Face-centered Tetragonal Phase Research Articles

Amplifying Mn Segregation and Enhancing Damping Capacity via Adding Sn in Mn–44Cu–1.5Al as‐Cast Alloys

As a metal functional material, the Mn–Cu‐based alloys are regarded to be able to cope with the vibration and noise from machines. In particular, the as‐cast alloys often exhibit an excellent damping capacity, which is attributed to the Mn segregation in the alloys. Herein, to amplify the kind of segregation, a trace of Sn is added in as‐cast Mn–Cu–Al alloys. The phase structures of the as‐cast Mn–44Cu–1.5Al alloys are analyzed in detail through X‐Ray diffraction (XRD). The distribution characteristics of face‐centered cubic (FCC) phases and face‐centered tetragonal (FCT) phases are observed using electron backscatter diffraction (BSE). The alloys’ dynamic mechanical spectra and internal friction (IF) are measured using an inverted torsion pendulum device. It is found that the addition of Sn promotes the Mn segregation in the as‐cast Mn–44Cu–1.5Al alloys. A large amount of FCT phases appears in the dendritic trunks, enhancing the damping capacity of the alloys. In the meantime, the Sn atoms enhance the twin boundary mobility in Mn‐rich dendritic trunks. As a result, the alloy containing 1 wt% Sn has the highest damping capacity in the alloys.

FePt: LaSrFeO4 nanocomposite film prepared by magnetron and pulsed laser co-deposition method

The extensive application of a multifunctional composite film of metal nanoparticles embedded in a dielectric matrix is remarkable. Due to the oxidation susceptibility of atomic iron, it is difficult to directly fabricate embedded Fe nanoparticles in an oxide dielectric matrix with a Fe target. Because La0.5Sr0.5FeO3 can be decomposed into LaSrFeO4 and α-Fe, ferromagnetic and optical absorption FePt:LaSrFeO4 composite films were successfully fabricated at room temperature using Pt and La0.5Sr0.5FeO3 as targets via magnetron and pulsed laser co-deposition. Further annealing was performed on the FePt:LaSrFeO4 composite films. FePt is chemically disordered face-centered cubic phase (A1 structure) below 600 oC annealing and chemically ordered face-centered tetragonal phase (L10 structure) above 600 oC annealing. With increasing the annealing temperature, a redshift of the absorption peak from 256 to 285 nm is seen, which can be attributed to the size growth of the LaSrFeO4 and FePt nanoparticles in the composite films. The strongest absorption peak at around 269 nm for the 600 oC annealed sample can be attributed to the high crystallographic quality and relatively tiny grain size of FePt particles with uniform distribution. FePt:LaSrFeO4 composite films are ferromagnetic and optically absorbent, making them suited for multifunctional applications. Furthermore, magnetron and pulsed laser co-deposition techniques have the potential to produce multiferroic oxides, in which the coupling of different ordering processes e. g. ferroelectricity and ferromagnetism provides the potential for a new breed of multifunctional devices.

Mechanism of heat-induced damping attenuation for Fe-added Mn–Cu–Al alloys

The thermotolerance is of great importance for Mn–Cu damping alloys. However, the excessive relaxation behavior of spinodal face-centered cubic (FCC) phases in some thermal environments weakens the kinetics of phase transition from face-centered cubic phase to face-centered tetragonal (FCT) phase, and consequently lower the damping capacity of the alloys. The composition of Fe is regarded as a stabilizing element for FCC phases, but little is known about the role of Fe on the relaxation performance of FCC phases at higher temperatures. The phase structure of the Mn–Cu–Al and Mn–Cu-Al–Fe alloys was analyzed using X-ray diffraction. And their precipitates were observed by using a scanning electron microscopy (SEM) and transmission electron microscope (TEM). Our results show that the excessive relaxation performance happens after holding from 128 to 256 h at 120 ℃. As a result, the amount of FCT phases are decreased and the internal friction has a distinct drop in the meantime. On the other hand, to some extent, the addition of Fe restrains the excessive relaxation performance of the FCC phases. The findings may be helpful for elucidating the mechanism of the heat-induced damping attenuation and promoting the industrial applications of the Mn–Cu alloys.

Unveiling Nanoscale Compositional and Structural Heterogeneities of Highly Textured Mg0.7Ti0.3Hy Thin Films.

