FeGa Films Research Articles

Magnetostriction Effect in Ferromagnetic Films with Easy-Axis and Easy-Plane Anisotropies

Magnetostriction properties of Ni and FeGa films with easy-plane anisotropy and Co/Pt multilayer structures with perpendicular anisotropy have been experimentally investigated. The magnetic properties of films have been studied by magneto-optical methods. Magneto-optical measurements have been performed with controlled bending of the substrate on which the magnetic film is deposited. It is shown that substrate bending induces rotation of the anisotropy axis of the Ni and FeGa films by 90° relative to its initial direction in an unstrained film. The value of perpendicular anisotropy in the Co/Pt multilayer films is shown to change at substrate bending. The layer parameters, at which the magnetostriction effect can be observed in films with perpendicular anisotropy, are established.

A study of high piezomagnetic (Fe-Ga/Fe-Ni) multilayers for magnetoelectric device

This paper sets out the research into (Fe-Ga/Fe-Ni)n films in order to obtain a large piezomagnetic coefficients of 8.1 ppm/Oe and enhance magnetoelectric coupling at near zero bias field. The exchange coupling between Fe-Ga and Fe-Ni magnetic film makes the magnetoelectric (ME) coefficient of (8 nm Fe-Ga/8 nm Fe-Ni)30/AlN/Mo/Si reach 607 V/cm Oe, and the bias magnetic field is reduced to 4 Oe. Multilayer (8 nm Fe-Ga/8 nm Fe-Ni)30 films also have good soft magnetic properties, high piezomagnetic coefficients and low losses which can be used as a driving element for micro-sensor and micro-electro-mechanical system (MEMS).

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.‎

Магнитострикционный эффект в ферромагнитных пленках с анизотропией типа "легкая ось" и "легкая плоскость"

AbstractMagnetostriction properties of Ni and FeGa films with easy-plane anisotropy and Co/Pt multilayer structures with perpendicular anisotropy have been experimentally investigated. The magnetic properties of films have been studied by magneto-optical methods. Magneto-optical measurements have been performed with controlled bending of the substrate on which the magnetic film is deposited. It is shown that substrate bending induces rotation of the anisotropy axis of the Ni and FeGa films by 90° relative to its initial direction in an unstrained film. The value of perpendicular anisotropy in the Co/Pt multilayer films is shown to change at substrate bending. The layer parameters, at which the magnetostriction effect can be observed in films with perpendicular anisotropy, are established.

Structural, magnetic and magnetostrictive properties of Fe83Ga17 films with a Ti adhesion layer

Abstract In this study, Fe83Ga17 thin films are deposited on Si(1 0 0) and Si(1 1 1) substrates with a Ti layer by using DC magnetron sputtering. The addition of Ti layer does not significantly change the magnetic and magnetostrictive properties of the Fe-Ga film, however it can effectively prevent the abscission of film during heat treatment. The Fe83Ga17 films deposited on Si(1 0 0) and Ti/Si(1 0 0) have relatively small coercive forces, low saturation magnetic fields, and the magnetostriction curves are easily saturated in a low field. The magnetostriction of Fe83Ga17 on Ti/Si(1 0 0) can reach 105 ppm. The Fe83Ga17 thin films on Si(1 1 1) and Ti/Si(1 1 1) have large saturation magnetic fields (about 61Oe) and the magnetostriction curve shows linearity, which can be used in magnetic field detection, micro actuators and magnetoelectric (ME) devices. Dendritic domains and stripe domains are observed in these samples due to the influence of different internal stresses. After a vacuum heat treatment, the internal stress was released. At the same time, the structure of both the dendritic domains and stripe domains turns into a dot domain. The EBSD results show that annealed Fe-Ga films sputtered on a Ti layer have a very weak texture.

