Fe Layer Thickness Research Articles

Magnetization reversal mechanisms in Fe/NiO bilayers grown onto nanoporous alumina membranes and Si wafers

We report on the magnetization reversal measured in two ferromagnetic/antiferromagnetic (F/AF) bilayer series: Fe/NiO/Al2O3 (nanoporous membranes, series N) and Fe/NiO/Si (wafers, series W). The Fe and NiO layers were deposited by pulsed laser ablation and magnetron sputtering, respectively. In both series different oxygen partial pressures were implemented in the Ar plasma during the NiO growth. The morphologies of both series (as imaged by atomic force microscopy) reflect those of their substrates and, particularly, the series N samples exhibit a six-fold columnar growth around each one of the membranes nanopores. The in-plane hysteresis loops measured upon field cooling the samples down to different temperatures in the range from 50 K up to 290 K evidenced i) 50 K, 0% oxygen coercivities that decreased markedly in both series samples with the increase of the Fe layer thickness (particularly the Fe 5 nm, series N sample exhibited a coercivity larger than the Fe magneto-crystalline anisotropy field), ii) a decrease of the coercivity with the increase of the NiO deposition oxygen partial pressure, observed in both series independently of the Fe layer thickness, iii) low temperature coercivities larger in the series N samples than in the series W ones. Our data are analyzed in correlation to the deposits morphology and in terms of the occurrence of either propagation mediated reversal (collective mode linked to spatially averaged interactions at the F/AF interface) or localized switching (defect ruled mechanism taking place in a spatially confined environment). It is concluded that i) the magnetization reversal mechanism active in series W samples corresponds to a weak pinning regime propagation of walls interacting with uncompensated moments at the F/AF interface, ii) in series N samples, the magnetization reversal does not involve propagation, and iii) in the latter series the reversal events are spatially restricted to the dot-like tops of the NiO columns surrounding the membrane pores.

Origin of large spin Hall magnetoresistance in Fe/CuOx bilayers

We have compared the spin Hall magnetoresistance (SMR) in Fe/Pt and Fe/CuOx (with natural oxidation) bilayers with varying the thickness of Fe layer. A larger SMR in Fe/CuOx bilayers has been found when the thickness of Fe layer is 3 nm. Moreover, the SMR of the two bilayers decrease with increasing the thickness of Fe from 3 nm to 10 nm, but that of Fe/CuOx drops more sharply due to shunting current effect. Through harmonic measurements, the emergent spin current is proved to be generated in the Fe/CuOx bilayers. The mixed phase of CuOx has been confirmed including CuO, Cu2O and Cu, which performs strong spin-orbit coupling and produce large spin current. On the other hand, the interface-generated spin current should be ruled out. All the results have been compared with those in Fe/Al2O3 bilayers with negligible spin current.

Fe thicknesses dependence of attenuated total reflection response in magnetoplasmonic double dielectric structures: angular versus wavelength interrogation

Al2O3/SiO2/Fe/Au structures with different Fe thicknesses were fabricated using different deposition techniques. Due to the cutoff condition of surface plasmon polaritons in the double-layer dielectric structure and magneto-optical effect, the reflectivity spectra show a minimum and its angular and wavelength positions can be modulated by the magnetic field. For thin Fe layers, the magnetic field modulates mainly the angular position, whereas for thick Fe layers both wavelength and angular positions are modulated. The proposed structure and the angular and wavelength dependence suggest two feasibilities of (1) two selectable interrogation modes: whereas for structures with thin Fe layers angular interrogation mode is preferred, with thick Fe layers wavelength interrogation mode is more appropriate, and (2) discrimination of analyte in the complex space: the refractive shift in the real part would dominantly appear in the angular interrogation, while the imaginary part in the wavelength interrogation.

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.

Magneto-optical Kerr effect and nuclear resonant scattering study of uni-directional anisotropy in hard-soft magnetic bilayers

