FePd Thin Films Research Articles

Electrochemical studies of Fe and Pd deposition and their influence on the co-deposition of the Fe–Pd alloy

Electrodeposition process of the Fe–Pd thin films was investigated using cyclic voltammetry, chronopotentiometry and chronoamperometry methods. Deposition process was first studied for single metals; Fe, Pd. On the end a comparison with Fe–Pd alloy was performed. It was found that the deposition of Fe starts at 50mV, deposition of Pd at 200mV and the deposition of Fe–Pd alloy at 150mV at more positive potentials, when instead of Au electrode as a working electrode Fe, Pd or Fe–Pd monolayered deposits are already present. Furthermore, a comparison of the deposition process of single metals with an alloy reveals that when Fe is accompanied with Pd, the deposition of Fe starts at more than 500mV at more positive potentials. To understand this phenomenon, galvanostatic deposition at −100μA/cm2 for 3600s and potentiostatic depositions from −0.6V to −1.3V were performed with the deposits’ composition and their microstructure studied. It was observed that in the case of the of Fe–Pd-alloy deposition, Pd deposits first and due to its catalytic behaviour it subsequently catalyses the reduction of Fe(II)Cit.

Magnetic property improvement of sputter-prepared FePd films on glass substrates with W underlayer

Magnetic properties and structure of sputter-prepared FePd thin films on the glass substrates with W underlayer have been studied. The structural analysis shows that FePd films have a (111) preferred orientation. All studied FePd films exhibit in-plane magnetic anisotropy. In the single layer samples, the coercivity (Hc) and magnetic energy product ((BH)max) are increased with Ta and reached the maximum value of 2.3kOe and 4.3MGOe in the sample annealing at 650°C. With further increase of Ta, magnetic properties drop rapidly. Dependence of magnetic hardening on Ta can be explained by dominant solid reactions in different region of Ta including ordering and grain growth. Interestingly, magnetic properties of L10-FePd are largely improved with the insertion of a 5-nm-thick W underlayer. Hc and (BH)max are significantly increased to 3.9kOe and 8.5MGOe, respectively. Structural results suggest that this magnetic enhancement is related to both higher ordering degree and refined microstructure.

Low precessional damping observed for L1-ordered FePd epitaxial thin films with large perpendicular magnetic anisotropy

High-quality L10 ordered 20 nm-thick FePd epitaxial thin films with a large perpendicular magnetic anisotropy were fabricated using a SrTiO3 substrate. The uniaxial crystalline magnetic anisotropy constant Ku evaluated for the films annealed above 500 °C was 14 Merg/cm3. A very low effective damping constant, αeff = 0.007, was observed for FePd thin films annealed at 500 °C. This value is smaller than that of other Fe-based ordered alloys with a large perpendicular magnetic anisotropy.

Epitaxy from the liquid phase: tuning metastable phases in Fe–Pd thin films by laser-assisted rapid solidification on substrates

Epitaxy by crystallization of thin liquid films on suitable substrates constitutes an alternative approach to molecular beam epitaxy, particularly if metastable phases are required. Employing laser-assisted rapid solidification, we demonstrate for the example of the body-centred-cubic, body-centred-tetragonal, face-centred-tetragonal and face-centred-cubic phases of Fe7Pd3 thin films, how the interplay of cooling rate and substrate-assisted nucleation affects the resulting metastable crystal phase and epitaxial relationship. Exemplarily employing lanthanum strontium aluminium tantalum oxide, MgO, and Si single crystals as substrates, this is experimentally demonstrated by an x-ray diffraction study and pole figure measurements. The underlying solidification kinetics are clarified using finite element calculations on the resulting time–temperature profile. Employing secondary ion mass spectroscopy we additionally demonstrate that the absence of interdiffusion is a central requirement for successful application.

Electric field control and effect of Pd capping on magnetocrystalline anisotropy in FePd thin films: A first-principles study

Using ab initio electronic structure calculations, we have investigated the effect of an electric field and of a heavy-metal cap of Pd on the magnetocrystalline anisotropy (MCA) of FePd ultrathin film. Analysis of the energy- and $k$-resolved distribution of the orbital character of the minority-spin band reveals that the perpendicular MCA of the uncapped film mainly arises from the spin-orbit coupling (SOC) between unoccupied Fe ${d}_{xy}$ and occupied Fe ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ states. On the other hand, the SOC between the Pd- and Fe-derived $d$ states yields negative contributions to the MCA. We find that the sensitivity of the surface anisotropy energy to the applied electric field is 18 fJ/(Vm) and is due to changes in the occupation of the surface Fe atoms ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and (${d}_{xz},{d}_{yz}$) orbitals. We demonstrate that the thickness of the Pd cap has a dramatic effect on the MCA and can even switch the magnetization from out-of- to in-plane orientation. The underlying origin is the change of the position and orbital character of the spin-polarized quantum well states induced in the Pd cap by varying its thickness. These results have important implications for exploiting heavy metals with large spin-orbit coupling (Ru, Pd, Ta, Pt, or Au) as contacts with ferromagnetic thin films to tailor the magnetic switching of spintronic devices by tuning the cap thickness.

