FePd Alloy Research Articles

Exchange spin waves in thin films with gradient composition

We report investigation of ferromagnetic resonance phenomenon in ferromagnetic thin films with essentially non-uniform composition. Epitaxial Pd-Fe thin film with linear distribution of Fe content across the thickness is used as the model material. Anomalous perpendicular standing spin waves are observed and quantified using the collective dynamic equation. Numerical analysis yields the exchange stiffness constant for diluted Pd-Fe alloy $D=2A/\mu_0M_s=15$~T$\cdot$nm$^2$ and the ratio of the effective magnetization to the saturation magnetization $M_{eff}/M_s=1.16$. It is demonstrated that, overall, engineering of thin films with non-uniform composition across the thickness can be used for high-frequency or low-field magnonic operations using exchange spin waves.

Morphological and Structural Transformations of Fe-Pd Powder Alloys Formed by Galvanic Replacement, Annealing and Acid Treatment.

In this article, we report the preparation and structural features of Fe-Pd powder alloys formed by galvanic replacement, annealing and selective dissolution of iron via acid treatment. The alloys were studied by the X-ray diffraction phase analysis, Mössbauer spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The Fe@Pd core–shell particles were obtained by a galvanic replacement reaction occurring upon treatment of a body-centered cubic (bcc) iron powder by a solution containing PdCl42− ions. It was found that the shells are a face-centered cubic (fcc) Pd(Fe) solid solution. HCl acid treatment of the Fe@Pd core–shell particles resulted in the formation of hollow Pd-based particles, as the bcc phase was selectively dissolved from the cores. Annealing of the Fe@Pd core–shell particles at 800 °C led to the formation of fcc Fe-Pd solid solution. Acid treatment of the Fe-Pd alloys formed by annealing of the core–shell particles allowed selectively dissolving iron from the bcc Fe-based phase (Fe(Pd) solid solution), while the fcc Fe-rich Fe-Pd solid solution remained stable (resistant to acid corrosion). It was demonstrated that the phase composition and the Fe/Pd ratio in the alloys (phases) can be tailored by applying annealing and/or acid treatment to the as-synthesized Fe@Pd core–shell particles.

Catalytic selective hydrogenation of acetic acid to acetaldehyde over the surface of the iron shell on Pd–Fe alloy nanoparticles

The Fe metal shell on Pd–Fe alloy nanoparticles formed by strong metal–support interaction (SMSI) promotes catalytic selective hydrogenation from acetic acid to acetaldehyde.

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.

Cyanogel-Derived Synthesis of Porous PdFe Nanohydrangeas as Electrocatalysts for Oxygen Reduction Reaction.

It is important to develop cost-efficient electrocatalysts used in the oxygen reduction reaction (ORR) for widespread applications in fuel cells. Palladium (Pd) is a promising catalyst, due to its more abundant reserves and lower price than platinum (Pt), and doping an earth-abundant 3d-transition metal M into Pd to form Pd–M bimetallic alloys may not only further reduce the use of expensive Pd but also promote the electrocatalytic performance of ORR, owing to the synergistic effect between Pd and M. Here we report a cyanogel-derived synthesis of PdFe alloys with porous nanostructure via a simple coinstantaneous reduction reaction by using K2PdIICl4/K4FeII(CN)6 cyanogel as precursor. The synthesized PdFe alloys possess hydrangea-like morphology and porous nanostructure, which are beneficial to the electrochemical performance in ORR. The onset potential of the porous PdFe nanohydrangeas is determined to be 0.988 V, which is much more positive than that of commercial Pt/C catalyst (0.976 V) and Pd black catalyst (0.964 V). Resulting from the unique structural advantages and synergetic effect between bimetals, the synthesized PdFe nanohydrangeas with porous structure have outstanding electrocatalytic activity and stability for ORR, compared with the commercial Pd black and Pt/C.

First-principles study of electronic structure and magnetic properties of L10-ordered FeNi, FePd, and FePt alloys

The structural, electronic, and magnetic properties of three spin configurations of L10-ordered FeM alloys (M = Ni, Pd, or Pt) were studied using the first-principles method. The calculations were carried out using Quantum ESPRESSO package within the framework of Density Functional Theory (DFT). The exchange-correlation functional potentials were studied using local density approximation (LDA) of Perdew-Zunger (PZ), the generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBE), Perdew and Wang 91 (PW91), and Perdew-Burke-Ernzerhof revised for solids (PBEsol). We found that the PBE approximation has the most accurate results for lattice parameters compared to the experimental values. Furthermore, our results reveal that the most stable spin configuration for the considered alloys is the ferromagnetic configuration, where all spins are aligned perpendicular to the (001) plane. However, in FePd and FePt alloys, a small variation in the tetragonality ratio c/a (from 0.98 to 0.92) can transform them from ferromagnetic to antiferromagnetic state. In an antiferromagnetic state, a pseudogap is observed just below fermi energy for each alloy. Moreover, our calculations reveal large magnetocrystalline anisotropies for FePt alloy in the order of 3 meV/f.u. On the other hand, FePd and FeNi show relatively lower values in the range of 0.18–0.42 meV/f.u. Finally, Heisenberg exchange interactions are calculated from first-principles and Green's functions formalism.

