CoPd Alloy Research Articles

Irreversible transformation of ferromagnetic ordered stripe domains in single-shot infrared-pump/resonant-x-ray-scattering-probe experiments

The evolution of a magnetic domain structure upon excitation by an intense, femtosecond Infra-Red (IR) laser pulse has been investigated using single-shot based time-resolved resonant X-ray scattering at the X-ray Free Electron laser LCLS. A well-ordered stripe domain pattern as present in a thin CoPd alloy film has been used as prototype magnetic domain structure for this study. The fluence of the IR laser pump pulse was sufficient to lead to an almost complete quenching of the magnetization within the ultrafast demagnetization process taking place within the first few hundreds of femtoseconds following the IR laser pump pulse excitation. On longer time scales this excitation gave rise to subsequent irreversible transformations of the magnetic domain structure. Under our specific experimental conditions, it took about 2 nanoseconds before the magnetization started to recover. After about 5 nanoseconds the previously ordered stripe domain structure had evolved into a disordered labyrinth domain structure. Surprisingly, we observe after about 7 nanoseconds the occurrence of a partially ordered stripe domain structure reoriented into a novel direction. It is this domain structure in which the sample's magnetization stabilizes as revealed by scattering patterns recorded long after the initial pump-probe cycle. Using micro-magnetic simulations we can explain this observation based on changes of the magnetic anisotropy going along with heat dissipation in the film.

Effect of substitutional defects on Kambersky damping in L1 magnetic materials

Kambersky damping, representing the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction, is calculated for L10 FePt, FePd, CoPt, and CoPd alloys versus chemical degree of order. When more substitutional defects exist in the alloys, damping is predicted to increase due to the increase of the spin-flip channels allowed by the broken symmetry. It is demonstrated that this corresponds to an enhanced density of states (DOS) at the Fermi level, owing to the rounding of the DOS with loss of long-range order. Both the damping and the DOS of the Co-based alloy are found to be less affected by the disorder. Pd-based alloys are predicted to have lower damping than Pt-based alloys, making them more suitable for high density spintronic applications.

CoPd alloy nanoparticles catalyzed tandem ammonia borane dehydrogenation and reduction of aromatic nitro, nitrile and carbonyl compounds

Addressed herein is a general and facile route for the reduction of aromatic nitro, nitrile, and carbonyl compounds to the corresponding primary amines and alcohols, respectively, under ambient conditions. Our reduction approach comprises the tandem AB dehydrogenation and hydrogenation of unsaturated organic groups catalyzed by reduced graphene oxide supported Co30Pd70 alloy nanoparticles (rGO-Co30Pd70) in water/methanol mixture (v/v=7/3) at room temperature. Monodisperse Co30Pd70 alloy NPs were synthesized by using an organic solution phase protocol involving the co-reduction of cobalt(II) acetylacetonate and palladium(II) acetylacetonate in oleylamine and borane-tert-butylamine mixture at 100°C. The colloidal Co30Pd70 NPs were assembled on reduced graphene oxide (rGO-Co30Pd70) before their use as catalysts in the tandem reactions. A variety of aromatic nitro, nitriles, and carbonyl compounds were tested by the rGO-Co30Pd70 catalyzed tandem reaction and all the corresponding primary amines or alcohols were obtained by the yields reaching up to 99% within reaction times of 5–15min.

