FeGa Thin Films Research Articles

Tuning the magnetic anisotropy of Ga-rich FeGa thin films deposited on rigid substrates

We have investigated the possibility of growing on outward bent rigid substrates to create an in-plane magnetic anisotropy in Ga-rich FeGa layers grown in the diffusive flow that in principle are expected to be magnetically isotropic in the sample plane when using non-bent rigid substrates. In this work, samples were grown by sputtering in the diffusive regime in rigid outward bent substrates, i.e. substrates under tensile stress. After the growth of the layers, the release of the substrate promotes a compression in the sample plane confirmed by x-ray diffractometry. This compression strain induces a uniaxial magnetic anisotropy axis in the sample plane perpendicular to the mechanical stress as expected for a material with a positive magnetostriction. Moreover, a value of 73 ppm for the magnetostriction constant has been inferred from the magnetic anisotropy measurements in the as-grown layer. A thermal treatment at a moderate temperature of 300 °C partially release the strain, but it does not modify the magnetic anisotropy either in magnitude or direction.

Temperature-Dependence of Static Magnetic Properties of FeGa Thin Film Fabricated by Pulsed Laser Deposition

FeGa thin films have been deposited onto (100)-oriented GaAs and (001)-oriented Si substrates at different temperatures by pulsed laser deposition. It has been shown that at different substrate temperatures, magnetic properties of FeGa films greatly change, which is mainly dependent on different crystal textures. The presence of the structure consisting of D03-ordered grain phase and bcc α-Fe crystal structure (A2) has been revealed using X-ray diffraction analysis. The diffraction peak of FeGa (001) direction, which ‎corresponds to the D03-ordered granular phase, was observed when the temperatures of the GaAs substrate were 400 and 600°C. The diffraction peak that corresponds to (110) direction of the bcc A2 structure has appeared at 800°C. However, the FeGa film on the Si substrate did not demonstrate any obvious structural change. The changes in the magnetic properties can be mainly attributed to changes in the roughness and the lattice mismatch between FeGa and Si.‎

Local and Medium Range Order Influence on the Magnetic Behavior of Sputtered Ga-Rich FeGa Thin Films

We have investigated the influence of the growth power on the structural properties of Fe100–xGax (x ca. 29) films sputtered in the ballistic regime in the oblique incidence. By means of different structural characterizations, mainly X-ray diffraction and X-ray absorption spectroscopy, we have reached a deeper understanding about the influence of the local and medium range order on the magnetic behavior of Ga-rich FeGa thin films. On the one hand, the increase of the growth power reduces the crystallite size (medium order) that promotes the decrease of the coercive field of the layers. On the other hand, the growth power also determines the local order as it controls the formation of the A2, B2, and D03 structural phases. The increase of the uniaxial in-plane magnetic anisotropy with growth power has been correlated with the enhancement of both Ga pairs and a tetragonal distortion. The results presented in this work give more evidence about the magnetic anisotropy sources in Ga-rich FeGa alloys, and therefore, it helps to understand how to achieve a better control of the magnetic properties in this family of alloys.

FeGaB(25 nm)/Al2O3/FeGaB(25 nm) Multilayer Structures: Effects of Variation of Al2O3Thickness on Static and Dynamic Magnetic Properties

Iron-gallium (FeGa) thin film has the unique advantages in designing integrated magnetic sensors or chips due to its relatively large magnetostrictive constant compared with other soft magnetic materials. In this work, non-magnetic doping and laminating methods have been employed to control the magnetic and electric properties of this alloy film. By doping a certain amount of boron (B), the coercivities are largely decreased for samples of thickness less than ∼30 nm. For thicker films, we find that inserting an ultrathin Al2O3 middle layer is very helpful to control the coercivities with negligible influence on saturation magnetization (Ms). The smallest easy-axis coercivity of 0.98×79.6 A/m is obtained in the multilayer film FeGaB(25 nm)/Al2O3(0.5 nm)/FeGaB(25 nm). In this case, the resistivity is enhanced by 1.5 times compared with the 50 nm single layer film. Structural characterizations indicate the reductions of crystalline quality and physical dimension of the magnetic grains playing important roles in softening the magnetic properties. Besides, the influences of magnetostatic interaction and morphology characteristics are also considered in facilitating domain reversal. High permeability spectra with gigahertz response are obtained for our multilayer films. The methodology applied here, i.e., enhancing magnetic and electric performance by introducing ultrathin non-magnetic layers, could be translated to other species of soft magnetic materials as well.

