FePd Phase Research Articles

Structural and phase transformations in Fe-Pd-Ag layered thin films by grain boundary diffusion

The influence of the stacking order and of an additional Ag layer on the formation of ordered phases in thin (< 50 nm) layered Fe/Pd and Fe/Ag/Pd films was investigated at 460 °C. The samples were prepared by magnetron sputtering at room temperature on Si/SiO2 substrate and were post-annealed in vacuum. Composition depth profiling and x-ray diffraction were used to characterize the processes. It has been shown, that the stacking order strongly influences the formation of ordered phases both in Fe/Pd bilayered and Fe/Ag/Pd trilayered films. In bilayered Fe/Pd films for both stacking orders the FePd3 phase appeared and it also showed L12 ordering for one stacking order. Addition of Ag layer between the Fe and Pd layers found to promote the formation of FePd phase which showed L10 ordering or A1 disordered structure depending on stacking order. Based on the analysis of the chemical depth profiles and XRD patterns the transformations were interpreted by grainboundary diffusion mechanisms including grainboundary diffusion induced grainboundary migration and solid state reaction.

Effect of Mo and W underlayers on ordered phase formation in Fe-Au-Pd multilayer thin films at low temperatures

Fe-Pd based thin films with Au intermediate layer fabricated on different substrates (SiO2, SiO2/Mo, SiO2/W) were investigated at annealing temperatures up to 460°C. The samples were deposited by magnetron sputtering and were post-annealed in vacuum. The ongoing processes were investigated by chemical depth profiling and X-ray diffraction. The experimental results showed that the intermediate Au layer always promoted the formation of FePd3 phase which also showed L12 ordered structure except in one case with W underlayer. However, in the samples with Mo buffer but without the Au interlayer the FePd phase formed and L10 ordered phase also appeared for one stacking order. Considering the low diffusivity arising from the annealing temperature the processes were explained by grain boundary diffusion induced reaction layer formation. The formation of the ordered FePd phases was interpreted by the stress accumulation due to the different diffusivity of the components, which relaxes by the shift of the grain boundaries and the transformation of swept over regions. It was concluded, that the effect of the Au interlayer is dominant over the effect of the Mo or W buffer layers.

Boosting hydrogen evolution performance of nanoporous Fe-Pd alloy electrocatalyst by metastable phase engineering

Nanoporous Fe-Pd alloy with metastable face-centered cubic (fcc Fe-Pd) phase is prepared by electrochemical dealloying as an electrocatalyst for hydrogen evolution reaction (HER). The nanoporous fcc Fe-Pd alloy achieves an overpotential of 58 mV at 10 mA cm−2 in 1 M KOH, outperforming those of stable body-centered cubic Fe-Pd alloy (bcc Fe-Pd) and commercial Pt/C catalyst. Density functional theory calculation reveals that the metastable fcc structure can tailor the coordination environment and electronic structure of Pd active sites in Fe-Pd alloy. As a result, the d‐band center of Pd active site shifts away from the Fermi level, which weakens the Pd-H interaction and reduces the energy barrier of water dissociation. In addition, the fcc Fe-Pd exhibits good mechanical properties, which maintains the catalytic performance in the deformation state. This work broadens the idea for designing and preparing HER catalysts via metastable phase structure design.

Changes in Raman spectra upon formation of ordered L10 FePd phase during annealing in vacuum and in hydrogen atmosphere

Changes in Raman spectra upon formation of ordered L10 FePd phase during annealing in vacuum and in hydrogen atmosphere

Relating the magnetic coercivity to the L10 ordered FePd phase in annealed FexPd100-x nanoparticles

Rare-earth-free or iron-based permanent nanomagnets are emerging as promising candidates for energy-conversion and information technologies. In this interest, FexPd100-x nanoparticles (x = 50, 55, 60, and 63) were prepared from iron acetate and palladium acetate by sonoelectrodeposition. After annealing the nanoparticles at various temperatures from 450 to 700 °C for 1 h, structural changes were observed, and the samples exhibit hard magnetic properties that depend strongly on chemical composition and annealing temperature. The major phase in the as-prepared nanoparticles has a disordered face-centered cubic structure, which, upon annealing, transforms into a multi-phase material containing a L10 ordered FePd phase. The fractions of different phases present in the annealed samples, including that of the L10 phase as functions of chemical composition and annealing temperature, are quantified by means of X-ray diffraction and scanning transmission electron microscopy. Magnetic measurements show the desirable hard magnetic properties for the samples annealed at 550–600 °C. A correlation between the magnetic coercivity and the L10 ordered FePd phase fraction is established for the first time in the FexPd100-x nanoparticles.

