Magnetic Properties Of Multilayers Research Articles

Thickness Dependence of Magnetic Properties of Tb–Co/Ti and Tb–Co/Si Multilayers

Nanoscale [Tb–Co/Ti]n and [Tb–Co/Si]n multilayers were designed and prepared by the rf-sputtering technique. Their structure and magnetic properties have been experimentally studied. Low-angle X‑ray diffraction studies confirmed that a well-defined layered structure was formed in all investigated cases. The change in the magnetic properties of multilayers with a decrease in the thickness of the Tb–Co layers was due to both the size effect and the influence of the material of the non-magnetic spacers, namely the reduction of the Co atom moment because of the electron charge transfer from atoms of the Ti or Si spacers to atoms of the cobalt.

Total film thickness controlled structural and related magnetic properties of sputtered Ni/Cu multilayer thin films

Abstract In this study, the impact of total film thicknesses on the structural and magnetic properties of multilayers was investigated. The multilayer films were produced by a DC magnetron sputtering system by considering different total thickness values as x[Ni(10 nm)/Cu(30 nm)] (x = 3, 6, 7). A face centered cubic crystalline structure with (1 1 1) preferential orientation was formed for all Ni/Cu multilayers investigated. The number of grains on surface immensely increased and their size significantly decreased as the total film thickness was systematically increased. And also, the arithmetic mean roughness deviation (Ra) and root mean square (Rq) values increased with the increase of total thickness of Ni/Cu films. From scanning electron microscope and atomic force microscope results, the surface roughness increased with increasing the total thickness. The saturation magnetization (Ms), remanent magnetization (Mr) and coercivity (Hc) values were also measured. The Ms values increased from 590 emu/cm3 to 615 emu/cm3, Mr values decreased from 396 emu/cm3 to 204 emu/cm3 and Hc values gradually decreased from 116 Oe to 89 Oe as the total film thickness increased from 120 nm to 280 nm. It was found that total thickness of Ni/Cu multilayers is an effective parameter and has a considerable role to adjust the magnetic properties for the intended purposes.

Modeling of magnetic properties (Cr/NiO/Ni) based multi-layers deposited by magnetron sputtering using Preisach model

In the present work, thin films of Cr/NiO/Ni are deposited on glass substrates using RF magnetron sputteringtechnique. The uniformity and homogeneity of the prepared films were controlled by varying the power of the source, the target-substrate distance and the pressure of the plasma gas which is argon. In order to test the Preisach Model, we carried outmeasurements according to two directions: parallel and perpendicular to the substrate plane using a Vibrating SampleMagnetometer at room temperature. Good agreement has been obtained by comparing the experimental hysteresis loops to theones determined using Preisach model. We conclude that this model is powerful in predicting the magnetic properties ofmultilayer systems. # Cr/NiO/Ni #MAGNETRON_SPUTTERING #PREISACH MODEL #MAGNETIC_HYSTERESIS

CoFeSiB–Pd multilayers and co-deposited alloy films exhibiting perpendicular magnetic anisotropies after heat treatment up to 500 °C

Ferromagnetic layers exhibiting perpendicular magnetic anisotropy (PMA) are essential components in magnetic random access memory cells. Various Co- and Fe-based multilayers (MLs) have been considered because the magnetic properties of MLs can be easily controlled by changing the ferromagnetic and nonmagnetic layer thicknesses and number of bilayers. However, MLs generally suffer from the loss of PMA after high-temperature heat treatments (beyond approximately 400 °C) during device processing, which are associated with back-end-of-line device fabrication. Moreover, ML deposition may limit the throughput of the film mass production. Here, we investigate the PMA stability of sputter-deposited CoFeSiB/Pd ML as well as CoFeSiB–Pd co-deposited alloy (CA) films exposed to various annealing temperatures. Although the ML films exhibited PMA, regardless of the annealing temperature up to 500 °C, the CA films started to exhibit strong PMA after 400 °C, which was maintained up to 500 °C. To understand the magnetic property changes, we performed microstructural analyses. The ML films in the as-deposited state exhibited well-defined layered microstructures and evolved into polycrystalline alloys at 500 °C. In contrast, the CA films in the as-deposited state exhibited an amorphous microstructure but transformed into polycrystalline alloys at 500 °C, similar to their ML counterparts. Both Co and Pd, the major constituents of the films, underwent interdiffusion and formed a Co–Pd ordered phase, which contributed to the appearance of PMA.

Interface effects on the magnetic properties of layered Ni2MnGa/Ni2MnSn alloys: A first-principles investigation

The effect of interfaces on the magnetic properties of multilayers is analyzed for Ni2MnGa/Ni2MnSn system using density functional theory. The Ni spin moments at the interface change by about 30% compared to the bulk value, whereas the effect on the Mn spin moments is much less pronounced. A similar strong effect is also observed for the Ni orbital moments at the interface. The magneto-crystalline anisotropy of the multilayer systems can be understood by the additive contribution of the respective values of strained bulk materials.

