FeGa Films Research Articles

Electric-field induced strain modulation of magnetization in Fe-Ga/Pb(Mg1/3Nb2/3)-PbTiO3 magnetoelectric heterostructures

Magnetostrictive Fe-Ga thin layers were deposited on ⟨110⟩-oriented Pb(Mg1/3Nb2/3)-30%PbTiO3 (PMN-30%PT) substrates by pulsed laser deposition. The as-prepared heterostructures showed columnar arrays aligned in the out-of-plane direction. Transmission electron microscopy revealed nanocrystalline regions within the columnar arrays of the Fe-Ga film. The heterostructure exhibited a strong converse magnetoelectric coupling effect of up to 4.55 × 10−7 s m−1, as well as an electric field tunability of the in-plane magnetic anisotropy. Furthermore, the remanent magnetization states of the Fe-Ga films can be reversibly and irreversibly changed by external electric fields, suggesting a promising and robust application in magnetic random access memories and spintronics.

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.

In-plane anisotropic converse magnetoelectric coupling effect in FeGa/polyvinylidene fluoride heterostructure films

We investigated the converse magnetoelectric (CME) effect in the Fe81Ga19/polyvinylidene fluoride (PVDF) heterostructure films. A weak in-plane uniaxial magnetic anisotropy was observed in the as-deposited magnetostrictive FeGa films. When a positive (negative) electric field is applied on the ferroelectric PVDF substrates, both the coercivity and the squareness of magnetic hysteresis loops of FeGa films for the magnetic field parallel to the easy axis become larger (smaller), but for the magnetic field parallel to the hard axis the coercivity and the remanence get smaller (larger), indicating an anisotropic CME effect in FeGa/PVDF heterostructure films.

Effect of buffer layer and external stress on magnetic properties of flexible FeGa films

We systematically investigated the effect of a Ta buffer layer and external stress on the magnetic properties of magnetostrictive Fe81Ga19 films deposited on flexible polyethylene terephthalate (PET) substrates. The Ta buffer layers could effectively smoothen the rough surface of PET. As a result, the FeGa films grown on Ta buffer layers exhibit a weaker uniaxial magnetic anisotropy and lower coercivity, as compared to those films directly grown on PET substrates. By inward and outward bending the FeGa/Ta/PET samples, external in-plane compressive and tensile stresses were applied to the magnetic films. Due to the inverse magnetostrictive effect of FeGa, both the coercivity and squareness of hysteresis loops for FeGa/Ta films could be well tuned under various strains.

Numerical study of the effective magnetocrystalline anisotropy and magnetostriction in polycrystalline FeGa films

The high interest in FeGa films is due to the high magnetostriction present in single crystal thin films. There is, however, significant reduction in the magnetostriction when grown using sputtering. The reduction is explained here using finite element analysis by considering the local magnetocrystalline and magnetoelastic behavior of the grains within the sample. It is shown that, if the saturation magnetostrictive constant for each grain in a polycrystalline structure is of the order of 400 ppm, this is reduced to less than 90 ppm when the crystallites are randomly orientated. Furthermore, the inherent stress due to the sample fabrication leads to an increase in the anisotropy field. This work suggests that, with low stress fabrication and aligning the in-plane orientation of the crystallites, the potential in unlocking FeGa as a thin film for sensory applications can be realised.

Electrodeposition and characterization of Fe80Ga20 alloy films

Due to its high magnetostriction and good mechanical properties Fe80Ga20 is interesting for magnetostrictive microactuators and sensors. Here we use electrodeposition to grow Fe–Ga films onto Au and Pt coated Si substrates by potentiostatic and pulse potential deposition. Composition, microstructure and structure are analysed. The desired composition of Fe80Ga20 was obtained at −1.4VSCE and −1.5VSCE, respectively. The origin of low reproducibility and high oxygen content up to 50at.% is investigated. Optimum deposition conditions to achieve dense, homogeneous films with low oxygen content are identified. In these films the saturation magnetization reaches a maximum value of 1.7T confirming the high quality of electrodeposited films.

Effect of fabrication parameters on the microstructure, in-plane anisotropy and magnetostriction of Fe-Ga thin films

The microstructure, in-plane anisotropy, and magnetic properties of Fe-Ga thin films were investigated by X-ray diffraction analysis, vibrating sample magnetometer, and capacitive cantilever method. The in-plane induced anisotropy is well formed by the applied magnetic field during sputtering, and the anisotropy field Hk decreases with the sputtering power increasing. The coercivity of Fe-Ga thin films decreases with increasing power when the sputtering power is less than 60 W and increases when the power is larger than 60 W. The magnetostriction of the thin films reaches 66 × 10−6 at the sputtering power of 60 W. Excellent Fe-Ga films, which exhibit good field sensitivity, low coercivity and high magnetostriction, have been fabricated at the power of 60 W, and they can be used as the materials of magnetostrictive transducers.

