Applications of the Mössbauer spectroscopy (MS) in the investigation of Fe-Cr alloys are reviewed. A high sensitivity of the hyperfine magnetic field to the presence of Cr atoms in the vicinity of the probe Fe atoms permits quantitative investigation of various aspects related both to the crystallographic as well as to the magnetic phase diagram of this alloy system. Concerning the former, presented is the relevance of MS for determining borders of the miscibility gap and kinetics of the phase decomposition, distinguishing between nucleation and growth and spinodal decomposition, identifying the sigma-phase and studying kinetics of its precipitation. Regarding the magnetic phase diagram, MS is useful for determining the Curie, the Néel and the spin-freezing temperature, hence studying paramagnetic-ferromagnetic, paramagnetic-antiferromagnetic and paramagnetic-spin-glass transitions. An effect of different heat treatments, strain and irradiation with various particles on a distribution of Cr atoms in the Fe matrix is demonstrated, too. For bcc-FeCr alloys relevance of MS for determining changes in spin and charge densities at Fe-sites induced by neighboring Cr atoms is illustrated, as well as its usefulness in studying changes caused by a high-temperature sulphidation and oxidation. Concerning properties of sigma-FeCr alloys the application of MS for determining the Curie and Debye temperature is reviewed. Application of MS to study an effect of magnetism on the lattice dynamics of Fe atoms in sigma-FeCr is also exemplified. Last but not least, determining a magnetic texture and mechanical alloying is addressed.
The present work reports the preparation of polycrystalline multiferroic $GdFeO_3$ (GdFO) and characterization with x-ray diffraction (XRD), magnetization, temperature dependent Raman spectroscopy, temperature and magnetic field dependent $^{57}Fe$ M$\ddot{o}$ssbauer spectroscopy measurements. The sample is found to be phase pure from Rietveld refinement of XRD pattern. The M$\ddot{o}$ssbauer spectra measured in the presence of external magnetic field show the signatures of field induced spin reorientation transition, which are corroborated by magnetization measurements. From the temperature d…
The ordered structure of MgO-ZnO alloy system is a versatile tunable optical material promising for diverse optoelectronic applications. However, isovalent and isostructural alloy compositions of MgO-ZnO are generally unstable at ambient conditions. Using state-of-the-art \textit{ab initio} evolutionary simulations, we predict and study the properties of stable phases of MgO-ZnO. We establish the dynamical stability of the predicted crystal structures through the phonon and Raman spectroscopy. Detailed analyses of two of the most stable structures reveal highly tunable properties that could be…
We present the results of lifetime positron annihilation spectroscopy (PALS) for the alloys Fe21Ga and Fe22.4Ga, whose defect structure is connected with annealing from 20 to 1000C along the phase diagram of Fe21Ga and Fe22.4Ga, at the L12-A2 transitions and in the sub-lattice of the D03 phase. In frames of the standard trapping model, we estimate the positron annihilation parameters for the bulk metal and for the different thermal vacancies herein. Also we define concentrations of these vacancy defects, which may be helpful for explanation of the physical properties of Ge-Ga alloys, including…
Short-range ordering (SRO) in Fe-Cr has been the subject of a number of recent experimental and theoretical investigations, as ordering effects are significant for the phase stability of this technologically important alloy. Recently, discrepancies regarding the SRO behavior of Fe-Cr have been reported between results obtained with Mössbauer spectroscopy and diffuse neutron scattering, respectively. As the methodology for reducing SRO parameters from Mössbauer spectra is indirect and relies on the determination of a large number of parameters, here a new method for directly connecting the Möss…
Sublattice spin reversal and field induced $Fe^{3+}$ spin-canting across the magnetic compensation temperature in $Y_{1.5}Gd_{1.5}Fe_{5}O_{12}$ rare-earth iron garnet
Why is EXAFS analysis for multicomponent metals so hard? Challenges and opportunities for measuring ordering in complex concentrated alloys using x-ray absorption spectroscopy