Magnetotransport Properties and Electronic Structure of Ni 8 1 Fe 1 9 /W 9 0 Ti 1 0 Multilayers

The magnetotransport properties of Ni81Fe19/W90Ti10 multilayers are investigated. The effect of the thicknesses of magnetic (Ni81Fe19) and nonmagnetic (WTi) layers on the magnetoresistance (MR) is theoretically discussed in the framework of the Johnson–Camley semiclassical approach based on the Boltzmann transport equation. A comparison between the calculated and measured MR ratios is obtained. The observed MR ratio oscillates for WTi layer thickness with an average period of 10 A. A weak MR(tNiFe) ratio for a fixed tWTi is obtained, and it presents a maximum peak of the MR with a value of 0.8 % located at tNiFe = 50 A. In addition, electronic and magnetic properties of multilayers are investigated by self-consistent ab initio calculations based on the Korringa–Kohn–Rostocker (KKR) approximation. Spin polarized within the framework of the coherent potential approximation (CPA) is considered for calculations.

Multilayer nanogranular films (Co40Fe40B20)50(SiO2)50/α-Si:H and (Co40Fe40B20)50(SiO2)50/SiO2: Magnetic properties

Magnetic properties of multilayers, consisting of nanogranular (Co40Fe40B20)50(SiO2)50 layers as thin as magnetic granule diameter alternating the α-Si:H or SiO2 layers and the single layer film (Co40Fe40B20)50(SiO2)50 with the thickness much larger than the magnetic granule diameter are reported and compared. The thick single layer film is ferromagnetic but the multilayer film with the ultrathin granular layers and SiO2 spacer is superparamagnetic. This is interpreted as the result of increasing percolation threshold in the 2D granular media above 50% concentration of magnetic granules in the multilayer with the nonmagnetic and dielectric SiO2 spacer. The multilayer with the α-Si:H spacer is superparamagnetic at 300 K but it becomes ferromagnetic, when temperature is below 250 K. It is assumed to be resulted from the exchange interaction of magnetic granules through the semiconductor α-Si:H layers. The value of exchange interaction through the semiconductor spacer is estimated.

Magnetic Properties and Electronic Structure of Ni81Fe19/Zr Multilayer Films

Magnetic properties of NiFe/Zr multilayer films, prepared by DC magnetron sputtering, have been studied by vibrating sample magnetometer and ferromagnetic resonance (FMR). Spin-wave resonances were observed in Ni81Fe19/Zr multilayer films in FMR experiments, and the spin wave was found to be sustained by both the whole films. Estimated small interlayer coupling constant shows weak exchange coupling effect between NiFe layers across Zr spacers. The FMR linewidth, in parallel geometry, of the uniform mode was found to increase with decreasing NiFe thickness (20 A ≤ \(t_{\mathrm{NiFe}}\) ≤ 120 A) indicating that it corresponds to an interfacial effect. In addition, electronic and magnetic properties of multilayers are investigated by self-consistent ab initio calculations based on Korringa–Kohn–Rostocker (KKR). Spin polarized within the framework of the Coherent Potential Approximation (CPA) is considered for calculations.

Effect of Spacer Layer Thickness on the Magnetic Properties of $({\hbox {SnO}}_{2}/{\hbox {Cu–Zn}}\ {\hbox {Ferrite}})_{\rm n}$ Multilayers

Multilayers (ML) of SnO2 and Cu-Zn Ferrite were deposited by rf-sputtering. The effect of spacer layer (SnO2) thickness on the structural and magnetic properties of ML were studied. The disorder and strain in the system is found to increase with increasing spacer layer thickness. The interlayer coupling is found to decrease with increasing SnO2 layer thickness. The FMR intensity, magnetization and the exchange coupling strength initially increases then decreases with increasing SnO2 thickness. This behavior may be attributed to the oscillation in the exchange coupling across the non magnetic layer due to quantum interference of the electron waves reflected from the interfaces. The ML exhibit uniaxial anisotropy and the ML are found to be more homogeneous when the film normal is at an angle of 40° with the applied field. Decreasing magnetic moment and increasing resonance field at low temperatures indicated the presence of antiferromagnetic interactions in these ML.

Monte Carlo Simulation of Magnetic Properties of Multilayer with Amorphous Surfaces

Monte Carlo simulation studies are performed to examine the effects of amorphous surfaces and the size of the system on magnetic critical properties of a face-centered cubic magnet modeled with a Heisenberg Hamiltonian. A Gaussian probability distribution of the exchange integrals is applied for the description of amorphous surfaces. The Spontaneous magnetization and magnetic susceptibility are calculated for both the inner and surface. A variety of phase diagrams have been also obtained. The simulated results can well explain the experimental facts.