Thin films often exhibit fascinating properties, but the understanding of the underlying mechanism behind such properties is not simple. This is partially because of the limited structural information available. The hurdle in obtaining such information is especially high for textured thin films such as Mg-rich MgxTi1-x, a promising switchable smart coating material. Although these metastable thin films are seen as solid solution alloys by conventional crystallographic methods, their hydrogen-induced optical transition is hardly understood by a solid solution model. In this study, we collect atomic pair distribution function (PDF) data for a Mg0.7Ti0.3Hy thin film in situ on hydrogenation and successfully resolve TiH2 clusters of an average size of 30 Å embedded in the Mg matrix. This supports the chemically segregated model previously proposed for this system. We also observe the emergence of a previously unknown intermediate face-centered tetragonal phase during hydrogenation of the Mg matrix. This phase appears between Mg and MgH2 to reduce lattice mismatch, thereby preventing pulverization and facilitating rapid hydrogen uptake. This work may shed new light on the hydrogen-induced properties of Mg-rich MgxTi1-x thin films.

Synthesis of PdM (M = Zn, Cd, ZnCd) Nanosheets with an Unconventional Face-Centered Tetragonal Phase as Highly Efficient Electrocatalysts for Ethanol Oxidation.

Recently, crystal-phase engineering has been emerging as a promising strategy to tune the physicochemical properties of noble metal catalysts and further improve their catalytic performance. However, the synthesis of noble metal catalysts with an unconventional crystal phase as well as desired composition and morphology still remains a great challenge. Herein, a series of PdM (M = Zn, Cd, ZnCd) nanosheets (NSs) with thickness less than 5 nm have been synthesized via a facile one-pot wet-chemical method. In particular, different from the conventional face-centered cubic (fcc) phase, PdM NSs possess an unconventional face-centered tetragonal (fct) phase. As a proof-of-concept application, the fct PdZn NSs exhibit significantly enhanced mass activity and stability in ethanol oxidation reaction, compared to the pure Pd NSs and commercial Pd black catalyst.

Ion-Implantation-Induced Disorder in FePt-C Thin Films

The effects of ion implantation through a mask on the structural and magnetic properties of FePt-C films were investigated. The mask pattern was fabricated using self-assembly of di-block copolymers. For implantation, high- (40 keV for 14N+ and 100 keV for 40Ar+) and low- (7.5 keV for 14N+ and 4.5 keV for 40Ar+) energy 14N+ and 40Ar+ ions were used to modify the structural and magnetic properties of these films. The X-ray diffraction and transport of ions in matter simulations were performed for understanding the structural changes due to the ion implantations. These results revealed the conversion of face-centered tetragonal phase to face-centered cubic (FCC) phase for 40Ar+ ion implantations and increase in inter-planar spacing of FCC FePt (111) planes for 14N+ ion implantations. Magnetic properties were then probed by using a vibrating sample magnetometer (VSM), torque magnetometer, and magnetic force microscopy (MFM). The results from VSM and torque magnetometer showed a change in anisotropy from out-of-plane to in-plane directions for all the implantation cases except for low-energy 40Ar+ ion implantations. The MFM images also showed an absence of stripe domains confirming the above-mentioned effects.

Room temperature superparamagnetism in ternary (Fe50Pt50)0.42Cu0.58 phase at interfaces on annealing of Fe50Pt50/Cu multilayer

The face- centered- tetragonal (FCT) or L10 phase of Fe50Pt50 (FePt) film is obtained on annealing FePt films at high temperature (∼600 °C), that usually grows as face-centered- cubic (FCC) phase. Cu as an additive up to ∼20 atomic%, which form ternary alloy FePtCu on mixing, is used to reduce the ordering temperature. We studied the formation of FePtCu ternary alloy: its structure, magnetic properties and grain growth at the interfaces of a FePt/Cu multilayer, as a function of annealing temperature (100 °C–600 °C), which is very less as compared to their melting temperatures. The study indicates the growth of a ternary alloy with composition of (FePt)0.42Cu0.58 in FCT phase on annealing the FePt/Cu multilayer at a moderate annealing temperature (∼400 °C). With a large addition of Cu at 56 atomic% in FePt, the ordering temperature reduces by ∼200 °C and form a ternary alloy with distinct magnetic properties. We observed rapid growth of ordered FCT phase with increase in crystallite size from 50 Å to 150 Å on annealing the multilayer in the range of 400 °C–600 °C. Interestingly, from macroscopic magnetization measurements we could identify the existence of a super-paramagnetic (SP) phase at room temperature with a typical particle size of ∼12 Å of ternary alloy on annealing the multilayer at 400 °C, which is much smaller than the crystallite size (∼50 Å). Annealing at 600 °C reduces the multilayer to a disordered magnetic phase. The room temperature SP nanoparticles of FePtCu alloy phase formed on annealing the multilayer at 400 °C are potential candidates in biomedical applications.

