Fe Film Thickness Research Articles

A comparison of ferromagnetic resonance and magneto optical Kerr effect on thin Fe films on InAs(001)

Abstract A combination of STM, SQUID magnetometry, FMR and MOKE is used to study the structural and magnetic properties of thin iron films grown on InAs(001) (4×2)/c(8×2). The different magnetic characterization methods of this paper allow measurements of the magnetic anisotropies in the saturated and non-saturated state. Here we show results of a SQUID/FMR investigation on a 12 monolayer thick Fe film. As expected, FMR measurements find a four-fold symmetry of the magneto crystalline anisotropy, but with an additional uniaxial contribution. The dependence of the remanence on the magnetization angle computed from the magnetic parameters obtained in the saturated state is compared to experimental remanence data measured using MOKE. Good agreement is found. The InAs-substrate quality prior to growth, the nucleation behavior and the thickness-dependent granular structure of the Fe-layer are studied with STM. The origin of the magnetic anisotropies is discussed in terms of these structural data.

Thickness and strain dependent magnetic anisotropy of ultrathin Fe/Ni films

Using the full potential linearized augmented plane wave method (FLAPW), the magnetic properties of ultrathin Fe/Ni films grown on Cu(0 0 1) surface have been investigated. We have varied both Ni and Fe film thicknesses and also have explored the strain effect on the magnetic anisotropy. For surface Fe atom, a typical surface enhancement of spin magnetic moment has been observed while the magnetic moments of other constituents are rather insensitive to the strain effect. Nonetheless, we have realized that the direction of magnetization is significantly affected by the strain factor. For instance, the Fe/Ni films always have perpendicular magnetization provided that they are grown on Cu(0 0 1) lattice constant. However, we have obtained a spin reorientation transition (SRT) phenomenon in the presence of strain effect.

Nonreciprocal spin wave spectroscopy of thin Ni–Fe stripes

The authors report on the observation of nonreciprocal spin wave propagation in a thin (∼200nm) patterned Ni–Fe stripe. The spin wave transmission spectrum is measured using a pair of microstrip lines as antennas. The nonreciprocity of surface wave dispersion brought about by an adjacent aluminum ground leads to a nonreciprocal coupling of the antennas. The effects of Ni–Fe film conductivity, thickness, and reflections caused by the lateral confinement of the magnetic stripe are discussed. The nonreciprocity observed in this structure can potentially be used to realize nonreciprocal microwave devices on silicon.

A comparative study of Co and Fe thin films deposited on GaAs(0 0 1) substrate

The magnetization and the coercivity of Co and Fe thin films in the thickness range 10–200 nm deposited onto GaAs(0 0 1) substrate were studied. Coercivity of Co and Fe thin films increases with increase in film thickness. Coercivity increased from 10 to 80 Oe as thickness of Co films increased from 50 to 100 nm. In the Fe/GaAs system, coercivity increased from 30 to 180 Oe as thickness of Fe films increased from 40 to 100 nm. The surface roughness measurements of Fe films indicate that enhancement of coercivity is due to surface roughness of the film. On the other hand, it was observed from the AFM study that the enhancement of coercivity was not due to surface roughness of Co film. It is speculated that the enhanced coercivity of Co/GaAs is due to a special interaction between Co film and GaAs substrate, since the enhancement of coercivity did not appear in Co films deposited on Si(0 0 1) substrate.