Even though, the crystal structure of the intermediate (S') and the equilibrium S (Al2CuMg) phase were subject of many investigations by using mostly imaging or diffraction techniques, the results remain still controversial. In this study, we used X-ray absorption spectroscopy (XAFS) to verify the correct structure considering the well-known models reported by Perlitz & Westgren (PW), Mondolfo, Radmilovic & Kilaas and Yan et al. The structure was confirmed by direct comparison to simulated XAFS spectra using the software tool FDMNES. Our results support the widely accepted PW model as the corr…
An amorphous Se$_{0.80}$S$_{0.20}$ alloy produced by Mechanical Alloying was studied by Raman spectroscopy, x-ray diffraction, extended x-ray absorption fine structure (EXAFS) and optical absorption spectroscopy, and also through reverse Monte Carlo simulations of its total structure factor and EXAFS data. Its vibrational modes, optical gap and structural properties as average interatomic distances and average coordination numbers were determined and compared to those found for an amorphous Se$_{0.90}$S$_{0.10}$ alloy. The results indicate that coordination numbers, interatomic distances and a…
Ge$_{1-x}$Sn$_{x}$ alloys are a promising candidate material to realise direct-gap group-IV semiconductors for applications in Si-compatible electronic and photonic devices. Here, we present a combined theoretical and experimental analysis of Raman spectroscopy in Ge$_{1-x}$Sn$_{x}$ alloys. We describe liquid-vapour-solid growth and structural characterisation of Ge$_{1-x}$Sn$_{x}$ ($x \leq 8$%) nanowires displaying high crystalline quality, and investigate the structural and vibrational properties of the nanowires using Raman spectroscopy. Our theoretical analysis is based on a fully analytic…
Distribution of Cr atoms in Fe_{100-x}Cr_x alloys with x \le 25 within the first two coordination shells, 1NN-2NN, around probe 57Fe atoms was studied by means of the Mössbauer Spectroscopy. Clear evidence was found that the distribution is characteristic of a given atomic configuration. Only the configurations with Cr atoms situated in 2NN exhibit a quiasi-random distribution, while those with Cr atoms present in 1NN shell and those with Cr atoms in both shells is evidently not random showing clastering or anticlastering features. These findings are novel and much more complete than the up-to…
In alloys exhibiting substitutional disorder, the variety of atomic environments manifests itself as a `disorder broadening' in their core level binding energy spectra. Disorder broadening can be measured experimentally, and in principle can be used to deduce information about specific atomic environments within a sample. However, progress in this endeavor is hampered by the lack of a model for this phenomenon which can treat complex systems. In this work we describe such a model. The model is used to elucidate the relationship between charge transfer, atomic environment, and disorder broadeni…
While producing comparable efficiencies and showing similar properties when probed by conventional techniques, such as Raman, photoluminescence and X-ray diffraction, two thin film solar cell materials with complex structures, such as quaternary compound CZTSe, may in fact differ significantly in their microscopic structures. In this work, laser induced modification Raman spectroscopy, coupled with high spatial resolution and high temperature capability, is demonstrated as an effective tool to obtain important structure information beyond that the conventional characterization techniques can o…
Monitoring Gallium-Induced Damage in Aluminum Alloys Using Nonlinear Resonant Ultrasound Spectroscopy
Institute of Thermomechanics, Czech Academy of Sciences（捷克科学院热力学研究所）；Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague（布拉格捷克理工大学核科学与物理工程学院）；DISAT, Condensed Matter Physics and Complex Systems Institute, Politecnico di Torino（都灵理工大学生化与物理技术系凝聚态物理与复杂系统研究所）
Quaternary Heusler alloys Co$_2$Cr$_{1-x}$Fe$_{x}$Al with varying Cr to Fe ratio $x$ were investigated experimentally and theoretically. The electronic structure and spectroscopic properties were calculated using the full relativistic Korringa-Kohn-Rostocker method with coherent potential approximation to account for the random distribution of Cr and Fe atoms as well as random disorder. Magnetic effects are included by the use of spin dependent potentials in the local spin density approximation. Magnetic circular dichroism in X-ray absorption was measured at the $L_{2,3}$ edges of Co, Fe, and …
