Nonmagnetic Layer Thickness Research Articles

Investigation of the effects of Cu layer thickness and annealing temperature under air atmosphere on the properties of Co/Cu multilayer films

In this study, the suitability of Co/Cu multilayer films with different physical conditions (varying thickness values and systematic annealing processes) in magnetic technology applications is discussed. Co/Cu films were deposited by the sputtering technique. The effects of different thicknesses of non-magnetic (Cu) layers and annealing temperature on magneto-structural properties were investigated. Different thicknesses of Cu layers were determined as 34 nm, 10 nm, 4 nm. Additionally, two annealed situations were considered to investigate the annealing effect. While the first one is exposing the films to 80 °C and 130 °C for 240 s, second one is annealing the films at 180 °C for different exposure times (50 s and 150 s). All films that have different thicknesses of Cu layers crystallized in (111) plane of the face centered cubic (fcc) structure. The intensity of this peak increased with increasing Cu layers thickness. Variation in the thickness of Cu layers has an important effect on the film surface. Saturation magnetization (Ms), coercivity (Hc) and squareness (Mr/Ms, Mr: remanent magnetization) were considerably affected by variation of the Cu content and film surface caused by the change in the thickness of the Cu layers. The film with 4 nm Cu layer thickness has the highest Ms, lowest Hc values and high Mr/Ms ratio. This indicates magnetically high efficient compared to the other films in the same series. The fcc structure continued to exist for the films annealed at 80 °C and 130 °C for 240 s. It was found that the annealing procedure transfigured the film surface and the differences in Ms and Hc values can be mostly attributed to this transfiguration because of the same film content revealed. An increase in Ms value, and a slight decrease in Hc and Mr/Ms values were detected for the annealed film at 130 °C, compared to the film annealed at 80 °C. It was also seen that the film structure was damaged at 180 °C because of excessive heat transfer.

Effects of structure, size and non-magnetic Cu layer thickness on magnetization switching behavior in Ni/Cu/M (M [formula omitted] Ni, Co) cylindrical nanowires

We have investigated the dependence of the magnetization switching behavior on the structure, size and nonmagnetic Cu layer thickness (tCu) in Ni/Cu/M (M = Ni, Co) cylindrical nanowires fabricated by electrodeposition using porous polycarbonate templates. The crystal structure of the Ni nanowires was (111)- or (200)-oriented polycrystalline fcc, while that of Co nanowires was (100)- or (101)-oriented hcp and/or (111)-oriented polycrystalline fcc. When the wire diameter (d) was 50 nm, the squareness ratio (Mr/Ms) for M = Ni, as estimated from the magnetization curve, is almost constant at Mr/Ms∼0.79 (Mr/Ms∼0.64 for M = Co) when tCu increases from 0 to 500 nm. When d=100nm, Mr/Ms decreases by 41% from 0.71 to 0.42 with increasing tCu from 0 to 700 nm for M = Ni, while Mr/Ms decreases by 25% from 0.53 to 0.40 with varying tCu from 0 to 500 nm for M = Co. The threshold Cu layer thickness (tCuth) beyond which Mr/Ms becomes constant at d=100nm is ∼500 nm for M = Ni and ∼300 nm for M = Co. The results are qualitatively consistent with those obtained from our micromagnetic simulation and analysis. The observed difference in the tCuth dependence of Mr/Ms between M = Ni and Co is attributed to the change in the magnetic domain structure of the nanowires as it sensitively varies with the magnetocrystalline anisotropy. On the other hand, the coercive force of the nanowires shows a small tCu dependence for both d=50 and 100 nm. These results indicate that the layered structure in the nanowires governs the magnetic domain structure, though the effect on the magnetization switching behavior is indeed relatively small.

