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The melting temperatures of Fe–Ni alloys and their densities in the liquid state at relevant pressure–temperature (P–T) conditions present in the core are of great importance for understanding the composition and thermal structure of the Earth's core. We measured shock temperatures of the Fe–11Ni–18Cr (wt. %) alloy up to ∼304 GPa using a special target configuration, a quasi-spectral pyrometer, and velocimeter diagnostics in a two-stage light-gas gun. The present results show that Fe–11Ni–18Cr starts to melt at the pressure of 210 (8) GPa and 4700 (300) K and completes at the pressure of 280 (10) GPa and 5250 (350) K under shock loading, which is ∼1000 K lower than some previous shock temperature measurements. The melting temperatures of the Fe–11Ni–18Cr alloy are 4100 (250) K and 5500 (450) K at the pressures present at the core-mantle boundary (∼136 GPa) and inner-core boundary (∼330 GPa), respectively, which are slightly lower than that of pure iron. Combined with the previous results of the pressure–density measurements at Hugoniot states, our results indicate that the presence of limited amounts of Ni and Cr into Fe has a minor effect on its melting curve and density in the liquid state, suggesting that sufficient light elements are required in the outer core to satisfy both the core density deficit and the reduced melting temperature. [ABSTRACT FROM AUTHOR]

Examines the microstructure and magnetostriction in rare-earth-iron alloys. Factors affecting the magnetostrictive performance of the alloys; Effect of composition and heat treatment on the microstructures of the alloys; Correlation between the detailed microstructure and magnetostrictive properties.

We investigate how the magnetic state influences the interaction of Cr substitutional impurities with ½⟨111⟩ screw dislocations in bcc Fe via density functional theory (DFT). We compare the paramagnetic state, modeled with a non-collinear disordered local moment (DLM) model, with the ferromagnetic state. In a previous work [Casillas-Trujillo et al., Phys. Rev. B 102, 094420 (2020)], we have shown that the magnetic moment and atomic volume landscape around screw dislocations in the paramagnetic state of iron are substantially different from that in the ferromagnetic state. Such a difference can have an impact in the formation energies of substitutional impurities, in particular, magnetic solutes. We investigate the formation energies of Cr solutes as a function of position with respect to the screw dislocation core, the interaction of Cr atoms along the dislocation line, and the segregation profile of Cr with respect to the dislocation in paramagnetic and ferromagnetic bcc iron. Our results suggest that with increasing temperature and connected entropic effects, Cr atoms gradually increase their occupation of dislocation sites, close to twice the amount of Cr in the DLM case than in the ferromagnetic case, with possible relevance to understand mechanical properties at elevated temperatures in low-Cr ferritic steels in use as structural materials in nuclear energy applications. [ABSTRACT FROM AUTHOR]

10.1063/5.0085292 85 R. Knepper, S. Rupper, S. DeJong, M. P. Marquez, D. E. Kittell, R. L. Schmitt, and A. S. Tappan, "Investigating growth to detonation in vapor-deposited hexanitrostilbene and pentaerythritol tetranitrate films using high-throughput methods", J. Appl. Phys. Such investigations can be applied to a wide range of materials such as pure metals,[[23], [25], [27]] steels,[29] other metallic alloys[[15], [30], [32]] including additively manufactured alloys,[[34]] ceramics,[36] polymers,[37] energetic materials,[38] or nanoporous materials.[[39]] B. Equation of state and phase transitions under shock compression I In situ i x-ray diffraction (XRD) has been used to investigate the occurrence and nature of phase transitions upon shock compression at large laser facilities, synchrotron, and x-ray free electron lasers. 10.1063/5.0076869 52 P. E. Specht, W. Reinhart, and C. Scott Alexander, "Measurement of the Hugoniot and shock-induced phase transition stress in wrought 17-4 PH H1025 stainless steel", J. Appl. Phys. R. Armstrong, H. B. Radousky, R. A. Austin, O. Tschauner, S. Brown, A. E. Gleason, N. Goldman, E. Granados, P. Grivickas, N. Holtgrewe, M. P. Kroonblawd, H. J. Lee, S. Lobanov, B. Nagler, I. Nam, V. Prakapenka, C. Prescher, E. J. Reed, E. Stavrou, P. Walter, A. F. Goncharov, and J. L. Belof, "Highly ordered graphite (HOPG) to hexagonal diamond (lonsdaleite) phase transition observed on picosecond time scales using ultrafast x-ray diffraction", J. Appl. Phys. [Extracted from the article]

In situ x-ray photoemission spectroscopy is used to study the deuterium and hydrogen oxygen etching effect in nitrogen-implanted iron alloys. A suitable deuterium-nitrogen mixture can increase the surface original steel hardness up to ∼40%. In similar conditions, hydrogen-nitrogen mixtures improves the hardness by ∼10%. On deuteration, the main change is the reduction of the zero-point energy of the hydrides bond. Due to this, the lower scission energy of hydrogen-metal bonds as compared with deuterium-metal bonds determines the favorable effect of deuterium on the nitriding process. [ABSTRACT FROM AUTHOR]

The giant magnetoelectric effect of laminated composites of rare-earth-iron alloys (Terfenol-D) and lead–zirconate–titanate (PZT) is calculated by using the finite element method. Our simulations show that the magnetoelectric response of the laminated Terfenol-D/PZT composites is strongly dependent on interfacial bonding between Terfenol-D and PZT layers. The giant magnetoelectric effect and its dependence on the interfacial bonding predicted by the finite element method for the composites are in good agreement with predictions by a recent analytical method and recent experimental observations available. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effects of stress relief on the magnetic characteristics of Fe-based metallic glass (MG) ribbons are investigated under external stress through various annealing treatments. We found that long-time annealing treatments benefit for making softer magnetic MGs under applied bending stress. We show that the irreversible domain wall movement region and the irreversible domain wall rotation region in the M-H curve represent the stress relief, which can be well reflected by the demagnified magnetic anisotropy. The magnetic coercivity and effective permeability variations in the lower frequency regime also represent the stress relief state. These observations have implications for understanding the relationship between the stress relief, microstructure change, and magnetic softness in magnetic MGs and might be helpful for the performance improvement of the ferromagnetic glassy materials. [ABSTRACT FROM AUTHOR]