In this study, X-ray absorption spectroscopy (XAS) experiments for Ni45Co5Mn36.7In13.3 metamagnetic shape memory alloy were performed under high magnetic fields up to 12 T using a pulsed magnet. Field-induced reverse transformation to austenite phase caused considerable changes in the magnetic circular dichroism (MCD) signals and the magnetic moments of the ferromagnetic coupling between Mn, Ni, and Co were determined. The spin magnetic moment, Mspin, and orbital magnetic moment, Morb, of Mn atom in the induced austenite ferromagnetic phase, estimated based on the magneto-optical sum rule, wer…
The different contributions to the entropy change linked to the austenite-martensitic transition in a Ni-Mn-Sn metamagnetic shape memory alloy have been determined by combining different experimental techniques. The vibrational contribution has been inferred from the vibrational density of states of both the martensitic and austenite phases. This has been accomplished by combining time-of-flight neutron scattering measurements and ab-initio calculations. Further, the electronic part of the entropy change has also been calculated. Since the martensitic transformation takes place between two par…
Surface alloying is shown to produce electronic states with a very large spin-splitting. We discuss the long range ordered bismuth/silver(111) surface alloy where an energy bands separation of up to one eV is achieved. Such strong spin-splitting enables angular resolved photoemission spectroscopy to directly observe the region close to the band edge, where the density of states shows quasi-one dimensional behavior. The associated singularity in the local density of states has been measured by low temperature scanning tunneling spectroscopy. The implications of this new class of materials for p…
In many common Al-Mg-Si alloys (6000 series) intermediate storage at or near 'room temperature' after solutionising leads to pronounced changes of the precipitation kinetics during the ensuing artificial ageing step at \approx 180°C. This is not only an annoyance in production, but also a challenge for researchers. We studied the kinetics of natural 'room temperature' ageing (NA) in Al-Mg-Si alloys by means of various different techniques, namely electrical resistivity and hardness measurement, thermoanalysis and positron lifetime and Doppler broadening (DB) spectroscopy to identify the stages…
Shape memory Ti-Ni alloys attracted much attention in the recent years, since they are shape memory, intelligent as well as functional materials. In the present investigation Ti51Ni49 and Ti51Ni45Fe4 alloys were synthesized through radio frequency (RF) induction melting. The alloy was characterized through x-ray diffraction (XRD), scanning electron microscopy (SEM), Mossbauer spectroscopy (MS) and positron annihilation techniques (PAT).The Fe substitution stabilized the TiNi type cubic (a=2.998 A) phase. The surface microstructure and presence of the oxide layer in Ti51Ni45Fe4 alloy have been …
Resonant photoemission spectroscopy has been used to investigate the character of Fe 3d states in FeAl alloy. Fe 3d states have two different character, first is of itinerant nature located very close to the Fermi level, and second, is of less itinerant (relatively localized character), located beyond 2 eV below the Fermi level. These distinct states are clearly distinguishable in the resonant photoemission data. Comparison between the results obtained from experiments and first principle based electronic structure calculation show that the origin of the itinerant character of the Fe 3d states…
Resonant ultrasound spectroscopy and magnetic susceptibility experiments have been used to characterize strain coupling phenomena associated with structural and magnetic properties of the shape-memory Heusler alloy series Ni$_{50+x}$Mn$_{25-x}$Ga$_{25}$ ($x=0$, 2.5, 5.0, and 7.5). All samples exhibit a martensitic transformation at temperature $T_M$ and ferromagnetic ordering at temperature $T_C$, while the pure end member ($x=0$) also has a premartensitic transition at $T_{PM}$, giving four different scenarios: $T_C>T_{PM}>T_M$, $T_C>T_M$ without premartensitic transition, $T_C\approx T_M$, a…
We report on the electrodynamics of a Heusler alloy Fe2TiSn probed over four decades in energy: from the far infrared to the ultraviolet. Our results do not support the suggestion of Kondo-lattice behavior inferred from specific heat measurements. Instead, we find a conventional Drude-like response of free carriers, with two additional absorption bands centered at around 0.1 and 0.87 eV. The latter feature can be interpreted as excitations across a pseudogap, in accord with band structure calculations.