Brillouin light scattering study of magnetic anisotropy in epitaxial Fe/ZnSe(0 0 1) ultrathin films

Fe/ZnSe(0 0 1) system is attracting interest because it is one of the rare successful example of ferromagnetic metal–semiconductor epitaxy, where both chemistry and magnetic properties of the interfaces remain stables up to 600 K. This can be very important in view of the production of spintronics devices. Epitaxial Fe films with thickness in the range between 0.7 and 5 nm were deposited on ZnSe(0 0 1) in ultra-high vacuum. Thermal spin-waves were detected in situ using Brillouin light scattering, i.e. inelastic scattering of light by thermal spin-waves. The evolution of magnetic anisotropy with Fe film thickness has been studied. Even if at large film thickness the expected biaxial anisotropy of magnetocrystalline origin is present, for low coverages an uniaxial magnetic anisotropy (UMA), of interface origin, dominates, in agreement to what previously observed in the Fe/GaAs system. Different from this latter system, however, we have verified that the introduction of a Cu capping layer, as well as annealing to high temperature, do not appreciably alter UMA in Fe/ZnSe films with thickness larger than 1 nm, suggesting that the physical mechanism responsible for the rise of the UMA is more stable in the Fe/ZnSe than in Fe/GaAs.

Growth and magnetic properties of ultrathin Fe films on Pt(1 1 1)

Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and surface magneto-optical Kerr effect (SMOKE) were used to investigate the growth mode, alloy formation, and magnetic properties of ultrathin Fe films deposited on Pt(1 1 1) surface. The growth mode of Fe films on Pt(1 1 1) at RT is at least 3 ML layer-by-layer growth before three-dimensional island growth begins. When the thickness of Fe films was 1 ML, no Kerr signal is observed at room temperature. Both the polar and longitudinal Kerr signals can be detected when the thickness of Fe films ( d Fe) is 1.5 ML. When the thickness of Fe films is higher than 1.5 ML, only the longitudinal Kerr signal can be observed. The easy axis of the magnetization is in the in-plane direction when d Fe > 1.5 ML. After the formation of Fe–Pt surface alloy for 5 ML Fe ultrathin films on a flat Pt(1 1 1) surface, the Kerr signal and the coercivity enhance to 150% and 1100%, respectively. The formation of Fe–Pt surface alloy was confirmed by AES. The evolutions of the magnetic properties are strongly relative to the diffusion process of Fe thin films into Pt substrate.

磁性めっき線のＦｅ薄膜の厚さに依存する渦電流形変位センサの直線範囲

A magnetoplated wire (MPW) is a copper wire whose circumference is plated with a magnetic thin film. The effects of using an MPW are a decrease in the proximity effect, an increase in inductance, and generation of more flux than when copper wire is used. The ratio of the linearity range Lo to the outer coil diameter D of the eddy current displacement sensor is extended by using MPW for the coil. However, the relationship between the Fe film thickness of MPWs and the linearity range characteristic has not been clarified. We measured the output voltage characteristics of MPW coils with Fe film thicknesses of 0.7 μm, 1 μm, and 1.1 μm, and calculated Lo/D ratios. As a result, we found that the Lo/D ratio of an MPW coil with a 1-μm-thick Fe film had a maximum value of 0.66.

Thickness-dependent magnetic anisotropy in ultrathinFe∕Co∕Cu(001)films

Using the full potential linearized augmented plane wave method, we have explored the thickness-dependent magnetic anisotropy of ultrathin Fe films with 1 ML Co underlayer on Cu(001) as well as other magnetic properties. It has been found that the magnetic moment of Co underlay is almost intact with increasing Fe film thickness. A similar trend has been observed in interior Fe layers, whereas the surface Fe magnetic moment is greatly enhanced compared to those in other layers. Through magnetic anisotropy calculations, we have found that the 1 ML Fe film on $\mathrm{Co}∕\mathrm{Cu}(001)$ has a perpendicular magnetic anisotropy, but the direction of magnetization changes to in-plane with increasing Fe coverage. It has been found that the spin-orbit interactions around the middle of Brillouin zone play an essential role in the spin reorientation transition.