The effect of the divacancy defect on magnetic properties of Fe94V6 alloys was investigated using the first-principles calculations based on density functional theory. The model of Fe28V2 super-lattice for a divacancy in Fe94V6 alloy was established, in comparison with the perfect Fe30V2 super-lattice. For the first time, the effect of the on-site Coulomb repulsion term was considered to correct the underestimation for the bandgap. The magnetism of the Fe, V atoms, and the super-lattice were analyzed by the electron hybridization of the atoms, and the interactions between V and four different neighboring Fe atoms were also investigated. The results show that both Fe28V2 and Fe30V2 super-lattices are ferromagnetic, which is determined mainly by the strong ferromagnetism of Fe 3d electrons, and the hybridizations between Fe 3d electrons and Fe 2p and V 3d electrons account for the weak anti-ferromagnetism. When the Fe divacancy exists, the average magnetic moments of the Fe28V2 super-lattice and Fe atoms inside increase, while that of V atoms decreases due to the change of the Fe-V charges. The variation of the magnetic moments of different neighboring Fe atoms with respect to V atoms depends on the charge transfer and the Fe-V interaction. [ABSTRACT FROM AUTHOR]

Knowledge of the dynamic magnetic susceptibility of patterned films is of great importance for exploring future data-storage applications and microwave devices. Since ferromagnetic resonance frequency is a function of the geometric parameters of a certain magnetic system, in this work, we investigate by micromagnetic simulations a set of stripe-patterned FeGa films, which have an identical thickness of 10 nm but a varying width in the range of 30–80 nm and a varying length in the range of 200–1000 nm. Fast-Fourier transform analysis of the simulation results for ferromagnetic resonance calculation identifies two distinct resonance peaks, which are assigned to a “bulk” mode and an “edge” mode. The presence of stress-induced anisotropy significantly affects both the two resonant modes. The occupation area of the spreading magnetization near the stripe ends is controllable by a tensile or compressive stress applied along the strip width. Consequently, the dynamic susceptibility of FeGa can be adjusted by an applied stress. [ABSTRACT FROM AUTHOR]

This paper is devoted to an experimental and 3D atomistic study of the influence of loading rate on fracture toughness in dilute Fe–Si alloys and in bcc iron. We analyze new and previous experimental results from fracture tests performed at room temperature on bcc iron–silicon single crystals with edge cracks (1 ¯ 10) [110] (crack plane/crack front). The specimens of single edge notch-type were loaded in tension mode I under different loading rates. The ductile–brittle behavior at the crack front was monitored online via optical microscopy together with external force and prolongation of the specimens. About 30% decrease in fracture toughness was monitored in the new experiment under the highest loading rate. The nanoscopic processes produced by the crack itself were studied at room temperature via 3D molecular dynamics (MD) simulations in bcc iron under equivalent boundary conditions as in experiments to reveal (explain) the sensitivity of the crack to loading rate. For this purpose, this MD study utilizes the self-similar character of linear fracture mechanics. The results show that the emission of blunting dislocations from the crack is the most difficult under the highest loading rate, which leads to the reduced fracture toughness of the atomistic sample. This is in a qualitative agreement with the experimental (macro) results. Moreover, MD indicates that there may be some synergetic (resonant) effect between the loading rate and thermal activation that promotes dislocation emission. [ABSTRACT FROM AUTHOR]

In this work, in order to develop new Fe-based amorphous alloys with room-temperature magnetocaloric effect and good magnetocaloric performance, high iron content Fe-based amorphous alloys were designed, and their Curie temperatures were adjusted to room temperature through the addition of Mo. As a result, a new Fe83Mo6Si1B7P2C1 amorphous alloy with room-temperature magnetocaloric effect was successfully prepared by melt-spinning technique, and it has the Curie temperature of 300 K, the maximum isothermal magnetic entropy change of 2.74 J kg−1 K−1 and the refrigerant capacity of 485.2 J kg−1 under an applied magnetic field of 5 T. Combining with the advantages of excellent magnetocaloric properties, negligible hysteresis loss, and low material cost, the present Fe83Mo6Si1B7P2C1 amorphous alloy should be a promising candidate as room-temperature magnetic refrigerants. [ABSTRACT FROM AUTHOR]

The interplay between chemical inhomogeneities and magnetic properties in iron alloys is a subtle question that affects several nanoalloys with potential technological and biomedical applications. Herein below, we focus on the FCC palladium rich-iron nanoparticle system, specifically in three samples that reflect the key influence of synthesis conditions. Magnetic measurements as a function of field and temperature have allowed detecting the onset of anomalous relaxation phenomena of the magnetization due to the strong weakening of the exchange coupling in nanoparticles prepared at low temperatures. Such effects are triggered by the lack of a good inter-diffusion of atomic species during core growth and directly affect the magnetic anisotropy. Electron Magnetic Resonance spectroscopy has confirmed that iron clustering leads to a gradual transition from a superparamagnetic state at low temperatures to a nearly paramagnetic behaviour at high temperatures. The measurements of the g-factor and the average magnetic moment per Fe atom do not account for a significant polarization in Pd atoms. [ABSTRACT FROM AUTHOR]

CoCrFeMnNi is a prototype fcc-structured high-entropy alloy. Numerous efforts have been paid to strengthen CoCrFeMnNi, by replacing Mn with other elements for an enhancement of the solid solution strengthening. 4d transition metals, including Zr, Nb, and Mo, are of interest for this purpose, since they have much larger atomic radii than that of Mn. However, Nb and Mo are known to have a low solid solubility in fcc-structured CoCrFeNi. Compared to Nb and Mo, Zr has an even larger atomic radius. The solid solubility of Zr in fcc-structured CoCrFeNi was investigated in this work, combining both experimental studies and thermodynamic calculations. In addition, based on previous results and new results obtained here, methods to predict the solid solubility in CoCrFeNiMx (M=Zr, Nb, and Mo) alloys were developed. Particularly, the average d-orbital energy level, Md, was re-evaluated in the present work, for an improved predictability of the solid solubility in fcc-structured high entropy alloys containing 4d transition metals. [ABSTRACT FROM AUTHOR]

Focuses on a study which examined the effects of aluminum and silicon additions on the frequency response of highly magnetostrictive terbium-dysprosium-iron alloys. Information on the piezomagnetic response of highly magnetostrictive rare earth-iron alloys; Methodology of the study; Results and discussion.