Effect of Annealing Time on Structural and Magnetic Properties of Fe68Pd32 Nanoparticles Synthesized by Sonoelectrodeposition

Fe68Pd32 nanoparticles were prepared by sonoelectrodeposition with subsequent annealing at 600 oC for a series of times from 1 h to 6 h. The annealing transformed disordered face-centered cubic (fcc) phase in the as-prepared samples into a multi-phase material containing an ordered L10 FePd, fcc FePd and body-centered cubic (bcc) Fe phases. After annealing at 600°C for 6 h the hard magnetic phase L10-FePd and soft magnetic fcc-FePd phase coexist. The structural and magnetic properties of the samples were studied in dependence of annealing time. The decrease of coercivity with increasing annealing time from 1 h to 4 h is suggested to occur by formation of multi-L10 domain particles, while the increase of coercivity with increasing annealing time from 4 h to 6 h is proposed due to the multiphase nature of the nanoparticles samples.

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.

Magnetic Properties and Biocompatibility of Different Thickness (Pd/Fe)n Coatings Deposited on Pure Ti Surface via Multi Arc Ion Plating.

The different thickness (Fe/Pd)n coatings were prepared by vacuum ion plating technology on a pure Ti substrate. The (Fe/Pd)n coatings were magnetized using an MC-4000 high-pressure magnetizing machine. Then, the effect of the (Fe/Pd)n coating thickness on the magnetic properties was studied. The surface and section morphology, composition, phase structure, magnetic properties, and biocompatibility of the (Fe/Pd)n coatings were studied by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and CCTC-1 digital flux field measurement. The results showed that the (Fe/Pd)n coatings were granular, smooth, and compact, without cracks. In addition the (Fe/Pd)n coatings formed an L10 phase with a magnetic face-centered tetragonal-ordered structure after heat treatment. With the increase in the thickness of (FePd)n coatings, the content of L10 FePd phase increased and the remanence increased. The remanence values of the Fe/Pd, (Fe/Pd)5, (Fe/Pd)10, and (Fe/Pd)15 magnetic coatings were 0.83 Gs, 5.52 Gs, 7.14 Gs, and 7.94 Gs, respectively. Additionally, the (Fe/Pd)n magnetic coatings showed good blood compatibility and histocompatibility.

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.

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.

Effect of the A1 to L10 transformation on the structure and magnetic properties of polycrystalline Fe56Pd44 alloy thin films produced by thermal evaporation technique

X-ray diffraction, conversion electron Mössbauer spectroscopy and superconducting quantum interference device magnetometer techniques have been used to characterize the evolution of the microstructure and of the magnetic properties of phase transformation from disordered FePd face-centred cubic (A1) phase, to an ordered phase L10 FePd of tetragonal structure. This study was carried out by isothermally annealing in vacuum at 550 °C, as a function of annealing time, a Fe56Pd44 thin film alloy deposited on silicon substrate.The structural transformations are accompanied by a decrease of the (c/a) ratio and by an increase of the coercive field as a function of annealing time. After 10 min of annealing, the (c/a) ratio is equal to 0.945, which indicates that the disordered FePd phase is completely transformed into the ordered L10 FePd phase. By increasing annealing time, the microstructure of the alloy evolves, antiphase boundaries and twin boundaries develop. In contrast to the relationship most commonly described in the literature, that the highest coercivity corresponds to a two-phase ordered/disordered mixture, in ours studies the maximum value for coercivity corresponds to the fully ordered state. Furthermore, we propose that the high coercivity in these films is due to pinning centres of magnetic domain walls by antiphase boundaries and twin boundaries.

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.

Experimental Investigation of the Isothermal Section in Fe-Gd-Pd Ternary System at 873 K

Isothermal section of Fe-Gd-Pd ternary system at 873 K has been established by means of x-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscope (SEM) with energy disperse x-ray spectroscopy (EDS) in backscattered electron imaging modes. The isothermal section consists of 14 single-phase regions, 25 two-phase regions, and 12 three-phase regions. At 873 K, no ternary compound was found and the binary inermetallic compounds Gd3Pd and Fe23Gd6 are not stable, whereas the compound Fe23Gd6 decomposes into compounds Fe17Gd2 and Fe3Gd. The XRD and the SEM/EDS analysis show that there is almost no solubility of Gd in the FePd and FePd3 phases, and the solubilities of Pd in Fe17Gd2, Fe3Gd and Fe2Gd and Fe in GdPd2, α-Gd3Pd4 and Gd3Pd2 are all less than 1 at.%. Meanwhile, the solubilities of Fe in GdPd3, α-GdPd and Gd7Pd3 are determined to be as high as 1.37, 5.31, and 4.18 at.% Fe, respectively.