An investigation of the effect of structural order on magnetostriction and magnetic behavior of Fe–Ga alloy thin films

This paper reports results from a comprehensive study of Fe–Ga films fabricated over a wide range of growth conditions. Polycrystalline Fe 100− x Ga x films (14 ⩽ x ⩽ 32) were deposited (using three different combinations of growth parameters) on Si(1 0 0) using a co-sputtering and evaporation technique. The growth parameters (sputter power, Ga evaporation rate and chamber pressure) were used primarily to control the Fe:Ga ratio in the films. X-ray diffraction showed that all films had 〈1 1 0〉 crystallographic texture normal to the film plane. The lattice parameter increased with % Ga up to x = 22 and was independent of growth parameters. Conversion electron Mössbauer spectroscopy studies showed a predominance of the disordered A2 phase in all films. It appears that the use of vacuum deposition with appropriate parameters can effectively suppress the D0 3 ordered phase. Systematic studies of the effective magnetostriction constant as a function of composition support this conclusion. It was found that films of high effective saturation magnetostriction constant and low stress could be fabricated using low Ar pressure, irrespective of sputter power or evaporation rate, giving properties useful for application in microelectromechanical systems.

Growth and characterization of epitaxial Fe0.8Ga0.2/0.69PMN-0.31PT heterostructures

Fe0.8Ga0.2 films were deposited on bulk single-crystal (001) 0.69PMN-0.31PT substrates by DC magnetron sputtering to make magnetoelectric bilayer composites. Films deposited at temperatures below 600°C were X-ray amorphous. Films deposited at temperatures of 600°C and higher exhibited a single-crystal (001) disordered BCC structure. The crystalline FeGa films demonstrate a 45° twisted cube-on-cube epitaxial relationship with the PMN–PT substrates. Heterostructures with an X-ray amorphous FeGa film exhibited zero magnetoelectric response. Heterostructures with a 990nm epitaxial FeGa film exhibited a large inverse magnetoelectric voltage coefficient of 13.4(Gcm)/V.

Effect of a forming field on the magnetic and structural properties of thin Fe–Ga films

The structural, magnetic, and magnetostrictive properties of 75nm Fe100−xGax films (0⩽x⩽30) have been studied to determine how a forming field during growth affects these properties. Two film sets were grown using a cosputtering-evaporation technique with and without a forming field of 65kAm−1. Using x-ray diffraction, the texture, lattice parameter, and the grain size were determined. An out-of-plane ⟨110⟩ texture was found for all films. The magnetization loops were measured on a magneto-optic Kerr effect magnetometer, from which the anisotropy symmetry was inferred from the remanent magnetization. It was found that the forming field produced a pronounced uniaxial anisotropy. The effective magnetostriction constant was measured using the Villari effect. The effective magnetostriction constant was compared with that calculated for a polycrystalline film with ⟨110⟩ out-of-plane texture using bulk constants, and the results are discussed.

Development of a cosputter-evaporation chamber for Fe–Ga films

A new deposition technique involving the dc magnetron sputtering of Fe simultaneously with Ga evaporation has been developed to fabricate thin Fe(1−x)Gax (0<x<0.4) films. Simultaneous sputtering and evaporation has been developed as an alternative to the sputtering of alloy targets, where the need for compositional variation can be hard to address. The new technique allows the freedom of composition that cosputtering would offer, but mitigates the issue of being unable to sputter Ga. The need for the preparation of alloy targets is also avoided. To control the concentration of the Ga in the films, the evaporation rate, the dc magnetron power, and the chamber pressure were varied. The films fabricated were studied to determine their magnetic and microstructural properties. The Fe–Ga films fabricated had magnetostriction constants which had increased by a factor of 5 compared to the same thickness of Fe film.

ＤＣマグネトロンスパッタリング法によるＦｅ‐Ｇａ合金薄膜の作製

The magnetostrictive properties of Fe-Ga (Ga: 8 at%-21 at%) alloy films prepared by DC magnetron sputtering system were investigated. Base pressure was less than 1.0×10-4 Pa and Fe-Ga films were deposited onto Single crystal Si(100) and polyimide substrate at room temperature with DC 200 W in an Ar atmosphere of 2.5×10-1 Pa. The lattice parameter of Fe-Ga films with a bcc structure increased with the increasing Ga concentration. The Fe-Ga films showed columnar grains with a crystalline orientation for ‹110› perpendicular to the film plane. The magnetostriction of Fe-Ga films increased with the increasing Ga concentration. Fe-21 at%Ga film showed a maximum magnetostriction of 180 ppm at an applied magnetic field of 1200 kA/m.

Development of Magnetostrictive Fe-Ga and Fe-Pd Thin Films

ABSTRACTThe giant magnetostrictive films exhibit promising device applications for micro-machines and sensor systems due to high response velocity and huge stress created by the magnetostriction. We developed magnetostrictive bimorph-type Fe70Pd30 or Fe83Ga17 (positive magnetostriction)/Al/Ni(negative magnetostriction) thin films by magnetron sputtering. Magnetostriction of these films measured by a bending cantilever beam method has reached 250–300 ppm in the small magnetic field of 1.0 kOe and exhibits little hysteresis. Moreover, the magnetostrictive characteristics do not change under low alternating magnetic field. The magnetoelastic coefficient of these films is 25∼30 MPa, which is comparable to the coefficient of the PbTiO3-PbZrO3 system. These metallic sensor/actuator materials are useful for applications in magnetostrictive 2D- scanners and remote-interrogated tire sensors.