FeGa Films Research Articles

Structural and Magnetization Studies of Cu Buffered Fe-Ga Films Grown on Si and Si/SiO2 Substrates

Structural and Magnetization Studies of Cu Buffered Fe-Ga Films Grown on Si and Si/SiO2 Substrates

Joule magnetostriction and volume magnetostriction of Iron Gallium thin films

The main aim of this work is to evaluate magnetostriction performances, including Joule magnetostriction and volume magnetostriction, of FeGa thin films synthesized by electrodeposition and ion-beam sputtering. This research demonstrated that the electrodeposited Fe(100-x)Gax (x: 19 ∼ 26) films had a tensile stress, and the ion-beam sputtered Fe81Ga19 film had a compressive stress. In both films, the easy axis of magnetization was in the in-plane direction. Both films exhibited nearly (110)-oriented polycrystalline structures. For the ion-beam sputtered Fe81Ga19 film, the observed volume magnetostriction was 39 ppm, approximately one-third of the Joule magnetostriction of 116 ppm. For electrodeposited Fe81Ga19, the Joule and volume magnetostrictions were 64 ppm and 46 ppm, respectively. An important conclusion of this research was that the FeGa films formed by non-equilibrium growth processes displayed a large volume magnetostriction.

Multilayering FeGa with NiFe and Al2O3 to enhance the soft magnetic properties

In this study, the impact of insulating Al2O3 interlayers on the static and dynamic magnetic properties of FeGa/NiFe multilayers was investigated. A multilayer structure consisting of ten (10 nm FeGa)/(2.5 nm NiFe) bilayers was first established to show a reduction in coercivity and high frequency losses compared to a single (100 nm FeGa)/(2.5 nm NiFe) bilayer, which itself shows better performance than a single 100 nm FeGa film. By strategically placing 2.5 nm Al2O3 interlayers in the FeGa/NiFe multilayers (after the FeGa layer but before the next NiFe layer), the composite displayed a reduced coercivity down to 3 Oe while retaining a strong uniaxial anisotropy. Due to the effectiveness of these ultra-thin Al2O3 layers in reducing the eddy current losses across the FeGa/NiFe multilayer stack, this multilayer structure exhibited excellent performance at high frequency, including a gilbert damping coefficient of 0.0081 and an inhomogeneous linewidth of 38 Oe. These results demonstrate that Al2O3 interlayers can improve the soft magnetic properties of (FeGa/NiFe)-based multilayers to enable integration in magnetoelastic and high frequency applications.

On‐chip Diamond MEMS Magnetic Sensing through Multifunctionalized Magnetostrictive Thin Film

AbstractElectrically integrable, high‐sensitivity, and high‐reliability magnetic sensors are not yet realized at high temperatures (500 °C). In this study, an integrated on‐chip single‐crystal diamond (SCD) micro‐electromechanical system (MEMS) magnetic transducer is demonstrated by coupling SCD with a large magnetostrictive FeGa film. The FeGa film is multifunctionalized to actuate the resonator, self‐sense the external magnetic field, and electrically readout the resonance signal. The on‐chip SCD MEMS transducer shows a high sensitivity of 3.2 Hz mT−1 from room temperature to 500 °C and a low noise level of 9.45 nT Hz−1/2 up to 300 °C. The minimum fluctuation of the resonance frequency is 1.9 × 10−6 at room temperature and 2.3 × 10−6 at 300 °C. An SCD MEMS resonator array with parallel electric readout is subsequently achieved, thus providing a basis for the development of magnetic image sensors. The present study facilitates the development of highly integrated on‐chip MEMS resonator transducers with high performance and high thermal stability.