Stress-controlled dynamic susceptibility in FeGa stripes

Knowledge of the dynamic magnetic susceptibility of patterned films is of great importance for exploring future data-storage applications and microwave devices. Since ferromagnetic resonance frequency is a function of the geometric parameters of a certain magnetic system, in this work, we investigate by micromagnetic simulations a set of stripe-patterned FeGa films, which have an identical thickness of 10 nm but a varying width in the range of 30–80 nm and a varying length in the range of 200–1000 nm. Fast-Fourier transform analysis of the simulation results for ferromagnetic resonance calculation identifies two distinct resonance peaks, which are assigned to a “bulk” mode and an “edge” mode. The presence of stress-induced anisotropy significantly affects both the two resonant modes. The occupation area of the spreading magnetization near the stripe ends is controllable by a tensile or compressive stress applied along the strip width. Consequently, the dynamic susceptibility of FeGa can be adjusted by an applied stress.

Electric-regulated enhanced in-plane uniaxial anisotropy in FeGa/PMN–PT composite using oblique pulsed laser deposition

The FeGa film with in-plane uniaxial magnetic anisotropy was fabricated onto different oriented single-crystal lead magnesium niobate–lead titanate using oblique pulsed laser deposition. An enhanced in-plane uniaxial magnetic anisotropy field of FeGa film can be adjusted from 18 Oe to 275 Oe by tuning the oblique angle and polarizing voltage. The competitive relationship of shape anisotropy and strain anisotropy has been discussed, which was induced by oblique angle and polarizing voltage, respectively. The (100)-oriented and (110)-oriented PMN–PT show completely different characters on voltage-dependent magnetic properties, which could be attributed to various anisotropy directions depended on different strain directions.

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.

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.

Effect of Film Thickness on the High Frequency Magnetic Properties of Polycrystalline Fe–Ga Films

This paper describes the effect of film thickness on the high frequency magnetic properties of polycrystalline Fe–Ga films. The damping constant ( $\alpha )$ increases markedly from approximately 0.015 to 0.081 for a film thickness below 20 nm, reaches a maximum value of 0.084 at a thickness of 30 nm, and then decreases to 0.068 as the thickness further increases to 100 nm. All the values are much larger than those of a single crystal Fe–Ga film, indicating that the extrinsic damping overlaps with the intrinsic damping. The inhomogeneous broadening in a zero field [ $\Delta H$ (0)] significantly increases with the film thickness due to the magnetic inhomogeneities, such as anisotropy dispersion and other effects. In addition, $\alpha $ increases markedly as the saturation magnetostriction ( $\lambda _{s})$ increases. This behavior is very similar to those of Ni–Fe and Ni–Fe–M films. Therefore, these results demonstrate that $\alpha $ is correlated with $\lambda _{s}$ regardless of the film thickness, and also sensitive to magnetic inhomogeneities.

Tuning static and dynamic properties of FeGa/NiFe heterostructures

In this work, the frequency-dependent magnetic properties of sputtered Galfenol/Permalloy (Fe85Ga15/Ni81Fe19 or FeGa/NiFe) magnetic multilayers were examined to tailor their magnetic softness, loss at microwave frequencies, permeability, and magnetoelasticity, leveraging the magnetic softness and low loss of NiFe and the high saturation magnetostriction (λs) and magnetization (MS) of FeGa. The total volume of each material and their ratio were kept constant, and the number of alternating layers was increased (with decreasing individual layer thickness) to assess the role of increasing interfaces in these magnetic heterostructures. A systematic change was observed as the number of bilayers or interfaces increases: a seven-bilayer structure results in an 88% reduction in coercivity and a 55% reduction in ferromagnetic resonance linewidth at the X-band compared to a single phase FeGa film, while maintaining a high relative permeability of 700. The magnetostriction was slightly reduced by the addition of NiFe but was still maintained at up to 67% that of single phase FeGa. The tunability of these magnetic heterostructures makes them excellent candidates for RF magnetic applications requiring strong magnetoelastic coupling and low loss.

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.

Controllable magnetic and magnetostrictive properties of FeGa films electrodeposited on curvature substrates

Magnetic properties of magnetostrictive FeGa films deposited by electrodeposition method on flexible curvature substrates were investigated under various mechanical stresses. The stresses of the bowed substrates were realized by series of different concentric circles. FeGa films exhibit a significant uniaxial magnetic anisotropy after the application of tensile or compressive stress, and the anisotropy of the film can be regulated by the residual stress. In addition, the magnetostriction of FeGa films is estimated through approximate calculation, indicating that the saturation magnetostrictive constant of films is enhanced with the increased tensile and compressive strains. These results provide another way to tune the magnetic properties and magnetostriction of flexible thin films, which is particularly important for the development of the flexible magneto-electronic devices.