Electrodeposition of Co-Pd Alloys from Chloride Solutions

A lot of attention has been devoted to synthesis of Co-Pd alloys mainly due to their electrocatalytic properties. Catalytic properties of these alloys for a 4-electron oxygen reduction reaction (ORR) are comparable to the properties of pure platinum. They also demonstrate high resistance to methanol activity, therefore, they can be successfully used in direct methanol fuel cells (DMFC). Significantly lower costs connected with the use of the alloys for electrodes applied in fuel cells in comparison to pure platinum make them an interesting alternative. The alloys play also an important role in magnetic data storage and microelectromechanical systems. The work presents results of the tests over the synthesis of Co-Pd alloys from acid chloride electrolytes. The main aim of the tests was to identify reactions responsible for alloy formation and to determine an influence of the electrolysis parameters i.e. working electrode potential, electrolyte composition and temperature on the composition of the resulted alloy coatings. Electrochemical investigations were performed by applying cyclic voltammetry (CV) combined with Electrochemical Quartz Crystal Microbalance (EQCM). The electrolyte composition was selected based on a thermodynamic analysis and spectrophotometric tests which were described in our previous papers [1, 2]. They allowed determination of equilibrium composition of the metals complex forms and a stability analysis of the electrolyte. The alloys were synthesized within the potentials from - 0.7 V to - 1.1 V. The tests indicate a possibility of alloys synthesis already at the potential range < - 0.5 V. The alloys composition was analysed with the use of the EDS technique. The obtained alloys featured Pd content from 0.84 to 71.37 at.%.1. Mech K, Żabiński P, Kowalik R (2013) Co-Reduction of Electrochemically Active [Co(H2O)6]2+ and [CoCl(H2O)5]+Complexes onto Gold Electrode. J Electrochem Soc 160 (6):D246 - D2502. Mech K, Żabiński P, Kowalik R, Fitzner K (2013) Kinetics and Mechanism of [PdCl x (H2O)4−x ]2−x (x = 3, 4) Complexes Electro-Reduction. J Electrochem Soc 160 (10):H770-H774

Magnetic field effect on properties of galvanostatically deposited Co-Pd alloys

Magnetic field effect on properties of galvanostatically deposited Co-Pd alloys

Interfacial perpendicular magnetic anisotropy in CoFeB/MgO structure with various underlayers

Interfacial perpendicular magnetic anisotropy (PMA) in CoFeB/MgO structures was investigated and found to be critically relied on underlayer material and annealing temperature. With Ta or Hf underlayer, clear PMA is observed in as-deposited samples while no PMA was shown in those with Pt or Pd. This may be attributed to smaller saturation magnetization of the films with Ta or Hf underlayer, which makes the PMA of CoFeB/MgO interface dominates over demagnetization field. On the contrary, samples with Pt or Pd demonstrate PMA only after annealing, which might be due to the CoPt (or CoPd) alloy formation that enhances PMA.

Enhancement in anomalous Hall resistivity of Co/Pd multilayer and CoPd alloy by Ga+ ion irradiation

In this paper, we report the effect of Ga+ ion irradiation on anomalous Hall effect (AHE) and longitudinal resistivity in [Co(3 Å)/Pd(5 Å)]80 multilayer and Co42Pd58 alloy. 4- and 2-fold increases in anomalous Hall resistivity in the Co/Pd multilayer and CoPd alloy have been observed after irradiations at doses of and , respectively. Skew scattering and side jump contributions to AHE have been analyzed based on the scaling relationship . For the Co/Pd multilayer, AHE is mainly affected by ion irradiation-induced interface diffusion and defects. For the CoPd alloy, the increase in doses above induces a sign change in skew scattering, followed by the skew scattering contribution to AHE overwhelming the side jump contribution, this phenomenon should be attributed to irradiation-induced defects and modifications in chemical ordering.

Nanostructure characterization of Co–Pd–Si–O soft magnetic nanogranular film using small-angle X-ray and neutronscattering

The nanostructure of a Co–Pd–Si–O nanogranular film was investigated with the combined use of small-angle x-ray (SAXS) and neutron scattering (SANS). Using a new, compact type of SANS instrument, the SANS profiles of individual particles with a diameter of about 2–4nm were successfully observed. The structures of magnetic regions were found to be the same as the chemical structures of the particles, and a sharp interface was observed between the matrix and the particles. The SAXS to SANS ratio clearly indicates that the particles are a CoPd alloy and the matrix is not pure SiO2. In fact, the matrix is composed of a meaningful amountof Co.

