Thickness Of Cu Layer Research Articles

Brillouin light scattering study of ferromagnetically coupled Cu/Fe(110)/Cu/Fe(110)/Cu/Si(111) heterostructures: Bilinear exchange magnetic coupling

Epitaxial $\mathrm{Cu}(60 \AA{})/\mathrm{Fe}(20\AA{})/\mathrm{Cu}{(d}_{\mathrm{Cu}})/\mathrm{Fe}(60\AA{})/\mathrm{Cu}(60\AA{})$ heterostructures with the Cu spacer thickness ${d}_{\mathrm{Cu}}$ ranging between $0$ and 33 \AA{} have been grown on $7\ifmmode\times\else\texttimes\fi{}7$ reconstructed surface of Si(111) substrates. Fcc(111) Fe films grow epitaxially on the Cu(111) buffer layer up to a thickness of 6--8 \AA{}, while, for larger thicknesses, one observes the appearance of three-dimensional bcc Fe(110) domains in the Kurdjumov-Sachs orientation. Brillouin light scattering (BLS) from thermally excited spin waves has been exploited in order to study the interlayer exchange coupling between the two Fe films at room temperature. The experimental spin-wave frequency dependence on the applied magnetic field is simulated using a simple model which includes first-order intrinsic volume and interface anisotropies and takes the bilinear exchange interaction between the two ferromagnetic layers into account. We have found that for thicknesses of the Cu spacer larger than $6 \AA{},$ the Brillouin spectrum consists of two spin-wave modes due to the Fe double layered structure which depends on the Cu-layer thickness. The coupling is found to be ferromagnetic for the whole range of Cu spacer thicknesses investigated. Using the magnetic parameters determined by the above analysis, we have carried out a detailed calculation of the BLS cross section assuming the dynamic magnetization to be constant across each magnetic film. A very good agreement between the calculated and the measured cross sections has been obtained.

Size and Interface Control of Novel Nanocrystalline Materials Using Pulsed Laser Deposition

We have developed a novel method based upon pulsed laser deposition to produce nanocrystalline materials with an accurate grain size and interface control. Using this method, the grain size in the case of Cu thin films was controlled by introducing a few monolayers of insoluble elements having high surface energy such as W, which increases interfacial energy and provides more nucleation sites. The grain size is determined by the thickness of Cu layer and the substrate temperature at which it transforms into islands (nanocrystalline grains) of fairly uniform size which we desgnate as self-assembling approach. Using this approach, the grain size was reduced from 160 nm (Cu or Si (100) substrate) to 70–80 nm for a simple W layer (Cu/W/Si (100)) to 4 nm for a multilayer (Cu/W/Cu/W/Si (100)) thin film. The hardness of these films was evaluated using a nanoindentation technique, a significant increase in hardness from 2.0 GPa for coarse-grained 180 nm to 12.5 GPa for 7 nm films was observed. However, there is decrease in hardness below 7 nm for copper nanocrystals. The increase in hardness with the decrease in grain size can be rationalized by Hall–Petch model. However, the decrease in slope and eventually the decrease in hardness below a certain grain size can be explained by a new model based upon grain-boundary deformation (sliding). We also used a similar materials processing approach to produce quantum dots in semiconductor heterostructures consisting of Ge and ZnO dots or nanocrystals in AlN or Al2O3 matrix. The latter composites exhibit novel optoelectronic properties with quantum confinement of phonons, electrons, holes and excitons. Similarly, we incorporated metal nanocrystals in ceramics to produce improved mechanical and optical properties.