Size-selective growth of double-walled carbon nanotube forests from engineered iron catalysts

We have succeeded in synthesizing vertically aligned doubled-walled carbon nanotube (DWNT) forests with heights of up to 2.2 mm by water-assisted chemical vapour deposition (CVD). We achieved 85% selectivity of DWNTs through a semi-empirical analysis of the relationships between the tube type and mean diameter and between the mean diameter and the film thickness of sputtered Fe, which was used here as a catalyst. Accordingly, catalysts were engineered for optimum DWNT selectivity by precisely controlling the Fe film thickness. The high efficiency of water-assisted CVD enabled the synthesis of nearly catalyst-free DWNT forests with a carbon purity of 99.95%, which could be templated into organized structures from lithographically patterned catalyst islands.

Measurement of spin waves and activation volumes in superparamagnetic Fe films on GaAs(100)

Spin wave frequencies are observed in ultra-thin Fe/GaAs(100) films at temperatures where the spontaneous zero field magnetization is zero. The films exhibit good cyrstalline structure, and the effect of magnetic anisotropies is apparent even though no zero field spin wave energy gap exists. An analysis is given in terms of a superparamagnetic model in which the film is treated as a network of non-interacting single domain magnetic islands. A spin wave analysis provides a means to separate measured values of anisotropy parameters from products involving anisotropy and island volume. In this way, a measure of the activation volume associated with superparamagnetic islands is obtained for different Fe film thicknesses. Results suggest that the island lateral area increases with increasing film thickness.

Magnetic anisotropy in nanoscaled materials probed by ferromagnetic resonance

Ferromagnetic resonance measurements probe the dynamical response of magnetic systems due to an excitation within the microwave regime. Offering high sensitivity and energy resolution in the μeV range of ferromagnetic resonance this technique is well suited for the investigation of magnetic anisotropy in nanoscale systems. Ferromagnetic Resonance experiments give direct and quantitative access to magnetic anisotropy based on an analysis that uses the Landau--Lifshitz equation of motion. This will be demonstrated for the case of ultrathin magnetic 5--20ML thick Fe films on {4×6}GaAs(001) (2D system) which have been grown and measured in situ in ultra high vacuum, magnetic MnAs stripes (1D system) grown on GaAs(001) as well as for arrays of highly monodisperse FePt nanoparticles (quasi 0D system).

Tuning the magnetic anisotropy of ultrathin Fe∕Ag(001) films from biaxial to uniaxial by ion sculpting

Ion sculpting of ultrathin Fe∕Ag(001) films induces the self-assembled formation of nanometric surface ripples oriented along the ion beam direction and the corresponding onset of an in-plane uniaxial contribution to magnetic anisotropy. The authors show that fine tuning of the ion dose impinging on the film allows to tailor the in-plane magnetic anisotropy of such films from purely biaxial in the as-grown state to purely uniaxial. The magnitude of magnetic anisotropy in the pure uniaxial state can be tailored by varying the Fe film thickness prior to irradiation.

Structural, magnetic, and chemical properties of thin Fe films grown on Rh(100) surfaces investigated with density functional theory

The structural, magnetic, and chemical properties of ultrathin Fe films grown on Rh(100) films have been investigated using ab initio density-functional calculations. The particular interest in this system stems from the fact that in view of the size mismatch between face-centered cubic (fcc) Rh and body-centered cubic (bcc) Fe, it is expected (and actually confirmed by the calculations) that the Fe films will form a tetragonal structure intermediate between bcc $\ensuremath{\alpha}$- and fcc $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$, leading to a conflict between the ferromagnetic character of $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Fe}$ and the antiferromagnetism of $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$. Indeed the calculations find a single monolayer of Fe on Rh(100) (which had been characterized on the basis of XMCD experiments as ``magnetically dead'') to order antiferomagnetically, while thicker Fe films have a ferromagnetic ground state. Independent of the film thickness we find that the magnetic energy differences between the magnetic ground state and possible excited magnetic states are always much smaller than the energy difference between the ground state and the nonmagnetic state. This suggests a lower magnetic ordering temperature than in bulk bcc Fe (in agreement with experiment) and the existence of a disordered local-moment state at higher temperatures. The chemical properties of the films have been tested by the adsorption of CO molecules. We find that the adsorption properties are strongly dependent on the magnetic state of the substrate---the breakdown of magnetic order always leads to a significant enhancement of the adsorption energy. At low coverages we predict the existence of a tilted adsorption geometry similar to that reported for the (100) surface of $\ensuremath{\alpha}$ Fe.

