Fe Multilayers Research Articles

The problem of absorption in the Fresnel fringe analysis

Fresnel fringes at interfaces of Co Cu , Fe Tb and Au Fe multilayers were simulated using a multislice algorithm in connection with a continuum model. The intensity profiles of a defocus series were calculated by treating the absorption in different ways. A first simulation uses absorption in the calculations. These simulated intensities were divided by the intensity of the in-focus image. This “division method” results in shapes of fringe intensities different from those of a second simulation using no absorption. This outcome is important because the division method is widely used to get rid of absorption in experimentally observed images. In a system like Co Cu where the absorption difference between the individual materials is small there is no need for a division because the simulations with and without absorption are very similar.

Band-theoretical investigation of the magneto-optical Kerr effect in Fe and Co multilayers.

A band theory of the magneto-optical (MO) properties of solids, based on the first-principles spin-polarized, relativistic linear muffin-tin orbital method, is described. Two expressions of the relativistic electron-photon-interaction matrix elements are implemented and their accuracies are investigated. It is found that the spin-polarized, relativistic band theory, together with the expression of the photon-absorption matrix elements, is able to give reliable optical conductivity and MO Kerr rotation spectra of bcc Fe that agree well with both experiments and recent calculations using a different method. The MO properties of several Fe and Co multilayers [Fe(Co${)}_{2}$${\mathrm{Cu}}_{6}$ fcc-(001), FeCu(Ag${)}_{5}$ fcc-(001), bcc-Fe/fcc-${\mathrm{Ag}}_{5}$ (001), bcc-${\mathrm{Fe}}_{\mathit{n}}$/fcc-${\mathrm{Au}}_{5}$ (001) (n=1,3), ${\mathrm{Co}}_{2}$${\mathrm{Pd}}_{4}$ fcc-(111), and ${\mathrm{Co}}_{2}$${\mathrm{Pt}}_{\mathit{m}}$ fcc-(111) (m=1,4,7)] are then investigated theoretically. The calculated MO Kerr effect in all the multilayers except ${\mathrm{Co}}_{2}$${\mathrm{Pt}}_{1}$ fcc-(111) is not larger than in bulk Fe and Co. Nevertheless, the results suggest that materials with larger Kerr rotations can be achieved by making Fe (Co) superlattices with ultrathin layers (few monolayers thick) of heavy elements possessing a partially filled d band (e.g., Pt and Os).Kerr rotation spectra for Fe(Co)/Cu(Ag, Au, Pd, Pt) bilayers [i.e., a thin layer of Fe (Co) on the Cu (Ag, Au, Pd, Pt) substrate] are also obtained from the calculated optical conductivity tensors of Fe, Co, Cu, Ag, Au, Pd, and Pt. It is found that the MO Kerr effect in the Fe (Co)/noble-metal bilayers is considerably enhanced near the plasma edge of the substrate. This indicates that one can obtain good MO materials by fabricating Fe (Co) bilayers using nonmagnetic metals with a sharp plasma edge (e.g., Ag and Al) as substrates. Calculated Kerr rotation spectra of the Fe and Co multilayers as well as bilayers are in satisfactory agreement with available experiments. The spin and orbital magnetic moments in the Fe and Co multilayers are also calculated, and possible correlations between these and MO properties of the Fe and Co multilayers are discussed.

Composition properties of [formula omitted] multilayers

Sputtered magnetic Tb Fe multilayers ( e Tb=1.0 nm and 1.9 nm, 0.2≤ e Fe≤2.4 nm) have been studied by X-ray diffraction, Mössbauer spectrometry and magnetization measurements in the temperature range 4–300 K. The results are in agreement with a composition modulation in the multilayers, with appearance of pure amorphous iron at the centre of iron layers from e Fe value depending on e Fe. Irradiation experiments on samples provide evidence for the change in magnetic properties related to the mixing of layers.

Mössbauer investigation of the growth of the Fe multilayer in Fe(100)/Ag(100) structures.