Investigation of Cu films by focused ion beam induced deposition using nuclear microprobe

The localized Cu deposition on Si by 30 keV Ga+ focused ion beam (FIB) using precursor gas has been investigated by a 300 keV Be2+ nuclear microprobe with a beam spot diameter of 80 nm. The Cu deposition and impurity incorporation were compared at different temperatures of precursor gas. The distribution of deposited Cu, Ga from the ion beam itself and low-Z elements from the precursor gas was obtained at and nearby the deposited areas by RBS mapping images. An RBS mapping image of Cu atoms for FIB induced deposition indicated the uniform Cu films in the case of lower temperature (25°C and 37°C) of precursor. On the contrary in the case of higher temperature (43°C and 50°C) of precursor gas, the RBS mapping image of Cu atoms shows irregular distribution and incorporated impurities. The micro-RBS spectra indicated the deposition behavior that the thickness of Cu layers increased with the decrease in temperature of precursor gas due to the enhancement in the adsorption of precursor gas on the target surface.

Effect of Pressure on the Giant Magnetoresistance for Co/Cu with Different Cu-Layer Thicknesses

Effect of Pressure on the Giant Magnetoresistance for Co/Cu with Different Cu-Layer Thicknesses

Anomalous Pressure Dependence of the Giant Magnetoresistance for Co/Cu Magnetic Multilayers

The effect of pressure of up to 2.2 GPa on the giant magnetoresistance (GMR) has been investigated for sputtered [Co(10.8 Å)/Cu( t Cu Å)] 15 magnetic multilayers with various Cu-layer thicknesses, t Cu . It was found that the MR ratio, Δρ/ρ s , showing oscillatory behavior with t Cu , is strongly affected by the application of pressure at 4.2 K for the samples near the first peak ( t Cu =9.8 and 11.7 Å): Δρ/ρ s for t Cu =9.8 decreases with increasing pressure, while Δρ/ρ s for t Cu =11.7 increases with increasing pressure. On the other hand, the pressure effect on Δρ/ρ s for the samples near the second peak ( t Cu =21.5 and 23.4 Å) is much smaller than that near the first peak.

Concurrent variation of giant magnetoresistance and saturation Kerr rotation in NiCo/Cu multilayers

The dependences of magneto-optical effect, effective optical constants, and giant magnetoresistance (GMR) on the thickness of Cu layers were investigated in NiCo/Cu multilayers prepared by rf magnetron sputtering. A peak of saturation polar Kerr rotation θK, occurred simultaneously with that of GMR ratio when the Cu thickness is around 1.0 nm, where a clear drop of the effective optical constants n and k appeared. The peak of θK is mainly caused by the reduction of the effective optical constants, which dominate over the small drop of the effective off-diagonal elements of the dielectric tensor. The concurrent variation of GMR and θK is related to antiferromagnetic interlayer coupling, which may change the electron band structure and thus the optical and magneto-optical transitions of electrons.

Oscillation effects in the magnetic and optical properties of Co-Al/Cu multilayers

A series of [Co 90Al 10(1.6 nm)/Cu] 30 multilayer samples were made to study the oscillatory interlayer coupling using a vibrating sample magnetometer (VSM), giant magnetoresistance (GMR), surface magneto-optical Kerr effect (SMOKE), magneto-optical Kerr effect (MOKE) and spectrscopic ellipsometry methods. The measured value of Δ R/R, in-plane saturation field ( H s), MOKE and effective dielectric constant ɛ were found to have an oscillation period of 0.9 nm as a function of the Cu-layer thickness. The oscillations observed in those experiments arises from the same origin related to the interlayer coupling or quantum-well effect.

Structure and magnetic properties of electrodeposited metallic multilayers

We have studied the structure and magneto-transport properties of Co/Cu multilayers prepared by electrodeposition. The oscillation of magnetoresistance ratio as a function of Cu-layer thickness is observed. The obtained values of magnetoresistance were 12% and 18% around 1st and 3rd peaks, respectively. The structure and magneto-transport properties of electrodeposited Co/Cu multilayers are discussed.