Structural Characterization of FePd, FePt, and CoPt Alloy Thin Films Epitaxially Grown on (001) Surface of Different Single-Crystal Materials

FePd, FePt, and CoPt alloy thin films are deposited on (001) single-crystal substrates of MgO, SrTiO3, and LaAlO3 at 600°C by using an ultra-high vacuum radio-frequency magnetron sputtering system. The c-axis distribution and the order degree are carefully studied. The FePd films deposited on MgO and SrTiO3 substrates consist of L10(001) crystals with the c-axis perpendicular to the film surface. The FePd film deposited on LaAlO3 substrate and the FePt and the CoPt films deposited on all the substrates include L10(100) crystals with the c-axis lying in the film plane. The c-axis distribution is influenced by the combination of film and substrate materials. Higher order degrees are observed for the film material CoPt <; FePt <; FePd and for the substrate material LaAlP3 <; SrTiO3 <; MgO. Order degree is influenced by atomic diffusion of deposited film material and by film strain caused by the lattice mismatch with substrate. The magnetic property reflects the c-axis distribution and the order degree.

$L1_{0}$ Ordered FePd, FePt, and CoPt Thin Films With Flat Surfaces Prepared on MgO(110) Single-Crystal Substrates

FePd, FePt, and CoPt alloy thin films are prepared on MgO(110) single-crystal substrates by using two different methods. One is one-step method consisting of deposition at an elevated substrate temperature of 600°C and the other is two-step method consisting of low-temperature deposition at 200°C followed by annealing at 600°C. The crystal structure, the crystallographic orientation, and the surface morphology are compared. L10 ordered FePd, FePt, and CoPt films epitaxially grow on the substrates with three variants, (110), (101), and (011), when deposited at 600°C. The c-axis of L10(110) variant is lying in the film plane, whereas those of L10(101) and L10(011) variants are 45° canted from the substrate surface. Disordered FePd, FePt, and CoPt single-crystal films of (110) orientation are formed by deposition at 200°C. An A1-L10 phase transformation occurs along A1[001], A1[010], and A1[001] by annealing the disordered films at 600°C. The annealed films thus consist of three L10 variants. Similar final crystal structure and orientation are realized in the FePd, the FePt, and the CoPt films prepared by employing the two different methods. The L10 ordered films prepared by one-step method have island-like surfaces involving facets, whereas those prepared by two-step method have very flat surfaces with the arithmetical mean roughness lower than 0.3 nm. The two-step method is useful for preparation of L10 ordered films with flat surfaces.

Thermoelastic strain in polycrystalline Fe–Pd shape memory alloy thin film

Thermoelastic strain in a polycrystalline Fe–Pd thin film due to shape memory effect was determined from Hooke's law using the measured residual stress and the elastic modulus obtained by the wrinkling method, and the variation in the thermoelastic strain was discussed in terms of thermally induced phase transformation. The measurement of thermoelastic strain from Hooke's law and the wrinkling method was in good quantitative agreement with previously reported data obtained from a digital camera. The variation of thermoelastic strain of the Fe-28.1at.% Pd thin film was associated with the martensitic transformation between the high-temperature face-centered cubic austenite and the low-temperature face-centered tetragonal martensite during a thermal cycle.

Preparation ofL10ordered FePd, FePt, and CoPt thin films with flat surfaces on MgO(001) single-crystal substrates

FePd, FePt, and CoPt alloy thin films are prepared on MgO(001) single-crystal substrates by employing a two-step method consisting of sputter deposition at low-temperature (room temperature) followed by high-temperature annealing at 600 °C. FePd, FePt, and CoPt single-crystal films with disordered structure (A 1) grow epitaxially on MgO substrates at room temperature. By annealing these disordered films at 600 °C, a transformation from A 1 to L 10 -ordered phase occurs. The order degrees of annealed FePd, FePt, and CoPt films are 0.63, 0.38, and 0.16, respectively. The films before annealing have very flat surfaces and the flat surfaces are kept after annealing. The arithmetical mean surface roughness values of annealed FePd, FePt, and CoPt films are 0.3, 0.1, and 0.2 nm, respectively. The two-step method is considered to be useful for preparation of FePd, FePt, and CoPt alloy thin films with flat surfaces, which are necessary for practical applications.

