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We have grown ultra-thin epitaxial Co films on (0 0 1) and (1 1 1) surfaces of Pd. Their magnetic properties are studied by magneto-optical Kerr effect (MOKE). They are correlated with surface morphology analyzed by scanning tunneling microscopy (STM). In agreement with theoretical predictions, reversed polar Kerr rotation loops with respect to those of thicker Co films were observed below the thickness of 2.5 monolayers. This is interpreted as being due to a dominating negative contribution of Co/Pd interface with respect to the positive contribution from the non-interface part of the Co film. There is no change of sign of the polar Kerr rotation at low Co coverage on Pd(1 1 1) due to the growth which starts by formation of double-layer patches in this case.

The magnetic domain wall contribution to the magnetoresistance was examined by the magnetoresistance measurements and magnetic force microscope observations for (0 0 1) oriented epitaxial Fe wires 2 μm wide with different thicknesses of 50 and 100 nm. The periodical domain structures with a period of 1 μm were observed in both the wires at room temperature. The evaluated domain wall contribution to the magnetoresistance is positive at room temperature and turns to be negative below 66 K, indicating that the domain walls enhance the conductivity of the wire at low temperatures.

We describe our magnetic and magneto-optic (MO) studies on some multilayers based on Ag, Au and Pt, such as Fe/Ag, Fe/Pt, CoNi/M (M = Pt, Au) prepared by evaporation under UHV conditions. In CoNi/M, the surface anisotropy increases linearly with the addition of Co verifying the single ion model. The Curie temperature can be tailored by the addition of Co without affecting adversely the properties of interest for MO storage applications. For instance, in Fe/Ag, the MO effect shows enhancement due to Ag plasma resonance and in Fe/Pt the effect is due to interaction of Pt. The spectra can be explained by a phenomenological model though quantitative agreement is not obtained. In Au-based multilayers, the MO Kerr spectra show the effect of plasma resonance of Au, particularly for thinner layers. Some of the results could be modelled by electromagnetic model. The Kerr spectra for CoNi alloy films could also be modelled with success using effective medium theory which also confirms the absence of any effect from hybridisation between Co and Ni a result which supports our conclusions on the surface anisotropy.

Polar magnetooptics (MO) is able to probe the magnetization depth profile in ultrathin magnetic film structures on a nanometer scale. This information can be deduced by modelling the MO effects in the considered layered medium when performing MO experiments with a compensator or changing the wavelength of the incident light beam. Spectroscopic MO measurements are then helpful for analysing this phenomenon in detail. The in-depth selectivity of MO effects for magnetization is demonstrated for a simple ultrathin film structure consisting of two magnetic Co layers with perpendicular anisotropy separated by a non-magnetic Au spacer layer. The individual magnetic contributions of the two Co layers may be observed directly when performing MO Kerr measurements at selected compensator phase shifts or photon energies. The experimental data are interpreted by MO calculations in both cases.

Complex polar Kerr and Faraday effects between 1.5 and 5.2 eV in ultrathin Au/M/Co/Au films, with M = Au, Ag or Cu, prepared by thermal evaporation under ultra high vacuum condition are reported. The structure in the dispersion spectra is dominated by the effect of the Au layer underneath the ultrathin Co film. Thanks to the high layer perfection and step-like interface profiles strong sharp peaks in Kerr rotation, centered at the Au plasma edge near 2.5 eV, are observed. The introduction of Ag or Cu overlayers, which also display plasma edge effects in the considered energy range, modifies the spectra. This behaviour is satisfactorily explained by the electromagnetic wave model in magnetic multilayers.

This paper deals with the study of magneto-optical effects exhibited in perfect Au/Co/Au ultrathin films structures as a function of magnetic field and photon energy. They stand as ideal basic structures to test theories describing the magneto-optical effects in multilayers. In both optical transmission and polar Kerr rotation dispersion spectra, the main feature is a prominent peak centered near the photon energy of 2.5 eV, which corresponds to the plasma edge and reflectivity minimum in gold. The observed trends in magneto-optical effects are explained using the electromagnetic wave theory starting from the published optical and magneto-optical constants values in gold and cobalt thick films. The polar Kerr effect in our samples is a sum of one independent plus one linearly dependent term on the Co film thickness. The nonzero value of the thickness-independent term indicates the presence of a contribution not accounted for by the employed electromagnetic wave model.