The present work reports the unconventional exchange bias (EB) phenomena in an exchange-coupled hard and soft magnetic bilayer system and the tunability of EB. The EB phenomena, i.e., shifting of the hysteresis loop of the soft (Fe) layer is observed when the hard magnetic (L10 FePt) layer is under the remanent state indicating the development of unidirectional anisotropy. The nuclear resonant scattering measurements clearly reveal the development of unidirectional anisotropy in the soft magnetic (Fe) layer, when the hard magnetic layer is under the remanent state. The magnetization reversal process is investigated by measuring two in-plane orthogonal components of magnetization, i.e., parallel (M∥) and perpendicular (M⊥) to the applied field using the magneto-optical Kerr effect (MOKE). When the magnetic field is applied parallel (antiparallel) to the biasing field direction, (HSAT) magnetization reversal is nonuniform, and on the other hand, the rotation of magnetization is observed when the magnetic field is applied away from the HSAT direction. In addition, the sign inversion of the M⊥ component is observed when the magnetic field is applied at the same angle on either side of the HSAT direction, which clearly imply the change in handedness of the chirality of spin structure during the magnetization reversal of the soft layer. Further, it is observed that the EB decreases with the increase of soft magnetic (Fe) layer thickness, demonstrating the tunable nature of EB phenomena even in these unconventional systems.

Parametric Characterizations of Sputtered Fe/Al Multilayer Thin Films

This study contains parametric characterizations of four different series of Fe/Al multilayer thin films sputtered under thicknesses of Al layers (7.5, 35 and 95 nm), deposition rates (0.02 and 0.06 nm/s), Fe layer thicknesses (7.5, 12.5 and 27.5 nm) and total thicknesses (100, 125 and 175 nm), separately. The X-ray diffraction measurements showed that all films have a mixture of face-centered cubic (fcc) and body-centered cubic (bcc) phase. The face-centered cubic (fcc) and mostly body-centered cubic (bcc) phase turned to the mostly fcc and bcc phase as the thickness of Al layer increased. On the other hand, the intensity of peaks belongs to bcc structure increased and mostly bcc structure was detected when the deposition rate increased. The roughness on the surfaces of Fe/Al multilayer increased as Al layer thickness decreased and deposition rate of layers increased. Saturation magnetization value changed coherently with the film content for all films. Coercivity, Hc value was significantly affected by different surface morphologies, and granular surface caused higher Hc values for Fe/Al multilayer thin films. It was found that crystalline structure, surface properties and magnetic properties of Fe/Al multilayer thin films depend strongly on the deposition parameters.

Fabrication and characterization of microwave phase shifter in microstrip geometry with Fe film as the frequency tuning element

Abstract A series of ultra-small planar broad-band phase shifters with wide range of phase shift are designed and tested in this investigation. To achieve this performance a series of microstrip transmission lines with Iron (Fe) films of various thicknesses (from 100 to 800 nm) were designed, fabricated and tested. The basic principle of operation of these phase shifters are based on ferromagnetic resonance (FMR). The influence of the thickness of the magnetic layer was studied for two frequency regions: below and above the ferromagnetic resonance. This is because for a real-device the insertion loss should be less than −3 dB (or as low as possible). In the high frequency region, the optimal frequency (corresponding to the highest change in phase shift) increased significantly with the increase of the Fe film thickness (from 27 GHz for the structure with 100 nm of Fe to 43 GHz for the structure with 800 nm of Fe film). In the low frequency region, however, the optimal frequency varied little with the Fe layer thickness. The highest change in phase shift (~90 deg/cm) corresponded to the structure with the thinnest Fe layer for the low frequency region and with the thickest Fe layer for the high frequency region. In the high frequency region the Figure-of-Merit was about 20 deg/dB at low magnetic fields (

Surface Roughening with Iron Nanoparticles for Promoted Adhesion of Spin Coated Microsupercapacitor Electrodes

AbstractMicrosupercapacitors (MSCs) are miniaturized energy storage devices that can be integrated in an on-chip platform as a component of a power supply for Internet of things’ sensors. Integration of these on-chip MSCs require them to be fabricated through CMOS compatible fabrication techniques such as spin coating. One of the biggest challenges in spin coated MSCs is the poor surface adhesion. In this work, we present a CMOS compatible electrode deposition process with enhanced adhesion and retention for reduced graphene oxide (rGO) using spin coating. In order to improve the adhesion and surface uniformity of the deposited electrode material, the surface of Si/SiO2 wafers was subjected to roughening through Fe nanoparticle formation. A 4 nm thick Fe layer deposition substantially magnified the average mean surface roughness of the substrates. In comparison with substrates without the Fe deposition, the treated ones have more than 300% improvement in surface coverage and rGO mass retention after sonication testing. These results suggest that the surface roughening has a positive influence on electrode deposition via a spin-coating method.

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.

