Properties Of Fe Thin Films Research Articles

Influence of misfit strain on the physical properties of Fe thin films

We investigate the growth of thin Fe layers on MgAl2O4 (001) and MgO (001) substrates using dc magnetron sputtering. The crystal quality of Fe layers deposited on MgAl2O4 is found to be substantially higher as compared to Fe grown on MgO substrates. The effects of the crystal quality on the magnetic and electronic transport properties are discussed.

Tuning the magnetic properties of Fe thin films with RF-sputtered amorphous carbon

RF-sputtered amorphous carbon (a-C) offers a simple and cheap pathway to tune the magnetic properties of transition metal thin films for magnetic memories and different spintronic applications. This paper describes changes in the magnetic properties of iron thin films with a-C overlayers. In as-deposited samples, hybridisation and intermixing at the Fe/a-C interface leads to magnetic softening (Liu et al., 2006) [1], with a reduction in the coercive field (Hc) up to a factor of five for Fe/a-C/Fe trilayers, and a 10–30% lower saturation magnetization as a function of the metal film thickness. After annealing at 500 °C, inter-diffusion and graphitization of the carbon layer results in up to a factor five increased coercivity due to increased pinning as shown via Kerr microscopy. Therefore, RF-sputtered carbon overlayers and post-processing can tune the anisotropy and domain configuration of metallic thin films in a synthesis methodology that is simple, cheap and sustainable.

Effect of rapid thermal annealing on the structure, microstructure and magnetic properties of Fe thin films

This paper reports the structure, microstructure and magnetic properties of as-deposited and rapid thermal annealed Fe thin films. Rapid thermal annealing was carried out at 550 °C for different time intervals such as 2, 5, 10, 20 and 30 min. The as-deposited and rapid thermal annealed films were found to exhibit A2 type bcc structure. However, microstructural studies indicated formation of Fe–Si phase for the annealed Fe films. Surface roughness estimated from atomic force microscopy studies displayed an increase in surface roughness with increase in annealing time. Room temperature magnetization studies showed a predominant in-plane magnetic anisotropy for all the films. In addition to this presence of strong out-of-plane anisotropy coupled with in-plane magnetization was clearly evidenced from the considerable increase in the out-of-plane coercivity with increase in annealing time. Magnetic force microscopy studies further confirmed the presence of out-of-plane magnetic anisotropy. Magnetic domain imaging studies showed long period band domain patterns with 180° domain wall for the as-deposited film. The band domains were found to get branched with increase in annealing time. From the hysteresis loops and domain imaging studies it was clear that the magnetization reversal is dominated by domain wall motion.

Magnetic resonances and microwave permeability in thin Fe films on flexible polymer substrates

Ferromagnetic resonance (FMR) and coaxial line techniques are employed for studying the high-frequency magnetic properties of thin Fe films deposited onto a flexible polymer substrate by magnetron sputtering. Multiple resonances are observed in the FMR spectra measured in X frequency range for films with thickness from 0.1 to 2.0 μm. The resonance magnetic fields are found to depend on of the film thickness and on the orientation of external magnetic field relative to the film plane. The variation of the FMR parameters with the layer thickness may be attributed to differences in the shape and size of nanocrystallites formed during the deposition of films of different thicknesses. Low-field resonance modes are found in addition to the homogeneous FMR of saturated magnetization. Qualitative agreement is observed between values of the resonance magnetic fields determined by FMR and coaxial line techniques.

Controlling magnetic interfaces using ordered surface alloys

We have investigated the growth and magnetic properties of Fe thin films on the clean W(100) surface and W(100)-M c(2 \ifmmode\times\else\texttimes\fi{} 2) ($M=\mathrm{Cu}$, Ag, Au) surface alloy substrates. The influence of the interface on magnetism is assessed experimentally by studying sensitive threshold behavior in magnetic ordering using spin-polarized low-energy electron microscopy. The onset of ferromagnetic order that occurs with increasing film thickness at room temperature due to finite-sized scaling of the Curie temperature varies reproducibly among films on W(100) and the surface alloys. Magnetic moments and exchange coupling constants of the magnetic ground states are also determined theoretically for films with ideal interfaces by first-principles density functional theory calculations. These microscopic quantities are consistently enhanced in Fe films on the noble metal-induced surface alloys compared to their values in films on the clean W(100) surface. We attribute the systematic variation of magnetic onset observed experimentally to the competition between the intrinsically enhanced magnetic coupling and moments on the surface alloy substrates and several extrinsic factors that could suppress magnetic ordering, including intermixing, substrate and film roughness, and surface alloy disorder. Tendencies for intermixing are explored theoretically by determining the energy barrier for noble metal segregation. Despite these possible extrinsic effects, the results suggest that the use of the broad class of ordered surface alloys as alternative substrates may offer greater opportunities for manipulating thin film magnetism.