A monolayer of $^{57}\mathrm{Fe}$ is used as a probe layer in molecular-beam-epitaxy-grown Ag/Fe(001)/Ag(001) structures. Different Fe sites can be distinguished in the iron multilayer based on the isomer-shift (i.s.) and quadrupole-splitting (QS) values of different components in the M\"ossbauer spectrum. This makes it possible to determine the concentration of $^{57}\mathrm{Fe}$ atoms in the different atomic Fe layers and obtain information about the growth processes for different regions of the Fe multilayer. It was found that after deposition of about 5-Fe ML the growth changes from a Fe multilayer formation mode to a quasi-layer-by-layer mode. The values of the i.s. and QS are the same for Fe atoms located at the top and bottom Ag/Fe interface. ${\mathit{H}}_{\mathrm{hf}}$ values, on the other hand, are different by 9 kOe at the top and bottom for a sample in which the upper Ag(001) layer is covered by another Fe(001) layer. This result may be due to a contribution to the top ${\mathit{H}}_{\mathrm{hf}}$ value from Ruderman-Kittel-Kasuya-Yosida-like spin-density oscillations that couple the ferromagnetic Fe multilayers across the nonmagnetic Ag spacer.

Measurements of Electron Attenuation Length using Metallic Multilayers.

We propose a new method for experimentally measuring the electron attenuation length in solid from Auger electron spectroscopic analysis on the aslant-smoothed surface of a metallic multilayer system. The demonstration is performed for the electrons with kinetic energies corresponding to Auger transitions using a ring pattern sputtered surface of Fe and Si02 multilayers. The obtained attenuation lengths are qualitatively in good agreement with the Seah-Dench formalism as well as the TPP-2 formalism for a kinetic energy region of 50 to 1600eV. The experimental values are quantitatively larger than the theoretical ones for Si02, but smaller than those for Fe.

Giant magnetoresistance related transport properties in multilayers and bulk materials (invited)

A systematic comparison of magnetoresistance, Hall effect, thermal conductivity, and thermoelectric power has been made on systems exhibiting giant magnetoresistance (GMR), Co/Cu/Ni(Fe) multilayers, and AgCo granular alloys, for examples. Each property exhibits field dependence characteristic of the GMR and justifies its own merit in characterizing the conduction-electron scattering responsible for the GMR. The comparison was extended to intermetallic compounds such as REGa2 and RECo2 (RE: rare earth element) which also show a large magnetoresistance.

First-principles calculation of magnetic x-ray dichroism in Fe and Co multilayers.

A relativistic, spin-polarized band theory of magnetic x-ray dichroism (MXD) in solids is briefly described. Calculated circular and linear dichroic x-ray absorptions at the ${\mathit{L}}_{2,3}$ edges from bulk Fe and Co as well as from their multilayers [${\mathrm{Fe}}_{2}$${\mathrm{Cu}}_{6}$ (001), ${\mathrm{FeAg}}_{5}$ (001), ${\mathrm{Co}}_{2}$Pd(Pt${)}_{4}$ (111), and ${\mathrm{Co}}_{2}$${\mathrm{Cu}}_{6}$ (001)] are presented. Large circular MXD is predicted in both the bulks and the multilayers while linear MXD due to magnetocrystalline anisotropy is found to be small (within 1%). Nevertheless, linear MXD due to a photon polarization change is about 3--8 %. The orbital magnetization sum rule of B. T. Thole et al., [Phys. Rev. Lett. 68, 1943 (1992)] is found to give orbital magnetic moments too small by about 20--35 %. We note that for each ion species, there is a simple linear relationship between the integrated circular MXD signal and the orbital magnetic moment, and we propose that one uses this linear relationship to measure the orbital magnetic moment of an ion in magnetic solids. The recently proposed spin magnetization sum rule [P. Carra et al., Phys. Rev. Lett. 70, 694 (1993)] is found to give rather accurate spin magnetic moments for the Co systems (errors within 15%). However, it does not hold qualitatively for highly anisotropic systems such as Fe multilayers.