Iron-based microstrip band-stop filters at higher microwave frequency range: Design optimization using shape anisotropy

Microwave filters that use thin films of ferromagnetic metals are now being established as an option compared to YIG based filters due to their higher frequency response at very small magnetic fields. The aim of the present investigation is to significantly boost the operating frequency of notch filters in very low applied magnetic fields. To do this, we fabricated a series of notch filters with Fe films of different thicknesses and shapes. The stop-band response of each of these filters cover four waveguide bands (X, KU, K and Ka) ranging from 8to40GHz with an applied magnetic field up to 4.5kOe. The frequency characteristics of these filters at zero field can be significantly changed by changing the geometry of the magnetic element. For example, an Fe film which is 7.5μm wide, 100nm thick, and 3mm long has a stop band centered at 9.5GHz, but this is increased to 22GHz for an 800nm thick Fe film. For narrower signal lines (4.5μm wide), we observed further increases in the frequencies: 11GHz for a 100nm Fe film increased to 25GHz for an 800nm thick Fe film. This upshift in frequency is due to the shape anisotropy of the Fe film. In addition, we investigated the temperature variations in the properties of the devices from room temperature to +85°C

Magnetization reversal of Fe films on Ag submicrometer pyramidal islands

Ag submicrometer pyramidal islands with a (100) truncated top and four (111) sidewalls were successfully fabricated on Si(100) substrates at a deposition temperature of 500/spl deg/C. The magnetization reversal of 30 nm thick Fe films grown on Ag pyramidal islands was studied by magnetic force microscopy. The magnetization reversal of Fe films was first started at the sidewalls of pyramidal islands. Then, the formation and propagation of wall-like structures were observed under a higher external magnetic field, namely 95 Oe. The magnetic domain images indicated that the Fe films grown on the sidewalls of pyramidal islands and the strength of external field played important roles on the magnetization reversal of Fe films.

Activation of SiC Surfaces for Vapor Phase Lubrication by Chemical Vapor Deposition of Fe

Vapor phase lubrication (VPL) has been proposed as a method for lubrication of high temperature engines. During VPL, lubricants such as tricresylphosphate (TCP), (CH3–C6H4O)3P=O, are delivered through the vapor phase to high temperature engine parts and react on their surfaces to deposit a thin, solid, lubricating film. Although ceramics such as SiC are desirable materials for high temperature applications, their surfaces are unreactive for the decomposition of TCP and thus not amenable to VPL. As a means of activating the SiC surface for TCP decomposition we have used chemical vapor deposition of Fe from Fe(CO)5. Modification of the SiC surface with adsorbed Fe accelerates subsequent decomposition of TCP and deposition of P and C onto the surface. In the temperature range 500–800 K, m-TCP decomposes more readily on Fe-coated SiC surfaces than on SiC surfaces. The C and P deposition rates depend on the thickness of the Fe film and are further enhanced by oxidation of the Fe. This work provides a proof-of-concept demonstration of the feasibility of using VPL for ceramics

Hollow to bamboolike internal structure transition observed in carbon nanotube films

The transition of the internal structure in microwave chemical-vapor-deposited carbon nanotubes is investigated using scanning electron microscopy and high-resolution transmission electron microscopy. By controlling the thickness of the iron catalyst layer, a sequence of carbon nanotube films was obtained with diameters ranging from a few nanometers to over 100nm. Experiments have established that by continuous reduction of the Fe layer thickness to <1nm, single- and double-wall carbon nanotube films can be produced, whereas for an Fe film thickness >1nm, multiwall carbon nanotube films can be synthesized. It was also found that for an Fe thickness ⩾5nm, interlayers (i.e., bamboolike or periodically compartmentalized nanotubes) were formed, while for an iron thickness <2nm the tubes were primarily hollow. For an intermediate Fe thickness the internal structure of the carbon nanotubes was a mixture of hollow and bamboolike. A growth model which considers bulk and surface diffusions of carbon into and∕or onto the Fe catalyst surface is proposed to describe this transition and the internal periodic structure.

