Iron Single Crystals Research Articles

Intermetallic formation and interdiffusion in diffusion couples made of uranium and single crystal iron

We studied the interfacial phase formation and diffusion kinetics in uranium–iron diffusion couples. A comparison was made between polycrystalline uranium (U) bonded with polycrystalline iron (FeP) and polycrystalline uranium bonded with single crystalline Fe (FeSC). After thermal annealing at 575 °C, 600 °C, 625 °C and 650 °C, respectively, diffusion and microstructures at the interface were characterized by scanning electron microscopy and transmission electron miscopy. The presence of grain boundaries in iron has a significant influence on interface reactions. In comparison with U–FeP system, interdiffusion coefficients of the U–FeSC system are significantly lower and were governed by much higher activation energies. Integrated interdiffusion coefficients and intrinsic diffusion coefficients were obtained. The intrinsic diffusion coefficients show faster diffusion of iron atoms in both U6Fe and UFe2 intermetallic phases than uranium.

A fluctuation method to calculate the third order elastic constants in crystalline solids

This paper derives exact expressions of the isothermal third order elastic constants (TOE) in crystalline solids in terms of the kinetic and potential energies of the system. These expressions reveal that the TOE constants consist of a Born component and a relaxation component. The Born component is simply the third derivative of the system's potential energy with respect to the deformation, while the relaxation component is related to the non-uniform rearrangements of the atoms when the system is subject to a macroscopic deformation. Further, based on the general expressions derived here, a direct (fluctuation) method of computing the isothermal TOE constants is developed. Numerical examples of using this fluctuation method are given to compute the TOE constants of single crystal iron.

A spin-wave logic gate based on a width-modulated dynamic magnonic crystal

An electric current controlled spin-wave logic gate based on a width-modulated dynamic magnonic crystal is realized. The device utilizes a spin-wave waveguide fabricated from a single-crystal Yttrium Iron Garnet film and two conducting wires attached to the film surface. Application of electric currents to the wires provides a means for dynamic control of the effective geometry of waveguide and results in a suppression of the magnonic band gap. The performance of the magnonic crystal as an AND logic gate is demonstrated.

Low-temperature resistivity, magnetoresistance, and domain-wall resistance of highly pure single- and polycrystalline iron

On a set of 12 bulk and highly pure [residual resistance ratio (RRR) up to 6000] iron single crystals with different crystallographic orientation and on polycrystalline material the ``hidden'' basic resistivity $\ensuremath{\rho}(T,B\ensuremath{\rightarrow}0)$ and magnetoresistive effects (anisotropic magnetoresistance, longitudinal and transverse Lorentz resistance) are quantitatively disentangled. The temperature-dependent basic resistivity for $T\ensuremath{\le}30\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ follows a $\ensuremath{\Delta}\ensuremath{\rho}(T,B\ensuremath{\rightarrow}0)=a{T}^{2}+b{T}^{5}$ law, proving that electron-electron and electron-phonon scattering (with a resistive Debye temperature ${\ensuremath{\Theta}}_{\mathrm{R}}\ensuremath{\cong}450\phantom{\rule{0.28em}{0ex}}\mathrm{K}$) are dominant also in iron, similar to nonferromagnetic transition metals. Here the crystal-orientation dependence of the intrinsic longitudinal magnetoresistance in the single-domain state could be quantitatively evaluated in accordance with the symmetry of the Fermi surface. The transverse magnetoresistance (TMR) turns out to be the sum of the so-called ``two-band conduction term'' and the unboundedly growing TMR term in compensated metals. It is proven that the second term is not restricted to the high-field limit (as usually discussed up to now) but acts down to lowest TMR or ${\ensuremath{\omega}}_{\mathrm{C}}\ensuremath{\tau}$ values. This conclusion is verified by TMR measurements on highly pure molybdenum single crystals (RRR \ensuremath{\cong} 100 000). Supported by Kerr microscopy, a small positive domain wall resistance (DWR) could be isolated from the dominating negative DWR in the multidomain state of iron, resulting in a relation of larger than 5:1 for the electrons to pass a domain wall with spin tracking compared to scattering with spin conservation.