Influence of Co layer thickness on the structural and magnetic properties of multilayers

The correlated effects of the insertion of a Pt spacer between ferromagnetic and antiferromagnetic layers and of the variation of the Co layers' thickness on the structural and magnetic properties of multilayers have been studied. Samples with n = 1 and 7, tCo = 0.4 and 0.6 nm, tPt = 0 and 0.4 nm have been investigated by tomographic atom probe and superconducting quantum interference device magnetometry. For spacer-free samples (tPt = 0), the structural investigation shows that when tCo = 0.4 nm, Mn and Ir atoms diffuse deeply into the (Pt/Co)3 multilayers. In contrast for tCo = 0.6 nm, the Mn and Ir diffusion is much reduced. Because Pt acts as a barrier against the Mn and Ir diffusion, this difference is less pronounced in samples with Pt insertion. The hysteresis loops shapes, the exchange bias fields and the saturation magnetization values were correlated with the structural properties of these samples and discussed, taking into account the susceptibility, exchange stiffness and perpendicular magnetic anisotropy.

Effect of Sputtering Deposition Process on Magnetic Properties of Magnetic Multilayers

The energy distribution of energetic particles produced in magnetron sputtering plasma was measured by varying the sputtering gas species and pressure, and Co/Pt, Gd/Fe, and Co/Cu multilayers were fabricated using the same sputtering cathodes as the diagnosed one in order to discuss the relationship between the plasma parameters and the magnetic properties of the multilayers. When a heavy mass target such as W or Pt was used in Ar gas sputtering, the energy of the recoiled Ar atoms from the target was found to reach up to 150 eV. The energy and flux of the recoiled atoms were reduced by using Kr or Xe gas in place of Ar gas, whereas they are rather independent of the sputtering pressure in the range of 0.3–0.5 Pa. Low-pressure sputtering was effective for increasing the energy of sputtered atoms, which was at most 10 eV. Layered structures of the magnetic multilayers were significantly influenced by the sputtering conditions. The atomic intermixing at the interface, i.e., degradation of the interface sharpness, was controlled mainly by using a heavy sputtering gas, while the surface or interface flatness mainly depended on the sputtering pressure. The perpendicular magnetic anisotropy of Co/Pt and Gd/Fe multilayers was enhanced by suppressing atomic intermixing rather than by improving the interface flatness, and the use of a heavy inert gas such as Kr or Xe was found to be effective to enhance the anisotropy. When Kr or Xe gas was used, the monatomic layered structure of the Co (1 ML)/Pt (1 ML) (ML: monatomic layer) multilayer was found to survive, and positive perpendicular anisotropy was observed. In contrast, the magnetoresistance ratio of Co (1.5 nm)/Cu (t nm) multilayers (t∼0.9 nm) increased to around 50% when they were sputtered in an inert gas at low pressure, while the use of Xe gas degraded their magnetoresistance ratio. In the Co/Cu multilayers, the interface flatness rather than the sharpness was critical for enhancing the magnetoresistance ratio.

Domain walls in systems with large magneto-crystalline anisotropy

Domain walls in magnetic thin films occurring at the interfaces of grains with different magnetic orientations can significantly influence the electronic properties of magnetic multilayers. We investigate the energy of formation of domain walls and their magnetic structure in systems with large magneto-crystalline anisotropy making use of the fully relativistic, spin-polarized screened Korringa–Kohn–Rostoker Green's functions technique for layered systems. Results are presented for Pt(001)/T/Pt(001), with T = Co, Co80Pt20. The calculated dependence of the formation energy on the domain wall width agrees with the predictions from the phenomenological Ginzburg–Landau theory. However, the ab initio calculations allow for a detailed layer resolved study of the domain wall formation. We observed that domain walls in Co80Pt20 can be easier formed as in pure Co, but the energy saved than compared to a direct flip of the magnetic orientation in one domain is smaller for the alloyed system.

High frequency properties of magnetic multilayers

The review of the experimental methods of the microwave giant magnetoresistive (GMR) effect measurement is presented. The absorption of the electromagnetic power in the cavity or any other resonant circuit and the direct penetration through the multilayer are the most usable methods. It was found that magnetic field dependence of microwave absorption in the metallic multilayers is governed by GMR effect. The direct correlation between the GMR and the transmission of electromagnetic waves through the metallic magnetic superlattices was established. The results of microwave transmission through the Fe/Cr superlattices are presented in the frequency range from 26 to 38 GHz.