Structure and Magnetic Properties of CoPt, CoPd, FePt, and FePd Alloy Thin Films Formed on MgO(111) Substrates

CoPt, CoPd, FePt, and FePd alloy thin films are deposited on MgO(111) single-crystal substrates by using a radio-frequency magnetron sputtering system. The effects of magnetic material and substrate temperature on ordered phase formation are investigated. CoPt, FePt, and FePd epitaxial films with the close-packed plane parallel to the substrate surface are obtained at substrate temperatures ranging between room temperature (RT) and 600 °C. CoPd films grow epitaxially at temperatures higher than 200 °C, whereas CoPd amorphous films are formed below the temperature. Metastable L11 ordered phase formation is recognized for the CoPt films prepared at temperatures ranging between RT and 400 °C. As the temperature increases from RT to 300 °C, the order degree of L11 phase increases. With further increasing the temperature, the degree declines. The CoPt films formed above 500 °C are with A1 disordered structure. L10 ordered FePt and FePd films with the c-axis 55 ° canted from the perpendicular direction are obtained at 600 °C, whereas A1 disordered FePt and FePd films are formed below the temperature. No ordered phase is formed in CoPd film. The L11 ordered CoPt films show perpendicular magnetic anisotropies. As the order degree of L11 phase increases, perpendicular anisotropy is enhanced. On the contrary, the L10 ordered FePt and FePd films have in-plane anisotropies. The magnetic properties are influenced by the kind of ordered phase and the order degree.

Alloy formation in the Co/Pd{111} system — A study with medium energy ion scattering and scanning tunnelling microscopy

The growth and annealing behaviour of ultrathin Co films on Pd{111} have been investigated by medium energy ion scattering and scanning tunnelling microscopy. Incremental annealing of Co/Pd{111} results in intermixing and the formation of an ordered CoPd alloy at 560K. Under these conditions, MEIS reveals that the top three layers consist of an approximately equimolar mixture of Co and Pd. STM and LEED provide evidence that the overlayer has a p(2×1) registry leading to the conclusion that the surface is terminated in the {111} plane of the CoPd L10 structure.

Structure and magnetization in CoPd thin films and nanocontacts

We present results showing the structural and magnetic properties of MBE-grown extended films and nanostructured elements of various CoPd alloys. X-ray diffraction studies show that the thin films are polycrystalline, yet exhibit a strong preferential growth orientation along the (111) direction. Magnetic force microscopy and SQUID are used to gain an understanding of the magnetic behavior of the CoPd system with respect to competing anisotropy contributions, based on temperature-dependent SQUID data, collected between 4 and 300K. The idea and potential implications of using CoPd as a contact material to achieve spin injection in carbon nanotube-based devices is discussed.

Template-Assisted CoPd Nanowire Arrays: Magnetic Properties and FORC Analysis

Highly hexagonally ordered CoPd alloy nanowire arrays were synthesized through electrochemical deposition techniques into the nanopores of anodic alumina membranes used as templates. Two different electrolytes were used for this purpose, one with pH = 4.1 and the other with pH = 7. Under applying different electrodeposition parameters and by adjusting both, the current density and the electrolyte composition, it could be possible make to vary the composition of CoPd alloy nanowires in a wide range. Their composition and morphology were investigated by SEM and EDX. The magnetic properties of the nanowires array have been measured with a VSM as a function of the temperature, ranging from RT down to 50 K, for different CoPd alloy nanowires composition. Also, the temperature influence on the reversible-irreversible magnetization processes related with the magnetization reversal of the CoPd nanowires array has been analyzed by first order reversal curve (FORC) method.

Influence of layer thickness on the structure and the magnetic properties of Co/Pd epitaxial multilayer films

Co/Pd epitaxial multilayer films were prepared on Pd(111)fcc underlayers hetero-epitaxially grown on MgO(111)B1 single-crystal substrates at room temperature by ultra-high vacuum RF magnetron sputtering. In-situ reflection high energy electron diffraction shows that the in-plane lattice spacing of Co on Pd layer gradually decreases with increasing the Co layer thickness, whereas that of Pd on Co layer remains unchanged during the Pd layer formation. The CoPd alloy phase formation is observed around the Co/Pd interface. The atomic mixing is enhanced for thinner Co and Pd layers in multilayer structure. With decreasing the Co and the Pd layer thicknesses and increasing the repetition number of Co/Pd multilayer film, stronger perpendicular magnetic anisotropy is observed. The relationships between the film structure and the magnetic properties are discussed.