Mixed exchange-coupled soft α-(Fe80Pd20) and hard L10FePd phases in Fe64Pd36 thin films studied by first order reversal curves

Fe64Pd36 thin films have been fabricated by thermal evaporation onto single-crystal Si(100) substrates. After suitable thermal treatments, we demonstrate that two different magnetic phases can coexist in the same alloy, one α-(Fe80Pd20) which is magnetically soft, and one L10 FePd which is magnetically hard, giving rise to exchange coupling between them through their interfaces, without needing to artificially nanostructure the material. The structural and magnetic properties of as-prepared and furnace annealed samples are therefore studied by means of X-ray diffractometry, conversion electron Mössbauer spectroscopy, atomic and magnetic force microscopy and high sensitivity magnetometry.As prepared samples are characterised by different phases having soft magnetic properties: α-(Fe80Pd20) and disordered (fcc) FePd phases with different compositions. Furnace annealing in vacuum at 600°C for one hour promotes the transformation of the fcc phases into the L10 one, while α-(Fe80Pd20) remains largely unaffected. The structural transformations are accompanied by an increase of the coercive field without any significant changes of the saturation magnetisation value. In the sample annealed at 600°C, magnetisation reversal occurs in two steps: one at lower fields, attributed to the soft phase, and one at much larger fields, attributed to the hard phase and to the fraction of the soft one coupled to it. The exchange coupling between the two phases is demonstrated and thoroughly analysed by means of first order reversal curves.

Structure and Magnetic Properties of Nanocrystalline Fe55Pd45 Processed by Sonoelectrodeposition

Fe55Pd45 nanoparticles were prepared from iron acetate and palladium acetate by sonoelectrodeposition. The as-prepared nanoparticles were annealed at various temperatures from 450°C to 700°C for 1 h in order to study the effect of heat treatment on the phase composition, particle size and magnetic properties. The phase composition and the crystallite size of the annealed samples were determined by x-ray diffraction while the particle size was studied by transmission electron microscopy. It was revealed that the magnetic properties of the samples depend on the phase composition of the material. The as-prepared nanoparticles had a disordered face-centered cubic (fcc) structure which transformed to a multi-phase material containing an ordered L10 FePd phase and a body-centered cubic Fe after annealing at 550°C; however, a disordered fcc FePd also remained in the material. The ordering in the structure yielded a significant increase in the room-temperature coercivity from 0.5 kOe to 1.1 kOe. At 700°C, the coercivity decreased due to the formation of a disordered fcc γ-FePd phase. In addition to the phase transformation, the average crystallite size grew from about 8 nm to 50–70 nm during annealing.

Microstructure and magnetic properties of self-assembled FePd–SiN films

Self-assembled FePd–SiN nanocomposite films were fabricated successfully by direct current (dc) reactive magnetron sputtering and then followed by vacuum annealing. The effects of Si–N matrix and annealing temperature on the structure and magnetic properties were investigated. The as-deposited films show typical magnetically soft behavior with face-centered cubic (fcc) FePd phase, which transforms into the face centered tetragonal (fct) structure after thermal annealing at 600 °C. The grain size of FePd increased with the annealing temperature but decreased with increasing Si–N content. Increasing Si–N content forms SiN-rich amorphous phase distributed between the FePd nanograins, which inhibits the growth of the FePd particles. The fct-FePd films annealed at 700 °C exhibited moderate coercivity, up to 2330 Oe at room temperature. These FePd–SiN films have shown promise for high-density magnetic recording medium.

Study of solid-state reactions and order-disorder transitions in Pd/α-Fe(001) thin films

The formation of the hard-magnetic ordered L10-FePd phase in thin bilayer Pd/α-Fe(001) films has been experimentally studied. Solid-state reactions initiated by thermal heating in bilayer Pd/α-Fe(001) films with a thickness of 50–60 nm (the atomic ratio Pd: Fe ≈ 50: 50) separated from the substrate have been studied using the in situ electron diffraction methods. It has been shown that the solid-state reaction between the palladium and iron layers in Pd/α-Fe(001) starts at 400°C with the formation of the disordered Fe-Pd phase. At 480°C, the ordered L10-FePd phase is formed. The order-disorder phase transition has been studied. It has been established that the transition of the ordered L10-FePd phase to the disordered FePd phase starts at 725°C. At 740°C, only the disordered FePd phase is present over the whole volume of the film. The observed temperature of the order-disorder phase transition is shifted from the equilibrium value by 35°C to higher temperatures. This effect is assumingly associated with the higher concentration of palladium atoms at the boundaries of the Fe-Pd crystal grains owing to the grain-boundary adsorption.