Magnetic Properties Regulation of FeGa and FeGaNi Films with Oblique Magnetron Sputtering

Magnetic FeGa and FeGaNi films with an in-plane anisotropy were deposited by employing oblique magnetron sputtering. With the increase in oblique angle, the crystallite size of FeGa decreases, which indicates that oblique sputtering can refine the crystallite size. The remanence ratio of FeGa films increases from 0.5 to 0.92 for an easy axis, and the coercivity increases with the decrease in the crystallite size. The calculated static anisotropic field shows that the in-plane magnetic anisotropy can be induced by oblique sputtering and the strength increases with the oblique sputtering angle. After doping Ni by co-sputtering, FeGaNi films exhibit a stable remanence ratio at 0.8, low coercivity and good anisotropy. With the low sputtering power of the Ni target, there is a competitive relationship between the effect of crystallite size and Ni doping which causes the coercivity of FeGaNi films to first increase and then decrease with the increase in the oblique angle. The FeGaNi film also shows high anisotropy in a small oblique angle. The variation of coercivity and anisotropy of FeGaNi films can be explained by the crystalline size effect and increase in Ni content. For the increasing intensity of collisions between FeGa and Ni atoms in the co-sputtering, the in-plane magnetic anisotropy increases first and then decreases. As a result, the magnetic properties of FeGa films were examined to tailor their magnetic softness and magnetic anisotropy by controlling the oblique sputtering angle and Ni doping.

Enhancement of magnetic sensing performance of diamond resonators coupling with magnetic-strictive FeGa films by various interlayers

The authors report the enhancement of the magnetic sensitivity of single-crystal diamond (SCD) MEMS magnetic sensor, which is composed of a SCD cantilever integrated with a magneto-strictive Galfenol (FeGa) thin film. To improve the magnetic sensing properties from room temperature to high temperatures, different interlayers of Ti film, WC film, and WC/Ti film are inserted between the SCD cantilevers and the FeGa thin films in the SCD-MEMS magnetic sensors. The thermal-stability of the microstructures, phase structures, and magnetic properties of the FeGa thin films are greatly enhanced by these interlayers. The FeGa thin films within the FeGa/SCD, FeGa/Ti/SCD, FeGa/WC/SCD, and FeGa/Ti/WC/SCD structures maintain high thermal-stability in surface morphologies, roughness, phase structures, and magnetic properties under the annealing temperature up to 573 K, 773 K, 573 K, and 673 K, respectively. The magnetic sensor with the FeGa/SCD structure has the weakest magnetic sensitivity of 1.96 Hz/mT @573 K and the FeGa/WC/Ti/SCD structure hosts the highest magnetic sensitivity of 75.40 Hz/mT @673 K. The present work provides a strategy to tailor the magnetic sensing properties of SCD MEMS for the applications under extreme conditions.

Seebeck-driven transverse thermoelectric generation in on-chip devices

An unconventional approach to enhance the transverse thermopower by combining magnetic and thermoelectric materials, namely the Seebeck-driven transverse thermoelectric generation (STTG), has been proposed and demonstrated recently. Here, we improve on the previously used sample structure and achieve large transverse thermopower over 40 μV K−1 due to STTG in on-chip devices. We deposited polycrystalline Fe–Ga alloy films directly on n-type Si substrates, where Fe–Ga and Si serve as the magnetic and thermoelectric materials, respectively. Using microfabrication, contact holes were created through the SiO x layer at the top of Si to electrically connect the Fe–Ga film with the Si substrate. These thin devices with simple structure clearly exhibited enhancement of transverse thermopower due to STTG, and the obtained values agreed well with the estimation over a wide range of the size ratio between the Fe–Ga film and the Si substrate.

Annealing enhanced ferromagnetic resonance of thickness-dependent FeGa films

We report the influence of different annealing temperatures on the magnetic property of FeGa thin films. The measurement was done for the film thickness from 42 to 420 nm. Our results show that the annealing temperature affects not only the microstructure but also the ferromagnetic resonance signal of the film. Annealing of a FeGa film improves the in-plane remanence ratio and reduces the in-plane ferromagnetic resonance linewidth by a factor of five. This annealing treatment promotes film texture and releases compressive stresses in the film. Our results demonstrate that the structural control via annealing is viable. The necessary magnetic softness of the FeGa film for microwave applications can be achieved.