NCFET Design Considering Maximum Interface Electric Field

Negative capacitance field-effect transistors (NCFETs) boost the electric field at the semiconductor-channel interface by virtue of the gate voltage amplification effect of a ferroelectric (fe) layer. NCFETs should be designed in such a way that this elevated field does not exceed the maximum electric field ( ${E}_{\max}$ ) determined by the reliability limit of the interfacial dielectric or NBTI/PBTI reliability. In this letter, a compact model-based methodology is presented to determine the NCFET design space considering several variables of the fe-layer and the baseline transistor, including the fe-layer thickness ( ${T}_{\mathrm {fe}}$ ), coercive field ( ${E}_{c}$ ), remnant polarization ( ${P}_{r}$ ), baseline transistor equivalent oxide thickness, supply voltage ( ${V}_{\mathrm {dd}}$ ), threshold voltage ( ${V}_{\mathrm {th}}$ ), and ${E}_{\max}$ . Using this methodology, an NC-FDSOI transistor is designed in TCAD, and the result shows that even without raising the maximum interface field as compared with the baseline transistor, NCFET achieves much better ${I}_ \mathrm{\scriptstyle ON}/{I}_ \mathrm{\scriptstyle OFF}$ ratio and sub-threshold swing while operating at lower ${V}_{\mathrm {dd}}$ .

Unexpected magnetic coupling oscillations for L10−MnGa/Co(Fe) films induced by quantum wells

Exchange magnetic coupling interactions between $L{1}_{0}\text{-MnGa}$ and ultrathin Co (Fe) films were studied by first-principles calculations. An unexpected oscillation of magnetic coupling was observed by varying the thickness of Co or Fe layer. Moreover, the coupling types are different for Co and Fe with $L{1}_{0}\text{-MnGa}$. The magnetic coupling maintains the ferromagnetic interaction for $L{1}_{0}\text{-MnGa}$/Fe, even if the thickness of Fe layer varies. Interestingly, a change from ferromagnetic to antiferromagnetic couplings appears alternately for $L{1}_{0}\text{-MnGa}$/Co till Co thickness is up to 11 atomic layers. The coupling oscillations were attributed to the quantum well states formed in the Co (Fe) films. The orbital characters of the quantum well states were analyzed. Our results are useful to further understand the magnetic coupling interactions and design new magnetic nanostructures.

Synthesis of Mg2FeH6 by hydrogenation of Mg/Fe powder mixture prepared by cold roll milling in air: Effects of microstructure and oxygen distribution

Herein, we describe the synthesis of Mg2FeH6 by hydrogenation of a 2.1 Mg:Fe (mol/mol) powder mixture prepared by cold roll milling (CRM) in air. The thickness of Fe layers and the amount and distribution of oxygen with number of CRM passes were systematically analyzed. CRM-induced microstructural changes were shown to play an important role in Mg2FeH6 formation. Although repeated CRM effectively decreased the Fe layer thickness to values sufficient for the fast formation of Mg2FeH6, too much CRM passes decreased the total degree of hydrogenation due to inevitable oxidation of Mg in air. Both microstructure refinement and minimal oxidation are the prerequisites for efficient Mg2FeH6 synthesis, with the former condition being achievable by optimizing the number of milling passes, and the latter one requiring CRM under an inert atmosphere.

Onset of magnetic order in multilayers of Fe and Ni on and embedded in fcc-Cu(100) substrates

We investigate magnetic correlations and local magnetic moments at finite temperatures in some Fe and Ni multilayers on and embedded in Cu(100). Our study is based on a mean-field theory of magnetic fluctuations for layered materials within the first-principles local spin-density functional theory. We find that although there is no significant local moments formation in the Ni layers, the Ni layers are not magnetically dead in the sense that they mediate magnetic interactions between Fe layers separated by Ni layers. The Curie temperature of FenNim/Cu(100) and NinFem/Cu(100) films is almost independent of the Ni layer thickness, however, in Fe1NinFe1/Cu(100) and Fe1CunFe1/Cu(100) films, the Curie temperature exhibits an interesting oscillatory behaviour as the spacer layer thickness is increased. We show that there is a connection between this behaviour and the spin-reorientation transition observed in some Ni films. In the Ni1FenNi1/Cu(100) and Cu1Fen/Cu(100) films we found that the nature and strength of the magnetic correlations depends upon the Fe layer thickness.