We use the many techniques of alloy theory to study antiferromagnetic NiO, considered as an alloy of spin-up and spin-down Ni atoms. The questions are: the true antiferromagnetic ground state and the possibility of obtaining ferrimagnetic configurations. Further we use the GGA/LDA- 1/2 technique to investigate the electronic excitation spectrum. We found two valence bands and band gaps, of 4.0eV consistent with bremsstrahlung-isochromat-spectroscopy (BIS) result, and 1.2eV consistent with the known 10Dq value for the Ni++ ion. The features of a Mott insulator are presented without recurring to…
Co-evolution of point defects and Cr-rich nano-phase in binary Fe-20 at.% Cr alloy: A comprehensive investigation using positron annihilation spectroscopy and atom probe tomography
The process of natural aging in pure ternary Al-Mg-Si alloys was studied by positron annihilation lifetime spectroscopy in real time in order to clarify the sequence and kinetics of clustering and precipitation. It was found that natural aging takes place in at least five stages in these alloys, four of which were directly observed. This is interpreted as the result of complex interactions between vacancies and solute atoms or clusters. One of the early stages of positron lifetime evolution coincides with a clustering process observed by differential scanning calorimetry (DSC) and involves the…
A review is presented on physical properties of the sigma-phase in Fe-Cr and Fe-V alloy systems as revealed both with experimental -- mostly with the Mossbauer spectroscopy -- and theoretical methods. In particular, the following questions relevant to the issue have been addressed: identification of sigma and determination of its structural properties, kinetics of alpha-to-sigma and sigma-to-alpha phase transformations, Debye temperature and Fe-partial phonon density of states, Curie temperature and magnetization, hyperfine fields, isomer shifts and electric field gradients.
The Fermi and Rashba energies of surface states in the Bi_xPb_{1-x}/Ag(111) alloy can be tuned simultaneously by changing the composition parameter x. We report on unconventional Fermi surface spin textures observed by spin and angle-resolved photoemission spectroscopy {that are correlated with a topological transition of the Fermi surface occurring at x=0.5. We show that the surface states remain fully spin polarized upon alloying and that the spin polarization vectors are approximately tangential to the constant energy contours. We discuss the implications of the topological transition for t…
A Fe89.15Cr10.75 alloy in a heavily strained (by cold rolling) and strain-relaxed states was studied by means of the conversion electrons Mössbauer spectroscopy (CEMS). Analysis of the spectra in terms of a two-shell model revealed significant differences between the studied samples, in particular, in values of the hyperfine field, a distribution of Cr atoms within the first two neighbor-shells, the latter was expressed in terms of the short-range order parameters, and in the magnetic texture.