Mechanical, magnetic and magnetostrictive properties of porous Fe-Ga films prepared by electrodeposition

Mechanical, magnetic and magnetostrictive properties of porous Fe-Ga films prepared by electrodeposition

Mechanical, magnetic and magnetostrictive properties of porous Fe-Ga films prepared by electrodeposition

Magnetostriction, known as the ability of magnetic materials to expand or contract in response to magnetic field, is a key property of Fe-Ga alloys exploited in various types of transducers. Usually, thin films of Fe-Ga deposited on rigid substrates suffer from a clamping effect that hinders the propagation of strain. Herein, Fe-Ga films with macroporous, not fully constrained, geometry are prepared by electrodeposition on metallized silicon substrates templated with sub-micrometer-sized polystyrene spheres. For comparison, fully-dense and inherently nanoporous films are prepared by sputtering and electrodeposition, respectively. The electrodeposition mechanism is discussed in terms of electrochemically active species distribution and partial current densities. The composition of the Fe-Ga films has been tuned (2–40 at.% Ga) by varying the electrodeposition parameters. A complete assessment of the nanomechanical and magnetic properties of the films with variable composition and porosity has been performed for an optimized performance. The magnetostriction has been studied by X-ray diffraction applying an in-situ magnetic field. The results demonstrate a larger magnetic-field-induced crystal deformation in templated (macroporous) films compared to the non-templated and fully-dense counterparts. The observed effects in porous Fe-Ga films are very appealing for the design of various strain-engineered nanomaterials, e.g., energy transducers or magnetoelectric composites.

Strain-Mediated Giant Magnetoelectric Coupling in a Crystalline Multiferroic Heterostructure.

Multiferroic heterostructures based on the strain-mediated mechanism present ultralow heat dissipation and large magnetoelectric coupling coefficient, two conditions that require endless improvement for the design of fast nonvolatile random access memories with reduced power consumption. This work shows that a structure consisting of a [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3 (001) substrate on which a crystalline FeGa(001)/MgO(001) bilayer is deposited exhibits a giant magnetoelectric coupling coefficient of order 15 × 10–6 s m–1 at room temperature. That result is a 2-fold increment over the previous highest value. The spatial orientation of the magnetization vector in the epitaxial FeGa film is switched 90° with the application of electric field. The symmetry of the magnetic anisotropy is studied by the angular dependence of the remanent magnetization, demonstrating that poling the sample generates a switchable uniaxial magnetoelastic anisotropy in the film that overcomes the native low 4-fold magnetocrystalline anisotropy energy. Magnetic force microscopy shows that the switch of the easy axis activates the displacement of domain walls and the domain structures remain stable after that point. This result highlights the interest in single-crystalline structures including materials with large magnetoelastic coupling and small magnetocrystalline anisotropy for low-energy-consuming spintronic applications.

Tunable high-frequency properties of flexible FeGa films with rotatable stripe domain

A comprehensive investigation of stress-induced anisotropy in 300 nm Fe81Ga19 (FeGa) thin films with stripe domain structures has been performed by comparing static and dynamic measurements. The formation and rotation of stripe domains under a compressive stress have been imaged by magnetic force microscopy and understood by micromagnetic simulations. A double magnetic anisotropy system, combing the stress-induced uniaxial magnetic anisotropy and the rotatable magnetic anisotropy caused by the stripe domain structure was achieved in FeGa thin films. The ferromagnetic resonance frequency of 300 nm FeGa thin films with stripe domains can be enhanced from 2.7 to 3.0 GHz without sacrificing the initial permeability. This found provides us a new approach via utilizing the double magnetic anisotropies in magnetic films with stripe domains to enhance the resonance frequency beyond the Snoek’s limit and extends the application for FeGa films to flexible microwave devices.

Enhanced magnetic sensing performance of diamond MEMS magnetic sensor with boron-doped FeGa film

The coupling of single crystal diamond (SCD) micro-electromechanical systems (MEMS) through with a functional hetero-material provides the strategy to develop diamond MEMS sensors. Here a noncontact magnetic sensor based on SCD MEMS resonance system functionalized with a boron-doped FeGa (FeGaB) thin film owning excellent magneto-strictive properties on diamond is demonstrated to improve the magnetic sensitivity. The amorphous FeGaB thin film is beneficial for high magnetic sensing performance. The FeGaB/Ti/SCD MEMS magnetic sensor exhibits magnetic sensitivity of as high as 152.1 Hz/mT, which is over four times of those of FeGa/Ti/SCD MEMS magnetic sensors. The derivative of the Young’s modulus change with magnetic field (dE/dH) reaches a maximum value of 4.5 GPa/mT at 1.77 mT. By tailoring the magnetic properties with impurity dopant, one can markedly improve the sensitivity of the diamond MEMS magnetic sensitivity toward satisfying the figure-of-merits of ultra-high sensitivity, low noise level and high-reliability magnetic field operation.

