FePd Thin Films Research Articles

Application of Cr-N and Fe-Pd Thin Films to Tactile Sensors for Simultaneous Strain and Temperature Measurement

Application of Cr-N and Fe-Pd Thin Films to Tactile Sensors for Simultaneous Strain and Temperature Measurement

Solid-State Dewetting as a Driving Force for Structural Transformation and Magnetization Reversal Mechanism in FePd Thin Films.

In this work, the process of solid-state dewetting in FePd thin films and its influence on structural transformation and magnetic properties is presented. The morphology, structure and magnetic properties of the FePd system subjected to annealing at 600 °C for different times were studied. The analysis showed a strong correlation between the dewetting process and various physical phenomena. In particular, the transition between the A1 phase and L10 phase is strongly influenced by and inextricably connected with solid-state dewetting. Major changes were observed when the film lost its continuity, including a fast growth of the L10 phase, changes in the magnetization reversal behavior or the induction of magnetic spring-like behavior.

Disordered to ordered phase transformation: Correlation between microstructure and magnetic properties in Fe–Pd thin films

The kinetics of the transformation from the disordered to the ordered phase has been studied in Fe56Pd44 thin films deposited on silicon substrates by Joule evaporation. Subsequent thermal treatments at 550 °C in vacuum were performed at different annealing times to promote the formation and the optimization of the ordered L10 FePd phase. X-ray diffraction allowed us to investigate the microstructure of the samples (grain size, volume fraction of the transformed phase, order parameter of the ordered phase, and average order of the alloy), whereas magnetic measurements allowed us to evaluate coercivity and to independently estimate the volume fraction of the ordered L10 phase. The kinetics of the transformation turned out to reach completion after 20 min of annealing time with the grain size growing with a power law with an exponent equal to 8.24. The resulting monophasic film has a high density of defects, which contribute to the magnetic coercivity. A linear relationship between the coercive field and the average order parameter of the alloy has been established. Finally, the evolution of the transformed phase obeys Avrami's law with an exponent of ∼0.4, indicating that the transformation is controlled by the nucleation mechanism without grain growth.

Exchange-bias dependent diffusion rate of hydrogen discovered from evolution of hydrogen-induced noncollinear magnetic anisotropy in FePd thin films

Hydrogenation-induced noncollinear magnetic anisotropy is observed from the evolution of the magnetic domains in FePd alloy thin films using magneto-optic Kerr effect (MOKE) microscopy. MOKE images reveal complicated competitions between different magnetic anisotropies during hydrogen diffusion into the film. An intriguing enhancement of the hydrogen diffusion rate due to the presence of an initial exchange bias induced by a high magnet field is thereby discovered, pointing to an additional scope of controllability of magnetic metal hydrides as potential future hydrogen sensing and storage materials.

Enhancement of a spin-wave self-focusing by a pulsed flat-top excitation field in a multi-domain state

We investigate a spin-wave (SW) self-focusing in a ferromagnetic FePd thin film with a perpendicular magnetic anisotropy by using micro-magnetic simulation. In a one-dimensional structure, a point-excitation of forward volume magnetostatic waves leads the SW propagation in the form of a wave packet. When SWs are excited over a wide area with a uniform amplitude distribution, the SW propagation occurs by taking not only a diverging component but also a focusing-like component. Interestingly, we can increase the focusing effect by reflecting the diverging waves at the magnetic phase boundary, such as domain walls. This SW focusing appears also in a two-dimensional system, and, furthermore, magnetic droplets can be easily formed at the focal points when the focused SW intensity exceeds an appropriate threshold. Based on these results, we can propose the flat-top excitation of the magnetostatic waves as an efficient way to generate the SW self-focusing and also to create magnetic droplets in a multi-domain state of perpendicularly magnetized systems.

L10 phase formation in FePd thin films induced by H2 during annealing

Equiatomic FePd thin films with a thickness of 5 nm were deposited at room temperature by magnetron sputtering on the thermally oxidized silicon substrates. Annealing in vacuum and in hydrogen atmosphere was used to transform the chemically disordered A1 FePd films into the chemically ordered L10 FePd phase. The influence of annealing atmosphere, annealing temperature, and annealing time on the ordering process of the films was studied. Annealing in hydrogen atmosphere at 650 °C accelerates the ordering process and leads to the L10 FePd phase. However, the incorporation of H also influences the electronic structure and thus the magnetic properties. A further increase in annealing time or temperature (over 650 °C) accelerates the L10 ordering process but also alters drastically the film morphology forming a fine grainy structure, which appears X-ray amorphous rares. The latter even results in a most likely superparamagnetic state.