Atomic‐Scale Modulation of Synthetic Magnetic Order in Oxide Superlattices

Atomic-scale precision control of magnetic interactions facilitates a synthetic spin order useful for spintronics, including advanced memory and quantum logic devices. Conventional modulation of synthetic spin order has been limited to metallic heterostructures that exploit Ruderman-Kittel-Kasuya-Yosida interaction through a nonmagnetic metallic spacer; however, they face issues arising from Joule heating and/or electric breakdown. The practical realization and observation of a synthetic spin order across a nonmagnetic insulating spacer will lead to the development of spin-related devices with a completely different concept. Herein, the atomic-scale modulation of the synthetic spiral spin order in oxide superlattices composed of ferromagnetic metal and nonmagnetic insulator layers is reported. The atomically controlled superlattice exhibits an oscillatory magnetic behavior, representing the existence of a spiral spin structure. Depth-sensitive polarized neutron reflectometry evidences modulated spiral spin structures as a function of the nonmagnetic insulator layer thickness. Atomic-scale customization of the spin state can move the field one step further to actual spintronic applications.

Tuning magnetostatic interaction and coercivity distributions of FeCo/Cu multilayer nanowire arrays by variation of magnetic and nonmagnetic layer aspect ratios

FeCo/Cu multilayer NW arrays are fabricated using a pulsed electrodeposition method in 50 nm pore diameter anodic aluminum oxide templates. The magnetic layer (LFeCo) and nonmagnetic layer (LCu) thicknesses range between 23–225 and 2–50 nm, respectively. These layer designations make it possible to find a thin Cu layer, in which the magnetic behavior of multilayer NWs is similar to that of alloy NWs. A threshold LCu is also obtained, representing dual behavior of the coercive field in FeCo/Cu multilayer NWs. These behaviors, in turn, are associated with an increase in magnetizing and demagnetizing interactions, as evidenced by hysteresis curve and first-order reversal curve experiments. By extracting magnetic parameters such as the average coercive field, irreversible coercive field, magnetostatic interaction distribution, and reversibility, the magnetic behavior of FeCo/Cu multilayer NWs is comprehensively explored as a function of LFeCo.

Correlation between the average composition of coherent superlattice and the GMR properties of electrodeposited Co–Cu/Cu multilayers

Abstract In contrast to vacuum-deposited Co/Cu multilayers the electrodeposited ones do not exhibit any oscillation behaviour in magnetic resistance properties as a function of the thickness of non-magnetic Cu layers. According to the magnetic investigations they show ferromagnetic and superparamagnetic character as a consequence of the lack of antiparallel coupling of neighbouring magnetic layers. Magnetic resistance observed on electrodeposited Co– Cu/Cu multilayers is believed to originate from the randomly antiparallel oriented magnetic domains. In the present paper the evolution of magnetic resistance properties is studied against the average Cu concentration of multilayers prepared under a Cu deposition potential of –0.25 and – 0.62 V, and the best magnetic resistance properties were found in the films with composition of 52% and 60% Cu, respectively. The average concentration was determined by electron microscopic and X-ray diffraction measurements.

Synthetic antiferromagnetic layer based on Pt/Ru/Pt spacer layer with 1.05 nm interlayer exchange oscillation period for spin–orbit torque devices

We investigated interlayer exchange coupling through Pt/Ru/Pt and Pt/Ru multilayers as candidates of nonmagnetic spacer layers in the synthetic antiferromagnetic (AF) layer, which is available for studying AF spintronics using current-induced spin–orbit torque (SOT) switching originating from the spin Hall effect. The AF interlayer exchange coupling with the oscillation period of Λ2 ∼ 1.05 nm was observed even for the face-centered cubic (fcc) Pt (tPt)/hexagonal Ru/fcc Pt (tPt) nonmagnetic spacer layer structures in the wide range of both Pt and total nonmagnetic spacer layer thicknesses (0 ≤ tPt ≤ 0.8 nm, 1.0 ≤ ttotal ≤ 2.3 nm), which would be useful for the systematic investigation of the SOT on the AF structure. Moreover, we observed the disappearance of the one oscillation period (Λ1 ∼ 1.65 nm) in the case of Pt(111)/Ru(0001) and Pt(111)/Ru(0001)/Pt(111) spacer layers, whereas the existence of two oscillation periods of AF interlayer exchange coupling (Λ1 ∼ 1.65 nm and Λ2 ∼ 1.05 nm) in the case of Ru spacer layer was observed. We expect that the Pt/Ru/Pt spacer layer with the oscillation period of Λ2 ∼ 1.05 nm will pave a way to the AF spintronics based on the multilayer systems.