In this work, the feasibility condition of Powder-In-Tube (PIT) processed wires of Fe(Se,Te) superconductor has been investigated. We faced several technical issues that are extensively described and discussed. In particular, we tested different metals and alloys as external sheaths (Cu, Ag, Nb, Ta, Ni, Fe, cupronickel, brass) concluding that the only sheath that does not affect substantially the Fe(Se,Te) phase is Fe. On the other hand, Fe sheath introduces excess iron in the Fe(Se,Te) phase, which affects the superconducting properties; we investigated the effects of the thermal treatments and of the powder composition in order to avoid it. The maximum Jc value obtained in our samples is 4 × 102A/cm2, comparable to other published values of PIT conductors of the 11 family. We conclude that the fabrication of Fe(Se,Te) wires by PIT method is quite challenging and other approaches should be developed. [ABSTRACT FROM AUTHOR]

We compare ferromagnetic resonance measurements of Permalloy Ni80Fe20 (Py) films sputtered onto Cu(111) films with and without a graphene (Gr) interlayer grown by chemical vapor deposition before Py deposition. A two-angle sputtering method ensured that neither Gr nor Py was degraded by the sample preparation process. We find the expected damping enhancement from spin pumping for the Py/Cu case and no detectable enhancement for the Py/Gr/Cu case. Since damping is sensitive to effects other than spin pumping, we used magnetometry to verify that differences in Py magnetostatic properties are not responsible for the difference in damping. We attribute the suppression of spin pumping in Py/Gr/Cu to the large contact resistance of the Gr/Cu interface. [ABSTRACT FROM AUTHOR]

Iron is a well-utilized material in structural and magnetic applications. This does not mean, however, that it is well understood, especially in the field of magnetostriction. In particular, the rhombohedral magnetostriction of iron, λ111, is anomalous in two respects: it is negative in sign, in disagreement with the prediction of first principles theory, and its magnitude decreases with increasing temperature much too rapidly to be explained by a power law dependence on magnetization. These behaviors could arise from the location of the Fermi level, which leaves a small region of the majority 3d t2g states unfilled, possibly favoring small internal displacements that split these states. If this view is correct, adding small amounts of Co to Fe fills some of these states, and the value of λ111 should increase toward a positive value, as predicted for perfect bcc Fe. We have measured the magnetostriction coefficients (λ111 and λ100) of pure Fe, Fe97Co3, and Fe94Co6 single crystals from 77K to 450 K. Resonant ultrasound spectroscopy has been used to check for anomalies in the associated elastic constants, c44 and c'. The additional electrons provided by the cobalt atoms indeed produced positive contributions to both magnetostriction constants, λ111 and λ100, exhibiting an increase of 2.8 × 10-6 per at.% Co for λ111 and 3.8×10-6 per at.% Co for λ100. [ABSTRACT FROM AUTHOR]

The microstructure that develops under low temperature irradiation in ferritic alloys is dominated by a high density of small (2-5 nm) defects. These defects have been widely observed to move via occasional discrete hops during in situ thin film irradiation experiments. Cluster dynamics models are used to describe the formation of these defects as an aggregation process of smaller clusters created as primary damage. Multiple assumptions regarding the mobility of these damage features are tested in the models, both with and without explicit consideration of such irradiation induced hops. Comparison with experimental data regarding the density of these defects demonstrates the importance of including such motions in a valid model. In particular, discrete hops inform the limited dependence of defect density on irradiation temperature observed in experiments, which the model was otherwise incapable of producing. [ABSTRACT FROM AUTHOR]

The black dot damage features which develop in iron at low temperatures exhibit significant mobility during in situ irradiation experiments via a series of discrete, intermittent, long range hops. By incorporating this mobility into cluster dynamics models, the temperature dependence of such damage structures can be explained with a surprising degree of accuracy. Such motion, however, is one dimensional in nature. This aspect of the physics has not been fully considered in prior models. This article describes one dimensional reaction kinetics in the context of cluster dynamics and applies them to the black dot problem. This allows both a more detailed description of the mechanisms by which defects execute irradiation-induced hops while allowing a full examination of the importance of kinetic assumptions in accurately assessing the development of this irradiation microstructure. Results are presented to demonstrate whether one dimensional diffusion alters the dependence of the defect population on factors such as temperature and defect hop length. Finally, the size of interstitial loops that develop is shown to depend on the extent of the reaction volumes between interstitial clusters, as well as the dimensionality of these interactions. [ABSTRACT FROM AUTHOR]

The one-dimensional charge density distribution along an electrically biased Fe atom probe needle is measured using a model-independent approach based on off-axis electron holography in the transmission electron microscope. Both the mean inner potential and the magnetic contribution to the phase shift are subtracted by taking differences between electron-optical phase images recorded with different voltages applied to the needle. The measured one-dimensional charge density distribution along the needle is compared with a similar result obtained using model-based fitting of the phase shift surrounding the needle. On the assumption of cylindrical symmetry, it is then used to infer the three-dimensional electric field and electrostatic potential around the needle with ~10 nm spatial resolution, without needing to consider either the influence of the perturbed reference wave or the extension of the projected potential outside the field of view of the electron hologram. The present study illustrates how a model-independent approach can be used to measure local variations in charge density in a material using electron holography in the presence of additional contributions to the phase, such as those arising from changes in mean inner potential and specimen thickness. [ABSTRACT FROM AUTHOR]

