Thickness Of Co Layer Research Articles

Oscillatory interlayer magnetic coupling of wedged Co/Cu/Co sandwiches grown on Cu(100) by molecular beam epitaxy.

Co/Cu/Co sandwiches were grown by molecular beam epitaxy onto a Cu(100) crystal with the intervening Cu layer fabricated to be wedge shaped. Electron diffraction was used to monitor the layer-by-layer growth. Films with 8, 14, and 20 monolayer- (ML) thick Co layers were investigated in situ by means of the magneto-optic Kerr effect. Characteristic hysteresis loops along the wedges, as a function of Cu thickness, unambiguously identify the oscillatory behavior in the sign of the exchange coupling between the two Co films. The oscillation periodicity (5.5 ML's of Cu) and, most importantly, the coupling strength are shown to be independent of the Co-layer thickness.

Nuclear magnetic resonance spin-echo studies in evaporated Co/Pt multilayers

Multilayered Co/Pt films with Co layer thickness ranging from 10 to 26 Å have been studied by the NMR spin-echo method at 2 K. The rapid increase of the signal around 210 MHz as the Co layer thickness is decreased indicates the alloy formation at the interfaces. This signal coincides with the resonance spectrum of Co3Pt alloy. The latter corresponds to a disordered alloy and is coherent with the shifts of the satellite lines observed in a dilute alloy. The layer thickness of Co forming Co3Pt alloy at each interface is estimated to be about 4 Å.

Ferromagnetic resonance in Co/W multilayers

Magnetic properties and structural contribution have been characterized in Co/W multilayers. FMR spectra have been measured in order to study the magnetic properties of Co layers in alternating W layers as a nonmagnetic counterpart. Three resonance modes have been found, and their spectra depend mainly on the layer thickness of Co. Bulk originated mode is dominant for thick Co layer, and surface associated mode is evident for thin Co layer case. Weak interface originated mode is also observed. The observed positive perpendicular magnetic anisotropy is ascribed to the surface of Co layer.

Structural study of cobalt-copper multilayers by NMR.

With this NMR study, we show that the quality of the growth of Co/Cu multilayers depends significantly on the Co- and Cu-layer thicknesses: The initial stacking of Co layers is fcc but the hcp stacking tends to develop with increasing Co-layer thickness. On the other hand, the thicker the Cu layers are, the better the fcc growth is. By a comparison of the NMR spectra with those expected from model interface structures, we show that the interfaces between copper and thin Co layers can be described as follows. If the presence of defects in the bulk of the Co layers is excluded, the NMR spectra observed in samples with thin Co layers must be explained by an intermixing of Co and Cu over three monolayers. However, such a model does not hold true for samples with thick Co layers where the existence of bulk defects is strongly suggested. In such a case, the spectra for all the samples studied can be explained by sharp Co/Cu interfaces, as in UHV-grown multilayers, and about 0.7% impurities in the bulk of the layers or possibly columnar grains with an in-plane diameter of about 90 A\r{}. Although model-agreement factors tend to favor the second model (sharp interfaces and bulk defects) rather than the first one (diffused interfaces), additional information on the nature of the bulk defects is needed.

Magnetic Co/Al multilayers prepared by planar magnetron sputtering

Structures and magnetic properties of Co/Al multilayers prepared by means of planar magnetron sputtering were investigated. We compare the results with those of the previously reported films fabricated by electron-beam deposition. It is found that remarkable differences exist between the films synthesized by the two methods. For example, the sputtered multilayers show a transition from in-plane to out-of-plane magnetization at a crossover thickness of Co layer from 14 to 7 Å. For samples with tCo ≤ 6 Å, the Co layers were discontinuous. Formation of the CoAl compound in the samples has not been observed.

NMR and magnetization studies of Co/Cu superlattices.

Co NMR and magnetization have been measured in a series of Co/Cu superlattices grown by molecular-beam epitaxy, with Co thicknesses varying from 5 to 100 \AA{}. The Co structure is mainly fcc for thicknesses of up to 65 \AA{}. For thicker Co layers the structure becomes hcp. For thin layers it is shown that the hyperfine field corresponding to fcc regions is nearly isotropic, whereas that arising from faulted (hcp) regions is anisotropic, with the symmetry axis parallel to the film normal. The anisotropic part of this field has the same sign and order of magnitude as in bulk hcp Co. For the sample with 5-\AA{} Co layers the dispersion of the magnetocrystalline anisotropy over the sample can be ascribed to Co-layer thicknesses which vary from 2 to 3 monolayers (4 to 6 \AA{}) throughout the sample.

