers and perpendicular anisotropy due to the thin Fe layers.

Using Ising model Monte Carlo simulations, we show a strong dependence of surface magnetization on surface miscut angle. For ferromagnetic surfaces, when surface spin exchange coupling is larger than that of the bulk, the surface magnetic ordering temperature decreases, toward the bulk Curie temperature, with increasing miscut angle; when surface spin exchange coupling is smaller than that of the bulk, a crossover behavior occurs: at low temperature, the surface magnetization decreases with increasing miscut angle; at high temperature, the reverse is true.

Starting from a tight binding formulation of the KKR (Korringa-Kohn-Rostocker) Green function method we developed a self consistent band structure code. By using a reference system containing repulsive muffin tin potentials we obtain structure constants which decay exponentially with distance. In the case of multilayered systems the numerical effort scales linearly with the number of monolayers in a unit cell. We report about calculations of CoCu(001) systems. With our method we are able to consider the electronic structure, the interlayer exchange coupling, and the transport properties (conductivity, giant magnetoresistance = GMR) on an equal footing.

Colossal magnetoresistance (CMR) in doped lanthanum manganite thin films (Lai.xMx, where M is a divalent ion) has been shown to result in a factor of 106 suppression of the resistance. The driving force for the CMR transition is thought to be the double-exchange (DE) interaction. Many studies of both the crystal structure and the local structure of the Lai.xMxMnO3 (with M = Ca, Sr and Ba, as well as Pb) system have now been carried out. As expected, these systems all show a strong coupling of the lattice to the CMR transition. On the other hand, neutron diffraction data and x-ray absorption studies for the Ti2mn2O7 pyrochlore, which also exhibits CMR, shows no deviations from ideal stoichiometry, mixed valency, or Jahn-Teller distortions of the MnO6 octahedron. We present results of crystallographic and local structural studies of these two important classes of CMR materials. compare the differences in structural response, and discuss the implications of these findings to our understanding of these materials.

Spin dependent tunneling has been investigated in tunnel junctions composed of a variety of materials. The best results thus far have been with either HfO2 or MgO as the barrier layer using CoFe, Fe, or Co as the magnetic electrodes. The maximum magnetoresistive (MR) response of these junctions has been at low temperatures on the order of 30% in HfO2 and 20% in MgO. We have also observed a variety of anomalous behavior in some of our tunnel junctions at low temperature. These include MR effects dependent on the angle of orientation of the tunnel junction in the applied magnetic field, transition fields greater than lOkOe, and negative MR effects on the order of 2%.

We have modelled the effects of bulk, outer-boundary, and interfacial disorder on conductivity and giant magnetoresistance (GMR) in Co101010/ trilayer taking into account its realistic electronic band structure. Calculations were performed using our model [E. Yu. Tsymbal and D.G. Pettifor, Phys. Rev. B 54 (1996) 15314] extended to the systems with two-dimensional periodicity and layer-dependent disorder. The model is based on the Kubo-Greenwood formula and spin-independent disorder in the on-site atomic energy levels, reflecting the scattering by defects, within an spd tight-binding approximation. Exploring the contributions to conductivity from different layers, we find that the influence on GMR of the boundary and interfacial scattering is similar to the bulk scattering, because the conductivity is non-local and the thicknesses of films are comparable to the electronic mean free path. Increasing the spin-independent disorder causes a decrease of GMR in the spin-valve for both interfacial, outer-boundary and bulk mechanisms of scattering. We have also investigated the effect of outer-boundary and interfacial paramagnetic Co layers on GMR in the trilayer. We find that the GMR, in this case, is strongly reduced due to the strong spin-independent scattering at the paramagnetic layers and hybridization of d states of the paramagnetic layers with the sp bands.

The results of first-principles calculations for the interlayer coupling in Fe/Cr/Fe trilayers are presented. We find that a spin-density wave in Cr gives rise to an additional contribution to the interlayer coupling. We investigate the relationship between the spacer magnetic moment and the interlayer coupling. Moreover we calculated the effect of interface adlayers of Cu on the interlayer coupling of a Fe/Cr/Fe trilayer.

Abstract Manganese layers were deposited on polycrystalline Fe-based soft magnetic films. The magnetic domain structure of thin Fe overlayers on top these Mn films was measured by secondary electron microscopy with polarization analysis. The Fe layers show spin polarization only beyond a certain critical thickness of about 20 Å. Beyond this thickness the domain structure of the substrate starts to appear in the Fe overlayer. This delayed onset of ferromagnetic order in the Fe layers is attributed to frustration of ferromagnetic order due to the strong coupling to the antiferromagnetically ordered Mn. With increasing Fe film thickness (between 20–30 Å) the magnetization increases and shows the same domain pattern as the substrate. We find that for all Mn thicknesses studied (up to 170 Å) the Fe overlayer domain structure reproduces the substrate domain structure and the magnetization is always aligned parallel with the substrate magnetization.