Buffer layer engineering of L1 FePd thin films with large perpendicular magnetic anisotropy

Development of L10 FePd thin films with large bulk perpendicular magnetic anisotropy and a low damping constant may permit superior scaling of next-generation ultra-high density magnetic memory elements. The buffer layer influences the L10-order parameter, static and dynamic magnetic properties of FePd and demands consideration for the design of high anisotropy strength and low damping films. In this report, we systematically investigate the perpendicular magnetic anisotropy and damping constant of the FePd thin films engineered through the Cr/(Pt, Ru, Ir, Rh), Mo/Ir, and Ir buffer layers. We observed that the Ir(001), Cr(001)/Ir(001), Cr(001)/Pt(001), Cr(001)/Rh(001), and Cr(001)/Ru(001) buffer layers can induce highly oriented (001) FePd films while the Mo/Ir buffer layer does not. Of all the buffer layers, the largest perpendicular magnetic anisotropy Ku ∼ 1.2 MJ/m3 and damping constant α ∼ 0.005 were achieved for the Cr/Pt buffered FePd sample, consistent with a high ordering parameter S ∼ 0.82. The Cr/Ru buffered FePd sample shows the lowest α ∼ 0.008, despite having a lower S ∼ 0.64 and a lower Ku ∼ 0.9 MJ/m3. These film-level properties would be sufficient for the engineering of devices that require thermally stable, sub-10 nm lateral size elements with low damping for applications of low energy-delay magnetic memory devices.

Low Gilbert damping and high thermal stability of Ru-seeded L10-phase FePd perpendicular magnetic thin films at elevated temperatures.

Bulk perpendicular magnetic anisotropy materials are proposed to be a promising candidate for next-generation ultrahigh density and ultralow energy-consumption spintronic devices. In this work, we experimentally investigate the structure, thermal stability, and magnetic properties of FePd thin films seeded by a Ru layer. An fcc-phase Ru layer induces the highly-ordered L10-phase FePd thin films with perpendicular magnetic anisotropy (K u ~ 10.1 Merg/cm3). The thermal stability of FePd samples is then studied through the annealing process. It is found that a K u ~ 6.8 Merg/cm3 can be obtained with the annealing temperature of 500 °C. In addition, the damping constant α, an important parameter for switching current density, is determined as a function of the testing temperature. We observe that α increases from 0.006 to 0.009 for as-deposited FePd sample and from 0.006 to 0.012 for 400 °C-annealed FePd sample as the testing temperature changes from 25 °C to 150 °C. These results suggest that Ru-seeded FePd provides great potential in scaling perpendicular magnetic tunnel junctions below 10 nm for applications in ultralow energy-consumption spintronic devices.

Plasma-induced magnetic patterning of FePd thin films without and with exchange bias

We demonstrate control of magnetic domain structures in continuous FePd thin films by patterning their surfaces with plasma treatment. The Fe-oxide layer formed on the surface upon ambient exposure of the FePd alloy thin film grown on an Al2O3(0001) substrate was patterned into microstructures by e-beam lithography followed by O2- or Ar-plasma treatment. Microscopic pinning of magnetic domain walls in the thin films is then observed by magneto-optic Kerr effect microscopy, with the magnetic field needed to reverse the magnetization of the plasma-treated areas being larger than that for the untreated areas. An intriguing competition between the uniaxial anisotropy and the exchange bias is also observed in the system. This study demonstrates that patterning of the film surface with plasma treatment can be an easy and efficient method for sophisticated engineering of magnetic structures in thin films, and therefore has potential application in developing future data-storage and spintronic devices.

Structural and Magnetic Properties of FePd Thin Film Synthesized by Electrodeposition Method.