Antiferromagnetic interlayer exchange coupling and large spin Hall effect in multilayer systems with Pt/Ir/Pt and Pt/Ir layers

We investigated Pt/Ir/Pt and Pt/Ir multilayers as candidates of nonmagnetic spacer layers in synthetic antiferromagnetic (AF) layers, which are available for the systematic study on AF spintronics. In these systems, we observed (i) AF interlayer exchange coupling in Pt/Ir/Pt and Pt/Ir nonmagnetic spacer layers sandwiched by Co layers and (ii) large spin Hall conductivity in Pt/Ir multilayer heavy-metal systems which is essential to achieve low power consumption spin-orbit torque switching. We found that total nonmagnetic spacer layer thickness $[{t}_{\mathrm{total}}={t}_{\mathrm{Pt}}(\mathrm{Pt}\phantom{\rule{0.16em}{0ex}}\mathrm{thickness})+{t}_{\mathrm{Ir}}(\mathrm{Ir}\phantom{\rule{0.16em}{0ex}}\mathrm{thickness})]$ range in which AF interlayer exchange coupling is observed is wide in Co/nonmagnetic spacer layer/Co with Pt/Ir/Pt and Pt/Ir nonmagnetic spacer layers. Moreover, the large spin Hall angle of ${\ensuremath{\theta}}_{\mathrm{SH}}=10.3%$ and low resistivity of ${\ensuremath{\rho}}_{xx}=35\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$ in Pt/Ir multilayer heavy metal are observed. These results indicate that Pt/Ir/Pt and Pt/Ir are nonmagnetic spacer layers allowing us to achieve the AF interlayer exchange coupling and generation of large spin-orbit torque via spin Hall effect in synthetic AF coupling layer system.

Spacer-Layer-Tunable Magnetism and High-Field Topological Hall Effect in Topological Insulator Heterostructures

Controlling magnetic order in magnetic topological insulators (MTIs) is a key to developing spintronic applications with MTIs and is commonly achieved by changing the magnetic doping concentration, which inevitably affects the spin-orbit coupling strength and the topological properties. Here, we demonstrate tunable magnetic properties in topological heterostructures over a wide range, from a ferromagnetic phase with a Curie temperature of around 100 K all the way to a paramagnetic phase, while keeping the overall chemical composition the same, by controlling the thickness of nonmagnetic spacer layers between two atomically thin magnetic layers. This work showcases that spacer-layer control is a powerful tool to manipulate magneto-topological functionalities in MTI heterostructures. Furthermore, the interaction between the MTI and the Cr2O3 buffer layers also leads to a robust topological Hall effect surviving up to a record-high 6 T of magnetic field, shedding light on the critical role of interfacial layers in thin-film topological materials.

Influence of interface anisotropy on ferromagnetic resonance in CoP/(NiP)am/CoP films

The paper presents the results of ferromagnetic resonance studies of three-layer magnetic films, where the magnetic layers are amorphous magnetically soft CoP layers, and the intermediate non-magnetic spacer is amorphous NiP layer. We found that, regardless of the nonmagnetic layer thickness, the interlayer interaction is ferromagnetic. Perpendicular anisotropy forms at the interface between the CoP and NiP layers. It is reasonable to suppose that the interlayer interaction is long-range, what is not typical for systems with metallic non-magnetic spacers.

Synthetic Antiferromagnetic Structures in Technology of Spintronic Devices

In this paper, we consider synthetic antiferromagnetic (SAF) structures and their influence in a fixed layer of a spin-tunnel junction on the magnitude of the magnetoresistive effect and temperature stability. The SAF structure consists of two ferromagnetic (FM) layers, between which a nonmagnetic film is located. The ion exchange interaction of two FM layers has an oscillating character and depends on the nonmagnetic layer thickness and the surface roughness of the FM layers. The mechanism of SAF magnetization reversal with fixation by an antiferromagnetic layer and in its absence, as well as the effect of the sequence of deposition of layers in the SAF structure on its properties, are considered. The main applications of SAF structures as a part of spintronic devices is described.