Perpendicular Magnetic Anisotropy Properties of CoFeB/Pd Multilayers

The perpendicular magnetic anisotropy (PMA) properties of CoFeB/Pd multilayers are investigated as functions of the thickness of the constituent layers of the multilayers and of the substrate type. A relatively strong PMA is formed at small CoFeB thicknesses of 0.3 and 0.5 nm over the entire Pd thickness range of 0.47 to 1.26 nm. At a fixed CoFeB thickness, the PMA tends to increase with increasing Pd thickness and this behavior can be attributed to the fact that the interface tends to become flatter and smoother at a higher Pd thicknesss, leading to a stronger surface anisotropy. A stronger PMA is observed for the glass substrate than for the MgO substrate. Since the thermal stress formed at the CoFeB layer is tensile for both the glass and MgO substrates, the magnetoelastic interactions suggest the possibility of forming a Co-Pd alloy with a negative saturation magnetostriction at the CoFeB/Pd interfaces.

Structural and magnetic properties of FePd and CoPd alloy epitaxial thin films grown on MgO single-crystal substrates with different orientations

FePd and CoPd alloy thin films were prepared on MgO single-crystal substrates of (001) B1 , (110) B1 , and (111) B1 orientations at 600 °C by ultra high vacuum rf magnetron sputtering. L1 0-FePd(001) films with the c-axis perpendicular to the substrate surface are obtained on MgO(001) B1 substrates. FePd epitaxial films consisting of L1 0(110) and L1 0(011) crystals are formed on MgO(110) B1 substrates. The c-axis of L1 0(110) crystal is parallel to the substrate surface, whereas that of L1 0(011) crystal is 44° canted from perpendicular direction. L1 0-FePd(111) films with the c-axis 54° canted from the perpendicular direction are formed on MgO(111) B1 substrates. L1 0 ordering degree of these FePd films varies depending on the substrate orientation. On the other hand, disordered CoPd thin films of (001) A1 , (110) A1 , and (111) A1 orientations epitaxially grow on MgO substrates of (001) B1 , (110) B1 , and (111) B1 orientations, respectively. The magnetization properties of L1 0 ordered FePd and A1 disordered CoPd thin films are influenced by the crystal structure, the ordering degree, and the film orientation.

Large converse magnetoelectric coupling effect at room temperature in CoPd/PMN-PT (001) heterostructure

We report a large converse magnetoelectric (CME) effect at room temperature in a multiferroic heterostructure formed from thin layers of perpendicularly magnetized CoxPd1-x alloys deposited on a piezoelectric single-crystal of lead magnesium niobate-lead titanate PMN-PT(001). The CME results from a strain-induced reorientation of the CoPd magnetization. By varying the composition and thickness of the CoxPd1-x film, a large converse magnetoelectric coupling constant, α=8×10−7 s/m, at room temperature was found for 10 nm Co0.25Pd0.75. This large CME effect results from combining a highly magnetostrictive CoPd alloy with highly piezoelectric PMN-PT.

Pt-Encapsulated Pd−Co Nanoalloy Electrocatalysts for Oxygen Reduction Reaction in Fuel Cells