Study of exchange bias effect in a patterned Fe/Pt multilayer with the thermal annealing

The present work reports the preparation of 5 μm wide and 10 μm grating periodicity patterned [Fe(2.0nm)/Pt(2.5nm)]X10 multilayer and its thermal annealing behavior. Intermixing across the Fe and Pt layers is observed with vacuum annealing at 650 K resulting in the formation of disordered face centered cubic (FCC) and ordered L10 face centered tetragonal (FCT) FePt phases. The longitudinal magneto-optical Kerr effect (L-MOKE) hysteresis loop, measured from the single 5 μm FePt stripe shows double loop behavior indicating the presence of two magnetic phases, one with the low coercivity (HC) and the second one with the higher HC values. This could be due to the presence of disordered FCC and ordered L10 FCT phases of FePt, known to be soft and hard magnetic phases. Conversion electron Mössbauer spectroscopy of the annealed sample shows the presence of FCC and FCT FePt phases corroborating the x-ray diffraction and MOKE measurements. The hysteresis loop of the soft phase shows the exchange bias effect with the remnant state of the hard magnetic phase as initial condition akin to the exchange bias as observed in conventional ferromagnetic - antiferromagnetic bilayers.

Composition and structure dependence of specific heat of disordered iron-palladium alloys

Depending on Pd content, disordered Fe-Pd alloys take various crystal structures: body-centered cubic (BCC), body-centered tetragonal (BCT), face-centered tetragonal (FCT) and face-centered cubic (FCC) structures. We have measured specific heat of Fe-Pd alloys to understand the lattice stability and electronic state of the alloys. At the phase boundary between FCT and FCC phases, electronic specific heat coefficient shows a local maximum and the Debye temperature shows a local minimum. A local maximum of electronic specific heat coefficient also appears in the BCC region with Pd content of near 10at.%.

Electrical controlled magnetism in FePt film with the coexistence of two phases

A series of FePt films with different magnetic structures are deposited on Pb(Mg1/3Nb2/3)O3–PbTiO3 substrates. By applying an electric field across the piezoelectric single crystal substrate, an magnetoelectric effect is observed in FePt/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructure due to the phase transformation between face-centered cubic and face-centered tetragonal phases in the film. Taking advantage of the different coercivity caused by the electric field, the sign of magnetization can be manipulated reversibly at room temperature with the electric field switching on or off. Based on this experimental result, we demonstrate a model for the technology of information storage, in which data can be written electrically without false writing.

Effect of functionalization on positional ordering of 3 nm FePt nanoparticles: Langmuir–Blodgett monolayer

Surface functionalization of nanoparticles helps to tailor positional ordering of FePt nanoparticles which is essential for potential application for density media recording. The FePt nanoparticles were synthesized using the chemical method. The size of the as synthesized monodispersed FePt nanoparticles was estimated to be ~3nm using TEM. Structural and magnetic phase transitions from a disordered face centered cubic to chemically ordered face centered tetragonal phase with a hard magnetic behavior were observed on heat treatment. The FePt nanoparticles prepared chemically were further coated with oleylamine, 11-mercaptoundecanoic acid (11-MUA) and stearic acid. The Langmuir–Blodgett monolayer depositions were carried out using functionalized FePt nanoparticles. The pressure–area (π–A) isotherm measurements were used to identify the appropriate pressure for the deposition of the monolayers on the substrates. TEM results show the long range positional ordering of micrometer range only for the amine functionalized FePt nanoparticles.