Enhanced magnetic properties of amorphous FeGaN film growth by plasma assisted pulsed laser deposition

The amorphous N-doped FeGa film were successfully deposited on Si (001) substrate using N2-plasma assisted pulsed laser deposition system at different temperatures. The enlarged saturation magnetization of FeGaN film has been investigated, which is higher than pure FeGa film under the same preparation condition. The optimal saturation magnetization of FeGaN film can reach up to 300 emu/cc, which also can be tuned by controlling the N2 flux during the deposition process. With the increase of deposition temperature, the antiferromagnetic, ferromagnetic and paramagnetic characters have also appeared respectively. The reason can be attributed to the change of the short-range order of lattice structure of FeGaN.

Bias voltage modulated resistance states in small-area Fe70Ga30 films on ferroelectric Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3TiO3) films

In this work, composite films consisting of small-area Fe70Ga30 (FeGa) on [Ba(Zr0.2Ti0.8)O3]–0.5(Ba0.7Ca0.3TiO3) (BZT-0.5BCT) films were deposited on Pt/Ti/SiO2/Si substrates. Tetragonal perovskite crystalline phase of BZT-0.5BCT films was obtained and the films possess uniform and ordered ferroelectric domain structures. Ferroelectric hysteresis loop and displacement voltage butterfly loop of BZT-0.5BCT films are studied. The results show that BZT-0.5BCT films exhibit good piezoelectric properties with displacement up to 64.2 Å. The BZT-0.5BCT/FeGa composite films exhibit well defined magnetic hysteresis loop with a coercive field of 3.8 kA/m. The current-voltage (I-V) curves are examined and the I-V behaviors of FeGa films on BZT-0.5BCT films could be modulated by applying bias voltages, which gives rise to remarkable bias voltage controlled resistance switching behaviors, a maximum resistance change of 79.8% was obtained with a bias voltage of 0.5 V.

Underlayer effect on the soft magnetic, high frequency, and magnetostrictive properties of FeGa thin films

The soft magnetic, microstructural, and magnetostrictive properties of Fe81Ga19 (FeGa) film sputter deposited onto 2.5-nm Ta, Cu, and Ni80Fe20 (NiFe) underlayers were investigated. The films deposited with an underlayer showed increased in-plane uniaxial anisotropy and a decrease in in-plane coercivity. The smallest coercivity was observed in FeGa deposited with a NiFe underlayer at 15 Oe, compared to 84 Oe for films deposited directly on Si. In addition, an effective Gilbert damping coefficient (αeff) as low as 0.044 was achieved for a 100-nm FeGa film with a NiFe underlayer. The coercivity and αeff were shown to decrease further as a function of FeGa film thickness. The FeGa films were also able to retain or increase their saturation magnetostriction when deposited on an underlayer. This enhancement is attributable to the impact of the underlayer to promote an increased (110) film texture and smaller grain size, which is correlated to the lattice match of the underlayer of the sputtered FeGa film. Among the underlayers studied, NiFe promoted the best enhancement in the soft magnetic properties for FeGa thin films, making it an attractive material for both strain-mediated magnetoelectric and microwave device applications.

Enhancing the soft magnetic properties of FeGa with a non-magnetic underlayer for microwave applications

An ultra-thin (∼2.5 nm) non-magnetic Cu underlayer was found to have a significant effect on the microstructure, magnetic softness, and magnetostriction of sputter-deposited Fe81Ga19 (FeGa) thin films. Compared to the experimental control where FeGa was deposited directly on Si without an underlayer, the presence of Cu increased the in-plane uniaxial anisotropy of FeGa and reduced the in-plane coercivity by nearly a factor of five. The effective Gilbert damping coefficient was also significantly reduced by a factor of four, between FeGa on Si and FeGa on a Cu underlayer. The FeGa films on Cu also retained a high saturation magnetostriction comparable to those without an underlayer. The enhancement of the desirable magnetic properties for microwave applications is attributed to the Cu underlayer, promoting the (110) film texture and increasing the compressive film strain. The results demonstrated that the structural control is viable to simultaneously achieve the necessary magnetic softness and magnetostriction in FeGa for integration in strain-mediated magnetoelectric and microwave devices.