Pt-encapsulated Pd(x)Co(100-x) nanoalloy electrocatalysts supported on carbon have been synthesized by a rapid microwave-assisted solvothermal (MW-ST) method within 15 min at as low as 300 degrees C. Subsequently, the samples have been heat treated at 900 degrees C in a reducing gas atmosphere to obtain Pt-Pd-Co nanoalloys. X-ray diffraction (XRD) analysis of the as-synthesized and 900 degrees C heat-treated samples reveals interesting changes in phase compositions and degree of alloying with Co and Pt contents and heat treatment. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) data of the as-synthesized samples confirm Pt enrichment on the surface of the Pd-Co nanoparticles. Rotating disk electrode (RDE) and single cell proton exchange membrane fuel cell measurements reveal that the as-synthesized Pt-encapsulated Pd(80)Co(20) (i.e., 75 wt % Pd(80)Co(20) + 25 wt % Pt) with 20 wt % total metal loading on carbon or 5 wt % Pt exhibit higher catalytic activity for the oxygen reduction reaction (ORR) compared to Pt with 20 wt % Pt loading on carbon. Significant changes in the catalytic activity for ORR occur on heat treatment at 900 degrees C as a result of changes in the phase composition and increase in particle size. This study demonstrates that the encapsulation of Pd-Co alloys with Pt offers a significant enhancement in activity for ORR per unit mass of Pt, offering a significant cost savings.

Magnetoresistance and Switching Properties of Co–Fe/Pd-Based Perpendicular Anisotropy Single- and Dual-Spin Valves

Switching characteristics and magnetoresistance of spin valves with perpendicular anisotropy based on Co-Fe/Pd multilayers deposited by ultrahigh vacuum (UHV) sputtering have been studied. In unpatterned thin films without exchange bias, high current-in-plane giant magnetoresistance (CIP-GMR) of 9.7% and 15.2% in single-spin valves (SSVs) and dual-spin valves (DSVs) was measured, a significant improvement over previous work. We describe the effects of a Ta seed layer and postdeposition annealing on the perpendicular anisotropy and magnetoresistance of Co-Fe/Pd spin valves, which can be attributed to improvements in the fcc (111) orientation of Pd and the formation of Co-Pd alloys at the Co-Fe/Pd interfaces, respectively. We also show that the coercivity of the layers can be tuned by varying the Co-Fe alloy composition in the multilayers, and describe the minor loops of perpendicular DSVs that exhibit four distinct resistance states, which is a potential structure for multistate storage devices.

Surface Oxide Film and its Influence on the Oxygen Reduction on Pd-Co and Pt-Co PEFC Cathodes

PtCo and PdCo alloy electrodes were investigated in a 0.5 M sulfuric acid solution by electrochemistry, ellipsometry, laser Raman scattering spectroscopy, XPS, and GD-OES. The corrosion resistibility of Pt-Co and Pd-Co alloys decreased with increase of Co addition. The increase of Co addition, however, enhanced the catalytic efficiency on the ORR. The alloy surfaces may be covered by CoOOH and Pt or Pd oxide 2-3nm thick. At the potential of 1.2V vs. Ag/ AgCl/ sat. KCl, the thickness of oxide film increased with the Co addition. The presence of the oxide film on the alloy electrodes increases the overvoltage for the ORR. The effect of the oxide thickness on the ORR was discussed.

Electrodeposited Pd-Co catalyst for direct methanol fuel cell electrodes: Preparation and characterization

Pd-Co alloy has been recently proposed as a catalyst for the cathode of direct methanol fuel cells with both excellent oxygen reduction activity and methanol tolerance, hence electrodeposition of this alloy is an attractive approach for synthesizing porous metal electrodes with high methanol tolerance in direct methanol fuel cells. In this study, we electrodeposited two types of Pd-Co films onto Au substrates by applying different current density (−10 or −200 mA cm −2); and then characterized them in terms of morphology, composition, crystal structure, and catalytic activity. Pd-Co deposited at −10 mA cm −2 was smooth and possessed smaller particles (ca. 10 nm), while that at −200 mA cm −2 was dendritic (or rough) and possessed larger particles (ca. 50 nm). Both the Pd-Co alloys were found to be almost the same structure, i.e. a solid solution of ca. Pd 7Co 3 with Pd-skin, and also confirmed to possess comparable activity in oxygen reduction to Pt (potential difference at 1.0 μA cm −2 was 0.05 V). As for methanol tolerance, cell-voltage was not influenced by addition of 1 mol dm −3 methanol to the oxidant solution. Our approach provides fundamental technique for synthesizing Pd-Co porous metal electrodes by electrodeposition.