Giant magnetoresistance of electrodeposited Co/Cu multilayers

We report on the structural and electrical characterization of electrodeposited Co/Cu multilayers grown in a single electrolyte based on CoSO4 and CuSO4. A high degree of crystallographic orientation and superlattice coherence is found in the growth on (100)- and (111)-oriented substrates. The magnetoresistance (MR), measured in the current-in-plane configuration at room temperature, is dominated by the giant MR effect for Cu-layer thicknesses dCu ≿ 3 nm and by the anisotropic MR effect for dCu ≾ 2.5 nm. A maximum of 14% is measured for dCu ≈ 4 nm. No evidence for antiferromagnetic coupling is found. Instead, the giant MR gradually diminishes with decreasing dCu < 4 nm which is attributed to ferromagnetic coupling due to magnetic pinholes. The influence of the Cu2+-ion concentration, the addition of levelling agents, and the Co-and Cu-layer thicknesses on the structure and magnetoresistance is systematically investigated. Especially the use of levelling agents has a catastrophic effect on the structural quality of the multilayers and on the magnitude of the MR.

Magnetoresistance and Interlayer Exchange Coupling between Magnetic Layers in Fe–Mn/Ni–Fe–Co/Cu/Ni–Fe–Co Multilayers

Magnetoresistance effects and interlayer exchange coupling between magnetic layers have been investigated in [Hf/Fe–Mn/Ni–Fe–Co/Cu/Ni–Fe–Co/Hf] multilayers by varying the thicknesses of the Ni–Fe–Co, Fe–Mn, and Cu layers. When the Fe–Mn layer is thicker than 5.0 nm, it applies a strong exchange-bias field to the neighboring Ni–Fe–Co layer. The multilayers show high magnetoresistance ratios at Cu-layer thicknesses between 2.0 and 3.0 nm, because the interlayer exchange coupling is weak. The interlayer exchange coupling between the two Ni–Fe–Co layers is always ferromagnetic at Cu-layer thicknesses between 0.5 and 5.0 nm.

Magnetoresistance in Ni-Fe/Cu multilayers formed by sputtering

The dependence of magnetoresistance on the thickness of Cu layer, the thickness of magnetic layer, the thickness of buffer layer, the number of layered stack and the composition of magnetic layer has been investigated for the Ni x Fe 100- x /Cu multilayers.

Dependence of giant magnetoresistance on Cu-layer thickness in Co/Cu multilayers: A simple dilution effect.

The dependence of the giant magnetoresistance in Co/Cu multilayers on Cu spacer layer thickness is shown to be surprisingly straightforward for multilayers comprised of thin Co layers. At 4.2 K the magnetoresistance decays simply as the inverse Cu spacer layer thickness, which we consider to be a result of dilution of the Co/Cu interfacial regions which give rise to the giant magnetoresistance effect. At 295 K there is an additional exponential decay whose decay length we attribute to volume scattering within the Cu layers. High-resolution cross-section transmission electron micrographs show a high degree of structural ordering within the Cu layers and across the Co/Cu interfaces, perhaps accounting for the long volume scattering lengths (\ensuremath{\simeq}300 \AA{} at 295 K) found within the Cu layers.

Growth temperature dependence of magnetoresistance in Co/Cu(111) wedged superlattices.

The relationship of the growth and structure of highly oriented (111) Co/Cu superlattices to their magnetotransport properties is discussed. To eliminate changes in growth parameters between different samples, wedged superlattice structures were prepared in which uniform Co layers are separated by Cu layers whose thickness is varied by more than a factor of 2 across the substrate. Smooth variations in magnetoresistance (MR) as a function of Cu-layer thickness were obtained. No evidence for oscillations in MR was found with the exception of a peak in MR for thin Cu layers centered at about 10 A

Femtosecond thermomodulation measurements of Co/Cu and Ag/Cu multilayer films

Femtosecond transient reflectivities of Co/Cu and Ag/Cu multilayer films were measured to study the electron-lattice relaxation in these systems. The measurement results suggest that the thickness of Cu layers does not influence the electron relaxation time. A slow decaying signal, which is absent in Ag/Cu films, was observed in Co/Cu films and it is attributed to the spin excitations in the Co layers.