Bimetallic nanomaterials in the form of thin film constituted by magnetic and noble elements show promising properties in different application fields such as catalysts and magnetic driven applications. In order to tailor the chemical and physical properties of these alloys to meet the applications requirements, it is of great importance scientific interest to study the interplay between properties and morphology, surface properties, microstructure, spatial confinement and magnetic features. In this manuscript, FePd thin films are prepared by electrodeposition which is a versatile and widely used technique. Compositional, morphological, surface and magnetic properties are described as a function of deposition time (i.e., film thickness). Chemical etching in hydrochloric acid was used to enhance the surface roughness and help decoupling crystalline grains with direct consequences on to the magnetic properties. X-ray diffraction, SEM/AFM images, contact angle and magnetic measurements have been carried out with the aim of providing a comprehensive characterisation of the fundamental properties of these bimetallic thin films.

Micromagnetic and Magnetooptical Properties of Ferromagnetic/Heavy Metal Thin Film Structures

The magnetic properties of CoPt, CoPd, and FePd thin films with different contents of a ferromagnetic material fabricated by electron beam evaporation have been compared. The micromagnetic structure investigations have shown a decrease in the magnetic domain size with an increase in the Co content in the CoPt and CoPd films, which has been attributed to the presence of two magnetic phases in the films. The magnetooptical studies have shown anomalously large Faraday angles and the absence of Kerr effect in the CoPt films, which make them attractive for application in optics. In the FePd films, the minimum coercivity values have been obtained from the magnetic-field dependences of the magnetization, which has also been related to the magnetic structure features.

Control of the stripe domain pattern in L10-ordered FePd thin films

Abstract L10-ordered FePd thin films with strong perpendicular magnetic anisotropy and self-organized domain patterns have been prepared using molecular beam epitaxy. We demonstrate reproducible growth methods for controlling the strength of the anisotropy and the lateral domain patterns. Neutron scattering experiments have been used to probe the FePd domain structure and were compared with simulations in the framework of the Distorted Wave Born Approximation.

Characteristics of Iron-Palladium alloy thin films deposited by magnetron sputtering

Abstract The microstructural features, magnetic, nanomechanical properties and wettability behaviors of Iron-Palladium (FePd) alloy thin films are investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), vibrating sample magnetometer (VSM), nanoindentation and water contact angle (CA) techniques, respectively. The FePd alloy thin films were deposited on glass substrates using a magnetron sputtering system. The post-annealing processes of FePd alloy thin films were carried out at 400 °C and 750 °C and resulted in a significant increase of both the average grain size and surface roughness. The XRD analysis showed that FePd alloy thin films exhibited a predominant (1 1 1) orientation. The magnetic field dependence of magnetization of all FePd thin films are measured at room temperature showed the ferromagnetic characteristics. The nanoindentation with continuous stiffness measurement (CSM) is used to measure the hardness and Young’s modulus of present films. The contact angle ( θ CA ) increased with increasing surface roughness. The maximum θ CA of 75° was achieved for the FePd alloy thin film after annealing at 750 °C and a surface roughness of 4.2 nm.

Coercivity enhancement of FePd thin films prepared by the post-annealing of off-stoichiometric magnetron-sputtered multilayers

Attainment of perpendicular coercivity higher than 900 Oe and accurate calculation of the degree of long-range order in an FePd alloy thin film is essential in the realization of the perpendicular magnetic recording media. Here, we prepared the off-stoichiometric FePd films through the multilayer growth of [Fe(2 nm)/Pd(2 nm)] × 30 deposited on MgO(001) substrates by magnetron sputtering. The effects of post-annealing these films at 700 °C for 1 and 10 h on their surface morphologies, and crystallographic and magnetic characteristics were investigated. The results show that, with increasing annealing time, the FePd thin films are predominantly (001)-oriented with a progressive increase of the grain size and surface roughness, as well as the improved crystallinity and reduced micro-strain. Accordingly, the perpendicular coercivity is significantly increased to the value of 1.5 kOe, and Pd loses its 4d electrons upon alloying. Furthermore, analysis of X-ray absorption data elucidates some structural details of the Fe scattering phase in addition to the dominant tetragonal FePd phase. We also present a way of determining the long-range order parameter for the FePd alloy thin film, using the combined information of the tetragonality ratio extracted from extended x-ray absorption fine-structure spectroscopy and the stoichiometric deviation of the thin film.