MOKE hysteresis loop method of determining the anisotropy constants of ferromagnetic thin films: fe on GaAs(1 0 0) with overlayers of Au and Cr

This paper presents a quantitative method used to determine the magnetocrystalline anisotropy constants of thin magnetic films from normalized magnetization data measured on a magneto-optic Kerr effect (MOKE) magnetometer. The method is based on a total magnetic energy density model, and incorporates higher order effects in the detected signal. By way of illustration, the method is used to determine the magnetocrystalline anisotropy constants of epitaxial thin Fe films on GaAs substrates, which have different overlayers. It is shown that a Cr overlayer on a 30 ML thick Fe film reduces the uniaxial contribution to the magnetic anisotropy compared with an Au overlayer.

Enhanced hyperfine magnetic fields for face-centered tetragonal Fe(110) ultrathin films on vicinal Pd(110)

The structure and hyperfine magnetic properties of epitaxial Fe ultrathin films on a vicinal Pd(110) surface have been investigated by means of low-energy electron diffraction (LEED), reflection high-energy electron diffraction (RHEED) and $^{57}\mathrm{Fe}$ conversion electron M\ossbauer spectroscopy (CEMS). LEED and RHEED provide evidence for initial pseudomorphic film growth. The RHEED determination of the in-plane atomic distance versus Fe film thickness demonstrates the stabilization of the metastable fcc-like Fe structure on Pd(110). This interpretation is supported by in situ $^{57}\mathrm{Fe}$ CEMS measurements which indicate an enhanced saturation hyperfine field of $\ensuremath{\sim}39\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ for a 3-monolayers-thick Fe film at 25 K. This is the highest value ever measured for Fe on a metallic substrate. Our results suggest that ultrathin fcc-like (face-centered tetragonal) Fe films on Pd(110) are in a ferromagnetic high-moment state with an enhanced hyperfine field due to electronic $3d\text{\penalty1000-\hskip0pt}4d$ hybridization at the Fe∕Pd interface.

Magnetostriction and magnetocrystalline anisotropy constants of ultrathin epitaxial Fefilms on GaAs, with Au overlayers

In this paper, we present the first measurements on the variation of the saturationmagnetostriction constant with film thickness of ultrathin epitaxial Fe films on GaAs(100)substrates. Furthermore, we explore whether there is a link between magnetostrictionand the uniaxial anisotropy in these Fe films. The Fe film thickness ranged fromseven monolayers (ML) (having only uniaxial anisotropy) to 50 ML (almost purecubic anisotropy). The anisotropy constants were determined from the normalizedmagnetization loops, using a magneto-optic Kerr effect (MOKE) fitting techniquethat convolutes a magnetic energy density model with the dependence of theMOKE signal on the angle between the pass plane of the analyser and the planeof incidence of the laser light on the sample. Each film was uniformly strainedalong the [011] direction, while the magnetization was measured along the direction using a MOKE magnetometer. From the change in anisotropy field as a functionof strain (Villari effect), the magnetostriction constant in the [011] direction was calculated.It is demonstrated that the saturation magnetostriction constant in the [011] direction issignificantly different to the equivalent value in bulk Fe, and increases in magnitude as thethickness of the Fe film decreases. It will also be shown that the uniaxial anisotropyconstant has a linear dependence on the magnetostriction constant for each film.