Phase transformations and magnetic structure of nanocrystalline Fe–Pd and Co–Pt alloys studied by in situ neutron powder diffraction

The formation of the ordered L10 structure from the A1 phase in nanocrystalline Fe100−xPdx (x=50–60) and Co100−xPtx (x=45–55) alloys is followed by in situ neutron powder diffraction. The A1→L10 transformation starts at about 620 and 730K in Fe50Pd50 and Co50Pt50, respectively, and proceeds faster in the Fe–Pd alloys. In both Fe–Pd and Co–Pt, a deviation from the equiatomic composition leads to the deceleration of the ordering process. The magnetic moment of iron in the L10 FePd phase decreases with increasing Fe concentration from 3.3μB in Fe40Pd60 to 3.0μB in Fe50Pd50. In the Co–Pt alloys, the Co magnetic moment is found to be independent of the composition and degree of chemical order and is equal to 1.9μB.

Synthesis of self-assembled monodisperse 3 nm FePd nanoparticles: Phase transition, magnetic study, and surface effect

Self-assembled monodisperse 3 nm face centered cubic (fcc) FePd particles are synthesized by modified polyol method using polyethylene glycol-600 as a reducing agent and oleic acid and oleyl amine as surfactants. As-synthesized FePd nanoparticles are superparamagnetic at room temperature and ferromagnetic below blocking temperature (TB=21 K). The significant enhancement in saturation magnetization is observed at 5 K. This is attributed to surface effect for 3 nm size particles. The nanoparticles are spherical with uniform dispersion as depicted in transmission electron microscopy study. The noninteracting behavior of as-synthesized FePd nanoparticles is verified through Langevin fit. The saturation magnetization (σs) and mean moment of (μm) particles are computed to be σs=22.73 emu/g and μm=4466μB, respectively. The ordered face centered tetragonal (fct) phase of composition Fe43Pd57 was obtained from disordered fcc FePd phase by annealing at 550 °C for 1 h under reducing atmosphere of (N2+H2) gas. The hard magnetic fct Fe43Pd57 phase exhibits high coercivity Hc=1180 Oe, saturation magnetization σs=65.2 emu/g, and hysteresis loop area of 1.5×106 erg/cm3 at 300 K.

Modification of local order in FePd films by low energy He+ irradiation

Owing to their strong perpendicular magnetic anisotropy, FePd, CoPd, and their Co(Fe)Pt counterparts are candidate materials for ultrahigh density magnetic recording. The stability and magnetic properties of such films are largely dependent on the orientation and local distribution of the L10 FePd phase fraction. Therefore, the formation and transformation of the L10 phase in such thin films have been the subject of continued interest. Highly ordered epitaxial FePd(001) thin films (with an L10 phase fraction of 0.81) were prepared by molecular-beam epitaxy on a MgO(001) substrate. The effect of postgrown room temperature, 130 keV He+ irradiation was investigated at fluences up to 14.9×1015 ions/cm2. X-ray diffraction and conversion electron Mössbauer spectroscopy revealed that with increasing fluence, the L10 FePd phase decomposes into the face centered cubic phase with random Fe and Pd occupation of the sites. A partially ordered local environment exhibiting a large hyperfine magnetic field also develops. Upon He+ irradiation, the lattice parameter c of the FePd L10 structure increases and the long range order parameter S steeply decreases. The Fe–Fe nearest-neighbor coordination in the Fe-containing environments increases on average from Fe47Pd53 to Fe54Pd46, indicating a tendency of formation iron-rich clusters. The equilibrium parameters corresponding to the equiatomic L10 phase were found at different fluences by conversion electron Mössbauer spectroscopy and by x-ray diffraction a difference, from which a plane-perpendicular compressive stress and a corresponding in-plane tensile stress are conjectured. The steep increase in the interface roughness above 7.4×1015 ions/cm2 is interpreted as a percolation-type behavior related to the high diffusion anisotropy in the L10 phase.