Remanence and coercivity in exchange coupled amorphous R-TM/Fe bilayers and multilayers (abstract)

We have investigated the hysteresis behavior of rare-earth (R)-transition metal (TM) bilayers and multilayers consisting of a fine mixture of hard and soft phases. The films with bilayer thickness in the range of 5–100 Å were fabricated using a dc sputtering system. X-ray diffraction was used to check the crystal structure and multilayer structure. The magnetic properties were measured with a SQUID magnetometer in the temperature range of 10–300 K with fields up to 55 kOe. A strong exchange coupling between the hard magnetic phase (R-TM) and the soft phase (Fe) leads to a smooth hysteresis loop in samples with a certain thickness range. The remanent magnetization is enhanced significantly at the expense of a reduced coercivity. For example, in NdFe/Fe multilayer films, the reduced remanence increases from 0.63 to 0.92 at 10 K while the coercivity decreases from 9.3 to 1 kOe as the Fe layer thickness is varied from 0 to 10 nm. The effect of interface roughness on the exchange coupling has been investigated via different sputtering pressures and rates. The dependence of magnetic hysteresis on the layer thickness and temperature has been examined and the results will be reported.

Structure and magnetic properties of Sm/Fe multilayers versus substrate temperature

Three Sm(2 /spl Aring/)/Fe(3 /spl Aring/) multilayers have been made using two electron beams in a high vacuum chamber onto very thin Kapton foils at different substrate temperatures, (T/sub s/=40/spl deg/C, 150/spl deg/C and 230/spl deg/C), with the same total thickness of 3000 /spl Aring/. We have found that the substrate temperature strongly affects structure and magnetic properties of the samples. For a substrate temperature of 150/spl deg/C the sample behaves as a three dimensional random magnet.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Anelasticity and Structural Transformations of Fe and Al Thin Films and Multilayers

Anelasticity and Structural Transformations of Fe and Al Thin Films and Multilayers

Thermpower and resistivity of Au/Co/Au/Ni(Fe) multilayers

We have measured the magnetic field dependence of thermopower (magneto-thermopower) and the T 2 term of resistivity on samples of the artificial magnetic multilayers Au/Co/Au/Ni(Fe) having variable thickness of non-magnetic Au layers. The importance of the scattering of conduction electrons in the up-spin band and the down-spin band at the interfaces is discussed.

Interface and growth-mode characterization of Ce/Fe and CeH≊2/Fe multilayers by x-ray diffraction and Rutherford backscattering spectroscopy

The detailed structural characterization of ion beam sputtered Ce/Fe and CeH≊2/Fe multilayers offers the possibility for a better understanding of their magnetic properties. In the case of the Ce/Fe multilayers the extension of the interface, as one of the most important features, is determined to 5–7 Å by means of Monte Carlo simulations of the small-angle x-ray scattering diagrams. Below a critical thickness of ≊24 Å Fe grows in an amorphous structure. Here the interface extension is enhanced. In contrast all CeH≊2/Fe multilayers show nearly abrupt interfaces. X-ray scattering experiments at higher angles in reflection and transmission mode provide information about the crystal structure, the texture, and the lateral dimensions of the grains in the samples. Depths profiles of the multilayers are generated by Rutherford backscattering spectroscopy, which confirm the well-ordered periodic structures. Surprisingly indications of an island-like growth mode of the Fe layers onto the Ce and CeH≊2 layers could be resolved by using this procedure.

The variation of anisotropy and magnetization orientation with temperature in Tb/Fe multilayers

On the basis of the co-effect of the crystal field with a random distribution and the molecular field and using anisotropic static magnetic couplings, we calculated the polar angle Θ of the magnetic moment in 15×(26 Å Tb/40 Å Fe)+40 Å Fe multilayers as function of temperature from 4.2 to 300 K, which agrees well with experiment. As a result of the calculation, the width of interface mixing layer and the coefficient of the crystal field are determined.

Oscillation of magnetoresistance in [Ni–Fe/Cu]20/Cu/Fe multilayers with thickness of Cu spacer neighboring Fe buffer layer

In [Ni–Fe (1.0 nm)/Cu(1.0 nm)]20/Cu(t nm)/Fe(5.0 nm) multilayers with giant magnetoresistance effects, oscillations of magnetoresistance ratio and preferred orientation depending on Cu spacer thickness t have been observed. Corresponding to the oscillation of the magnetoresistance ratio, the preferred orientation oscillates between &amp;lt;100≳ and &amp;lt;111≳, though the thicknesses of each Ni–Fe and Cu layer in the multilayer are fixed. Both the periods of the oscillations are about 0.6 nm. When the multilayers have stronger &amp;lt;100≳ and weaker &amp;lt;111≳ preferred orientations, they show higher magnetoresistance ratios.