Synthesis, Structural, and Magnetic Properties of Fe Thin Films

A series of iron thin films have been deposited under vacuum, by thermal evaporation, onto polycrystalline Cu substrates. The film thickness ranges from 13 to 69 nm. An X-ray diffraction (XRD) technique, working in the 𝜃–2𝜃 mode with the K α Cu radiation (λ = 1.54056 A), has been used to perform the structural properties. The static magnetic measurements were carried out using a vibrating sample magnetometer (VSM), with the external magnetic field applied parallel and normal to the surface of the films. All the films are polycrystalline and present well-defined Bragg peaks. The easy magnetization axis lies in the film plane for all the samples, and no in-plane magnetic anisotropy has been detected for all films. High values of squareness have been measured in the longitudinal configuration. All the findings will be presented and discussed.

Effect of nitrogen and cobalt additions on surface morphology and magnetic properties of Fe thin films

Fe, FeN, and FeCoN films were fabricated by direct-current (DC) magnetron sputtering. The dependence of surface morphology, magnetic properties, and resistivity on phase structure was systematically investigated. α″-Fe16N2 (202) phase occurred with the incorporation of nitrogen (N) and cobalt (Co), and the surface morphology evolved from random-leafs-like shapes to triangular-pyramid-like islands. Clear reproducible striped domains appeared at the FeCoN film surfaces, because of high perpendicular anisotropy in the film. The additions of Co enhanced the formation of the α″-Fe16N2 phase, which caused the saturation magnetization (Ms) value of the FeCoN film to increase to 2088 emu/cm3, considerably higher than that of pure Fe. Moreover, the significant amount of α″ phase leads to higher resistivity and therefore improved high-frequency permeability.

Texture and magnetic properties of Fe thin films fabricated by field-sputtering vs field-annealing

The effect of the external magnetic field during magnetic thin film fabrication process on texture formation and magnetic properties has been studied by conducting and comparing the field-sputtered vs the field-annealed Fe thin films. The crystal orientations of the films were analyzed in both perpendicular direction and lateral direction in relation to the film surface, using a 3-axis-rotation X-ray goniometer. When the external magnetic field was imposed on the direction parallel to the film surface during the field-sputtering and the field-annealing, the <110>//normal direction fiber texture in the no-field-sputtered Fe film was substantially reduced, whereas the <110>//field direction fiber texture was enhanced. The field-sputtering was much more effective than the field-annealing in the formation of the perpendicular magnetic anisotropy because of the decline of the <110> orientations in the out-of-plane direction and its enhancement in the in-plane direction.

Microstructural evolution and magnetic properties of nanocrystalline Fe films prepared in a high magnetic field

In this study we have explored how a high magnetic field (HMF) affects the structure and magnetic properties of Fe thin films fabricated on Si (100) substrates at various substrate temperatures by using a thermal evaporation method. At a substrate temperature of room temperature (RT), the HMF increased the width of column and the formation energy of the films. This behavior occurred because the HMF induced an excess energy-Zeeman energy which is larger than the sum of the kinetic energy and thermal energy of Fe without the HMF. This increased the particle size and decreased the roughness of the film deposited at RT and 6 T. When the substrate temperature was increased to 400 °C, the growth mode is changed from columnar (RT) to layered (400 °C). The HMF increased the grain size. The film deposited at RT and 6 T had much improved soft magnetic properties from its modified microstructure. While thermal disturbances decreased the effect of HMF on the magnetic properties of the film deposited at 400 °C. In particular, the influence of HMF on the microstructure and magnetic properties of Fe films is significant not in the evaporation stage but in the condensation process of film.