Stabilizing skyrmions by nonuniform strain in ferromagnetic thin films without a magnetic field

Magnetic skyrmions with topologically protected spin textures have recently attracted much attention due to their fascinating properties and potential application in advanced spintronics devices. For ferromagnetic thin films, skyrmions usually appear only in the presence of magnetic field. The stabilization of skyrmions in the absence of magnetic field remains an important challenge. Here, using a real-space phase field model based on Ginzburg-Landau theory, we demonstrate that a nonuniform strain can stabilize skyrmions in the FeGa thin film without a magnetic field. The phase field simulations show that the FeGa thin film exhibits a metastable skyrmion phase in the absence of magnetic field when a nonuniform strain with a cosine profile is applied. It is found that the metastable skyrmions can be transformed into a helical phase if a localized magnetic field or pulse of spin-polarized current is applied, resulting in the coexistence of skyrmion and helical phases in the ferromagnetic thin films. Furthermore, the skyrmion and helical phases can remain dynamically stable during the motion driven by a spin-polarized current. The coexistence of skyrmion and helical phases in the ferromagnetic thin films without magnetic field has potential application in skyrmion-based spintronic devices.

Structure and Magnetic Properties of Magnetostrictive FeGa Film on Single-Crystal (100) GaAs and (001) Si Substrate Fabricated by Pulsed Laser Deposition

FeGa thin film has been deposited on (100)-oriented GaAs and (001)-oriented Si substrates with different film thicknesses and laser energy densities at room temperature by pulsed laser deposition system. Materials structure and static magnetic of FeGa film have great changes depending on the substrate and energy density of pulsed laser. X-ray diffraction reveals the presence of first-order order–disorder structure of D03-ordered grain phase and disordered bcc A2 structure on GaAs substrate. The coercivity and remanence of FeGa film on GaAs substrate ratio show a regular dependence on the thickness and energy densities. However, film on Si substrate did not exhibit structure change, which can be attributed to a large lattice mismatch between FeGa and Si.

Enhancement of magnetostrictive properties of Galfenol thin films

The present study investigates the role of substrate temperatures on the structural, morphological, magnetic and magnetostrictive properties of DC sputtered FeGa thin films grown on Si substrates. These films were deposited at various substrate temperatures between 50 and 350 °C. The structural characterization of the films revealed columnar growth and the transformation of surface morphology from prismatic to spherical at high substrate temperatures. Both L12 and B2 phases of FeGa existed in the films, with the L12 phase dominating. The in-plane and out-of-plane vibration sample magnetometry measurements showed the evolution of magnetic anisotropy in these films. It was revealed from the magnetostriction measurements that the films deposited at 250 °C exhibited the maximum value of 59 ppm.

Tuning high frequency magnetic properties and damping of FeGa, FeGaN and FeGaB thin films

A series of FeGa, FeGaN and FeGaB films with varied oblique angles were deposited by sputtering method on silicon substrates, respectively. The microstructure, soft magnetism, microwave properties, and damping factor for the films were investigated. The FeGa films showed a poor high frequency magnetic property due to the large stress itself. The grain size of FeGa films was reduced by the additional N element, while the structure of FeGa films was changed from the polycrystalline to amorphous phase by the involved B element. As a result, N content can effectively improve the magnetic softness of FeGa film, but their high frequency magnetic properties were still poor both when the N2/Ar flow rate ratio is 2% and 5% during the deposition. The additional B content significantly led to the excellent magnetic softness and the self-biased ferromagnetic resonance frequency of 1.83 GHz for FeGaB film. The dampings of FeGa films were adjusted by the additional N and B contents from 0.218 to 0.139 and 0.023, respectively. The combination of these properties for FeGa films are helpful for the development of magnetostrictive microwave devices.

Influence of ion implantation parameters on the perpendicular magnetic anisotropy of Fe-N thin films with stripe domains