Giant elastic response and ultra-stable elastocaloric effect in tweed textured Fe-Pd single crystals

The limit of elastic deformation in conventional metals and alloys is usually within 0.1%. When deformed further, these materials show plastic deformation effects, which are a consequence of dislocation movements. Here, we report that a much larger elastic-like strain of more than 4% can be achieved in a tweed textured Fe-Pd single crystal under a compressive stress of 300 MPa. We show that this giant elastic response gives rise to significant and homogenous elastocaloric effect (∼4.1 K) that can sustain 106 or even more mechanical cycles without degradation. The large and stable elastic-like strain in Fe-Pd originates from the continuous and reversible structural change associated with the tweed texture under stress as confirmed by the in-situ high energy X-ray diffraction tests. Phase field simulation also confirms this giant elastic response and ultra-stable elastocaloric effect under a compressive stress in the Fe-Pd alloy.

Scalable memory elements based on rectangular SIsFS junctions

We explore the concept of the Josephson magnetic memory element based on a multilayer two-barrier SIsFS Josephson junction storing the digital state by means of the orientation of magnetization in the F-layer. A diluted PdFe alloy with 1% magnetic atoms is used as a ferromagnet (F), and a tunnel AlOx layer (I) ensures a high voltage in the resistive state. We have studied two junctions of a rectangular shape in which two digital states are defined by the orientation of the residual F-layer magnetization set along or across the junction in the plane of the ferromagnetic barrier. Implementations of both binary and ternary logic elements are demonstrated. A scalability of rectangular memory elements is analyzed using micro-magnetic modeling.

Slag design and iron capture mechanism for recovering low-grade Pt, Pd, and Rh from leaching residue of spent auto-exhaust catalysts

Recovery of platinum group metals (PGMs) from secondary resources has attracted worldwide attention from environmental and economic points of view. Pyrometallurgical routes exhibit the superiority in terms of efficiency and contamination control compared to hydrometallurgical process. However, traditional pyrometallurgical processes face the challenges of excessive flux and energy consumption. In this paper, an iron capture process was proposed to recover low-grade PGMs from leaching residue of spent auto-exhaust catalysts. Slag design was explored aimed at reducing the addition amount of flux. The optimized smelting conditions were as follows: 1400 °C for 30 min, adding 40.0 wt% CaO, 22.7 wt% Na2CO3, 5.0 wt% Na2B4O7, 5.0 wt% CaF2, 15.0 wt% Fe, and 5.0 wt% C. The concentrations of Pt, Pd and Rh remaining in the smelting slag were 0.83 g/t, 4.99 g/t, and 1.47 g/t, respectively. Furthermore, the 50 kg-scale experiment implied positive economic feasibility because of saving flux dosage and smelting time. The capture mechanism was revealed by investigating the formation of the metals phase and slag phase. Matrix formed slag phase and separate with metals phase owing to differences in chemical bonding, density, viscosity, and surface tension. PGMs were proved solubilized in α-Fe as substitutional solid solutions. The formation energies for FePt, FePd, and FeRh alloys were −4.149 eV, −4.040 eV, and −4.360 eV, respectively. Finally, the obtained CaO-SiO2-Al2O3-Na2O glass slag was used for producing glass ceramics. To sum up, the iron capture process realized low energy and material consumption, high recovery efficiency of PGMs, and resource utilization of the glass slag.

Solubility of Palladium in Alumina-Iron Silicate Melts

Dissolution and solubility of palladium in iron silicate melts saturated with alumina–iron spinel at 1300°C has been measured using an equilibration-drop quenching technique combined with electron probe microanalysis and laser ablation–inductive coupled plasma–mass spectrometry analysis from polished sections. Composition of the resulting Fe-Pd alloy allowed estimation of the activity of palladium at different oxygen partial pressures, and, thus, the solubilities of palladium in the studied slags in conditions typical of copper and nickel smelting as well as slag cleaning at pO2=10-5 to 10-10 atm. The mechanism of palladium dissolution in the studied iron silicate slags was oxidation by formation of the monovalent oxide species PdO0.5 over the entire oxygen activity range of this study. Testing the applicability of the various palladium isotopes for quantitative analyses of Pd in these types of matrices resulted in a good fit of measured concentrations of 104Pd and 105Pd with interference-corrected 106Pd and 108Pd.