Nonmagnetic Layer Thickness Dependence of Exchange Bias and Coercive Fields in NiFe/NM/FeMn (NM = Cu, Ru) Trilayers with Long-Range Exchange Bias Effect

Trilayer films consisting of ferromagnetic NiFe, nonmagnetic Cu or Ru, and antiferromagnetic FeMn layers were prepared by sputtering technique. The long-range exchange bias properties were investig...

The Effect of the Structural‐Phase State and Diffusion Processes on Electrical Conductivity of Nanocrystalline FexCo100−x/Cu/ FexCo100−x Thin Films (0 < x < 100)

AbstractThe complex investigation of the crystal, diffusion processes, and electrical conductivity of FexCo100−x (0 < x < 100) film alloys and FexCo100−x/Cu/FexCo100−x/Sub three‐layer films with a ferromagnetic layer thickness dF = 20–50 nm and a nonmagnetic layer thickness dN = 2–30 nm has been carried out. For both as‐deposited and annealed at 700 K films at x = 50, 80 at%, the phase composition corresponds to bcc‐FexCo100−x (single‐layer films) or bcc‐FexCo100−x + fcc‐solid solution of Fe and Co atoms that isomorphically replace each other in the Cu lattice (three‐layer film). At x = 20 at%, the phase composition of as‐deposited single‐layer films corresponds to bcc‐FexCo100−x + hcp‐Co and bcc‐FexCo100−x + fcc‐Cu + hcp‐Co in the case of three‐layer films. After heat treatment at 700 K, the phase composition corresponds to bcc‐FexCo100−x + fcc‐Co (single‐layer films) and bcc‐FexCo100−x + fcc‐s.s. Cu (Fe, Co) (three‐layer film). For three‐layer samples with dF = 30–50 nm, dN = 10–30 nm, annealing at 700 K does not lead to complete mixing of the layers, their original order is preserved. In the temperature dependence of the resistivity, three characteristic regions, where the various electron scattering mechanisms dominate, are distinguished and grounded.

PENGUKURAN NILAI INDUKTANSI PELAT ALUMINIUM BERDASARKAN VARIASI KAPASITANSI MENGGUNAKAN MODUL EVB LDC 1000

The method that has been done in metal thickness measurement is a plate thickness measurement method using an eddy current based sensor. Eddy current sensors can measure the thickness of non-magnetic metal layers through an inductance relationship with variations in thickness where the thickness used for Cu is 0.4 mm, 0.9 mm, 1.5 mm, 2 mm, 4 mm, while Al is used ie 0.4 mm, 0.5 mm, 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, 2.2 mm, 4 mm, 5 mm with a single frequency of 1 Hz with a capacitance value of C0 5 pF. The inductance vs. thickness curve for aluminum and copper has an exponential relationship. The distance between the sensor and non-magnetic material is kept constant at 2 mm. Variations in the value of capacitance C0 used in the measurements are then varied to 100 pF, 200 pF, and 300 pF to see the effect of inductance on the thickness of the plate as a function of the capacitor (C) oscillation.

The abnormal damping behavior due to the combination between spin pumping and spin back flow in Ni80Fe20/Rut bilayers

The spin pumping effect of the Ni80Fe20/Rut bilayers was studied by ferromagnetic resonance method. A shutter shift technique was adopted to prepare the wedge-like Ru caplayer on the Ni80Fe20 film with homogeneous thickness and damping constant. Thanks to this special preparation method, the very tiny variation of damping constant due to the spin pumping at the Ni80Fe20/Rut interface was precisely measured and extracted from that of Ni80Fe20 films. Comparing with the conventional monotonically approaching saturation curve of damping constant vs. non-magnetic Ru layer thickness tRu, an additional damping peak was observed. The abnormal damping-tRu curves can be understood as the combined action of spin pumping at Ni80Fe20/Rut interface and spin back flow due to the reflection at Ru surface and Ru/Ni80Fe20 interface.