Chemical order and crystallographic texture of FePd:Cu thin alloy films

FePd thin films have been recently considered as promising materials for high-density magnetic storage devices. However, it is necessary to find a proper method of fabrication for the (001)-textured and chemically well-ordered alloy. In this paper, we present the detailed investigations of lattice parameters, chemical order degree, grain sizes, and crystallographic texture carried out on FePd alloys with 10 at.% of Cu addition. The initial [Cu(0.2 nm)/Fe(0.9 nm)/Pd(1.1 nm)]5 multilayers were thermally evaporated in an ultrahigh vacuum on MgO(100), Si(100), Si(111), and Si(100) covered by a 100-nm-thick layer of amorphous SiO2. In order to obtain a homogeneous FePd:Cu alloy, the multilayers were annealed in two different ways. First, the samples were rapidly annealed in nitrogen atmosphere at 600 °C for 90 seconds. Next, the long annealing in a high vacuum for 1 h at 700 °C was done. This paper focuses on quantitative investigations of the chemical order degree and crystallographic texture of ternary FePd:Cu alloys deposited on four different substrates. In order to obtain both quantities, we have taken a novel approach to consider the problem of dopant atoms located in the FePd structure. The studies of the structure were done using XRD performed with synchrotron radiation and pole figures measurements. We have found that the addition of Cu changes the FePd lattice parameters and lattice distortion. We have also shown that, using different substrates, it is possible to obtain a FePd:Cu alloy with different chemical order and texture. Moreover, it was observed that the texture category is substrate-dependent.

Promotion of L1 ordering of FePd films with amorphous CoFeB thin interlayer

The L10-ordered FePd thin films were prepared using an ultrahigh vacuum magnetron sputtering system on MgO(001) substrates at 300 °C. The crystallographic and magnetic properties and the surface morphology of films with and without a very thin amorphous CoFeB intermediate layer inserted between the FePd and the MgO layers were systematically investigated as a function of the thickness of the FePd layer. The perpendicular anisotropy of the samples was increased by inserting the thin CoFeB as an intermediate layer below the FePd with a thickness of 4.0 nm. The reason for the enhancement by inserting the amorphous CoFeB layer is attributed to: (i) the promotion of the L10 ordering of the FePd due to the reduction of the lattice mismatch between the MgO and FePd, and (ii) the fact that thin CoFeB has a perpendicular anisotropy at the interface of the MgO, which superposed the perpendicular anisotropy of the L10-FePd.

L1 ordered phase formation in FePt, FePd, CoPt, and CoPd alloy thin films epitaxially grown on MgO(001) single-crystal substrates

The FePt, FePd, CoPt, and CoPd epitaxial thin films are prepared on MgO(001) single-crystal substrates by ultrahigh vacuum RF magnetron sputtering. The effects of the magnetic material and the substrate temperature on the film growth, the film structure, and the magnetic properties are investigated. The L10 ordered phase formation is observed for FePt, FePd, and CoPt films prepared at temperatures higher than 200, 400, and 600 °C, respectively, whereas that is not recognized for CoPd films. The L10-FePd(001) single-crystal films with the c-axis normal to the substrate surface are formed, whereas the FePt and CoPt epitaxial films include L10(100) crystals whose c-axis is parallel to the substrate surface, in addition to the L10(001) crystals. Upon increasing the substrate temperature, the ordering degree increases. A higher ordering parameter is observed in the order of FePd &amp;gt; FePt &amp;gt; CoPt. The magnetic properties are influenced by the crystal structure, the crystallographic orientation of the L10 crystal, and the ordering degree.

Energetic and thermodynamic aspects of structural transitions in Fe-Pd ferromagnetic shape memory thin films: Anab initiostudy

Although Fe-Pd alloy thin films are highly promising for magnetic shape memory actuation in biomedical applications and miniaturized devices, phase formation and thermodynamic properties are still poorly understood. In the present study we employ density-functional theory and ab initio molecular-dynamic simulations on the Fe${}_{68.75}$Pd${}_{31.25}$ system to exemplarily study the ground-state and finite-temperature properties, viz. free energy and entropy, as a function of tetragonality from austenite to martensite in the optional presence of open surfaces. We discuss the underlying thermodynamics and demonstrate how different phases and structures can be stabilized by an interplay of finite temperatures, open surfaces, and film thicknesses.

Influence of the phenomena occurring at the soft/hard interface on the coercivity behavior in exchange-spring magnets

L 1 0 -ordered FePd thin films were grown onto MgO-(100) monocrystalline substrates at 450 and 650 °C by means of a molecular beam epitaxy system. Fe/FePd bi-layers were grown by covering the L 1 0 -FePd hard films with Fe layers of different thickness. For a soft/hard thickness ratio up to 1, these bi-layers show behavior typical of a single phase hard magnet while, for a higher thickness ratio, they behave as exchange-coupled magnets characterized by two critical fields. The bi-layers’ coercivity decreases as a function of the deposited Fe when it is controlled by the domain wall pinning mechanism, while it initially increases and then decreases, when the nucleation of reversed domains is the predominant coercivity mechanism. These different behaviors are due to the phenomena occurring at the soft/hard interface and in particular to the degree of Fe/FePd intermixing and to the composition of the thin interfacial layer.