Spectroscopic ellipsometry and the polar Kerr effect were studied for Pd-Ni and Co-Pt multilayers as well as the corresponding homogeneous alloys. Additional features in the dielectric function and the plasma frequency as well as the magneto-optic properties were observed to depend on the modulation and the layer thicknesses. The magneto-optic properties of Co-Pt were found to correspond more to the alloy than in Pd-Ni.

The competition between the magnetocrystalline and shape anisotropies was studied by using a submicron-size epitaxial (10/spl middot/0) Co rectangular dots array. The measured torque curves exhibit the magnetic anisotropy with a four-fold symmetry, indicating a clear magnetic easy-axis reorientation. The results were successfully interpreted by taking into account the first order magnetocrystalline, shape and non-negligible second order magnetocrystalline anisotropies.

Observations of enhanced coercive force in NiFe films exchange coupled with FeRh-Ir ordered alloy antiferromagnets epitaxially grown on MgO vicinal surfaces are reported. For NiFe thickness near 2.5 nm and miscut angle of 11.3 degrees the coercive force was increased by approx. 40% with respect to the flat NiFe/FeRh-Ir interface. The exact mechanism of this enhancement is not completely understood. However, it seems related to an increased number of pinning centers at the stepped interface. In addition to this effect we could also detect a usual step-induced uniaxial anisotropy. However, the effect of this uniaxial anisotropy on the coercive force was much weaker than the enhancement due to the steps at the NiFe/FeRh-Ir interface.

We have grown ultrathin epitaxial Co films on three low-index surfaces of Pd. Their magnetic properties studied by the magneto-optical Kerr effect are correlated with the surface morphology analyzed by scanning tunneling microscopy. A perpendicular magnetic anisotropy in the films appeared after exposure to residual gas atmosphere at low temperature, after coverage with an Au overlayer or after annealing at $370\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and above. For one- and two-monolayer-thick films the hysteresis loops are reversed with respect to those of thicker Co films. This is due the negative polar Kerr rotation contribution from the $\mathrm{Co}∕\mathrm{Pd}$ interface dominating over the positive polar Kerr rotation contribution from the noninterface part of the Co film. Reversed loops are not seen when the Co films grow in a three-dimensional mode. This indicates a clear correspondence between the mode of growth and the magneto-optical response. Near the film thickness where the Kerr rotation changes sign a remarkable temperature behavior is observed which is discussed as a superposition of two different magneto-optical contributions. The results qualitatively agree with the available ab initio band-structure calculations for the $\mathrm{Co}∕\mathrm{Pd}$ multilayer structures with variable thickness of the Co layers.

The authors discuss magnetooptical spectroscopic studies of Pt/Ni and Pd/Ni multilayers. The films were grown onto glass (Pt/Ni) and mica (Pd/Ni) substrates by dual electron beam evaporation. In the Pt/Ni set the thickness of Pt layers was kept constant at 2 nm while that of Ni layers was 1.2 and 2.9 nm. For the Pd/Ni set the individual Ni and Pd layer thicknesses varied between one and ten monoatomic layers. Simultaneous polar and longitudinal magnetooptical Kerr rotation and ellipticity experiments were carried out in the spectral range between 1.5 and 5.2 eV. The observed line broadening, shift and/or splitting are assigned to an effect of the interface Ni-Pd (or Ni-Pt) layers. >

The magnetic multilayers consisting of ultrathin 3d‐transition metal and Pt or Pd layers are considered for the magneto‐optical storage media with increased information density. This paper reports on the magneto‐optical polar Kerr rotation and ellipticity spectra in Pt‐Ni multilayers at photon energies from 1.5 to 5.2 eV prepared by evaporation onto glass substrates. The thickness of individual Pt layers was kept constant at 2 nm in all samples studied while that of Ni layers varied between 0.9 and 3.9 nm. The prominent feature of the Kerr rotation spectra is a broad negative peak the amplitude of which increases with the individual Ni‐layer thickness. The multilayer spectra show less structure than that of pure Ni. Nevertheless the trends in multilayer spectra when the thickness of individual Ni layers changes can be reasonably simulated using the electromagnetic wave theory and permittivity spectra in bulk (or thick film) Ni and Pt.