Magnetostrictive iron gallium thin films grown onto antiferromagnetic manganese nitride: Structure and magnetism

We report structural and magnetic properties of magnetostrictive Fe100−xGax (x ≈ 15) alloys when deposited onto antiferromagnetic manganese nitride and non-magnetic magnesium oxide substrates. From X-ray diffraction measurements, we find that the FeGa films are single crystalline. Scanning tunneling microscopy imaging reveals that the surface morphologies are dictated by the growth temperature, composition, and substrate. The magnetic properties can be tailored by the substrate, as found by magnetic force microscopy imaging and vibrating sample magnetometry measurements. In addition to pronounced tetragonal deformations, depositing FeGa onto manganese nitride leads to the formation of stripe-like magnetic domain patterns and to the appearance of perpendicular magnetic anisotropy.

Giant magnetoimpedance effect in Fe75.5Cu1Nb3Si13.5B7 ribbon/FeGa film composite

Optimized giant magnetoimpedance effect of Fe75.5Cu1Nb3Si13.5B7 amorphous ribbon/Fe80Ga20 film composites has been investigated. FeCuNbSiB amorphous ribbons as the substrates are commercially available, magnetostrictive FeGa films are deposited on one or both sides of the ribbons by ion-beam sputtering. Compared with the GMI curves without FeGa layer, the GMI effect of FeCuNbSiB amorphous ribbon has been obviously improved with FeGa film covered (from 4% to 16%). Moreover, the details exhibit an interesting phenomenon: at a certain frequency, when the FeGa film covered on one side of the ribbon, the GMI ratio decreases with the thickness of the FeGa film; however, when the FeGa films covered on both sides of the ribbon, the GMI ratio increases with the thickness of the FeGa film. We mainly attribute the reason to strain-induced anisotropy, which is induced by magnetostrictive effect under a longitudinal applied magnetic field.

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.

Magnetic Anisotropy and Reversal in Epitaxial FeGa/MgO(001) Films Deposited at Oblique Incidence

We have epitaxially deposited FeGa films onto MgO(001) substrates at an oblique angle $\varphi $ varying from 0° to 45° and systematically investigated their magnetization reversal. The square and two-step hysteresis loops were observed in the samples deposited at $\varphi = 0 {^{\circ }}$ and 15°. The reversed two-step and three-step hysteresis loops were observed in the samples deposited at $\varphi =30 {^{\circ }}$ and 45°, in which a strong uniaxial magnetic anisotropy $K_{u}$ was induced by the oblique deposition. A model based on domain wall (DW) nucleation and propagation was employed to quantitatively describe the angular-dependent behaviors of FeGa epitaxial films, which indicates that, for the samples deposited with increasing $\varphi $ , the 180° magnetic transitions occurring in the magnetic field orientation between −45° and 45° gradually change from the two successive 90° DW nucleations to the 180° DW nucleation.

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.

Electric-field control of magnetic anisotropy in Fe81Ga19/BaTiO3 heterostructure films

We investigate the control of magnetism with an electric field in Fe81Ga19(FeGa)/BaTiO3(BTO) heterostructure films. The as-prepared FeGa/BTO samples present a uniaxial magnetic anisotropy, which is ascribed to be induced by the spontaneous ferroelectric polarization of the BTO substrates. With the electric field applied on the BTO substrates increasing from 0 to 6 kV/cm, the coercivity of FeGa films measured along the BTO[110] direction increases from 28 to 41 Oe, while the squareness of the hysteresis loop decreases from 0.99 to 0.31, which indicates that the easy and hard axes of FeGa films are swapped. The ferroelectric domains of BTO substrates and the magnetic domains of FeGa films exhibit the same dependence on the applied electric fields, manifesting the strong magnetoelectric coupling between the ferroelectricity of BTO substrates and the magnetism of FeGa films.