Anisotropic optical properties of Fe/GaAs(001) nanolayers from first principles

We investigate the anisotropy of the optical properties of thin Fe films on GaAs(001) from first-principles calculations. Both intrinsic and magnetization-induced anisotropy are covered by studying the system in the presence of spin-orbit coupling and external magnetic fields. We use the linearized augmented plane wave method, as implemented in the WIEN2k density functional theory code, to show that the $C_{2v}$ symmetric anisotropy of the spin-orbit coupling fields at the Fe/GaAs(001) interface manifests itself in the corresponding anisotropy of the optical conductivity and the polar magneto-optical Kerr effect. While their magnetization-induced anisotropy is negligible, the intrinsic anisotropy of the optical properties is significant and reflects the underlying $C_{2v}$ symmetry of the Fe/GaAs(001) interface. This suggests that the effects of anisotropic spin-orbit coupling fields in experimentally relevant Fe/GaAs(001) slabs can be studied by purely optical means.

Effect of Thickness and Deposition Rate on the Structural and Magnetic Properties of Evaporated Fe/Al Thin Films

We report experimental results on the structural and magnetic properties of Fe thin films deposited by thermal evaporation onto polycrystalline Al substrates. The effect of thickness t (in the 76 to 431 nm range) and deposition rate are investigated. The texture, the strain, and the grain size values were derived from X-ray diffraction (XRD) experiments. The thinner film (76 nm) has no texture, while all other samples have a texture. The strain values e are small and negative (compressive stress) and equal to −0.1 % for films with t less than 100 nm, it decreases (in absolute value) to −0.07 % and then remains constant for t greater than 100 nm. The grain size values D are found to be between 44 and 73 nm. The grain size decreases with increasing deposition rate regardless of t. Hysteresis curves, inferred from the vibrating sample magnetometer (VSM), show an in-plane magnetic anisotropy for all samples. The squareness S increases and the coercive field H C decreases with increasing D up to D = 55 nm, then they remain constant beyond this grain size value. Higher deposition rates led to smaller grain, smaller remnant magnetization, and higher coercive field. For t = 99 nm, the decrease of the temperature T from room temperature to −130 °C led to 20 and 5 % increases in H C and S, respectively.

Tuning structural and magnetic properties of Fe films on Si substrates by hydrogenation processing

• Fe films have been grown on Si(0 0 1) substrates and subsequently hydrogenated. • As deposited films present soft magnetic character and a strong magnetic texture. • Structural and magnetic properties can be tuned via hydrogenation treatments. • Ferromagnetic/semiconductor interfaces might be manipulated via hydrogenation. In order to study specific phenomena at ferromagnetic/semiconducting interfaces, of potentially high interest in spintronics and information technology, structural aspects and magnetic properties of Fe thin films grown on Si(0 0 1) substrates by RF sputtering have been investigated using 57 Fe conversion electron Mössbauer spectroscopy (CEMS) and magneto-optic Keer effect (MOKE). Films of different thicknesses have been deposited either directly on crystalline Si substrates or on Cu buffer layers. An inherent Fe oxide layer is observed in all as prepared films, with a relative thickness decreasing drastically with the deposition time. The Cu buffer layer does not diminish either the interfacial diffusion or the oxidation process. An efficient method to prepare sharper oxygen- and silicon-free interfaces for an improved spin injection, via thermal treatment in hydrogen atmosphere, is proposed. Accordingly, the hydrogenation treatments are very efficient in the modification of the ferromagnetic film structure, phase composition, magnetic properties and interfacial mixing.

Tuning the lattice and magnetic anisotropy of Fe thin films

Fe (001) thin films with different crystal lattice were epitaxially grown on single crystal MgO substrates under the various sputtering pressures. It is found in this paper that the tetragonality and magnetic anisotropy of Fe thin film is tuned by varying the working sputtering pressures. The tunability of the crystal lattice and the magnetic anisotropy of Fe films were characterized by X-ray reflectivity, X-ray diffraction and vibrating sample magnetometer. The tunable structure and magnetic properties of Fe thin films may attribute to the rearrangement of Fe atoms on MgO substrate induced by controlling the atomic kinetic energy under different sputtering pressure.

Magneto-transport properties of Fe thin films in an external electric field

Magneto-transport properties in Fe thin films in an external electric field (E-field) were investigated by means of the first-principles full-potential linearized augmented plane-wave method. Results for an Fe monolayer predict a reduction (enhancement) in the in-plane dc electric (intrinsic Hall) conductivity due to a change in the band structure around the Fermi energy when the E-field is introduced. In addition, a magnetization reorientation from the out-of-plane direction to the in-plane direction leads to an abrupt change in the conductivity. Modification of the ac electric conductivity by an E-field is also presented.