Nitrogen-martensite thin films are known to present a perpendicular magnetic anisotropy (PMA) depending on the nitrogen content. Additionally, weak magnetic stripe domains have been studied in Fe-N samples made by ion implantation. In this work, ion implantation proves to be a good technique to make nitrogen-martensite thin films presenting both tunable PMA and stripe domains. We report on the changes in magnetic and structural properties of nitrogen-implanted iron thin films, resulting from various implantation conditions. Fluences from 1.8 × 1016 N2+/cm2 to 3.5 × 1016 N2+/cm2 at 26 keV and 5.3 × 1016 N2+/cm2 at 40 keV were used to implant iron thin films epitaxially grown on ZnSe/GaAs(001). X-ray diffraction measurements disclosed the presence of body-centered tetragonal nitrogen-martensite whose c-axis is perpendicular to the thin film plane and the c-parameter increases with fluence. Vibrating sample magnetometer measurements revealed that nitrogen implantation induced strong changes in magnetic properties such as an increasing PMA with fluence. Therefore, this PMA may originate from the magnetocrystalline anisotropy of nitrogen-martensite and stress-induced anisotropy. Magnetic stripe domains are notably observed by magnetic force microscopy for the highest fluences. Furthermore, ferromagnetic resonance measurements lead to the magnetic anisotropy constants calculation. The results show a significant increase of the PMA, related to the presence of nitrogen-martensite whose c-parameter is close to that of α′-Fe8N, which reaches a maximum value of 4.9 × 106 erg/cm3. In addition, an interesting comparison is done between the anisotropy constants of Fe-N and Fe-Ga samples. Fe-Ga thin films are also well known to present PMA and stripe domains.

Static and dynamic magnetic properties of sputtered Fe-Ga thin films.

We present measurements of the static and dynamic properties of polycrystalline iron-gallium films, ranging from 20 nm to 80 nm and sputtered from an Fe0.8Ga0.2 target. Using a broadband ferromagnetic resonance setup in a wide frequency range, perpendicular standing spin-wave resonances were observed with the external static magnetic field applied in-plane. The field corresponding to the strongest resonance peak at each frequency is used to determine the effective magnetization, the g-factor and the Gilbert damping. Furthermore, the dependence of spin-wave mode on field-position is observed for several frequencies. The analysis of broadband dynamic properties allows determination of the exchange stiffness A = (18 ± 4) pJ/m and Gilbert damping α = 0.042 ± 0.005 for 40 nm and 80 nm thick films. These values are approximately consistent with values seen in epitaxially grown films, indicating the potential for industrial fabrication of magnetostrictive FeGa films for microwave applications.

Phase evolution and magnetic properties of DC sputtered Fe-Ga (Galfenol) thin films with growth temperatures

We report on the evolution of phases, morphology and magnetic properties of DC magnetron sputtered FeGa thin films with the different growth temperatures: room temperature, 100 °C, 200 °C, and 300 °C. These films were grown on Si substrate and were analysed for their morphological, structural and magnetic properties. The X-ray diffraction analysis reveals that the films are nanocrystalline and improve their crystallinity as the growth temperature increases from room temperature to 300 °C. Scanning electron microscopy images indicate grain growth and the morphology changes from spherical to platelets with increase in substrate temperatures. The films deposited at room temperature and 100 °C show very low magnetization and coercivity. On increasing the substrate temperature to 200 °C, it is observed that the M-H curves are isotropic with the films not attaining saturation. At 300 °C, there is substantial increase in coercivity and magnetization observed due to the larger grains present in the films. Magnetic properties also depend on in-plane (463 G, 46.557 emu/cc) and out-of-plane (860 G, 42.774 emu/cc) orientations with small anisotropy. Such an increase in magnetic properties is attributed to increase in grain size and change in morphology.

Structural and Magnetic Properties of Sputter-Deposited Mn–Fe–Ga Thin Films

We investigated structural, magnetic and electrical properties of sputter deposited Mn-Fe-Ga compounds. The crystallinity of the Mn-Fe-Ga thin films was confirmed using x-ray diffraction. X-ray reflection and atomic force microscopy measurements were utilized to investigate the surface properties, roughness, thickness and density of the deposited Mn-Fe-Ga. Depending on the stoichiometry, as well as the used substrates (SrTiO3 (001) and MgO (001)) or buffer layer (TiN) the Mn-Fe-Ga crystallizes in the cubic or the tetragonally distorted phase. Anomalous Hall effect and alternating gradient magnetometry measurements confirmed strong perpendicular magnetocrystalline anisotropy. Low saturation magnetization and hard magnetic behavior was reached by tuning the composition. Temperature dependent anomalous Hall effect measurements in a closed cycle He-cryostat showed a slight increase in coercivity with decreasing temperature (300K to 2K). TiN buffered Mn2.7Fe0.3Ga revealed sharper switching of the magnetization compared to the unbuffered layers.