An outstanding challenge in developing a complete equation of state for materials at elevated pressure and temperature is a robust method of determining the bulk temperature state under dynamic conditions. In metals, the determination of bulk temperature states by optical pyrometry is complicated by the small optical depth and thermal conduction effects. These effects lead to observed temperatures differing by 20% or more from the bulk temperature state. In this work, we show the presence of thermal conduction effects in temperature measurements of tin and iron coatings during dynamic compression experiments. We demonstrate that tin, in contrast to iron, coatings can fail to converge to a bulk temperature source over the time scale of the experiment, requiring the experimenter to modify assumptions, design, or analysis. This work bounds thermal transport at shocked conditions. [ABSTRACT FROM AUTHOR]

The Fe4+/3+ donor level is experimentally determined to be 0.70 eV (±0.05 eV) above the valence band maximum in β-Ga2O3. Electron paramagnetic resonance (EPR) is used to monitor Fe3+ ions that are unintentionally present in an Mg-doped β-Ga2O3 crystal (with a low Fermi level). For temperatures near 255 K, exposure to 325 nm laser light converts a portion of the Fe3+ ions to Fe4+ and Fe2+ ions and, at the same time, forms neutral magnesium acceptors (Mg Ga 0) and neutral Ir donors (Ir3+). After removing the light, the intensity of the Fe3+ EPR spectrum has a significant additional decrease as holes thermally released to the valence band from rapidly decaying neutral Mg acceptors are trapped at Fe3+ ions and form even more Fe4+ ions. This demonstrates that the Mg0/− acceptor level, near 0.65 eV, is closer to the valence band than the Fe4+/3+ level. Following the fast initial post-light decrease, the Fe3+ spectrum then slowly recovers as Fe4+ ions are destroyed by electrons thermally excited from the valence band. An activation energy for the thermal decay of the Fe4+ donors, and thus a value for the Fe4+/3+ level, is obtained from the analysis of five Fe3+ isothermal recovery curves taken from the Mg-doped crystal between 250 and 270 K. A first-order kinetics model is used, as minimal retrapping is observed. In separate experiments, EPR shows that Fe4+ ions are also produced in an Fe-doped β-Ga2O3 crystal (without Mg acceptors) during exposures to laser light at temperatures near 255 K. [ABSTRACT FROM AUTHOR]

The AC susceptibilities of Fe1-xCoxSi (0.1≤x ≤0.7) alloys were measured and compared with that of MnSi. The range of skyrmion phase in the H-T phase space was enlarged and moved to higher temperatures when approximately 1/3 of the Fe was substituted with Co. Comparing with MnSi, the skyrmion phase of Fe0.7Co0.3Si was found thermodynamically more stable under a much lower and narrower critical field near 280 ± 50 Oe. The stability range in the H-T phase space and the free energy reduction ΔE (as a function of the applied magnetic field) for both the Fe0.7Co0.3Si and MnSi were compared. [ABSTRACT FROM AUTHOR]

In structurally ordered magnetic thin films, the Curie temperature (TC) of ferromagnetic films depends on the exchange integral of the short range ordered neighboring atoms. The exchange integral may be adjusted by controlling the elemental substitutional concentration at the lattice site of interest. We show how to control the TC in high anisotropy L10 Fe50 Pt50 magnetic thin films by substituting Rh into the Pt site. Rh substitution in L10 FePt modified the local atomic environment and the corresponding electronic properties, while retaining the ordered L10 phase. The analysis of extended x-ray Absorption Fine Structure spectra shows that Rh uniformly substitutes for Pt in L10 FePt. A model of antiferromagnetic defects caused by controlled Rh substitution of the Pt site, reducing the TC, is proposed to interpret this phenomenon and its validity is further examined by ab initio density functional calculations. [ABSTRACT FROM AUTHOR]

The Fe-W system is systematically investigated through a combined use of first-principles calculation, cluster expansion, special quasirandom structures, and experiments. It is revealed that the ferro-magnetic state of BCC Fe-W solid solution has lower heat of formation than its nonmagnetic state within the entire composition range, and intermetallic λ-Fe2Wand μ-Fe7W6 phases are energetically favorable with negative heats of formation. Calculations also show that the Fe-W solid solution has much lower coefficient of thermal expansion than its mechanical mixture, and that the descending sequence of temperature-dependent elastic moduli of each Fe-W solid solution is E>G>B. Moreover, magnetic state should have an important effect on mechanical properties of Fe-W phases, and electronic structures can provide a deeper understanding of various properties of Fe-W. The derived results agree well with experimental observations, and can clarify two experimental controversies regarding structural stability and magnetic property of Fe-W phases in the literature. [ABSTRACT FROM AUTHOR]

Focuses on polycrystalline iron-boron-silicon alloys with nanoscale grain sizes prepared by the crystallization method. Use of positron lifetime and Doppler-broadened line-shape measurements; Kinds of defects in the interfaces of the nanocrystalline iron alloys; Relationship between the structure-sensitive properties, grain sizes and crystalline states.