2505 Fundamental study on crystalline structure for development of functional surface

In this paper, functional surface development by controlling crystalline structure on surfaces of materials is suggested. In order to reveal the mechanism of crystalline structure change by Nano Plastic Forming method, plastic deformation characteristics of single crystal pure iron are examined experimentally by means of shearing tests. Stress-strain curves are measured and Critical Resolved Shear Stresses of activating slip systems are calculated based on crystal plasticity theory. Besides shearing tested specimens are annealed and crystalline structure are analyzed by EBSD for study of effects of microscopic plastic deformation and annealing on recrystallization.

Neutron scattering at high temperature and levitation techniques

Studies of the liquid state present an obvious fundamental interest and are also important for technological applications since the molten state is an essential stage in various industrial processes (e.g. glass making, single crystal growing, iron and steel making).Most of the physical properties of a high-temperature liquid are related to its atomic structure. Thus it is important to develop devices to probe the local environment of the atoms in the sample. At very high temperature, it is difficult to use conventional furnaces, which present several problems. In particular, physical contact with the container can contaminate the sample and/or modify its structural properties. Such problems encouraged the development of containerless techniques, which are powerful tools to study high-temperature melts. By eliminating completely any contact between sample and container, it is possible to study the sample with a very high degree of control and to access very high temperatures. An additional advantage of levitation methods is that it is possible to supercool hot liquids down to several hundred of degrees below their equilibrium freezing point, since heterogeneous nucleation processes are suppressed.

Current-controlled giant magnetoimpedance of iron single crystals

Abstract Extended magnetoimpedance measurements on iron single crystals(whiskers) with 〈 100 〉 growth direction were performed at room temperature as a function of the applied longitudinal magnetic field and of the magnitude of the applied current in the low frequency regime. It is observed that there is a current threshold for inducing a giant magnetoimpedance effect. Calculations based on the standard skin effect formalism permit the determination of the effective circumferential permeability of the whiskers. It is found that the effect has its origin in the circumferential magnetic domain structure of the specimen. For comparison, impedance measurements on an iron wire were performed where no current threshold and continuous increase of the effective circumferential permeability is observed.

Effect of crystal orientation on the strengthening of iron micro pillars

Abstract Micro pillar compression testing has been performed on bcc iron single crystals to determine the mechanical properties and deformation mechanisms and their dependency on size and crystal orientation. Slip traces on the surface of post-compressed pillars were scrutinised to determine the operating slip system. The size dependency of the flow curves was investigated and the power law constants, K and n , and the orientation dependency of the resolved shear stresses were determined. The slip trace analysis revealed that the slip follows the { 110 } 〈 111 〉 family of slip systems. The size dependency of the flow stresses follows the power law relation where the power law exponent n is in general between 0.5–0.8 and depend on orientation and the strain. The power law coefficient K increases as a function of strain. The shape is similar for the different loading directions, but varies in magnitude. The shear stress resolved to the ( 1 ¯ 01 ) [ 111 ] slip system shows an orientation dependent relation. Size and strain have little effect on this relation.

Investigation of slip system activity in iron at room temperature by SEM and AFM in-situ tensile and compression tests of iron single crystals

Iron single crystals of wide range of orientations are tested in-situ at room temperature in tension and compression using a Scanning Electron Microscope (SEM) and in tension using an Atomic Force Microscope (AFM). The active slip systems are identified using several and complementary experimental observations and analyses. Firstly, we compare the orientation of slip lines with theoretical traces of the possible dense crystallographic planes (namely {110} and {112}). Secondly, we compare the observed rotations of the sample axes with those resulting theoretically from different slip scenarios. Lastly we compare the shear stress–shear strain curves for the different observed active slip systems. Results confirm that slip is locally of a crystallographic nature and that {112} planes contribute per se to slip in iron. However, planar slip bands parallel to the {112} planes are short and their height is not uniform along the slip bands.

Control of magnetic contrast with nonlinear magneto-plasmonics.

The interaction between surface plasmons (SP) and magnetic behavior has generated great research interest due to its potential for future magneto-optical devices with ultra-high sensitivity and ultra-fast switching. Here we combine two surface sensitive effects: magnetic second-harmonic generation (MSHG) and SP to enhance the detection sensitivity of the surface magnetization in a single-crystal iron film. We show that the MSHG signal can be significantly enhanced by SP in an attenuated total reflection (ATR) condition, and that the magnetic contrast can be varied over a wide range by the angle-of-incidence. Furthermore, the magnetic contrast of transverse and longitudinal MSHG display opposite trends, which originates from the change of relative phase between MSHG components. This new effect enhances the sensing of magnetic switching, which has potential usage in quaternary magnetic storage systems and bio-chemical sensors due to its very high surface sensitivity and simple structure.