Spin currents during ultrafast demagnetization of ferromagnetic bilayers

Ultrafast spin currents induced by femtosecond laser excitation of ferromagnetic metals have been found to contribute to sub-picosecond demagnetization, and to cause a transient enhancement of the magnetization of the bottom Fe layer in a Ni/Ru/Fe layered structure. We analyze the ultrafast magnetization dynamics in such layered structures by element- and femtosecond time-resolved x-ray magnetic circular dichroism, for different Ni and Fe layer thicknesses, Ru and Ta interlayers, and by varying the pump laser fluence. While we do not observe the transient enhancement of the magnetization in Ni/Ru/Fe discovered previously, we do find a reduced demagnetization of the Fe layer compared to a Ni/Ta/Fe layered structure. In the latter, the spin-scattering Ta layer suppresses spin currents from the Ni layer into Fe, consistent with previous results. Any spin current arriving in the lower Fe layer will counteract other, local demagnetization mechanisms such as phonon-mediated spin-flip scattering. We find by increasing the Ni and Fe layer thicknesses in Ni/Ru/Fe a decreasing effect of spin currents on the buried Fe layer, consistent with a mean free path of the laser-induced spin currents of just a few nm. Our results suggest that in order to utilize ultrafast spin currents in an efficient manner, the sample design has to be optimized with these considerations in mind, and further studies clarifying the role of interfaces in the employed layered structures are needed.

Exchange coupled L10 FeCuPt/Fe heterostructures: Magnetic properties and reversal behavior at elevated temperatures

Exchange-coupled heterostructures were prepared by combining hard magnetic L10 FeCuPt alloy films with soft magnetic Fe thin films. For the FeCuPt thin film, the addition of Cu allows adjusting magnetic properties such as perpendicular magnetic anisotropy, coercivity, saturation magnetization, and Curie temperature. The coupling to thin Fe layers, providing high saturation magnetization and high Curie temperature, leads to lowering of the switching field of the hard magnetic FeCuPt layer and to a reduction of thermally induced recording errors. We have investigated the influence of the Fe layer thickness on the switching behavior of the hard layer, revealing a strong reduction for Fe layer thicknesses larger than the exchange length of Fe of about 2nm. Furthermore, superior performance of bilayer structures in comparison to single FeCuPt layers has been demonstrated by recording experiments at temperatures below 150°C, employing a scanning magnetoresistive microscope.

Iron layer-dependent surface-enhanced raman scattering of hierarchical nanocap arrays

In this report, we fabricated the multi-layer Ag/Fe/Ag sandwich cap-shaped films on monolayer non-closed packed (ncp) polystyrene colloidal particle (PSCP) templates through a layer-by-layer (LBL) depositing method. This research focused on the surface-enhanced Raman scattering (SERS) effect of the thickness of the deposited Fe film which was controlled by the sputtering time. The SERS intensities were increased firstly, and then decreased as the thickness of Fe layer grows gradually, which is attributed to the charge transition from the Fermi level of the Ag NPs to Fe layer. The use of multi-layer Ag/Fe/Ag sandwich cap-shaped films enables us to evaluate the contribution of surface plasmon resonance and charge distribution between Ag and Fe to SERS enhancement. Our work introduced a novel system (Ag/Fe/Ag) for high performance SERS and extended the SERS application of Fe. Furthermore, we have designed the Ag/Fe/Ag SERS-active substrate as the immunoassay chip for quantitative determination of AFP-L3 which is the biomarker of hepatocellular carcinoma (HCC). The proposed research demonstrates that the SERS substrates with Ag/Fe/Ag sandwich cap-shaped arrays have a high sensitivity for bioassay.

Effect of ultrathin Fe dusting layer on electrical transport properties of few-layer MoS2 field-effect transistors

Transition-metal-doped MoS2 has been predicted to be a potential candidate for a two dimensional dilute magnetic semiconductor, while the effect of transition metal dopants on the electrical properties of MoS2-based devices has received relatively less attention so far. Here, the authors report on a systematic electrical transport study of Fe-dusted few-layer molybdenum disulfide (MoS2) field-effect transistors via repeated in situ Fe deposition (total nominal thickness ≤ 2 nm) and electrical measurements in ultrahigh vacuum. It is found that an ultrathin Fe adsorption layer (≪0.5 nm) n-dopes MoS2 without noticeably affecting the electrical characteristics of the device. In contrast, a thicker Fe layer (0.5–2 nm) results in the loss of the carrier tunability and a nonlinear current-voltage characteristic with the differential conductance approximately linear to drain voltage. The authors show through result analysis and qualitative modeling that Fermi level pinning in MoS2 directly underneath Fe nanoclusters plays an important role in causing these degradations. The pinning effect can be partially removed by in situ oxidizing the Fe nanoclusters for a short duration of 16 min. The mechanism of Fermi level pinning is discussed.