Equiatomic FeAu nanoclusters were produced by inert-gas condensation and embedded in a W matrix. Transmission electron microscopy investigation shows that three kinds of clusters are present: mono-crystalline, polycrystalline, and partially crystalline clusters. It demonstrates that during their formation, the structure of nanoclusters evolves from an amorphous to a crystalline structure. Crystallisation starts at the surface of nanoclusters and currently leads to the formation of poly-crystalline nanoclusters in the end. Most of the investigated objects consist in a duplex amorphous core-crystalline shell structure. Their magnetic properties were investigated by magnetization measurements as a function of magnetic field (hysteresis loops) or temperature (ZFC/FC curves). They show evidence at low temperatures of ferromagnetic and antiferromagnetic states, and ordering as well as superparamagnetism or spin-glass behaviour. Measurements performed after cooling the samples under various applied fields reveal the occurrence of exchange-spring phenomenon, related to the presence of the W matrix, through RKKY coupling between ferromagnetic and antiferromagnetic nanoclusters. [ABSTRACT FROM AUTHOR]

The electronic thermal conductivity of iron at the Earth's core conditions is an extremely important physical property in the geophysics field. However, the exact value of electronic thermal conductivity of iron under extreme pressure and temperature still remains poorly known both experimentally and theoretically. A few recent experimental studies measured the value of the electronic thermal conductivity directly and some theoretical works have predicted the electronic thermal conductivity of iron at the Earth's core conditions based on the Kubo-Greenwood method. However, these results differ largely with each other. A very recent research has confirmed that for iron at the Earth's core conditions, the strength of electron-electron scattering could be comparable to that for electron-phonon scattering, meaning that the electron-electron scattering should also be considered when evaluating the electronic thermal conductivity in the Earth's core situations. Here, by utilizing a newly developed methodology based on direct non-equilibrium ab initio molecular dynamics simulation coupled with the concept of electrostatic potential oscillation, we predict the electronic thermal conductivity of iron in h.c.p. phase. Our methodology inherently includes the electron-phonon and electron-electron interactions under extreme conditions. Our results are comparable to the previous theoretical and experimental studies. More importantly, our methodology provides a new physical picture to describe the heat transfer process in ϵ -iron at the Earth's core conditions from the electrostatic potential oscillation point of view and offers a new approach to study the thermal transport property of pure metals in the planet's cores with different temperature and pressure. [ABSTRACT FROM AUTHOR]

The effects of Si element on structural and magnetic properties of Fe-rich Fe85.2B10-XP4Cu0.8SiX (x = 0-2.5 at. %) alloys were investigated. Our results show that addition of Si significantly reduces the activation energy for nucleation of α-Fe and increases the activation energy for grain growth. As a result, it is much easier to obtain a finer and uniform nanogranular structure (grain size ∼18 nm) made from densely packed α-Fe grains after annealing in the case of Si-containing alloys (Fe-B-P-Si-Cu) in comparison to Si-free alloys (Fe-B-P-Cu). However, addition of Si on the expense of B reduces the amorphous forming ability of the alloy, which results in lower reproducibility. The reproducibility improves significantly in Si-free alloy, but the structure of the alloy is relatively unstable on annealing, which means more strict annealing treatment is required. After optimum annealing treatment, Si-free alloys (Hc ∼ 6 A/m, Js ∼ 1.83 T) show superior soft magnetic properties than the Si-containing alloys (Hc ∼ 10 A/m, Js ∼ 1.78 T). Results show that the excellent soft magnetic cores can be obtained only if the extra heat generated on nano-crystallization of as-quenched amorphous phase can be released efficiently. The toroidal core of Si-free alloy (core-loss, W ∼ 0.58 W/kg at ∼1.7 T, 50 Hz) exhibits lower magnetic core loss than the Si containing alloys (core-loss, W ∼ 1.51 W/kg at ∼1.7 T, 50 Hz). [ABSTRACT FROM AUTHOR]

This paper presents a comparative study on the tetragonal magnetostriction constant, λγ,2, [ = (3/2)λ100] and magnetoelastic coupling, b1, of binary Fe100-xZx (0 < x < 35, Z = Al, Ga, Ge, and Si) and ternary Fe-Ga-Al and Fe-Ga-Ge alloys. The quantities are corrected for magnetostrains due to sample geometry (the magnetostrictive form effect). Recently published elastic constant data along with magnetization measurements at both room temperature and 77 K make these corrections possible. The form effect correction lowers the magnetostriction by ∼10 ppm for high-modulus alloys and by as much as 30 ppm for low-modulus alloys. The elastic constants are also used to determine the values of the magnetoelastic coupling constant, b1. With the new magnetostriction data on the Fe-Al-Ga alloy, it is possible to show how the double peak magnetostriction feature of the binary Fe-Ga alloy flows into the single peak binary Fe-Al alloy. The corrected magnetostriction and magnetoelastic coupling data for the various alloys are also compared using the electron-per-atom ratio, e/a, as the common variable. The Hume-Rothery rules link the e/a ratio to the regions of phase stability, which appear to be intimately related to the magnetostriction versus the solute concentration curve in these alloys. Using e/a as the abscissa tends to align the peaks in the magnetostriction and magnetoelastic coupling for the Fe-Ga, Fe-Ge, Fe-Al, Fe-Ga-Al, and Fe-Ga-Ge alloys, but not for the Fe-Si alloys for which the larger atomic size difference may play a greater role in phase stabilization. Corrections for the form effect are also presented for the rhombohedral magnetostriction, λ&eh;,2, and the magnetoelastic coupling, b2, of Fe100-xGax (0 < x < 35) alloys. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of 20-nm-thick FexPt100-x films that were processed by 20 ms flash-lamp annealing were investigated. A maximum in coercivity of (10.4 ± 0.5) kOe was achieved for a composition of Fe53Pt47, which shows also a high degree of L10 chemical order. A variation of the chemical composition toward either higher or lower Fe content leads to a lowering of the coercivity, which can be attributed to a reduction in L10 ordered volume fraction. Thus, in the millisecond time regime, the fastest ordering transformation occurs for slightly Fe-rich FePt films. [ABSTRACT FROM AUTHOR]