Electric-field coupling to spin waves in a centrosymmetric ferrite.

We experimentally demonstrate that the spin-orbit interaction can be utilized for direct electric-field tuning of the propagation of spin waves in a single-crystal yttrium iron garnet magnonic waveguide. Magnetoelectric coupling not due to the spin-orbit interaction and, hence, an order of magnitude weaker leads to electric-field modification of the spin-wave velocity for waveguide geometries where the spin-orbit interaction will not contribute. A theory of the phase shift, validated by the experiment data, shows that, in the exchange spin wave regime, this electric tuning can have high efficiency. Our findings point to an important avenue for manipulating spin waves and developing electrically tunable magnonic devices.

Nickel/Iron Oxide Nanocrystals with a Nonequilibrium Phase: Controlling Size, Shape, and Composition

Mixed nickel iron oxide nanomaterials have great potential for use in fields as wide-ranging as optics, water oxidation catalysis, and biomedical applications; large-scale deployment for any of these applications is possible due to the abundance of iron and nickel in the earth’s crust. Here, we describe single-crystal mixed nickel iron oxide nanoparticles with a rocksalt crystal structure and an iron content greater than >10 at%. The nanoparticles were synthesized via thermal decomposition of nickel and iron oleates, yielding monodisperse nanoparticles <12 nm in size. A range of compositions were accessible, ranging from iron-poor to iron-rich. Despite the predicted poor solubility of iron in the NiO lattice, as based upon the equilibrium phase diagram, and the general tendency of pure FexO to oxidize, the single-crystal nanoparticles are nonetheless kinetically persistent even at elevated temperatures (200 °C). Furthermore, by controlling the drying conditions and decomposition time of the oleate precursors as well as the initial ratio of nickel to iron in the precursor oleate mixture a variety of nanoparticle shapes–namely stars, cubes, and spheres–were formed. This control of shape and composition affords tunability of physical properties, exemplified by magnetic properties herein.

Molecular dynamics simulation of fatigue crack propagation in bcc iron under cyclic loading

The mechanism of crack propagation under cyclic loading in iron single crystal was investigated using molecular dynamics simulation. The cyclic loading was strain controlled and three typical specimens of pre-existing center crack of [001](010), [001¯](110) and [112¯](111) models were chosen to study the effect of orientation on fatigue crack propagation. The slip bands, vacancies and voids nucleation were observed during the process of crack growth under cyclic loading, the rate of crack growth and slip direction were different for the three models. No significant slip band was observed in [112¯](111) model, and the crack propagation was brittleness. In addition, the influences of grain boundary on crack growth were analyzed on ∑3〈112〉{111} and ∑5〈310〉{001} models. No significant effect was observed for ∑3 on crack propagation, while ∑5 resisted crack growth remarkably and resulted in a decreasing rate of crack growth, during which a little hexagonal close-packed (hcp) slip bands appeared in the plastic deformation zone.

Anisotropy of the Linear Magnetic Birefridence of Europium Iron Garnet

The results of investigation of magnetic linear birefringence (MLB) and magnetic linear dichroism (MLD) of Eu3Fe5O12 (EuIG) iron garnet on 7F07F6 optical transitions upon variation of the directions of the magnetization vector I relative to the electric vector E linearly polarized light that propagates through single crystal iron garnets are presented. The measurements were made on Eu3Fe5O12 single-crystal samples in the form of plates 100 μm thick cut in the (110) and (100) plane at the temperatures T = 82 and in a magnetic field H= 25 kOe. The absorption spectra of the linearly polarized light were studied. It is shown that MLB and dichroism in the region of the 7F07F6 absorption band reach values 10-3. First experimentally discovered nonreciprocity of MLB spectra and dichroism with the change of the relative orientation of the magnetization vector I and the light wave vector. This effect may use as a base for the design of the different transducers, for example, magnetooptical optical channels commutator.

Thermal control of the spin pumping damping in ferromagnetic/normal metal interfaces

A model is presented for the control of the magnetic relaxation in a ferromagnetic insulator (FMI) in contact with a normal metal (NM) under a thermal gradient applied across the thickness of the bilayer. We show that the thermal gradient modifies the spin pumping damping created by the contact of the NM with the FMI. This results from the bulk magnon spin current generated through the longitudinal spin Seebeck effect that superimposes to the spin pumping current at the FMI/NM interface, changing the FMI magnetic damping. The results of the model explain the experimental data on the control of the magnetic relaxation by thermal gradients measured by the linewidth of the ferromagnetic resonance absorption and by the attenuation of spin-wave packets propagating along a film of single-crystal yttrium iron garnet covered by a very thin platinum layer. Depending on the sign of the gradient, the relaxation rate can be increased or decreased, leading in the latter case to an apparent amplification.

