Metallic Multilayer Structures Research Articles

Structure and Magnetic Properties of Metallic Multilayers Exhibiting Giant Magnetoresistance

The paper reviews results of structural and magnetic (hysteresis loops measured by vibrating sample magnetometer, magnetooptical Kerr effect and magnetoresistance) studies of permalloy/copper multilayers obtained by sputtering. The influence of the layers thicknesses on the magnetic and magnetoresistance properties of the system has been investigated. It is demonstrated that the correct choice of the parameters is necessary to observe giant magnetoresistance (GMR) effect, suitable for applications. The influence of imperfections in the multilayer structures such as roughness of the interfaces and discontinuities of Cu sublayers, on the interlayer exchange coupling and value of GMR effect is also discussed.

Low voltage electro-optic polymer light modulator using attenuated total internal reflection

An improved electro-optic (EO) polymer light modulator based on attenuated-total-internal-reflection (ATR) is demonstrated. The modulator consists of a prism–metal–EO-polymer–metal multilayer structure. An applied electric field across the EO polymer layer electrically modulates the energy coupling efficiency of incoming light into guided wave resonance at fixed angles. Compared with conventional ATR modulators based on surface plasmon resonance, the driving voltage for this modulator has been greatly reduced because of the newly chosen working interior angle. It also offers advantages in terms of insertion loss and aperture size over other techniques for the amplitude modulation of a collimated light beam.

Magnetic circular dichroism of Gd/transition metal multilayer structures around the Gd M 5,4-edges

Magnetic Gd/Fe and Gd/Co multilayer structures with d-spacing of about 1 nm were probed with elliptically polarized synchrotron radiation (SR). The intensity dependence of the magnetic circular dichroism (MCD) around the 3d absorption edge of Gd at room temperature was measured as a function of the degree of circular polarization in order to utilize the MCD effect for quantitative polarization analysis of SR in soft X-ray range.

Polarization elements for controlling of a beam of the compact discharge X-ray laser

The high average power of the compact discharge X-ray laser makes feasible various applications in optical instrumentation and material science. Among them there are polarization measurements that are especially important for optical element characterization and investigation of material properties. An accuracy of polarization measurements strongly depends on a quality of polarizes and phase shifters that are used to change the polarization state of a beam. In this work several types of polarizing elements for the wavelength 46.9 nm are considered. The main attention is paid to those (based on Si/3d-transition metal) multilayer structures that were shown to provide high performance mirrors in this spectral range.

Transport in Metallic Multilayers with Both Specular and Diffuse Scattering at Interfaces

ABSTRACTBy using a rather simple model potential we calculate the influence of specular and diffuse scattering at interfaces on the resistance for currents perpendicular to the plane of the layers (CPP) in multilayered metallic structures. We find that if one maintains the same interfaces between layers, their contribution to the total resistance of the system depends on the thickness of the intervening layers. Their contribution is constant only if the distance between interface is larger than the electron mean free path in the bulk of the layers. The error incurred by neglecting the dependence of the interface resistance on layer thickness depends on the amount of diffuse scattering at interfaces and the height of the potential step at the interface. For a Fe-Cr or Co-Cu multilayer consisting of three or five layers with realistic interfaces where both specular and diffuse scattering may occur, the error reaches 15-20%; this exceeds the experimental error. We suggest systems where this effect may be observed.

High-Frequency Magnetoresonance and Magnetoimpedance in Co/Cu Multilayers with Variable Interlayer Thickness

The paper is devoted to the investigation of high frequency magnetic features of multilayered metallic structures (Co/Cu) demonstrating the Giant Magnetic Resistance effect (GMR-effect) and Giant Magnetic Impedance effect (GMI-effect). Dynamic features have been investigated in dependence on the distance between magnetic Co-layers and analyzed in comparison with static magnetic features. Ferromagnetic resonance response as well as non-resonance magnetoimpedance at small applied static magnetic field have been studied. Experiments were carried out at room temperatures in frequency band 20-37GHz for the ferromagnetic resonance technique and in frequency band 30-140GHz for study the low field non-resonance magnetoimpedance effects.

Nuclear magnetic resonance investigations of the structure and magnetic properties of metallic multilayers and nanocomposites

As a probe of the short-range chemical and topological order, nuclear magnetic resonance (NMR) has proved useful to investigate the nanostructure of magnetic multilayers or granular systems and, in particular, to evaluate the nature, sharp or diffuse, of interfaces in such nanocomposites. These structural aspects are shortly reviewed in the paper. A larger emphasis is given to the magnetic properties that are accessed by the technique. As a first output of an NMR experiment in ferromagnets, the hyperfine field gives a direct insight on the local magnetization. Hence, for example, one can estimate the magnetization profile at a diffuse interface between a magnetic and nonmagnetic phase. In addition, NMR can probe selectively the magnetic anisotropy or exchange energy in different parts of a composite sample. Therefore NMR is a unique tool to investigate the correlation, at a local scale, between the nanostructure and the magnetic properties of a sample. For example, one can evidence the different magnetic hardness of the interface and bulk moments in multilayers, or of the magnetic clusters and alloyed regions in nanogranular alloys. Some relevant results are presented, which have been obtained in the course of investigations of Co-based multilayers, ultrathin films and granular systems.