Influence of the sputtering flow regime on the structural properties and magnetic behavior of Fe-Ga thin films (Ga ∼ 30 at.%)

In this paper we analyze the structure of Fe-Ga layers with a Ga content of \ensuremath{\sim}30 at.% deposited by the sputtering technique under two different regimes. We also studied the correlation between the structure and magnetic behavior of the samples. Keeping the Ar pressure fixed, we modified the flow regime from ballistic to diffusive by increasing the distance between the target and the substrate. X-ray diffraction measurements have shown a lower structural quality when growing in the diffusive flow. We investigated the impact of the growth regime by means of x-ray absorption fine structure (XAFS) measurements and obtained signs of its influence on the local atomic order. Full multiple scattering and finite difference calculations based on XAFS measurements point to a more relevant presence of a disordered $A2$ phase and of orthorhombic Ga clusters on the Fe-Ga alloy deposited under a diffusive regime; however, in the ballistic sample, a higher presence of $D{0}_{3}/B2$ phases is evidenced. Structural characteristics, from local to long range, seem to determine the magnetic behavior of the layers. Whereas a clear in-plane magnetic anisotropy is observed in the film deposited under ballistic flow, the diffusive sample is magnetically isotropic. Therefore, our experimental results provide evidence of a correlation between flow regime and structural properties and its impact on the magnetic behavior of a rather unexplored compositional region of Fe-Ga compounds.

Surface morphology and magnetic property of wrinkled FeGa thin films fabricated on elastic polydimethylsiloxane

We investigated the surface morphology and the magnetic property of wrinkled Fe81Ga19 (FeGa) thin films fabricated in two different processes onto elastic polydimethylsiloxane (PDMS) substrates. The films obtained by directly depositing Ta and FeGa layers on a pre-strained PDMS substrate display a sinusoidally wrinkled surface and a weak magnetic anisotropy. The wavelength and amplitude of the sinusoidal morphology linearly increase with the metallic layer thickness, while the magnetic anisotropy decreases with increasing FeGa thickness. The other films grown by depositing FeGa layer on a wrinkled Ta/PDMS surface show a remarkable uniaxial magnetic anisotropy. The strength of magnetic anisotropy increases with increasing FeGa thickness. The magnetic anisotropy can be ascribed to the surface anisotropy, the magnetostrictive anisotropy, and the shape anisotropy caused, respectively, by the magnetic charges on wavy morphology, the residual mechanical stress, and the inhomogeneous thickness of FeGa films.

Growth and Magnetic Properties of RF Sputtered Fe-Ga Thin Films

We report the growth and characterization of Fe-Ga thin films. These films were RF sputtered onto Si, MgO and quartz substrates by controlling the parameters such as the deposition time, power and substrate temperature. The deposited films were characterized using X-Ray Diffraction, Atomic Force Microscopy and Vibration Sample Magnetometry measurements. The effect of substrates on the structure and magnetic properties were studied. XRD pattern of the deposited films showed the formation of DO3 phase with L12 ordered structure at higher sputtering power. The room temperature deposited films demonstrated higher magnetization (0.08 emu/g) as compared to higher substrate temperature (300 °C) deposited films. The Mr/Ms ratio was found to be 0.037 for films deposited at room temperature and 0.009 for the substrate temperature 300 °C. L12 order was observed in films deposited on MgO and Quartz substrates. Magnetization was also found to be high (Ms out of plane = 518 emu/cm3, Ms in plane = 707 emu/cm3) for films deposited on MgO substrate.

Static and high frequency magnetic properties of FeGa thin films deposited on convex flexible substrates

Magnetostrictive FeGa thin films were deposited on the bowed flexible polyethylene terephthalate (PET) substrates, which were fixed on the convex mold. A compressive stress was induced in FeGa films when the PET substrates were shaped from convex to flat. Due to the effect of magnetostriction, FeGa films exhibit an obvious in-plane uniaxial magnetic anisotropy which could be enhanced by increasing the applied pre-strains on the substrates during growth. Consequently, the ferromagnetic resonance frequency of the films was significantly increased, but the corresponding initial permeability was decreased. Moreover, the films with pre-strains less than 0.78% exhibit a working bandwidth of microwave absorption about 2 GHz. Our investigations demonstrated a convenient method via the pre-strained substrates to tune the high frequency properties of magnetic thin films which could be applied in flexible microwave devices.