Four fold in-plane magnetic anisotropy in sputtered (100)MgO/Fe epitaxial films

We report structural and magnetic properties of Fe thin films, deposited onto (100)MgO substrates by rf magnetron sputtering. The successful epitaxial growth of Fe<100>(100) parallel to MgO<110>(100) was achieved at a practical growth rate of 0.73 nm/s. The M-H hysteresis measured along Fe<100> directions exhibits a superior squareness with a low coercivity (Hc = 5 Oe). The saturation field along <110> directions, exceeding 500 Oe, demonstrates the crystalline cubic anisotropy comparable to the bulk Fe. The anisotropic properties of the initial susceptibility against an oscillation field of 1 mOe amplitude were also confirmed with inductive measurements.

Magnetic shape anisotropy calculations of Fe nanostructures at the Si/Fe(1 1 1) interface

The influence of Si capping layers on the magnetic properties of thin Fe films grown on Si(1 1 1) has been studied by means of shape anisotropy calculations. Fe surface morphology simulations are realized using experimental STM data. Surface modifications induced by the interaction between the Si overlayer and the Fe surface are performed in agreement with the model proposed in a previous work by Stephan et al. [J. Magn. Mater. 293 (2005) 746]. Calculations of the uniaxial anisotropy energy constant K u are then performed on the modified Fe surface morphology for different Si deposition geometries as proposed in the model. The relevant data deduced by this method such as anisotropy constants and their related easy axis direction, are directly compared to the experimental ones obtained by ex situ magneto-optical Kerr effect (MOKE) measurements at room temperature using the transverse bias initial inverse susceptibility and torque (TBIIST) method. We show that a very good agreement between those results leads to a confirmation of the proposed model.

Effect of obliquely evaporated Au cap layer on the magnetic properties of thin Fe films on Si(111)

The influence of Au capping layers on the magnetic properties of thin Fe films grown on Si(111) has been studied by means of room temperature magneto-optic Kerr effect (MOKE). MOKE measurements show a peculiar behavior of the magnetic anisotropy of Fe films grown at normal incidence and covered with obliquely evaporated Au cap layers. The magnetic anisotropy is dependent on the thickness of the deposited Au layer as well as on the growth conditions. First, the initial Fe sixfold in-plane magnetocrystalline anisotropy is replaced by an in-plane uniaxial one for Au thicknesses below 2 ML. Then, for increasing Au film thickness we observe an in-plane switching of the magnetic direction depending of the Au evaporation direction with respect to the substrate. Consider, for example, oblique Au depositions below 2 ML along the [1¯21¯]Si direction. These peculiar deposition conditions lead to a uniaxial anisotropy with easy axis perpendicular to the incidence plane of the Au flux. For thicker Au thicknesses, the uniaxial easy axis undergoes an in-plane switching reorientation of 90° corresponding to the Au evaporation direction. Angular resolved ultraviolet spectroscopy and ion scattering spectroscopy investigations reveal that this complex anisotropy behavior can be attributed partly to Au/Fe interfacial interdiffusion.

High frequency characteristics of soft magnetic Fe–O alloy thin films fabricated by helicon plasma sputtering

The effect of oxygen-doping has been studied on the magnetic properties of Fe thin films produced at room temperature by a helicon-plasma-enhanced RF magnetron sputter-deposition. A reduction in magnetic coercivity due to grain refinement was achieved using very low dose of oxygen, which did not lead to the formation of crystalline Fe oxides with the low saturation magnetization. Moreover, it was demonstrated that oxygen-doping also enhances the in-plane uniaxial magnetic anisotropy of Fe films and thus can be applied beneficially to increase high-frequency permeability which is needed in microwave applications.

Influence of Ag Underlayer on the Microstructure and the Magnetic Properties of Fe Thin Films

Fe thin films were deposited directly and via Ag underlayer on glass and MgO(100) substrates by MBE. Polycrystal Fe films grew on the glass substrate while single crystal films grew on the MgO(100) substrate. Fe film growth followed the Volmer-Weber mode for both cases. The Fe film structure was influenced by the surface roughness of Ag underlayer at the early stage of film growth. The relationships between the Fe thin film morphology and the magnetic properties are discussed.

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.