Intermetallic compounds Zr7Ni10 and Hf7Ni10 have been studied by perturbed angular correlation (PAC) spectroscopy considering the fact that Zr7Ni10 has application as hydrogen storage material in fuel cell. In stoichiometric Zr7Ni10, the phase Zr2Ni7 is found to be dominant (~38%) while a fraction of ~25% is found for the Zr7Ni10 phase at room temperature. In this compound, a phase due to Zr8Ni21 (~10%) is found from room temperature up to 773 K but, this is not found at 873 K and above. In the stoichiometric Hf7Ni10 sample, the phase due to Hf7Ni10 is found as a minor phase (~22%) at room tem…
Recently, a giant spin splitting has been observed in surface alloys on noble metal (111) surfaces as a result of a strong structural modification at the surface as well as the large atomic spin-orbit interaction (SOI) of the alloy atoms. These surface alloys are an ideal playground to manipulate both the size of the spin splitting as well as the position of the Fermi level as it is possible to change the atomic SOI as well as the relaxation by varying alloy atoms and substrates. Using spin- and angle-resolved photoemission spectroscopy in combination with quantitative low energy electron diff…
Monophasic and homogeneous Ni10Zr7 nanocrystalline alloy films were successfully grown at room temperature by co-sputtering in an indigenously developed three-gun DC/RF magnetron sputtering unit. The films could be produced with long-range crystallographic and chemical order in the alloy, thus overcoming the widely acknowledged inherent proclivity of the glass forming Ni-Zr couple towards amorphization. Crystallinity of these alloys is a desirable feature with regard to improved efficacy in applications such as hydrogen storage, catalytic activity and nuclear reactor engineering, to name a few…
This work reports on the bulk properties of the quaternary Heusler alloy Co$_2$Mn$_{1-x}$Fe$_x$Si with the Fe concentration $x=$. All samples, which were prepared by arc melting, exhibit $L2_1$ long range order over the complete range of Fe concentration. Structural and magnetic properties of Co$_2$Mn$_{1-x}$Fe$_x$Si Heusler alloys were investigated by means of X-ray diffraction, high and low temperature magnetometry, M{öß}bauer spectroscopy, and differential scanning calorimetry. The electronic structure was explored by means of high energy photo emission spectroscopy at about 8 keV photon en…
The valence states of Mg-Al alloys are compared to those of reference materials (pure Mg and Al metals, and intermetallics). Two methods based on X-ray emission spectroscopy are proposed to determine the phases and their proportion: first, by analyzing the Al valence spectra of the Mg-rich alloys and the Mg valence spectra of the Al-rich alloys; second, by fitting with a linear combination of the reference spectra the Al spectra of the Al-rich alloys and the Mg spectra of the Mg-rich alloys. This enables us to determine that Al and Al3Mg2 are present in the 0-43.9 wt% Al composition range and …
Ageing mechanisms of the U-7\%wtNb alloy have been investigated on samples exposed to temperatures of 150$^{o}$C for up to 5000\,hours. A variety of surface and bulk analytic techniques have been used to investigate microstructural, chemical and crystallographic changes. Characterisation of the alloy's evolving behaviour was carried out through secondary electron microscopy, energy dispersive x-ray spectroscopy, electron backscatter diffraction, transmission electron microscopy and x-ray diffraction. Vickers hardness testing showed evidence of a strong thermal hardening relationship with agein…
We report the structural and magnetic behavior of single phase inverse Heusler alloys Cr$_2$Co$_{(1-x)}$Cr$_x$Al ($x = $ 0, 0.2, 0.4) using x-ray diffraction (XRD), Raman spectroscopy, isothermal magnetization, and magnetic susceptibility measurements. Interestingly, the Rietveld refinement of XRD data with the space group I$\bar{4}m2$ reveal a tetragonal distortion with c/a ratio around 1.38 in these inverse Heusler structures. The bulk compositions have been confirmed by energy dispersive x-ray spectroscopy measurements. The active Raman mode F$_{2g}$ is observed at 320~cm$^{-1}$, which conf…
Segregation, precipitation, and phase separation in Fe-Cr systems is investigated. Monte Carlo simulations using semiempirical interatomic potential, first-principles total energy calculations, and experimental spectroscopy are used. In order to obtain a general picture of the relation of the atomic interactions and properties of Fe-Cr alloys in bulk, surface, and interface regions several complementary methods has to be used. Using Exact Muffin-Tin Orbitals method the effective chemical potential as a function of Cr content (0-15 at.% Cr) is calculated for a surface, second atomic layer and b…
Mn 2p soft X-ray absorption (XAS) spectroscopy excited with circularly polarized synchrotron radiation has been applied to a new class of material, c(2x2)CuMn/Cu(001) two-dimensional ordered surface alloy. A significant X-ray magnetic circular dichroism (XMCD) signal has been clearly observed at T=25K, indicating the existence of the ferromagnetic state under the external magnetic field of 1.4 Tesla. The lineshape analyses of the XAS and XMCD spectra clearly show that the Mn 3d state is rather localized and has a high spin magnetic moment due to its half-filled character.