Magnetic and Mössbauer studies of L10–FePt/Fe/Ta multilayer structures

Magnetic L10–FePt(10 nm)/Fe(t, nm)/Ta(2 nm) (t is the Fe film thickness that is varied from 0 to 15 nm) multilayer structures have been prepared by magnetron codeposition. The 2-nm-thick Ta layer is a corrosion protection. The magnetization reversal processes and the magnetic interactions have been studied. The hysteresis loops measured in the plane of a single-layer L10–FePt films demonstrate a near-linear behavior. N the magnetic multilayer FePt(10 nm)/Fe(t, nm)/Ta(2 nm) system, in which the Fe layer thickness is smaller than 3 nm, the FePt/Fe system behaves as a single-phase magnetic material and the coercivity is close to the values determined by the Zeeman energy. In the case when the Fe layer thickness in the magnetic multilayer FePt(10 nm)/Fe(t, nm)/Ta(2 nm) structure is larger than 3 nm, the hysteresis loops measured in the structure plane indicate that the FePt/Fe film possesses the properties analogous to the properties of a soft magnetic material. The Mossbauer studies showed that the minimal deviation of the magnetic moments on the normal to the multilayer structure surface was observed as the Fe layer thickness is 1 nm. The increase in the Fe layer thickness to values higher than 1 nm led to the increase in the angle of deflection θ to ~40° at t = 15 nm. In this case, the coercivity of the multilayer structure slowly decreased, because of the limitations of the exchange bond length between the FePt and Fe layers. The measured values of the coercivity were optimized using relationship 1/t Fe 1.15.

Deuterium permeation and retention behaviors in erbium oxide-iron multilayer coatings

Hydrogen isotope migration behaviors in ceramics-metal multilayer coatings have been elucidated for a further improvement of fueling system and radiological safety. Erbium oxide (Er2O3) coatings were fabricated by filtered vacuum arc deposition (VAD) on reduced activation ferritic/martensitic steel substrates. An iron (Fe) layer was fabricated by radio-frequency magnetron sputtering or covered with an Fe foil on the Er2O3 coating. An Er2O3-Fe-Er2O3 three-layer coating was also fabricated by the VAD on the Er2O3-Fe coating. The grain boundary diffusion model was constructed based on the results of grain structure analysis and deuterium depth profile for the Er2O3 single-layer coating from our previous works. The Er2O3-Fe two-layer coatings with different Fe layer thickness showed no significant difference in deuterium permeability. The Er2O3-Fe-Er2O3 three-layer coating showed a PRF of up to 104 due to a contribution of two diffusion barriers of the inner and outer Er2O3 layers. In addition, the three-layer coating had three times higher deuterium concentration than the Er2O3-Fe coating, although the concentration will be negligibly small from the perspective of tritium inventory in the fuel system.

Magnetization and anomalous Hall effect in SiO2/Fe/SiO2 trilayers

SiO2/Fe/SiO2 sandwich structure films fabricated by sputtering were studied by varying the Fe layer thickness (tFe). The structural and microstructural studies on the samples showed that the Fe layer has grown in nanocrystalline form with (1 1 0) texture and that the two SiO2 layers are amorphous. Magnetic measurements performed with the applied field in in-plane and perpendicular direction to the film plane confirmed that the samples are soft ferromagnetic having strong in-plane magnetic anisotropy. The temperature dependence of magnetization shows complex behavior with the coexistence of both ferromagnetic and superparamagnetic properties. The transport properties of the samples as studied through Hall effect measurements show anomalous Hall effect (AHE). An enhancement of about 14 times in the saturation anomalous Hall resistance () was observed upon reducing the tFe from 300 to 50 Å. The maximum value of = 2.3 Ω observed for tFe = 50 Å sample is about 4 orders of magnitude larger than that reported for bulk Fe. When compared with the single Fe film, a maximum increase of about 56% in the was observed in sandwiched Fe (50 Å) film. Scaling law suggests that the Rs follows the longitudinal resistivity (ρ) as, , suggesting side jump as the dominant mechanism of the AHE. A maximum enhancement of about 156% in the sensitivity S was observed.