Analytical approach to the Camley-Barnas-acute theory for giant magnetoresistance in magnetic layered structures.

We present an analytical treatment of the Camley-Barnas theory of the magnetoresistance (MR) in magnetic layered structures and obtain an exact and general expression for the MR. Particular attention is given to the multilayer effect for the enhancement of MR change. It is proposed that the MR formula obtained from a single sandwich system can be used to calculate the MR effect of a multilayer structure provided an effective specularity factor for the reflection by the surfaces is introduced as a function of the number of bilayers. The theoretical results are in good agreement with experimental data for the epitaxial (Fe/Cr) n /Fe multilayers

Microstructural evolution of ion-beam-mixed Al-Fe multilayers for the formation of quasicrystalline or amorphous homogeneous alloys.

Al and Fe multilayers thermally evaporated on sapphire substrates have been mixed by irradiation with 800-keV ${\mathrm{Xe}}^{+}$ ions at two different temperatures (liquid-nitrogen temperature and 493 K) and with fluences ranging from 2\ifmmode\times\else\texttimes\fi{}${10}^{15}$ to 3\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ions/${\mathrm{cm}}^{2}$. The structural evolution of the irradiated samples has been followed using complementary characterization techniques such as transmission electron microscopy and conversion-electron M\ossbauer spectroscopy. Homogeneous amorphous or quasicrystalline phases are obtained at doses of 3\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ions/${\mathrm{cm}}^{2}$ at 77 K or 8\ifmmode\times\else\texttimes\fi{}${10}^{15}$ ions/${\mathrm{cm}}^{2}$ at 493 K, respectively. Different evolutions with ion dose are observed in both cases involving combinations of various sites that tend to final states with dominant local environments characteristic of amorphous or quasicrystalline phases.

Soft magnetic properties of Fe multilayered films with amorphous intermediate layers

Amorphous intermediate layers are studied to improve soft magnetic properties of Fe-based multilayers, since the interfacial stresses between layers are assumed to be low. Fe multilayers with crystalline intermediate layers (e.g., Ni-Fe alloy) required heat treatment to release interfacial stress to achieve soft magnetic properties. Multilayers Fe/B4C, Fe/SiC, and Fe/C (B4C, SiC, and C layers are amorphous when formed by ion beam sputtering) show relative permeabilities over 2000 and coercivities below 56 A/m (=0.7 Oe), even without heat treatment. In particular, Fe/B4C multilayers with B4C thicknesses over 0.5 nm show clear periodic structures, even smaller crystallite sizes, and relative permeabilities above 3000, while the films have saturation magnetic flux densities above 1.8 T.

AB-INITIO BAND STRUCTURE CALCULATION FOR MAGNETIC MULTILAYERS

The magnetic properties of magnetic multilayers are studied using first principles total energy calculations. In this paper we present our results for bcc Fe multilayers with a (001) stacking direction. Using Nb as a spacer material we find an oscillating exchange coupling with a period of about 4.6 Å( ≈3 Nb monolayers). A detailed study of the magetic moments in the Nb spacer is given. Furthermore we discuss the dependence of the exchange coupling strength as a function of the thickness of the Fe slabs.

Strain, Stress, and Magnetic Surfaceanisotropy of Epitaxial FE(110)/MO (110) Multilayers

ABSTRACTGrazing incidence and asymmetric X-ray diffraction were used to measure the stress and strain state of Fe(110)/Mo(110) Multilayers. The highest stress in the Fe constituent of the multilayer was along the [110] in-plane direction and was due to interaction with the substrate. The Magnetic anisotropy of the Fe Multilayer constituent was measured and the magnetic surface anisotropy, which favored in-plane [001] magnetization, was deduced. In contrast, the magnetic surface anisotropy of a single layer of Fe on W preferred in-plane [110] magnetization, in agreement with the Néel Model.

Low angle polarized neutron diffraction from Tb/Fe multilayers

Low angle polarized neutron scattering experiments have been performed on a Tb(61 Å)/Fe(55Å) multilayer. The evolution of the intensities ( I + and I -) of the first peak shows that the average magnetizations of Tb and Fe are in the applied field direction. The intensities of the second and the third peaks indicate that there is an interface effect which is going along with the terbium magnetization. It is presumably the result of the antiferromagnetic coupling between iron and terbium.