We report here a systematic study of the magnon-drag induced thermoelectric properties of Fe-rich, Fe-Co body-centered-cubic alloys. The sign of the low temperature behavior of thermopower is explained well by the hydrodynamic theory for magnon-drag, informed by density functional theory calculations of the ground state of Fe-Co alloys. The high-temperature thermopower of some of the alloys, and indeed that of elemental iron, changes the sign, as previously observed. We propose a mechanism to elucidate this hitherto unexplained observation. Further, the power factor of Fe72Co28 peaks around 35 μV/cm K2 at 500 K, comparable to the standard thermoelectric material Bi2Te3. Because of their high thermoelectric power factor, Fe-Co alloys are potential candidate thermoelectric metals for active cooling of electronic devices. [ABSTRACT FROM AUTHOR]

Hyperfine parameters of iron nuclei such as isomer shift, quadrupole splitting, and asymmetry parameter are calculated for β -FeSi 2 with and without vacancies, using density functional theory. They are applied, in combination with parameters of α -FeSi 2 obtained earlier, for analyzing Mössbauer and X-ray diffraction experiments on the mechanical alloying of silicon with iron in the range of 1–33 at. % of Fe. Such an approach allows more detailed and precise information to be obtained on the structure of Fe–Si samples. In particular, the fraction of vacancies in α - and β -FeSi 2 is estimated, and the mechanism of formation of these phases and their transformation into each other is discussed. A new model is developed for analyzing experiments on hyperfine interaction, such as Mössbauer spectroscopy, time-differential perturbed-angular correlation, and the like, for Fe–Si systems with a high Si content. [ABSTRACT FROM AUTHOR]

The interaction of plasticity and martensitic transformation in iron bicrystals under shock has been investigated via nonequilibrium molecular-dynamic simulations with our modified analytic embedded-atom model potential. Our results show that grain boundaries (GBs) can change the kinetics of α → ɛ martensitic transformations. The condition that GBs trigger strain induced transformation (SIT) is revealed, that is, the local structure of GBs can be converted to a hexagonal close packing (HCP) lattice with a lower potential barrier than the BCC → HCP transformation (stress assist transformation, SAT) because the driving energy of transition can be partly provided by the energy of GBs. It can explain why the threshold of the phase transition can be greatly reduced in samples containing some types of GBs. The threshold of SIT is lower than that of SAT, which agrees well with experimental results. Then, the nucleation kinetics of phase transition induced by dislocations are described. The propagation of dislocation provides the driving force for the nucleation of the phase transition. The dislocations can be directly emitted from the GBs under shock, which provides a new view that the phase transition is not always preceded by dislocations near GBs. In addition, dislocations can be induced by pre-existing dislocations under shock, which makes it understandable that GBs can emit dislocations. Our findings have an important significance for experimental studies and macroscopic and mesoscopic scale simulations regarding iron martensitic transformation. [ABSTRACT FROM AUTHOR]

Employing the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, we calculated the total energy and local magnetic moments of paramagnetic Fe-Cr-M (M = Cr, Mn, Fe, Co, Ni) alloys along the tetragonal distortion (Bain) path connecting the body centered cubic (bcc) and the face centered cubic (fcc) structures. The paramagnetic phase is modeled by the disordered local magnetic moment scheme. For all alloys, the local magnetic moments on Fe atoms decrease from the maximum value corresponding to the bcc phase toward the minimum value realized for the fcc phase. Cobalt atoms have non-vanishing local magnetic moments only for tetragonal lattices with c/a < 1.30, whereas the local magnetic moments of Mn show weak crystal structure dependence. We find that Cr stabilizes the bcc lattice and increases the energy barrier as going from the bcc toward the fcc phase. Both Co and Ni favor the fcc lattice and decrease the energy barrier relative to the bcc phase. On the other hand, the tetragonal distortion around the fcc phase is facilitated by Cr and to a somewhat lesser extent also by Ni, but strongly impeded by Co. Manganese has negligible effect on the structural energy difference as well as on the energy barrier along the Bain path. Our findings on the alloying induced softening or hardening of Fe-Cr based alloys against tetragonal distortions are important for understanding the interstitial driven martensitic transformations in alloy steels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

From measurements of the current-perpendicular-to-plane magnetoresistance of magnetic multilayers and exchange-biased spin-valves combining the ferromagnetic (F) alloys Co50Fe50 and Co70Fe30 with the nonmagnetic metal Cu, we extract values of the bulk scattering asymmetry, βF, the spin-diffusion length, lsfF, the interface scattering asymmetry, γF/Cu, and twice the enhanced specific resistance, 2ARF/Cu*. The parameters of the two alloys lie within mutual uncertainties of each other. The values of βF∼0.88 are unusually large, those of lsfF∼10 nm are moderate and consistent with values for other F-alloys, and those of 2ARF/Cu*∼0.6 fΩ m2 and γF/Cu∼0.6 are both less than those for Co/Cu. We do not need to include any spin-flipping at the F/Cu interfaces to fit our data. [ABSTRACT FROM AUTHOR]

Large auxetic properties of iron-gallium and iron-aluminum alloys have been investigated with both theoretical and experimental approaches. Tensile tests of single-crystal iron-gallium alloys with compositions of 12%–25% gallium were conducted to determine the composition dependent values of the Poisson’s ratio. Systematic density functional calculations revealed a simple correlation between the Poisson’s ratio and tetragonal shear modulus. We attribute the auxetic properties of these intermetallic alloys to the drastic reduction in C′ with the presence of metalloid atoms in the DO3-type structures. [ABSTRACT FROM AUTHOR]

A series of ≈12 nm thick FePt thin films deposited onto glass substrates have been annealed with multiple 1064 nm wavelength laser pulses. The fluence was varied using pulse widths of 10.0, 5.0, and 2.5 ms. The peak temperature for each individual pulse was kept near 700 °C. The A1 to L10 phase transformation was confirmed by x-ray diffraction. A single pulse was not sufficient to obtain a fully ordered state. A maximum order parameter of 0.89 and coercivity of 10.6 kOe was obtained after 5×10 ms pulses. This particular annealed film showed the greatest amount of grain growth with a mean size of 55.1 nm. This grain size is 20% smaller than that of a furnace annealed sample which was annealed for 60 s and yielded an approximately equivalent order parameter. Similar order parameters, grain sizes, and coercivity values were observed for films that had equivalent total annealing times regardless of pulse widths. [ABSTRACT FROM AUTHOR]