Effect of Thickness on Mechanically Tunable Magnetic Anisotropy of FeGa Thin Films Deposited on Flexible Substrates

A practical way to manipulate the magnetic anisotropy of magnetostrictive FeGa thin films grown on flexible polyethylene terephthalate (PET) substrates is introduced in this study. The effect of film thickness on magnetic properties and magnetostriction constant of polycrystalline FeGa thin films was investigated. The anisotropy field Hk of flexible FeGa films, i.e., the saturation field determined by fitting the hysteresis curves measured along the hard axis, was enhanced with increasing the tensile strain applied along the easy axis of the thin films, but this enhancement via strain became unconspicuous with increasing the thickness of FeGa films. In order to study the magnetic sensitivity of thin films responding to the external stress, we applied different strains on these films and measure the corresponding anisotropy field. Moreover, the effective magnetostriction constant of FeGa films was calculated from the changes of both anisotropy field and external strain based on the Villari effect. A Neel’s phenomenological model was developed to illustrate that the effective anisotropy field of FeGa thin films was contributed from both the constant volume term and the inverse thickness dependent surface term. Therefore, the magnetic properties for the volume and surface of FeGa thin films were different, which has been verified in this work by using vibrating sample magnetometer (VSM) and magneto-optic Kerr effect (MOKE) system. The anisotropy field contributed by the surface of FeGa film and obtained by MOKE is smaller than that contributed by the film volume and measured by VSM. We ascribed the difference in Hk to the relaxation of the effective strain applied on the films with increasing the thickness of films.

Influence of substrate temperature on structure, microstructure and magnetic properties of sputtered Fe–Ga thin films

This paper reports the structure, microstructure and magnetic properties of Fe–Ga thin films deposited using DC magnetron sputtering technique on Si(100) substrate kept at different temperatures. Structural studies employing X-ray diffraction and TEM revealed the presence of only disordered A2 phase in the film. Columnar growth of nanocrystalline grains from the substrate was observed in the film deposited at room temperature. With increase in substrate temperature the grain size as well as surface roughness was found to increase. The magnetization of the films deposited at higher substrate temperatures were found to saturate at lower magnetic field as compared to the room temperature deposited film. Coercivity was found to decrease with increasing substrate temperature upto a minimum value of ~2Oe for the film deposited at 450°C and with further increase in substrate temperature it was found to increase. A maximum magnetostriction of 200µ-strains was also observed for the film deposited at 450°C.

Electrodeposition of Fe–Ga thin films from eutectic-based ionic liquid

Abstract In the present work, a novel process for Fe–Ga thin films electrodeposition is addressed and the magnetic properties of the films are studied. The electrodeposition was carried out under ambient conditions using an ionic liquid electrolyte consisting of a mixture of choline chloride and ethylene glycol in the molar ratio 1:2, containing 0.3 M FeCl2 and 0.1 M GaCl3, either in the absence or in the presence of oxalic acid at 4 or 17 mM concentration. The effect of oxalic acid on the discharge reaction of the single ionic species Fe2+ and Ga3+ and on their codeposition was investigated by linear sweep voltammetry, suggesting a specific action of oxalic acid on the cathodic reduction of Ga3+ ionic species. Depending on deposition potential and oxalic acid concentration, alloy films with Ga content variable in the range up to about 20 at.% could be obtained. The Fe–Ga thin films showed a disordered body-cantered cubic phase (A2) with (1 1 0) preferred orientation and columnar microstructure, with a drastic change from pyramidal to granular surface morphology revealed raising the deposition potential. No superlattice reflections, indicating the formation of the D03 structure, were observed. A vibrating sample magnetometer was employed to measure hysteresis loops by applying longitudinal and transversal magnetic field on the Fe–Ga film plane. The saturation magnetization of as-deposited film reached 1.75 T for Fe83Ga17 thin films, confirming that good quality films were obtained. For the same alloy composition, the coercivity values were 67 Oe and 200 Oe, with applied field parallel and perpendicular to the film plane, respectively.

Electrodeposition and characterization of magnetostrictive galfenol (FeGa) thin films for use in microelectromechanical systems

In this paper, we investigate the challenges related to electrodeposition and characterization of magnetostrictive galfenol thin films as well as techniques used to overcome these issues. Successful deposition and evaluation of galfenol thin films is necessary for the design of galfenol based microelectromechanical devices. Stress is a primary concern because thick films and poor adhesion to substrates (e.g., silicon oxide) can lead to delamination and peeling. In addition, magnetostriction measurements require films that are uniform in thickness and composition over the sample area. Various adhesion layers were tested, and delamination was eliminated with Cr/Cu, which provided robust adhesion to the glass substrates used in capacitance bridge measurements. Uniformity and composition were controlled by the use of a rotating disk electrode for electrodeposition, which created a uniform boundary condition across the sample during deposition. The capacitance bridge technique was calibrated with Ni/glass samples, after which a magnetostriction of 140 ppm was measured for Fe83Ga17 films. These results represent the first magnetostriction measurements of electrodeposited galfenol.