The influence of the interlayer on the magnetic and structural properties of three-layer systems

This article is dedicated to the influence analysis of the thickness and composition of nonmagnetic intermediate layers, tNM, on the magnetic and structural properties of Co/Mo/Co, Co/Si/Co, Co/Bi/Co and Fe1/PDP/Fe2 thin-film systems, as well as comparing the mechanisms of exchange interaction between ferromagnetic, FM, layers through NM spacers. The thicknesses of Co layers are equal to 5.0 nm and the thickness of Fe layers is varied from 14.0 to 50.0 nm. The thickness of NM layers, depending on its composition, is changed from 0.2 to 50.0 nm. It is found that the hysteresis loops for some samples measured in a magnetic field applied parallel to the easy magnetization axis have a rectangular form and for others – more complex two-step ones. The saturation field, HS, of Co/Mo/Co, Co/Si/Co and Co/Bi/Co samples oscillates in magnitude. These data are explained by the presence of exchange coupling between the Co layers through a NM spacer. Fe1/PDP/Fe2 samples have a two-step hysteresis loops, which at tPDP ≥ 10 nm are explained by the exchange coupling between the Fe layers through the PDP layer, and at tPDP > 10 nm - by the magnetostatic interaction between the Fe layers due to the difference in their thickness.

Preparation and nanoscale characterization of electrodeposited CoFe-Cu multilayer nanowires

CoFe-Cu multilayered nanowires have been fabricated by pulse electrodeposition into the pores of ∼100 nm diameter anodized aluminum oxide (AAO) templates. Here, we investigate three samples, where the magnetic layer thickness is increased by extending the pulse time tCoFe 10 s, 13 s and 16 s while keeping the non-magnetic layer thickness constant (tCu = 30 s). Scanning electron microscopy and transmission electron microscopy confirm uniform, continuous and densely packed wires. By increasing the CoFe deposition time the aspect ratio enhanced and a layer stacking is demonstrated. The EDX line scan along the single nanowire indicates that they are Cu-rich with the composition of 10–15% Co, 0–5% Fe and 75–80% Cu. Magnetic measurements reveal a temperature dependency of the coercivity. The increase in coercivity is associated with the inherent shape and magnetocrystalline anisotropy of the nanowires. Magnetic measurements at low temperature exhibited the increase in coercivity of CoFe-Cu nanowires as a result of the freezing of thermal fluctuations.

Nuclear Magnetic Resonance and X-ray Reflectometry of Co/Cu Superlattices

The state of interfaces in Co/Cu superlattices with various thicknesses of non-magnetic Cu layers (tcu) has been studied by the methods of nuclear magnetic resonance (NMR) and X-ray reflectometry. The samples glass/Fe(5 nm)/[Co(1.5 nm)/Cu(tcu)]10/Cr(3 nm) were fabricated by the method of magnetron sputtering on glass substrates under constant current in the ULVAC MPS-4000-C6 device. The 59Co NMR spectra were taken in a local magnetic field in the frequency range of 90–240 MHz at 4.2 K in the pulsed NMR spectrometer. The spin echo signal was formed by a sequence of two coherent radio-frequency pulses (τp)x − tdel − (τp)y − tdel – echo forming an alternate magnetic field with the round component amplitude H1 of about 10 Oe in a resonance coil. It has been shown both by NMR and X-ray reflectometry that the structure of interfaces deteriorates with an increase of the Cu layers thickness, and similar dependences of the parameters characterizing structural imperfection of interfaces were obtained by these two methods.