Enhancing Delta E Effect at High Temperatures of Galfenol/Ti/Single-Crystal Diamond Resonators for Magnetic Sensing

A conventional wisdom is that the sensing properties of magnetic sensors at high temperatures will be degraded due to the materials' deterioration. Here, the concept of high-temperature enhancing magnetic sensing is proposed based on the hybrid structure of SCD MEMS resonator functionalized with a high thermal-stable ferromagnetic galfenol (FeGa) film. The delta E effect of the magnetostrictive FeGa thin film on Ti/SCD cantilevers is investigated by varying the operating temperature from 300 to 773 K upon external magnetic fields. The multilayer structure magnetic sensor presents a high sensitivity of 71.1 Hz/mT and a low noise level of 10 nT/√Hz at 773 K for frequencies higher than 7.5 kHz. The high-temperature magnetic sensing performance exceeds those of the reported magnetic sensors. Furthermore, an anomalous behavior is observed on the delta E effect, which exhibits a positive temperature dependence with the law of Tn. Based on the resonance frequency shift of the FeGa/Ti/SCD cantilever, the strain coupling in the multilayers of the FeGa/Ti/SCD structure under a magnetic field is strengthened with increasing temperature. The delta E effect shows a strong relationship with the azimuthal angle, θ, as a sine function at 300 and 773 K. This work provides a strategy to develop magnetic sensors for high-temperature applications with performance superior to that of the present ones.

Unveiling the Different Physical Origins of Magnetic Anisotropy and Magnetoelasticity in Ga-Rich FeGa Thin Films

The aim of this work is to clarify how in-plane magnetic anisotropy and magnetoelasticity depend on the thickness of Ga-rich FeGa layers. Samples with an Fe72Ga28 composition were grown by sputtering in the ballistic regime in oblique incidence. Although for these growth conditions uniaxial magnetic anisotropy could be expected, in-plane anisotropy is only present when the sample thickness is above 100 nm. By means of differential X-ray absorption spectroscopy, we have determined the influence of both Ga pairs and tetragonal cell distortion on the evolution of the magnetic anisotropy with the increase of FeGa thickness. On the other hand, we have used the cantilever beam technique with capacitive detection to also determine the evolution of the magnetoelastic parameters with the thickness increase. In this case, experimental results can be understood considering the grain distribution. Therefore, the different physical origins for anisotropy and magnetoelasticity open up the possibility to independently tune these two characteristics in Ga-rich FeGa films.

Strain gradient mediated magnetoelectricity in Fe-Ga/P(VDF-TrFE) multiferroic bilayers integrated on silicon

The primary advantage of magnetoelectric heterostructures exhibiting direct magnetoelectric effect is the possibility to induce and modulate the electrical response of the ferroelectric phase directly with an external magnetic field (i.e., wirelessly, without applying electric field). Nevertheless, the magnetoelectric coupling in such heterostructures is commonly limited by substrate clamping which hinders effective strain propagation. In this work, 1 μm thick ferromagnetic Fe-Ga layers were electrodeposited onto rigid Si/Cu substrates and subsequently coated with ferroelectric P(VDF-TrFE). Under magnetic field, the (110) textured Fe-Ga alloy is compressed along the z-direction by 0.033%, as demonstrated by X-ray diffraction. The experimental results suggest that while the bottom of the Fe-Ga layer is clamped, its air side exhibits a pronounced tetragonal deformation thanks to the residual nanoporosity existing between the columnar grains, that is, a strain gradient develops across the thickness of the Fe-Ga film. This strain gradient in Fe-Ga induces a change in the piezoresponse of the adjacent ferroelectric P(VDF-TrFE) layer. These results pave the way to the design of high-performance microelectromechanical systems (MEMS) with magnetoelectric response integrated on rigid substrates.