The Perpendicular Magnetic Anisotropy and Structure of Sputtered Ag/Co, Pd/Co, and AgPd/Co Multilayered Films

AbstractThe structural and magnetic properties of sputtered Ag/Co, Pd/Co, and AgPd/Co multilayered films were investigated. When substrate temperature during deposition (Ts) was set at room temperature, the easy magnetization axis of the Pd/Co films with Co thickness less than 7Å was normal to the film plane and that of the Ag/Co films was parallel. AgPd/Co multilayered films showed a transition of the preferred direction of magnetic moment from lying in the film plane towards lying along the film normal when increasing the Pd concentration above 81 at%. Moreover, an anomalous reduction of the saturation magnetization was found. The perpendicular magnetic anisotropy of Pd/Co films with low Ts increased with decreasing the thickness of Co layer. However, the Pd/Co films with high Ts showed opposite tendency.

Magnetic anisotropy in epitaxial Co superlattices.

A series of epitaxial Co-Au and Co-Cu superlattices has been grown by molecular-beam-epitaxy techniques, with Co thicknesses varying from 5 to 40 \AA{} and constant Au and Cu thicknesses of 16 and 25 \AA{}, respectively. We compare the magnetic properties of both types of superlattice. Crossover to an easy axis normal to the film plane occurs at a thickness of 19 \AA{} of Co in the Co-Au series and 10 \AA{} of Co in the Co-Cu series. We show that the observed magnetic behavior of both of these systems can be accounted for by contributions from demagnetization, magnetocrystalline anisotropy, and magnetoelastic anisotropy. The magnetoelastic term depends on the strain present in Co layers, which in turn is a function of the Co-layer thickness. In our calculation we employ measured Co-layer strains, determined by x-ray scattering, in combination with the known elastic and magnetostriction constants of bulk Co.

Magnetostriction constant of multilayer Co/Ag films

The saturation magnetostriction constant lambda /sub s/ has been measured at room temperature in Co/Ag multilayer films prepared by evaporation in ultrahigh vacuum. It was found that in addition to the surface magnetostriction term, an additional one due to reduced symmetry of the magnetoelastic interaction should be incorporated to explain the peculiar dependence of lambda /sub s/ on the thickness of the Co layer. The dependence of the anisotropy constant K/sub u/ on the Co-layer thickness in the films investigated resembles the dependence of lambda /sub s/, indicating that the same mechanisms are important in both cases. The results obtained are shown to be related to the reduced symmetry in the nanometer-scale multilayer films. >

Anisotropy and magneto-optical studies in evaporated Co/Pt multilayer

Co/Pt multilayer films have been prepared by evaporation under UHV (ultrahigh-vacuum) conditions, and their magnetic and magnetooptical properties were studied. For samples with Co-layer thickness below about 1 nm, rectangular loops are observed with H/sub c/ on the order of 1 kOe. For these samples, the uniaxial anisotropy is as high as 1*10/sup 7/ erg cm/sup -3/, and it depends on the relative thicknesses of both Pt and Co. While the polar Kerr rotation decreases with decreasing Co-layer thickness, the Faraday rotation, on the contrary, is seen to increase strongly. This increase has been attributed to the presence of a Co-Pt alloy layer formed by mixing at the interfaces; its thickness has been estimated to be about 0.3 nm. Faraday rotation study is hence a useful tool in characterizing the multilayers. It is suggested that this layer plays an important role in the origin of K/sub u/. It has been found that M and K/sub u/ are practically independent of temperature for 5<T<300 K. The T/sub c/ is well above 600 K.<<ETX>>

Structures of Silver/Cobalt Metallic Superlattice and Changes Due to Annealing

AbstractAg/Co metallic superlattices were grown onto Ag buffer layers pre-deposited on sapphire or MgO substrates by ultrahigh vacuum alternate deposition technique. In-situ RHEED observations during superlattice growth and ex-situ XRD measurements revealed that structures of the superlattices were strongly affected by the condition of Ag buffer layer preparation. In case where the Ag buffer layers were single crystals with smooth (111) surfaces, Co layers were epitaxially grown on the buffer layers even in the presence of large lattice mismatch, and whole the superlattices were grown with an epitaxial relation. Interface smoothness was strongly related to the growth temperature. Spotty RHEED patterns of Co layers for a low growth temperature indicated that the Co layers had an FCC structure. Post-annealing of the samples, in some cases, destroyed a superlattice structure completely. From relations between magnetic anisotropy and Co-layer thickness obtained with VSM measurements, it was found that Ag/Co superlattice exhibited in-plane magnetic anisotropy down to a Co thickness of 4A and that the anisotropy was correlated with roughness of the interfaces.