Chemical interaction and changes in local electronic structure of Cr, Fe, Co, Ni and Cu transition metals (TMs) upon formation of an $Al_{8}Co_{17}Cr_{17}Cu_{8}Fe_{17}Ni_{33}$ compositionally complex alloy (CCA) have been studied by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. It was found that upon CCA formation, occupancy of the Cr, Co and Ni 3d states changes and the maximum of the occupied and empty Ni 3d states density shifts away from Fermi level ($E_f$) by 0.5 and 0.6 eV, respectively, whereas the Cr 3d empty states maximum shifts towards $E_f$ by 0.3 eV, compared…
Alloy engineering of excitonic properties in TMD monolayers
Foundation for Research and Technology-Hellas（希腊研究与技术基金会）；Univ Toulouse, INSA, CNRS, LPCNO（图卢兹大学、国立应用科学学院、法国国家科学研究中心、低压与纳米电子物理实验室）；Department of Materials Science and Engineering, University of Crete（克里特大学材料科学与工程系）；Research Center for Materials Nanoarchitectonics, National Institute for Materials Science（日本国立材料研究所材料纳米架构研究中心）；Research Center for Electronic and Optical Materials, National Institute for Materials Science（日本国立材料研究所电子与光学材料研究中心）；Department of Inorganic Chemistry, University of Chemistry and Technology Prague（布拉格化工大学无机化学系）；Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, Ministry of Education, School of Physics and Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology（北京理工大学物理学院教育部先进光电子量子结构与测量重点实验室及北京市纳米光子学与超精细光电系统重点实验室）；Institut Universitaire de France（法兰西学院）
X-ray diffraction (XRD) and Mössbauer spectroscopy techniques combined with theoretical calculations based on the Korringa-Kohn-Rostoker (KKR) electronic structure calculation method were used to investigate σ-phase Fe_{100-x}Re_{x} alloys (x = 43, 45, 47, 49 and 53). Structural data such as site occupancies and lattice constants were derived from the XRD patters, while the average isomer shift and distribution curves of the quadrupole splitting were obtained from the Mössbauer spectra. Fe-site charge-densities and the quadrupole splittings were computed with the KKR method for each lattice si…
We report on the perpendicular magnetic anisotropy (PMA) behavior of heavy metal (HM)/ Fe alloy/MgO thin film heterostructures after an ultrathin HfO2 passivation layer is inserted between the Fe alloy and the MgO. This is accomplished by depositing one to two atomic layers of Hf onto the Fe alloy before the subsequent rf sputter deposition of the MgO layer. This Hf layer is fully oxidized during the subsequent deposition of the MgO layer, as confirmed by X-ray photoelectron spectroscopy measurements. As the result a strong interfacial perpendicular anisotropy energy density can be achieved wi…
Ageing mechanisms of the U-5\,\%wtNb system have been investigated on samples exposed to temperatures of 150$\,^{\circ}$C for up to 5000\,hours. A variety of surface and bulk analytic techniques have been used to investigate phase, chemical and crystallographic changes. Characterisation of microstructural evolution was carried out through secondary electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and x-ray diffraction (XRD). This investigation suggests crystallographic defects such as twinning…
Modern engineering alloys have bespoke microstructures, where features such as precipitates are used to control properties. In many Ni-based alloys, carbo-nitride precipitates are introduced to strengthen and improve performance. These precipitates can be distributed throughout the microstructure and niobium rich carbides are often found at grain boundaries. In this work, we used combined energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) to characterise the population of these precipitates. Processing of the EDS signal is used to label the Mo/Nb-rich precip…