Effect of Oxygen Stoichiometry on Microstructural and Magnetic Properties of FePt/TaO$_{\rm x}$ Bilayer Fabricated by Ion-Beam-Bombardment Deposition

The effect of TaOx capping layer on microstructures and magnetic properties of FePt thin films via annealing was studied. The structural ordering of FePt from face-centered cubic to face-centered tetragonal phases depends strongly on the oxygen contents in the capping TaOx layer. The role of the TaOx layer is used to separate the FePt grains, as revealed by TEM. The annealed FePt/TaOx (15%O2/Ar) exhibited the largest out-of-plane coercivity (~2.4 kOe) amongst all samples, compared to that (Hc ~ 4.2 kOe) in the reference FePt layer. At low oxygen content in FePt/TaOx bilayers, the Ta atoms may act as defects to obstruct the FePt ordering whereas at high oxygen contents, the excess oxygen atoms diffuse into the FePt layer and react with Fe to form iron oxides which give rise to the low coercivities, as characterized by the XPS depth profile and binding energy analysis.

Pt diffusion driven L10 ordering in off-stoichiometric FePt thin films

Pt/Fe3Pt thin films were deposited on the 〈100〉 silicon substrates at room temperature using DC sputtering. As-deposited Pt (25nm)/Fe3Pt (70nm) bilayers were subjected to heat treatment and a systematic study was carried out to investigate the structural and magnetic phase transition as a function of annealing temperature. The as-obtained films show an A1 disordered, face centered cubic phase which exhibit a magnetically soft behavior. After annealing at 300°C for 1h, the set in of L10 face centered tetragonal phase was observed and is attributed to the atomic diffusion at Pt/Fe3Pt interface. A coercivity of 6.8kOe was obtained for Pt/Fe3Pt at 300°C which increases to 12.5kOe at 400°C due to enhanced fct phase formation. Rutherford back scattering study has also been performed to investigate the inter-layer diffusion of Fe3Pt and Pt, along with estimation of film thickness and atomic composition with annealing temperature. The thickness and composition of films annealed at 600°C was found to be 73nm and Fe54Pt46, respectively. Lower temperature ordering is achieved for these bilayer films.

Effect of the CrW sublayer on the structure and magnetic properties of thin FePt films

Multilayer Fe55Pt45(20 nm)/Pt(5 nm)/Cr100 − xWx(80 nm)/glass structures, in which the Fe55Pt45 magnetic film has a face-centered tetragonal (FCT) structure of the L10 phase with the (001) texture, have been prepared using magnetron sputtering. The microstructure and texture of the FePt films have been studied as functions of the W content in the Cr100 − xWx sublayer, where 0 < x < 25. It has been established that an increase in the W ion concentration leads to the formation of the (200) texture in the Cr100 − x sublayer and to an increase in the Cr lattice constant. This is accompanied by a decrease in the temperature at which the facecentered cubic phase transforms into the FCT phase of the FePt films as a result of the increase in tensile stresses along the a axis. It has been found that the coercivity of FePt films deposited on CrW substrates increases with increasing W content in the Cr100 − xWx sublayer because the CrW alloy thus formed precludes diffusion between the FePt film and the CrW sublayer. An additional 5-nm-thick intermediate Pt layer is also deposited to suppress diffusion between the FePt and CrW layers. As a result, the highly textured FePt(001) films intended for ultra-high density magnetic information recording are deposited on a substrate heated to a temperature of 400°C and the Cr85W115 sublayer.

Multiple‐Step Phase Transformation in Silver Nanoplates Under High Pressure

Silver nanoplates with multiple twin planes parallel to their basal surfaces exhibit multiple steps of structural distortion and phase transformation under increasing external pressure in a diamond-anvil cell. The disappearance of local hexagonal close-packed lamellae and a transformation from face-centered cubic to face-centered tetragonal phase are observed.

Study of Fe-rich FePt nanoparticles synthesized by a single step reverse micelle route

Fe-rich FePt nanoparticles with an average size of 5 nm were prepared using a reverse micelle route. As synthesized FePt powders were disordered face centered cubic in structure. DSC thermogram displays phase transformation at 575 °C, based on which heat treatments were carried in the temperature range of 500–600 °C. XRD patterns show that the degree of ordering increased with the increase in heat treatment temperature. An utmost coercivity of 3.2 kOe was observed for 600 °C heat-treated sample. The M– H loops were asymmetric in nature suggesting the presence of a second phase, Fe-oxide (Fe 3O 4) that is also observed from the XRD patterns. Mössbauer spectra reveals that on heat treatment the super-paramagnetic phase transforms into an ordered face centered tetragonal phase. The presence of 23% super-paramagnetic phase even after heat-treating at 600 °C reveals that the phase transformation is incomplete.