In near-field imaging with partially coherent x-rays, the phase shifting properties of the sample are encoded in the diffraction fringes that appear as an additional intensity modulation in the x-ray projection images. These Fresnel fringes are often regarded as purely an enhancement of the visibility at the interfaces. We show that retrieving the phase information contained in these patterns significantly advances the developments in fast micro-tomography. Improving temporal resolution without intensifying radiation damage implies a shortening of the exposure time rather than increasing the photon flux on the sample. Phase retrieval, to a large extent, compensates the consequent photon count moderation in the images, by fully exploiting the stronger refraction effect as compared with absorption. Two single-distance phase retrieval methods are evaluated for the case of an in situ 3 Hz micro-tomography of a rapidly evolving liquid foam, and an in vivo 6 Hz micro-tomography of a blowfly. A new dual-detector setup is introduced for simultaneous acquisition of two near-field diffraction patterns. Our goal is to couple high temporal, spatial and density resolution in a single imaging system in a dose-efficient manner, opening further options for dynamic four-dimensional studies. © 2013 IOP Publishing Ltd.

Magnetoresistivity effects in association with the magnetic domain structure were studied by using 1 pm wide epitaxial (10.0) CO wires oriented parallel and perpendicular to the magnetic easy (Ol) axis. The parallel wire exhibited a large anisotropy magnetoresistivity ratio of -11 % at 5 K, which turned to be negative above 214 K due to the temperature variable anisotropic magneto- resistivity effect. A negative domain wall contribution to the resistivity was observed only in the temperature range from 200 K to 220 K. On the contrary, the perpendicular wire exhibited a small positive wall contribution ranging from 3 x mcm at 5 K to 6.9 x 10" pQcm at 300 K.

International audience; This paper is devoted to magnetic and structural properties of anisotropicγ-Fe 2 O 3 γ-Fe2O3 superparamagnetic particles dispersed in a transparent xerogel matrix. The effect of frozen anisotropy axes and magnetic texture, induced by a magnetic field applied during the solidification of the matrix on the in-field magnetization process, is studied by alternating gradient force magnetometry and first and second order magneto-optical effects. The changes of magnetization curves with respect to the ferrofluid solution at the same particle concentration are interpreted on the basis of an existing statistical approach extended to systems with particle size distribution, which has to be taken into account for real samples. A very good agreement between the experiment and theory was achieved for a log-normal distribution of diameters which well resembles that deduced from electron microscopy observations in different imaging modes. This structural analysis states the parameter values used in calculations and confirms the relevance of basic assumptions of the model for the specimens studied. The experimental results and the related theoretical discussion should be of use to understand magnetic properties of other magnetically textured superparamagnetic systems.

Nous decrivons nos etudes magnetiques et magneto-optiques sur des multicouches Co-Ni/M (M = Pt, Au) preparees par evaporation sous ultra vide. L' anisotropie de surface K s augmente lineairement avec la teneur en Co ce qui verifie le modele a un ion. La teneur relative de Ni permet d'ajuster la temperature de Curie afin de pouvoir utiliser ces materiaux pour l'enregistrement thermomagnetique. La rotation Kerr presente un pic vers 4 eV pour les multicouches a base de Pt, qui se situe vers 2,5 eV pour celles d'or. On discute des resultats.

The authors consider magnetooptical spectroscopic studies of Pt/Co multilayers grown onto glass by dual electron beam evaporation an RF-sputtered Co rich Pt/sub x/Co/sub 1-x/ alloy films. Simultaneous polar and longitudinal magnetooptical Kerr experiments were carried out in the spectral range between 1.5 and 5.2 eV. The effect of the deposition temperature and that of subsequent heat treatment on the Kerr spectra is studied. In alloys Kerr rotation reached the value of 0.66 deg at 4.3 eV for x=0.41. >