Discrete interfacial effects of organic lead halide perovskite coating on magnetic underlayer: MAPbBr[formula omitted]/FePd heterostructure

Recent studies have shown promising results regarding the power conversion efficiency, band-gap tunability, and interfacial charge carrier ability of organic lead halide perovskites. In light of these fundamental abilities, we fabricated a heterostructure: MAPbBr3 spin-coated on an FePd alloy layer, consisting of both magnetic and optical capabilities. The perovskite’s discrete coverage across the FePd underlayer was confirmed by atomic force microscope, as made up of separate disc-like nanostructures that stand at ∼400 nm in height and a size width of up to ∼2 µm. We studied the thermal endurance and the inter-facial diffusion stability between MAPbBr3 and FePd alloy by post-annealing it to temperatures ranging 100–170 ∘C. The instable interfacial effects of perovskite/FePd was observed at 120 ∘C, as indicated by the drastic reduction in magnetic coercivity of FePd and the photoluminescence of MAPbBr3. This interfacial diffusion behavior between perovskite and FePd advances as the post-annealing temperature reaches 170 ∘C, supported by the enhanced noise to Kerr signal ratio.

Combining the core-shell construction with an alloying effect for high efficiency ethanol electrooxidation

Summary Combining core-shell construction with an alloying effect is effective for optimizing the electronic and lattice strain effects for achieving highly catalytic efficiency for a given electrochemical reaction. Here, we report the use of core-shell Au@FePd nanoparticles with an Au core and a sub-nano FePd alloy shell to demonstrate this concept. The Au core modifies the electronic configuration of Pd atoms, while the Fe component in thin shells reduces the lattice expansion of Pd induced by the Au core, both of which endow the Pd shell with an appropriate d-band center, favorable for the electrooxidation of ethanol through the C1 pathway. In particular, the as-prepared core-shell Au@FePd nanoparticles at an optimized Fe:Pd ratio exhibit a mass activity of 13.3 A mg−1 and a specific activity of 20.2 mA cm−2 for the ethanol electrooxidation in an alkaline medium, which outperform those of a majority of the recently reported Pd-based electrocatalysts.

Structural, Wetting and Magnetic Properties of Sputtered Fe70Pd30 Thin Film with Nanostructured Surface Induced by Dealloying Process

FePd alloys in the thin film form represent a multipurpose and versatile material with relevant chemical and physical properties studied in different research fields. Moreover, the ability to manipulate and fine-tune the film surface with nanometric scale precision represents a degree of freedom useful to adapt these thin film properties to the demands of different desired applications. In this manuscript, Fe70Pd30 (at. %) thin films are prepared with a thickness of 50 and 200 nm by means of the widely used co-sputtering deposition technique. Subsequently, selective removal of the iron element from the alloy and the consequent surface diffusion of the palladium was induced by a dealloying treatment under free corrosion conditions in hydrochloric acid. The size and shape of the grains of the as-deposited thin films determine the dissolution rate of the iron element with a direct consequence not only on the surface morphology and the stoichiometry of the alloy but also on the wetting and magnetic properties of the sample. X-ray diffraction, Scanning Electron Microscopy (SEM) images, contact angle and magnetic measurements have been performed to provide a thorough characterisation of the fundamental properties of these nanostructured bimetallic thin films.

Boron interstitials in ordered phases of Fe-Pd binary alloys: A first principle study

Magnetic properties of L10-type tetragonal FePd, L12-type cubic FePd3, CuZr2-type tetragonal FePd2 and Pt5Ga3-type orthorhombic Fe3Pd5 binary alloys with interstitial boron doping are investigated using supercell approach within first principles density functional calculations for various doping concentrations. The magnetic moments around dopant sites are suppressed slightly both on Fe and Pd atoms whereas the per-unit magnetization almost remains unaffected in the supercell. Magnetocrystalline anisotropy energy enhances by a considerable amount and the Curie temperature decreases but remains well above room temperature. Overall, we report the magnetic properties of various Fe-Pd phases with boron doping with slight compromise in magnetization and considerable gain in magnetic anisotropy energy.

P-doped SnFe nanocubes decorated with PdFe alloy nanoparticles for ethanol fuel cells

In this study, a three-dimensional SnFeP nanocube was prepared, and then PdFe alloy was decorated over it. A single cell with PdFe/SnFeP@rGO anode catalysts exhibited promising power densities in ethanol and hydrogen fuels at low temperature.