The effect of carbon addition on the magnetostriction of Fe–Ga and Fe–Al alloys was investigated and is summarized in this study. It was found that the addition of carbon generally increased the magnetostriction over binary alloys of Fe–Ga and Fe–Al systems. The formation of carbide in the Fe–Ga–C alloys with a composition near D03 phase region decreased the magnetostriction drastically. Fe–Al–C and Fe–Ga–C alloys responded differently to thermal treatments; the magnetostriction in the quenched Fe–Al–C alloys is equal to or slightly lower than that of the slow cooled as is observed in binary Fe–Al alloy; in contrast, the magnetostriction is generally higher in quenched Fe–Ga–C alloys than slow cooled condition, consistent with the behavior of binary alloys of Fe–Ga. A significant increase in magnetostriction between 25% and 165% depending on the phase region in Fe–Ga–C alloys by quenching was observed in the A2+D03 two-phase region and D03 single phase region. [ABSTRACT FROM AUTHOR]

The magnetocaloric response of mechanically alloyed Fe75Nb10B15 powders was studied for samples with different amorphous and nanocrystal volume fractions. Thermomagnetic properties scale following a Ω3 law for different milling processes, where Ω is the milling frequency. Curie temperature of the amorphous phase increases as the amorphous fraction increases due to its progressive enrichment in B. The peak magnetic entropy change, |ΔSMpk|, as well as the refrigerant capacity increase with increasing amorphous fraction. The field dependence of |ΔSMpk| can be explained by the multiphase character of the studied samples. [ABSTRACT FROM AUTHOR]

In situ stress measurements during sputtering deposition of amorphous Fe80B20 films are used to control their stress and magnetoelastic properties. The substrate curvature induced by the deposited film is measured optically during growth and quantitatively related to the deposition induced accumulated stress. The resulting magnetic properties are later correlated with the measured stress for a wide range of sputtering pressures [(2-25)×10-3 mbar]. A significant tensile stress develops at the film-substrate interface during the early growth stages (initial 2–3 nm). At a critical thickness, a transition is observed from tensile to compressive stress, which is associated with amorphous island coalescence. By further increasing the thickness, a compressive stress follows, which is related to the local distortion induced by the ion peening effect. The Monte Carlo simulations of the sputtering process describe quantitatively the experimental results as a function of the Ar pressure and target bias voltage. [ABSTRACT FROM AUTHOR]

Mechanical alloying of a number of blended elemental powders of Fe-based alloy systems containing four or five components was undertaken to determine if amorphous phases could be produced and also to compare the glass-forming ability achieved by mechanical alloying and that obtained by solidification-processing methods. Amorphous phase formation was achieved in all the alloy systems investigated, the time for the amorphous phase formation being a function of the glass-forming ability of the alloy system investigated. However, in some alloy systems it was noted that on milling, beyond the time required for the formation of the amorphous phase, the amorphous phase started to crystallize, a phenomenon designated as mechanical crystallization. The present paper specifically discusses the results of mechanical crystallization obtained in the Fe42Ge28Zr10B20 and Fe42Ni28Zr10C10B10 alloy systems as representatives of the typical quaternary and quinary (five-component) systems, respectively. In the case of the quaternary system, mechanical crystallization led to the formation of a supersaturated solid solution of all the solute elements in Fe, while in the quinary system, a mixture of the solid solution and intermetallic phases has formed. The possible reasons for mechanical crystallization and the reasons for the differences in the behavior of the quaternary and quinary systems are discussed. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry is used to investigate the A1 to L10 ordering transformation in binary FePt films with compositions in the range of 39.3-55.3 at. % Pt and ternary FePt-based films with additions of Cu up to 20 at. % and Ni up to 25 at. % for a range of Fe/Pt ratios. For FePt and FeCuPt, these are extensions of previously studied ranges [K. Barmak, J. Kim, D. C. Berry, W. N. Hanani, K. Wierman, E. B. Svedberg, and J. K. Howard, J. Appl. Phys. 97, 024902 (2005); D. C. Berry, J. Kim, K. Barmak, K. Wierman, E. B. Svedberg, and J. K. Howard, Scr. Mater. 53, 423 (2005)]. Parameters including the A1 and L10 phase Curie temperatures, the kinetic ordering temperature, the activation energy, and the transformation enthalpy are reported. For FePt, the L10 Curie temperature reaches a maximum of 457 °C near 45 at. % Pt. In contrast, the A1 Curie temperature has an essentially constant value of 300 °C across the full composition. Both the kinetic ordering temperature and activation energy show a minimum near 46 at. % Pt, while the magnitude of the transformation enthalpy has its maximum near 50 at. % Pt. Ni additions to FePt in general lower the L10 Curie temperature, but they increase the A1 Curie temperature. The kinetic ordering temperature and the activation energy increase for all Ni additions, whereas the transformation enthalpy decreases measurably only for Ni additions over ∼10 at. %. Cu additions to FePt act as magnetic diluents regarding both the A1 and L10 phase Curie temperatures, with increased Cu content resulting in decreased Curie temperature. Conversely, Cu additions have no significant effect on the kinetic ordering temperature, activation energy, or transformation enthalpy when compared to equivalent binary alloys. The relevance of our findings to alloy development for ultrahigh density magnetic recording media is discussed, with specific focus on the potential for heat-assisted magnetic recording. [ABSTRACT FROM AUTHOR]