Double ring formation on Co2MnSi (CMS) films is observed at electrical breakdown voltage during local anodic oxidation (LAO) using atomic force microscope (AFM). Corona effect and segregation of cobalt in the vicinity of the rings is studied using magnetic force microscopy and energy dispersive spectroscopy. Double ring forma-tion is attributed to the interaction of ablated material with the induced magnetic field during LAO. Steepness of forward bias transport characteristics from the unperturbed region of the CMS film suggest a non equilibrium spin contribution. Such mesoscopic textures in m…
Three novel precipitation strengthened bcc alloys which exhibit a smooth microstructural gradient with composition have been fabricated in bulk form by induction casting. All three alloys are comprised of a mixture of disordered A2-(Fe, Cr) and L2$_1$-ordered (Ni, Fe)$_{2}$AlTi type phases both as-cast and after long-term annealing at 900 $^{\circ}$C. The ratio of disordered to ordered phase, primary dendrite fraction, and overall microstructural coarseness all decrease as Cr is replaced by Al and Ti. Differences in phase composition are quantified through domain averaged principal component a…
The thermal decomposition behavior, the microstructural evolution and its influence on the mechanical properties of a supersaturated Cu Co solid solution with ~100 nm average grain size prepared by severe plastic deformation is investigated under non-isothermal and isothermal annealing conditions. Pure fine grained Cu and Co exhibit substantial grain growth upon annealing, whereas the Cu Co alloy is thermally stable at the same annealing temperatures. The annealed microstructures are studied by independent characterization methods, including scanning electron microscopy, electron energy loss s…
In this paper we report phonon dynamics in chemically synthesized Zn1- xMgxO (0\leqx\leq0.07) and Zn1-yCdyO (0\leqy\leq0.03) alloy nanostructures of sizes ~10 nm using non-resonant Raman and Fourier Transformed Infrared Spectroscopy (FTIR). Substitution by Mg makes the unit cell compact while Cd substitution leads to unit cell expansion. On alloying, both A1(LO) and E1(LO) mode of wurtzite ZnO show blue shift for Zn1-xMgxO and red shift for Zn1-yCdyO alloy nanostructures due to mass defect and volume change induced by the impurity atoms. Significant shift has been observed in E1(LO) mode for Z…
A redistribution of Cr atoms related to a phase decomposition (PD) caused by an isothermal annealing at 415 C in a 15.15 at%Cr Fe-Cr alloy was studied in an ex-situ way by the conversion electrons Mössbauer spectroscopy. Analysis of the spectra in terms of a two-shell model enabled determination of probabilities of 17 different atomic configurations and average numbers of Cr atoms within the first (1NN) and the second (2NN) neighbor shells versus annealing time, separately. The annealing-time evolution of these numbers, expressed in terms of the Cowley-Warren short-range order (SRO) parameters…
We have studied the possibly half metallic Co2FeSi full Heusler alloy by means of spin- and time-resolved photoemission spectroscopy. For excitation, the second and fourth harmonic of femtosecond Ti:sapphire lasers were used, with photon energies of 3.1 eV and 5.9 eV, respectively. We compare the dependence of the measured surface spin polarization on the particular photoemission mechanism, i.e. 1-photon-photoemission (1PPE) or 2-photon photoemission (2PPE). The observed differences in the spin polarization can be explained by a spin-dependent lifetime effect occurring in the 2-photon absorpti…
Spin-split Rashba bands have been exploited to efficiently control the spin degree of freedom of moving electrons, which possesses a great potential in frontier applications of designing spintronic devices and processing spin-based information. Given that intrinsic breaking of inversion symmetry and sizeable spin-orbit interaction, two-dimensional (2D) surface alloys formed by heavy metal elements exhibit a pronounced Rashba-type spin splitting of the surface states. Here, we have revealed the essential role of atomic orbital symmetry in the hexagonally warped Rashba spin-split surface state o…