Promotion of L10 Ordered Phase Transformation by the Si3N4 Top Layer on FePd Thin Films

Structure and magnetic properties of FePd thin films substrate on the glass with Si3N4 to player have been investigated. The results suggested that ceramic Si3N4 component distributed around the FePd nanograins, which inhibits the growth of the FePd particles and refined grain size of FePd films. Compared with the pure FePd thin films the coercivity and remanence ratio of FePd/Si3N4 films reached to the maximum value of 3.3 and 0.98 kOe, respectively. With further increase of the annealing time, magnetic properties of FePd/Si3N4films do not drop rapidly, but keep high magnetic properties at a relatively wide temperature range. Defects, inclusions and intermixing phenomena occurred between the FePd layers and the Si3N4 top layers promoted the improvement of L10 ordered phase transformation.

Transmission electron microscopy on as–deposited and freestanding single crystalline Fe70Pd30 ferromagnetic shape memory alloy thin film

Within this transmission electron microscopy study, we explore the atomic structure of Fe-Pd thin films with and without supporting single crystalline (001) MgO substrate. We observe a phase structural transition depending strongly on spatial limited stresses. While around the film-substrate interface edge dislocations form to minimize stresses due to the lattice misfit between MgO and Fe-Pd, preferring the face-centered cubic phase, upper sample regions show twinning structures with the face- and body-centered tetragonal phase, respectively. In freestanding films, bct and bcc phases are observed. Compared to unprocessed lift-off films, no hierarchical structure was existent anymore, based on changed stress distributions.

Influence of L10 order parameter on Gilbert damping constants for FePd thin films investigated by means of time-resolved magneto-optical Kerr effect

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Shock wave induced martensitic transformations and morphology changes in Fe-Pd ferromagnetic shape memory alloy thin films

Combining experimental methods and classical molecular dynamics (MD) computer simulations, we explore the martensitic transformation in Fe70Pd30 ferromagnetic shape memory alloy thin films induced by laser shock peening. X-ray diffraction and scanning electron microscope measurements at shock wave pressures of up to 2.5 GPa reveal formation of martensitic variants with preferred orientation of the shorter c-axis of the tetragonal unit cell perpendicular to the surface plane. Moreover, consequential merging of growth islands on the film surface is observed. MD simulations unveil the underlying physics that are characterized by an austenite-martensite transformation with a preferential alignment of the c-axis along the propagation direction of the shock wave, resulting in flattening and in-plane expansion of surface features.

Hard Magnetic Property Improvement of Sputter-Prepared FePd Films on Glass Substrates by Underlayering With Refractory Nb, Mo, and W Elements

Magnetic properties and structure of sputter-prepared FePd thin films on the glass substrates by underlayering with refractory elements M (M = Nb, Mo, and W) have been studied. The structural analysis shows that FePd films have a (111) preferred orientation. All studied FePd films exhibit in-plane magnetic anisotropy. For single-layer FePd films, the coercivity ( $H_{c})$ and magnetic energy product [(BH) $_{\mathrm {max}}]$ are increased with annealing temperature ( $T_{a})$ and reached the maximum value of 1.3 kOe and 3.8 MGOe in the sample annealing at 600 °C. With the further increase of $T_{a}$ , magnetic properties drop rapidly. Dependence of magnetic hardening on $T_{a}$ can be explained by dominant solid reactions in different region of $T_{a}$ including ordering and grain growth. Interestingly, magnetic properties of L10-FePd are largely improved by underlayering with 5 nm-thick Nb, Mo, and W layers. Both the coercivity and energy product are significantly increased to 1.6 kOe and 4.9 MGOe for M = Nb, 2.5 kOe and 6.4 MGOe for M = Mo, and 3.3 kOe and 8.7 MGOe for M = W, respectively. Structural analysis suggests that this magnetic enhancement is related to both higher ordering degree and refined microstructure.

Effects of post-annealing on the structural and nanomechanical properties of sputter-deposited FePd thin films

The effects of post-annealing on the microstructures, surface morphologies and nanomechanical characteristics of FePd thin films are investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and nanoindentation techniques. The FePd thin films were deposited on the glass substrates at room temperature by magnetron sputtering system. Post-annealing was carried out at 500, 600 and 700 °C, respectively, resulting in progressive increase of the average grain size and surface roughness of FePd thin films, as well as the improved film crystallinity. XRD results show that FePd thin films are predominantly (111)-oriented, indicating a well-ordered microstructure. The hardness and Young's modulus of FePd thin films measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option indicated that both mechanical properties are decreased with increasing the annealing temperature. Furthermore, the relationship between the hardness and films grain size appears to follow closely with the Hall–Petch equation.