The effect of strain rate on mechanical properties at room temperature (RT) and a cryogenic temperature (77 K) was studied in a nanocrystalline Ni–20%Fe alloy (grain size: 22 nm). The activation volume, strain rate sensitivity, strain hardening rate, and microstructural changes were also characterized. The results show that this nanocrystalline alloy has a combination of high strength and large plastic strain at both temperatures. At 77 K, the strength increased dramatically without a loss in the plasticity. Calculations demonstrate that the effect of temperature on yield strength, activation volume, and strain rate sensitivity is strongly dependent on the grain size. The high strain rate sensitivity and strong yield strength dependence on temperature are due to small activation volumes at fine grain sizes. In addition, at 77 K, both the activation volume and strain rate sensitivity exponent decreased significantly. The effect of temperature on the strain hardening capability in this nanograined alloy is opposite to what was observed for the large-grained metals. Comprehensive analysis suggests that the deformation at 20 nm is still dominated by dislocations. However, the dislocation generation models may be different at RT and 77 K. [ABSTRACT FROM AUTHOR]

Linear and volume magnetostrictions were investigated in the as-cast Fe81Ga19 and Ge doped Fe81(Ga1-xGex)19 (x=0.1, 0.2, and 0.3) alloys by measuring the change in length along the three-dimensional directions of the samples. For as-cast Fe81Ga19 alloy, when the applied field was lower than about 0.3 T, the linear magnetostriction was positive along the direction of the field, but became negative in another two orthogonal directions normal to the applied field. Volume expansion was observed along all the three directions at the applied field over 0.3 T. Due to the contribution of the volume expansion, namely, volume magnetostriction, the longitudinal magnetostriction increased from 27 ppm at 0.3 T to 47 ppm at 2.0 T. The saturation of volume magnetostriction was absent at 2 T and should be higher with further increasing field. Not only the linear magnetostriction but also the volume magnetostriction can be drastically enhanced by doping Ga in Fe. The same phenomena were observed in Fe81(Ga1-xGex)19 alloys. The as-cast Fe81Ga19 alloy exhibits mainly a disordered bcc A2 phase, and the Ge doped Fe81Ga19 alloys keep the A2 structure with a smaller lattice constant. [ABSTRACT FROM AUTHOR]

Microstructure and magnetic properties of interfacially disordered FePt nanoparticles with a diameter of about 10 nm were investigated. Sputter deposition of amorphous Al2O3 overlayer caused the disordering of L10-FePt particles at the interface. The assembly of these partially disordered FePt nanoparticles is equivalent to the composite medium consisting of the exchange coupled soft and hard layers. Coercivity Hc of the interfacially disordered FePt nanoparticles significantly decreased with increasing thickness of the disordered layer. Comparison with theoretical calculations has shown that this reduction of Hc is attributed to the so-called spin flop state during the magnetization reversal. The interfacial disordering method has been demonstrated to be a promising technique for fabricating FePt-based soft/hard stacked composite media. [ABSTRACT FROM AUTHOR]

We present a quantitative, systematic study of the effect of magnetostriction on the dynamical properties in NiFe alloys. Both the ferromagnetic resonance frequency and the damping times are correlated to the magnetostriction. In addition, we find that the Gilbert damping parameter varies by more than 100% over the range of Ni percentage tested (61.9%–86.7%). [ABSTRACT FROM AUTHOR]

Chemically ordered, self-assembled FePt nanoparticle arrays with high magnetic anisotropy are considered as a candidate medium for data storage beyond 1 Tbit/in². We report comprehensive structural and magnetic studies on thin (three-layer) assemblies of polyethylenimine (PEI) and 4 nm Fe58Pt42 nanoparticles using x-ray diffraction, small angle neutron scattering, and magnetometry. We show that prior to annealing FePt nanoparticles in the PEI-FePt assembly consist of a metallic magnetic core surrounded by a weakly magnetic or nonmagnetic shell. High temperature annealing creates the desired L 10 chemical ordering and results in high coercivity FePt nanoparticles. However, we find that the high temperatures necessary to establish full chemical ordering leads to particle sintering and agglomeration. Understanding the magnetic and physical properties of these assemblies allows future research directions to be clarified for nanoparticle arrays as data storage media. [ABSTRACT FROM AUTHOR]

Soft magnetic amorphous and nanocrystalline Fe[sub 81-x]Ni[sub x]Zr[sub 7]B[sub 12] (x = 0-40) alloys with very low coercivity and improved mechanical properties, as compared with the NANOPERM alloys, were prepared by a melt-quenching technique. The nanostructure was formed by annealing amorphous precursors in the temperature range T[sub A] = 440-620 °C. Formation of the nanocrystalline phase was studied by Mössbauer spectroscopy, differential scanning calorimetry, and x-ray diffraction techniques. The composition of the nanocrystalline phase strongly depends on the Ni content in the alloy. For x < 30 the dominating nanocrystalline phase is the bcc Fe, similarly to the NANOPERM alloys. However, the alloy with x=40 behaves in a clearly different way. Annealing of the Fe[sub 41]Ni[sub 40]Zr[sub 7]B[sub 12] alloy at T[sub A] = 520-620 °C causes the formation of the nanograins of magnetically ordered cubic (FeNi)[sub 23]B[sub 6] and FeNi phases, as identified by the Mössbauer and x-ray diffraction measurements. Annealing at temperatures exceeding 590 °C leads to the M&oum;ssbauer spectra at room temperature dominated by a single-line nonmagnetic component. Mössbauer measurements performed at low temperatures reveal a superparamagnetic origin of this spectral component. The superparamagnetic relaxation at the sample surfaces is restricted by the stress induced surface anisotropy related to the crystallization of the amorphous phase as revealed by the conversion electron Mössbauer results. The conversion electron Mössbauer measurements which allowed the comparison of the surface and bulk crystallization of Fe[sub 81-x]Ni[sub x]Zr[sub 7]B[sub 12] alloys show clear differences between the surface and bulk crystallization for all alloy compositions. Unconventional Mössbauer studies utilizing radio frequency (rf) fields provide information on the soft magnetic nature of the alloys by observing the degree of rf-induced collapse of... [ABSTRACT FROM AUTHOR]