Size dependence on the ordering process in colloidal FePt nanoparticles

An alternative method to study the effects of annealing process on colloidal FePt nanoparticles (2–4 nm) has been achieved. Annealing experiments at temperatures between 773 and 1073 K under inert atmosphere flux were performed in powder samples with excess of surfactant molecules on nanoparticle surface. Transmission electron microscopy, x-ray diffraction and magnetic measurements were performed to evidence the evolution of the chemically disordered fcc to chemically ordered face-centered tetragonal phase transformation. Magnetization measurements under zero-field-cooling and field-cooling (MZFC−MFC) conditions, and hysteresis loops are extremely sensitive to the particle size distribution and were strongly affected by the annealing treatment.

Effect of Pt Substitution by Cu on Structural and Morphological Changes in Fe-Pt Nanoparticles during Annealing as Studied by &lt;I&gt;In-situ&lt;/I&gt; Transmission Electron Microscopy

Effects of substitution of Pt by Cu on the structural and morphological changes of Fe-Pt nanoparticles with chemical homogeneity and mono-dispersion, which were synthesized by the reverse micelle method, have been investigated by in-situ electron diffraction and HREM observation. In the Fe-Pt particles, initially with a chemically disordered face-centered cubic phase (Al), the phase transformation from Al to a chemically ordered face-centered tetragonal phase (L1 0 ) took place between 650 and 680°C. Polycrystalline Fe-Pt particles were reconstructed into Al single crystals between 550 and 650°C, followed by phase transformation from Al to L1 0 . The coalescence began almost concurrently with the phase transformation, i.e., between 650 and 680°C. Then, they turned to round-shaped single crystalline particles between 680 and 720°C. In the Fe(Pt,Cu) particles, the phase transformation from Al to L1 0 occurred between 550 and 600°C. Same processes, that is, the reconstruction to single crystals, the phase transformation from Al to L1 0 , the coalescence and the round-shaped particle formation were also observed in the Fe(Pt,Cu) nanoparticles. The temperatures, at which these processes took place, were substantially lower than those for the Fe-Pt nanoparticles.

Electrodeposited CoPt and FePt alloys nanowires

We have investigated CoPt and FePt alloys with the face centered tetragonal phase L10, which present very large magnetocrystalline anisotropy. Equiatomic CoPt nanowires exhibiting large coercive fields up to 1.1 T have been successfully prepared by electrodeposition into nanopores of commercial and home-made alumina membranes from a very simple electrolyte. The as-deposited material has the FCC structure with soft magnetic properties. An annealing treatment at 700 °C is crucial to transform this phase into the L1 0 phase, which presents hard magnetic properties. Nanowires of annealed samples consist of small grains around 20 nm, with their c axes randomly distributed. The coercivity does not depend on the morphology and porosity of the two types of membranes but only on the deposited material elaborated with the appropriate thermal annealing process. Our preliminary results with FePt alloy indicate a more complicated system since the as-deposited material shows no magnetization. Magnetism appears only after annealing at 700–750 °C. Coercivity up to 0.85 T has been obtained at room temperature but with inhomogeneous phase composition. To achieve a single hard phase L1 0, it is essential to get for the as-deposited sample the equiatomic composition and then to employ the suitable annealing parameters (temperature and time) to change the whole FCC phase into the FCT ordered L1 0 phase.

Vibration based electromagnetic micropower generator on silicon

This paper discusses the theory, design and simulation of electromagnetic micropower generators with electroplated micromagnets. The power generators are fabricated using standard microelectromechanical system processing techniques. Electromagnetic two-dimensional finite element anlysis simulations are used to determine voltage and power that can be generated from different designs. This paper reports a maximum voltage and power of 55mV and 70μW for the first design, incorporating microfabricated two-layer Cu coils on a Si paddle vibrating between two sets of oppositely polarized electroplated Co50Pt50 face centered tetragonal phase hard magnets. A peak voltage and power of 950mV and 85μW are obtained for the second design, which includes electroplated Ni45Fe55 as a soft magnetic layer underneath the hard magnets. The volume of the device is about 30mm3.