Mössbauer study of magnetic Fe/FeSi multilayers

Many useful properties of magnetic multilayers depend on the coupling between the ferromagnetic layers. The coupling often oscillates with the thickness of non-magnetic spacer layers: it is ferro- or antiferromagnetic or even non-collinear near a critical thickness. We investigated the magnetron-sputtered Fe/FeSi multilayers with spacer thickness around 1.7 nm by means of Conversion Electron Mossbauer Spectroscopy with oblique incidence of the γ beam in order to gain information on the orientation of the local magnetic moments in the multilayer plane. The results show that the local moments make an angle of 45°–50° with the direction of the remanent magnetization. This is consistent with strong biquadratic coupling which in turn is expected at this spacer thickness from our magnetic measurements. An analysis of the distribution ofBhf corresponding to different numbers of n.n. Si atoms in the bcc Fe structure points to weak diffusion of Si through the Fe/FeSi interface characterized by a diffusion length of about twice the substrate roughness.

Mössbauer Studies on Magnetic Multilayers

Mossbauer spectroscopy is a useful tool to study the magnetic properties of multilayers from microscopic viewpoints. Recent experimental results relating to the issues on giant magnetoresistance (GMR) and interlayer coupling are briefly described. For the study of magnetic layers, 57Fe is a suitable Mossbauer isotope. On the other hand, in order to estimate spin polarization in non-magnetic layers, 119Sn and 197Au are used as microscopic probes. It is also introduced that the antiferromagnetic order of ultrathin Cr layers is investigated from Mossbauer spectra of inserted 119Sn probe layers with a monatomic thickness.

X-ray Probes of Magnetic Multilayer Structure

ABSTRACTWe discuss the application of x-ray scattering and fluorescence to the problem of unravelling the relationship between the structural and magnetic properties of magnetic multilayers. Particular attention is paid to the use of grazing incidence diffuse scatter to determine the compositional gradient, out-of-plane roughness amplitude, in-plane correlation length and fractal parameter of buried interfaces. Anomalous scattering provides information on the local environment of specific atoms and grazing incidence fluorescence is a depth -sensitive probe of chemical composition. We present examples indicating the sensitivity limits and the reproducibility of the techniques, all from multiple layer structures of magnetic metals.

Magnetic properties of multilayers and interfaces by Mössbauer spectroscopy

The usefulness of Mössbauer spectroscopy for studies of magnetic multilayer systems is discussed. By applying 57Fe Mössbauer spectroscopy, the behavior of ultra-thin magnetic layers is studied. Position-specified information is available by preparing samples in which 57Fe probes are located as desired, to provide depth selectivity. For the studies on non-magnetic layers, hyperfine field observations by 197Au and 119Sn probes are worthwhile. Spin polarizations in Au layers penetrating from neighboring ferromagnetic 3d layers are estimated from Au Mössbauer spectra. Spin polarizations in Au layers are also studied by inserted Sn probes in Au/3d multilayers. In Sn spectra for Cr/Sn multilayers, it is found that remarkably large spin polarization penetrates into the Sn layers from a contacting Cr layer, which suggests that Cr atoms in the surface layer have a ferromagnetic spin alignment.

CORRELATION BETWEEN THE POTENTIAL CONTRIBUTION AND MAGNETIC TRANSPORT PROPERTIES FOR MAGNETIC MULTILAYERS

We discuss the exchange potential and impurity scattering potential effect on the magnetic transport properties of magnetic multilayers. In the case of Hartree–Fork approximation, the model Hamiltonian with respect to the magnetization and potential contribution is presented. The expression of giant magnetoresistance is obtained by considering both interface and bulk magnetization contribution. The results show that the giant magnetoresistance in magnetic multilayer is different for different layer thickness. Meanwhile, we also clarify the interface and bulk contribution of the giant magnetoresistance in magnetic multilayer for different exchange potential and impurity scattering potential.

Optimized epitaxial growth of Fe on Ag(001)

We report on a comprehensive study of the growth of 5-nm-thick epitaxial Fe(001) films on Ag(001) substrates which are deposited on Fe-precovered GaAs(001) wafers. We characterize the films in situ by scanning tunneling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy, and depth profiling to obtain information about the geometrical and chemical surface structure. We find that the surface morphology is improved by either growing or postannealing the films at elevated temperatures. During deposition at and above room temperature, however, an atomic exchange process is activated that results in a thin Ag film (up to 1 ML) ``floating'' on top of the growing Fe film. We propose and confirm a growth procedure that yields clean, Ag-free surfaces with a morphology superior to the other films. This optimized recipe consists of two steps: (i) low-temperature growth of the first 2 nm in order to form a diffusion barrier for the Ag substrate atoms, and (ii) high-temperature deposition of the final 3 nm to take advantage of the improved homoepitaxial growth quality of Fe at elevated temperatures. The relevance of these results with respect to magnetic properties of multilayers is discussed.