Fe/MgO/Fe single-crystalline magnetotunneling structures were epitaxially grown on GaAs(001). An independent magnetization switching in the Fe electrodes was achieved by pinning the magnetization of the Fe-top electrode by antiferromagnetic coupling across a Cr spacer to another Fe film. Such Fe/Cr/Fe/MgO/Fe/GaAs(001) structures exhibit in-plane anisotropy, which ensures a discrete switching behavior of magnetization simplifying the shape of the hysteresis loop. The field dependence of magnetization was measured along the [110] and [100] crystallographic directions of GaAs(001) substrate and modeled by minimizing the total magnetic energy of the system. A peculiar magneto-optical behavior (similar to a reversed hysteresis loop) is explained by magneto-optical phase angles, which are determined mainly by the optical properties of the semiconducting GaAs substrate.

Fe ∕ Mg O ∕ Fe ∕ Cr ∕ Fe tunneling structures were epitaxially grown directly on GaAs(001) without buffer layer. Interdiffusion in the Fe ∕ Ga As interface was investigated using conversion electron Mossbauer spectroscopy. An independent magnetization switching in the Fe electrodes was achieved by pinning the magnetization of the Fe-top electrode by antiferromagnetic coupling across a Cr spacer to another Fe film. For transport measurements, optical lithography and ion etching were applied to reduce the junction area. A tunneling magnetoresistance of 10%–12% at room temperature was found.

The magneto-optic (MO) polar-Kerr-rotation and ellipticity were studied at room temperature, between 1.5–5.2 eV, for CoPt, Co[CoPt], Co[CoPd] and Pt[CoPt] multilayers grown on Kapton, Si and glass in UHV. The MO properties were found to depend on the modulation-layer thicknesses. The results were reproduced theoretically in conjunction with the alloying modulations.

Magneto-optical (MO) polar Kerr effect spectra in Ni Pt multilayers at 80 K show a strong increase in the spectra amplitudes, which exceeds that predicted by the model based on electromagnetic theory. An enhancement of the Kerr effect is observed at photon energies above 3 eV, similar to that in Co Pt and Fe Pt .

Polycrystalline Pt–Co multilayers with intentionally alloyed layers were grown by e-beam evaporation on polyimide, Si, and glass substrates. X-ray diffraction spectra show that the multilayered structure of the samples degrades as compared to conventional Pt–Co multilayers. This degradation depends on the compositional variation of the intentionally alloyed layers. Magnetometry measurements reveal enhanced magnetization values for all samples, exceeding even by 90% the one of bulk Co, at a temperature of 10 K. This is attributed to both Pt-induced and enhanced Co magnetic moments, according to x-ray magnetic circular dichroism experiments. Spectroscopic magneto-optic measurements reveal large negative polar Kerr rotation maxima at photon energies between 4 and 4.4 eV due to the intense magneto-optic response of spin-polarized Pt.

We have prepared COxNi1-x /Pt multilayers by evaporation under UHV conditions and studied their magnetic and magneto-optical properties. By adjusting the Co content it is possible to tailor the Curie temperature (TC) for magneto-optical storage application without trading off the other useful characteristics. For instance for x=0.3, for magnetic layers of the order of 5 A one has a rectangular M-H loop with coercivity as high as 1.4 kOe with a polar Kerr rotation peak of 0.3 deg at the photon energy of 4 eV and a TC = 180°C. For x=0.5, one has similar properties but with a TC of 200°C. These materials hold very good promise for high density magneto-optical recording in the blue light.

Magnetism of ultrathin Co films grown on clean and atomically flat surfaces of Pd single crystals is investigated using the magneto-optical Kerr effect (MOKE). The film deposited at room temperature exhibits a perpendicular magnetic anisotropy (PMA) after an exposure to a residual atmosphere at low temperatures (70 K) most likely due to hydrogen adsorption. MOKE analysis shows a gradual appearance of PMA and indicates the rotation of the magnetization vector from the sample plane. Upon increasing the temperature, the magnetization vector rotates back to the plane for temperatures approaching 200 K. Annealing above room temperature also supports PMA of the Co films on Pd substrates. The polar MOKE loops change sign at a certain critical thickness, t/sub c/, which varies for different substrate planes and growth conditions. The reversed loops are a property of the Co/Pd interface, even for samples grown at room temperature only.