Study of optical properties of metallic Au x(SiO 2) 1− x and Ni x(SiO 2) 1− x films

To study the optical properties of the metal–insulator granular films, a series of Ni x (SiO 2) 1− x and Au x (SiO 2) 1− x granular films was made with a variation of x and the annealing process. The complex dielectric function was measured in the 1.5–4.8-eV photon energy range. New spectral features were found in the dielectric functions. For Au x (SiO 2) 1− x samples, a new peak in the ε 2 spectra is seen around 2 eV, especially for x=0.67. The ε 1 spectra change continuously from positive to negative in the low photon energy range, resulting in a true zero of ε 1 associated with the plasmon occurring at 2.0–2.5 eV and at about 3.6 eV for the Au- and Ni-based films, respectively. Compared to previous data, the experimental results obtained in this work provide richer information to understand better the optical properties of the metal-granular films that are not well predicted by the theoretical model. The effect will be useful in the metallic multilayer structure design and applications.

Characterization of thin-film devices for gas sensing

In this report are summarized the results of our investigations of gas sensors, based on thin films of metal oxides and multilayer structures, carried out by using surface analysis techniques during the last few years. For the studies of surface chemical composition and its variation in depth, the following experimental techniques have been employed: XPS, selected-area XPS depth profiling, scanning Auger-microscopy (SAM) and SIMS. The morphology of the sensors was investigated by means of SEM and scanning tunnelling microscopy (STM). Most of the devices investigated in our work were based on thin films of polycrystalline tin oxide, doped or surface-activated with diverse metals (Pt, Au, Cu, Ag, etc.). In addition, the thin films of mixed Ti-W oxides with very promising gas-sensing characteristics were analysed. A new family of multilayer devices consisting of one or more ultrathin metal films (Pt, Au, Mo, Ni, etc.) and a top layer of tin oxide was also examined. Another type of multilayer structure with interesting gas-sensing parameters was based on an ultrathin film of Pt covered with titanium bis-phthalocyaninate. The experimental cases of surface analysis and optimization of different types of gas sensors are discussed, revealing the main uncertainties in preparation technology and emphasizing the benefits of surface-sensitive techniques for this application.

Study of optical properties of metallic Au : SiO 2 and Ni : SiO 2 films

To study the optical properties of the metal–insulator granular films, a series of Ni x SiO 2(1 −x) and Au x SiO 2(1 −x) granular films was made with variation of x and the annealing process. The complex dielectric function was measured in the 1.5–4.8 eV photon energy range. New spectral features were found in the dielectric functions. For AuSiO 2 samples, the new peak in ε 2 spectra is seen around 2 eV, especially for x=0.67. The ε 1 spectra change continuously from positive to negative at the low–photon energy range, resulting in a true ε 1 associated with the plasmon occurred at 2.0–2.5 eV and at about 3.6 eV for the Au- and Ni-based films, respectively. Comparing to previous data, the experimental results obtained in this work provide richer information to understand better the optical properties of the metal-granular films that are not well predicated by the theoretical model. The effect will be useful in the metallic multilayer structure design applications.

Imaging metallic multilayer structures through ultrafast optically driven excited electron transport

Imaging metallic multilayer structures through ultrafast optically driven excited electron transport

Transverse thermoelectricity in a tilted metallic multilayer structure.

Thermoelectricity is investigated in a material designed to show anisotropic transport properties: Copper/constantan/copper \( \cdot \cdot \cdot \) multilayer structures were prepared by sintering of a compressed stack of alternating foils of these materials and are described by effective “in-plane” properties \(S_\parallel \) and \(k_\parallel \) for the Seebeck-coefficient and the thermal conductivity along the layers, and “out-of-plane”-properties \(S_ \bot \) and \(k_ \bot \) along the stack axis. Samples in form of thin slabs prepared by cutting the stack obliquely to the stack axis showed thermoelectric fields transverse to temperature gradients across the slab due to off-diagonal elements in the Seebeck-tensor, and may be used as devices for detection of laser radiation.

Transverse thermoelectric response of a tilted metallic multilayer structure

Thermoelectric fields transverse to an applied temperature gradient have been observed in artificially created tilted multilayer structures. Copper-constantan multilayer structures were prepared by sintering of a compressed stack of copper/constantan/copper foils and by cutting the stack obliquely to its axis. Tilted multilayer structures represent a new class of thermoelectric devices, and applications for detection of light are demonstrated.