Oscillatory Giant Magnetoresistance of Electrodeposited Fe/Cu/Ni Multilayered Structures—Effect of Non-Magnetic and Magnetic Layer Thicknesses

Giant magnetoresistance (GMR) behavior in electrodeposited N[Fe/Cu/Ni] multilayered (ML) structures is investigated as a function of non-magnetic (Cu) and ferromagnetic (Fe and Ni) layers’ thicknesses. Detailed structural and magnetic analyses of the ML structures are studied before looking into the GMR behavior. Structural analyses reveal that all peaks are well matched with Ni (face-centered cubic) being the top most layer during ML deposition. Shifting of preferred orientation, between (220) and (111) planes, is observed with the thickest layer of copper spacer. Refined structural parameters are calculated and details of fittings are discussed with reference to layer thicknesses. Crystallite size, dislocation density, stacking fault probability, and strain all show oscillatory behavior with variation in thicknesses. Magnetic behavior shows strong dependence of magnetization on thickness of each layer. Saturation magnetization ( $M_{s})$ increases up to a value of 10.12 emu/cm3 with increasing Fe and Ni layer thicknesses. Whereas, oscillatory behavior of magnetization is observed with variation in Cu layer thickness. Magnetoresistance (MR) measurements show oscillatory GMR behavior as a function of intervening layer thickness. Highest value of GMR ~12% is observed at a Cu layer thickness of 9.6 nm. Structural, magnetic, and MR properties of N[Fe/Cu/Fe] are observed on the basis of variation of thicknesses of non-magnetic (Cu) and ferromagnetic (Fe and Ni) layers. It is observed that layer thicknesses play a dominant effect on the nature (i.e., oscillatory) and on the value of GMR.

The Role of Cu Length on the Magnetic Behaviour of Fe/Cu Multi-Segmented Nanowires.

A set of multi-segmented Fe/Cu nanowires were synthesized by a two-step anodization process of aluminum substrates and a pulsed electrodeposition technique using a single bath. While both Fe segment length and diameter were kept constant to (30 ± 7) and (45 ± 5) nm, respectively, Cu length was varied between (15 ± 5) and (120 ± 10) nm. The influence of the non-magnetic layer thickness variation on the nanowire magnetic properties was investigated through first-order reversal curve (FORC) measurements and micromagnetic simulations. Our analysis confirmed that, in the multi-segmented Fe/Cu nanowires with shorter Cu segments, the dipolar coupling between Fe segments controls the nanowire magnetic behavior, and its performance is like that of a homogenous Fe nanowire array of similar dimensions. On the other hand, multi-segmented Fe/Cu nanowires with larger Cu segments act like a collection of non-interacting magnetic entities (along the nanowire axis), and their global behavior is mainly controlled by the neighbor-to-neighbor nanodisc dipolar interactions.

Electrochemical Deposition of CoCu/Cu Multilayers: Structural and Magnetic Properties as a Function of Non-magnetic Layer Thickness

Abstract Electrochemical deposition of CoCu/Cu multilayers was performed on titanium substrates from a single bath as a function of the Cu layer thicknesses. The deposition potentials were selected as −1.5 V for the magnetic layers and −0.3 V for the non-magnetic layers with respect to the saturated calomel electrode. The current-time transients were obtained during the deposition process, and the Co layer deposition and capacitive transients were calculated. On the basis of structural analysis, the multilayers were found to be polycrystalline with both Co and Cu layers adopting the face-centered cubic structure. The calculated lattice parameters of the multilayers slightly increase from 0.3585 to 0.3615 nm with increase in the Cu layer thickness, which is consistent with the bulk value of Cu. The inter-planar distance of the peaks of the multilayers is closer to that of Cu (d 111=0.2087 nm) and Co (d 111=0.2046 nm), and they become close to that of bulk Cu with increasing Cu layer thickness. In magnetic measurements, the magnetization decreases from 156 to 44 emu/cm3 depending on the Cu layer thickness. Furthermore, the coercivity of the multilayers increases from 20 to 140 Oe. These values show that the magnetic behaviour of the multilayers lie between those of soft and hard magnetic materials, but the multilayer having 2.5 nm Cu layer thickness shows hard magnetic property. For the CoCu(4 nm)/Cu(0.7 nm) multilayer, the magnetoresistance measurement shows 5.5 % giant magnetoresistance (GMR).