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.

X-ray absorption fine structure and x-ray diffraction studies of crystallographic grains in nanocrystalline FePd:Cu thin films

FePd alloys have recently attracted considerable attention as candidates for ultrahigh density magnetic storage media. In this paper we investigate FePd thin alloy film with a copper admixture composed of nanometer-sized grains. [Fe(0.9 nm)/Pd(1.1 nm)/Cu(d nm)]×5 multilayers were prepared by thermal deposition at room temperature in UHV conditions on Si(100) substrates covered by 100 nm SiO2. The thickness of the copper layer has been changed from 0 to 0.4 nm. After deposition, the multilayers were rapidly annealed at 600 °C in a nitrogen atmosphere, which resulted in the creation of the FePd:Cu alloy. The structure of alloy films obtained this way was determined by x-ray diffraction (XRD), glancing angle x-ray diffraction, and x-ray absorption fine structure (EXAFS). The measurements clearly showed that the L10 FePd:Cu nanocrystalline phase has been formed during the annealing process for all investigated copper compositions. This paper concentrates on the crystallographic grain features of FePd:Cu alloys and illustrates that the EXAFS technique, supported by XRD measurements, can help to extend the information about grain size and grain shape of poorly crystallized materials. We show that, using an appropriate model of the FePd:Cu grains, the comparison of EXAFS and XRD results gives a reasonable agreement.

Fe–Pd thin films as a model system for self-organized exchange coupled nanomagnets

In equilibrium the Fe–Pd system on the iron rich side of the phase diagram demixes into Fe and L10-ordered FePd. Here, we examine the suitability of the demixing process for self-organized formation of exchange coupled thin film magnets. In this way the benefit of the high magnetization of Fe is combined with the high magnetocrystalline anisotropy of FePd. By using combinatorial methods the influence of composition and thickness on structure, microstructure, and magnetic properties is analyzed. Experiments show the different thermodynamic and kinetic conditions required for demixing and ordering. In particular, for nanostructures the interface energy during demixing must be considered.

Shape Memory Effect in Fe-Pd Magnetic Shape Memory Alloy Thin Films

The shape memory effect (SME) and magnetic shape memory effect (MSME) Fe-Pd thin film are using the film curvature method. The corresponding residual stress change due to theSME and MSME in Fe-Pd film is measuredduring thermal cycling and magnetic field changing. AFe-Pd thin film with a lateral composition gradient is deposited onto micromachined x7 cantilever beam arraysubstrate,such that each of the cantilever beams is coated with a film of different composition.There is abrupt stress change in only .1 at % Pd as the temperature of the film is cycled, and the corresponding stress change was measured as 0.16 GPa. The film with .4 at % Pd showsthe abrupt stress change at 0.7 Tesla, which means that the composition has the MSME.

Temperature-driven microstructural, compositional, and magnetic changes in electrodeposited Fe–Pd thin films

Equiatomic Fe–Pd thin films with thicknesses of 200 nm were deposited from a single electrolyte onto glass-based, Au-coated substrates using the electrodeposition method. The as-deposited films were annealed at temperatures from 400 to 600 °C for 1 h in Ar+7% H2. The phase formation, microstructure and the magnetic properties were analyzed. The L10 ordering was found to coincide with the grain growth and the interdiffusion reaction between the substrate and the thin film when temperatures above 500 °C were used, which resulted in lower coercivities. The highest coercivity of 870 Oe was achieved when modest temperatures (400 °C) were used.

On the exchange coupling interaction between Fe and L10-ordered FePd thin films

Hard L10-ordered FePd ultra-thin films were epitaxially grown by means of a molecular beam epitaxy system on MgO-(100) monocrystalline substrates. Because of the very low thickness of the films, small amounts of superparamagnetic L10-FePd particles were also formed on the surface. The magnetic properties of the films are typical of highly coercive systems showing a strong perpendicular anisotropy. These hard films were used for the development of soft/hard exchange-spring magnets, by depositing different thickness of iron. Fe reacts with the surface FePd small particles giving rise to a Fe(Pd) compound with a broad distribution of particle sizes. The resulting systems are bi-layers constituted by a soft Fe(Pd) and a hard L10-FePd layer intercalated by a very thin region of small particles. For soft/hard thickness ratio nominally equal to 1 the magnetic behaviour is typical of a single-phase hard magnet. By increasing the nominal thickness ratio up to 3, the behaviour becomes typical of an exchange-coupled magnet with hysteresis loops characterized by two critical fields.