Temperature and high strain rate dependence of tensile deformation behavior in single-crystal iron from dislocation dynamics simulations

We conduct dislocation dynamics simulations of Fe periodic single crystals under tensile load at several high strain rates and temperatures. The simulations are connected to the atomistic scale via recently developed, temperature-dependent dislocation mobility relations. We explore strain rates from 104 to 106s-1 at temperatures of 100, 300 and 600K. We compute the flow stress as a function of strain rate and temperature, and find very good agreement with experimental data for Fe, suggesting that strain hardening is the dominant materials response mechanism in the range of conditions explored here.

Crystal plasticity model for BCC iron atomistically informed by kinetics of correlated kinkpair nucleation on screw dislocation

The mobility of dislocation in body-centered cubic (BCC) metals is controlled by the thermally activated nucleation of kinks along the dislocation core. By employing a recent interatomic potential and the Nudged Elastic Band method, we predict the atomistic saddle-point state of 1/2〈111〉 screw dislocation motion in BCC iron that involves the nucleation of correlated kinkpairs and the resulting double superkinks. This unique process leads to a single-humped minimum energy path that governs the one-step activation of a screw dislocation to move into the adjacent {110} Peierls valley, which contrasts with the double-humped energy path and the two-step transition predicted by other interatomic potentials. Based on transition state theory, we use the atomistically computed, stress-dependent kinkpair activation parameters to inform a coarse-grained crystal plasticity flow rule. Our atomistically-informed crystal plasticity model quantitatively predicts the orientation dependent stress–strain behavior of BCC iron single crystals in a manner that is consistent with experimental results. The predicted temperature and strain-rate dependencies of the yield stress agree with experimental results in the 200–350K temperature regime, and are rationalized by the small activation volumes associated with the kinkpair-mediated motion of screw dislocations.

Plane Strain Compression Test and Simple Shear Test of Single Crystal Pure Iron

Material tests of single crystal pure iron are reported in this paper. Four kinds of specimens with various crystal orientations were cut out from a single crystal rod by WEDM. These specimens were subjected to plane strain compression tests and simple shear tests. Stress-strain relationships were obtained from the load-stroke curves measured in these material tests. These results showed that the stress-strain relationship depends strongly on the crystal orientation. Effects of the crystal orientation on the stress-strain relationship were discussed by the comparison with calculation based on the crystalline plasticity theory. In addition, plastic deformation of single crystal specimens by the material tests was studied by using Electron Back Scattering Diffraction (EBSD) analysis.

Surface plasmon-enhanced transverse magnetic second-harmonic generation

We present experimental studies on surface plasmon (SP) enhanced transverse magnetic second-harmonic generation (T-MSHG) in single-crystal iron films grown by molecular beam epitaxy at room temperature on MgO (001) substrates. We show that it is possible to achieve both strongly enhanced T-MSHG intensity and high magnetic contrast ratio under attenuated total reflection configuration without using complex heterostructures because MSHG is generated directly at the iron surface where SPs are present. The T-MSHG has a much larger contrast ratio than transverse magneto-optical Kerr effect (T-MOKE) and shows great potential for a new generation of bio-chemical sensors due to its very high surface sensitivity. In addition, by analyzing the experimental results and the simulations based on SP field-enhancement theory, we demonstrate that the second-order susceptibility of MSHG shows great anisotropy and the tensor χ(xzz)(odd) is dominant in our sample.

Dual wavelength magneto-optical imaging of magnetic thin films

A magneto-optical imaging approach for the simultaneous imaging of multiple magnetization components is demonstrated. The method is applied to investigate complex magnetization reversal processes in single crystal iron and patterned amorphous magnetostrictive ferromagnetic structures. The use of a splitted optical illumination and observation path allows for the direct extraction of different complementary magnetic information. Real-time in-plane vector magnetization imaging reveals complicated domain arrangement processes in magnetostrictive films due to locally varying stress induced magnetic anisotropy. Magnetic domain features concealed by standard domain imaging techniques are directly exposed.