ChemInform Abstract: Magnetic Properties and Structure of Metallic Multilayers Investigated by NMR

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The medium-related optical constants of noble metals observed by ellipsometric study

The optical constants used in metallic multilayer structures may differ from those measured in air using a two-phase model and thus will affect the design performance of an optical device. To understand the effect better, we used Dove prisms with different refractive indices as the substrates. The spectroscopic ellipsometry method was used to measure directly the optical constants of Ag and Au films which were thermally or electron-beam evaporated on the bottom of the prisms. In this configuration, the optical constants of the films can be measured at the metal-air and metal-substrate interfaces. Upon data reduction, we found that the optical constants of a given film measured at the metal-substrate interface do change with the refractive index of the substrate and differ from those measured at the metal-air interface in both of the Drude and interband transition regions. These results agree with those obtained by other authors in a liquid-contacting situation, and need to be studied in great detail in the future.

Analysis, design, and optimization of spiral inductors and transformers for Si RF ICs

Silicon integrated circuit spiral inductors and transformers are analyzed using electromagnetic analysis. With appropriate approximations, the calculations are reduced to electrostatic and magnetostatic calculations. The important effects of substrate loss are included in the analysis. Classic circuit analysis and network analysis techniques are used to derive two-port parameters from the circuits. From two-port measurements, low-order, frequency-independent lumped circuits are used to model the physical behavior over a broad-frequency range. The analysis is applied to traditional square and polygon inductors and transformer structures as well as to multilayer metal structures and coupled inductors. A custom computer-aided-design tool called ASITIC is described, which is used for the analysis, design, and optimization of these structures. Measurements taken over a frequency range from 100 MHz to 5 GHz show good agreement with theory.

Interfacial roughness and magnetoresistance in [formula omitted] multilayers

The structure and magnetic properties of Co Cu multilayers, grown on a float glass, in a molecular beam epitaxy (MBE) system are discussed. Structural characterization of samples was performed in-situ by means of a reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES), as well as ex-situ by X-ray reflectometry. For the first time, we show successful analysis of layered structure of metallic multilayers by scanning tunneling microscopy (STM). Magnetization and in-plane magnetoresistance were measured as functions of Co and Cu sublayer thicknesses. The evidences of oscillatory coupling of magnetic sublayers with varying thicknesses of nonmagnetic spacer are presented. Co Cu multilayers also display giant magnetoresistance (GMR) effect. The influence of buffer layer roughness on GMR is clearly shown.

Patterning of Cu, Co, Fe, and Ag for magnetic nanostructures

Wet and dry etching of thin metallic multilayer structures is necessary for the development of sensitive magnetic field sensors and memory devices based on spin–valve giant magnetoresistance elements. While it is well established that Cu, Co, and Fe are soluble in HNO3 and H3PO4 at room temperature, little effort has been made to investigate selective wet and dry etch chemistries. For example, we find Ag is not etched in H2SO4, HCl, or H3PO4 under conditions where etch rates for the other metals are in the range of 2000–60 000 Å/min. Electron cyclotron resonance (ECR) SF6/Ar plasmas provide etch selectivities of ⩾5:1 for Ag over Cu, Co, and Fe, while lower selectivities are obtained with CH4/H2/Ar. Cl2-based plasma chemistries leave significant metal–chlorine surface residues, which can be removed in situ by low ion energy H2 or Ar plasma treatments that eliminate corrosion problems. Cu etch rates in excess of 3000 Å/min at 25 °C can be obtained in ECR Cl2/Ar discharges because the high ion flux prevents formation of a CuClX-rich selvedge layer, which normally only is volatile for etch temperatures ⩾220 °C in conventional reactive ion etch systems. Photoresist masks suffer severe reticulation under ECR conditions, at least for microwave powers >400 W, and SiO2 or SiNX thin films offer much better etch resistance.

Magnetic Properties and Structure of Metallic Multilayers Investigated by NMR

ABSTRACTAs a probe of the short range chemical and topological order, NMR is useful for structural investigations of magnetic multilayers (interface structure and composition, bulk phases and defects, strains). The magnetic character of the raw data makes it also possible to study local magnetic properties of these composite systems, and to correlate them with local structural features. The hyperfine field is the first output of an NMR experiment which gives a direct insight on the local magnetization in ferromagnets. NMR is also sensitive to the restoring torque exerted on the electronic moment by the local magnetic anisotropy and/or exchange and dipolar couplings. Combined with the fact that the various parts of a sample (atomic planes involved in the interfaces, bulk phases and bulk defects) can be discriminated in the spectra, the magnetic information contained in the data allows to probe quantitatively or, at least, to place on a relative scale, the different magnetic responses of the different parts of a sample. We present here the relevant results which we have obtained in the course of our investigations of Co based multilayers and spin valves (interface magnetic profiles, inhomogeneities of magnetic anisotropy and of magnetic coupling).

Magnetic structure and magnetoresistance of metallic multilayers

Giant magnetoresistance (GMR) phenomena are briefly introduced and the relationship between the magnetic structure and the magnetoresistance of multilayers is argued. The merits of non-coupled-type multilayers, for technical applications and also for fundamental studies, are described. The results achieved on samples with doped interface layers indicate that the spin-dependent scattering occurs primarily at the interface sites. MR measurements in a new geometry, with the current at an angle to the plane, were carried out by depositing non-coupled-type multilayers on substrates with V-shaped microgrooves, and enhanced MR ratios were observed.