Magnetic properties of compositionally modulated FeSi/Cu films

FeSi/Cu compositionally modulated films (CMFs) with different modulation wavelengths have been obtained by rf sputtering. When the thickness of Cu layers is fixed, the saturation magnetization and the Curie temperature of CMFs decrease with a decreasing thickness of magnetic layers. This result is caused by a dead layer effect and dimensional effects. For FeSi/Cu CMFs with the thickness of FeSi layers of 9 Å, a linear thermomagnetic relation, i.e., the two-dimensional magnetism is obtained. Varying the thickness of Cu layers with fixed FeSi layer thickness, it is found that for Cu layers thinner than 15 Å, the exchange coupling between FeSi layers appeared, but it caused the saturation magnetization of CMFs to decrease. A “mictomagnetic-like” phenomenon is observed at low temperature and low fields. This behavior is a consequence of irreversible effects due to the domain wall pinning.

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.

Magnetoresistance in FeSi/Cu Compositionally Modulated Films

FeSi/Cu compositionally modulated amorphous films with different thicknesses of Cu layers have been obtained by radio-frequency sputtering. We studied the resistivity and magnetoresistance of these samples at room temperature. The resistivity of FeSi/Cu compositionally modulated films (CMFs) increases with decreasing the thickness of Cu layers. The FeSi/Cu CMFs show a negative magnetoresistance effect. The magnetoresistance decreases with decreasing the Cu layer thickness dc when dc is over 20 Å, but it turns to increase with decreasing dc when dc is below 20 Å. This is probably caused by the polarization of conductive electrons of Cu.

Proximity Effect-Induced Superconductivity and NMR Relaxation in Nb-Cu Multilayers

The nuclear spin lattice relaxation rate, T 1 -1 , for 63 Cu in zero field from 8 K down to 0.3 K, has been measured in Nb-Cu multilayered thin films where both the Nb- and Cu-layer thicknesses are much smaller compared to the coherence lengths. A BCS-like temperature dependence of T 1 -1 replaced gradually by a Korringa-law-like one at low temperatures has been found. A dependence of the relaxation on the Cu-layer thickness at low temperatures has also been found. It has been proposed and confirmed by a series of experiments that superconductivity in the Cu-layer induced by the proximity effect has an anisotropic energy gap, reflecting the geometrical feature of a thin film.

Magnetic properties of multilayered Fe/Cu film deposited by facing targets sputtering (abstract)

Iron and copper both form solid solutions with only a few atomic percent in ultimate concentration. Thus, multilayered films of ferromagnetic Fe and diamagnetic Cu provide unique means for investing the magnetic interaction among Fe thin layers distinctly separated by Cu layers and the role of Fe/Cu interface. Facing targets sputtering (FTS) apparatus has been developed for preparing multilayered films composed of very thin continuous layers of different metals with high mobility adatoms and low energy bombarding particles. Multilayered Fe/Cu films have been prepared on glass slide substrates by depositing alternatively Fe and Cu layers with 99.99% in purity using FTS apparatus. The thickness of individual Fe and Cu layers is in the range of 5–70 Å. Small-angle x-ray diffractometry indicates that the multilayered structure is formed even for each layer as thin as 5 Å. Saturation magnetization 4πMs of the Fe layer as thin as about 7 Å is comparable to that of bulk Fe. However, 4πMs of the films with an Fe layer thinner than 7 Å is remarkably small than that of the films with the thicker Fe layer. Coercivity Hc monotonously decreases with decreasing thicknesses of Fe and Cu layers from 70 Å to about 10 Å. The hysteresis M-H loop of the multilayered films with Fe layers thinner than 10 Å shows rotatable anisotropy, impling perpendicular anisotropy. When the thickness of the Fe layer is fixed at 13 Å, perpendicular anisotropy increases with decreasing the thickness of the Cu layer in the range below 13 Å. Heat treatments of the multilayered films up to 300 °C resulted in a change of layer structure and also magnetic properties. Dependence in magnetic properties and multilayered structures on annealing temperature will be discussed in detail.