Combining Core-Shell Construction with Alloying Effect for High Efficiency Ethanol Electrooxidation: A Case of Core-Shell Au@Fepd Nanoparticles with Sub-Nano Alloy Shells

Combining the core-shell construction with an alloying effect is an effective way to optimize the electronic and lattice strain effects generated in core-shell configurations for achieving highly catalytic efficiency for a given electrochemical reaction. To demonstrate this concept, we herein report the use of core-shell Au@FePd nanoparticles with an Au core and a sub-nano FePd alloy shell to promote the electrocatalytic oxidation of ethanol. In these core-shell structures, the Au core modifies the electronic configuration of Pd atoms through differences in electronegativity, while the Fe component in thin shells reduces the lattice expansion of Pd induced by the Au core, both of which endows the Pd shell with an appropriate d-band center, favorable for the electrooxidation of ethanol molecules through C1 pathway. In particular, the as-prepared core-shell Au@FePd nanoparticles at an optimized Fe/Pd ratio of 0.5/1 (Au@FePd-0.5) exhibit a mass activity of 13.3 A mg-1 and a specific activity of 20.2 mA cm-2 for the ethanol electrooxidation in an alkaline medium, which significantly outperform those of a majority of the recent reported Pd-based electrocatalysts. This study highlights the concept of engineering the geometry and surface composition of a nanostructure for designing highly efficient electrocatalysts for a large variety of electrochemical applications.

Magnetoresistance of a Ferromagnet/Superconductor/Ferromagnet Trilayer Microbridge Based on Diluted PdFe Alloy

A negative magnetoresistive effect has been observed for ferromagnet/superconductor/ferromagnet (FSF) microbridges based on diluted ferromagnetic PdFe alloy containing as small as 1% of magnetic atoms. The effect is represented by sharp negative peaks in magnetoresistance at magnetic fields opposite in sign to the initial saturated magnetizations. Microstructuring of the FSF trilayers does not suppress the effect: the most pronounced dips were obtained for the smallest bridges 6–8 µm wide and 10–15 µm long. The negative magnetoresistance peak was observed at temperatures within the superconducting transition and reaches a noticeable value of up to 1.3% of the normal state resistance.

Exploration of new phase structure of FePd crystalline alloy with a stoichiometric of 1:1

FePd crystalline alloy with chemical stoichiometry of 1:1 is important permanent magnets and ultrahigh magnetic recording material, however there is few reports on its stable crystal structures under normal and high pressures. Thus, the stable crystal structures of FePd alloy were explored here by using particle swarm optimization algorithm and the soft-mode phase transition theory. Four new phases of FePd were discovered, namely, Imma, Cmmm-I, Cmmm-П, and P4/nmm. The structure, magnetisim, elasticity and lattice dynamics of the system were systematically investigated by first-principles calculations. It was found that the ferromagnetic state of these structures is more energetically favorable than the non-magnetic state below their respective critical pressure of ferromagnetic collapse. The phonon dispersion curves have no imaginary frequency and elastic constants fulfill Born’s criteria demonstrated that these four structures are dynamically and mechanically stable at pressure range of 0 to 59.1 GPa. These four new phases were found have negative formation enthalpy and the three orthorhombic structures were identified to be meta-stable in the pressure range of 0 to 59.1 GPa since they possess very small enthalpy difference which could not be firmly distinguished by our calculations relative to the experimentally known L10 phase. After 59.1 GPa, P4/nmm structure became the energetically most stable structure accompanied by simultaneous collapse of magnetic moments and lattice volume. The underlying mechanism was analyzed and attributed to be the simultaneously collapse of magnetoelastic force of Fe-Fe.

Continuous flow reduction of organic dyes over Pd-Fe alloy based fibrous catalyst in a fixed-bed system

Continuous flow chemistry has been considered as a green technology for modern catalytic industry as it not only improves the manufacture efficiency but also facilitates the sustainability. Herein we report a facile method for synthesizing bimetallic Pd-Fe alloy nanoparticles catalysts anchored on N doped carbon (NC) functionalized fibrous aluminium silicate fibers (ASFs). The as-prepared ASF@NC/PdFe catalytic fibers are packed into a column to construct a fixed-bed system, which exhibits excellent treatment capacity and durability for continuous catalytic hydrogenation of organic dyes. Typically, the flow rate of the fixed-bed is high up to 200 mL/min for 4-nitrophenol and methylene blue reduction, which is one of the most efficient fixed-bed catalytic systems. The catalytic turnover frequency is calculated to be as high as 59.6 min−1 due to the enhanced synergetic effect of Pd and Fe. Furthermore, only slight loss of activity for the fixed-bed is observed even after nine successive catalytic cycles.

Nano PdFe Alloy Assembled Film as a Highly Efficient Electrocatalyst toward Hydrogen Evolution in Both Acid and Alkaline Solutions

A series of nano PdFe alloy film electrodes with different ratios were prepared by high-vacuum magnetron sputtering under the action of high-strength magnetic field. Among them, the Pd3Fe alloy fil...