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We use the Variational Exact Diagonalization to investigate the single polaron properties for four different dual models, combining a short-range off-diagonal (Peierls) plus a longer-range diagonal (Holstein or breathing-mode) coupling. This allows us to investigate the sensitivity of various polaron properties both to the range of the diagonal coupling and to the specific diagonal coupling chosen. We find strong sensitivity to the range for all duals models as the adiabatic limit is approached, however considerable sensitivity is observed for some quantities even for large phonon frequencies. Also, the strong dependence of the results on the specific form of the diagonal coupling is observed everywhere in the parameter space. Taken together, these results suggest that careful consideration must be given to the specific coupling and its proper range when quantitative comparisons with experiments are sought., 9 pages, 12 figures, submitted to Physical Review B

This article reports exchange bias (EB) and memory effect in nanocrystalline CoCr2O4 with a detailed understanding of the origin of the observed effect. In order to investigate the EB effect in nanocrystalline CoCr2O4, two samples are synthesized with particle sizes 12 and 7 nm via sol-gel route (the second one is embedded in amorphous silica host). For both the samples, despite usual core-shell interaction or ‘surface’ domination, conventional EB effect is observed where the EB field sharply decreases with temperature and vanishes over the spiral ordering temperature (TS) of the samples. A bulk sample of the same composition, with particle size greater than 150 nm, reproducing similar characteristics, rules out the origin of EB due to surface effect. Results indicate that the exchange bias is due to inherent magnetic inhomogeneity: interaction between spiral spin order and collinear ferrimagnetic order below TS. The ac-susceptibility measurement points towards absence of surface glassiness in the sample with 12 nm particle size. However, the sample with particle size 7 nm reveals the characteristics of superspin-glass (SSG), confirmed by magnetic memory effects both in time (t) and temperature (T) dependent magnetization protocols.

The present article describes the application of Taguchi's experimental design methodology to investigate the erosion wear behavior of in situ-formed A356-5TiB2 composite subjected to thixoforming. The effects of process parameters—such as impact velocity, erodent temperature, erodent size, standoff distance, and impingement angle—on the erosion rate have been analyzed. The results indicated that impact velocity is the most significant factor and accounts for 42.31% of the total effect on the erosion rate of the thixoformed A356-5TiB2 composite. It is found that material loss during erosive wear is primarily due to microploughing (i.e., abrasive type) and microfracture (i.e., impact type). The erosion rate of thixoformed A356-5TiB2 in situ composite was found to be 48.82 mg/kg, which is nearly 44% lower than that of as-cast alloy.

Physical review / B covering condensed matter and materials physics 100(11), 115162 (2019). doi:10.1103/PhysRevB.100.115162, The presence of orbital degree of freedom in strongly correlated systems leads to unusual orderings. In this paper we use a combination of density-functional theory calculations and various experimental investigations to reveal a unique ground state for a Ti 3 + containing spinel oxide, MnTi2O4, which hosts an exotic combination of a rare tetramer orbital (associated with Ti3+ 3d1 electron) ordering along equivalent ⟨111⟩ directions involving all three t2g orbitals, a ferrimagnetic Mn-Ti, and a ferromagnetic Ti-lattice spin ordering. A combination of spin-orbital superexchange and Jahn-Teller-effect related strain-energy optimization provides a microscopic understanding for the stabilization of the unique ground state, which is found to be also electrically polar. The tetramer orbital ordering induces Ti-Ti bond length modulations and the short and long Ti-Ti bonds form helices around the crystallographic c-axis with a particular winding direction, causing the ground state structure to become spatial chiral., Published by Inst., Woodbury, NY

In the present work, A356 alloy and in situ A356-5TiB2 composite feedstock was produced by employing Cooling slope casting technique. The technique resulted in near spherical morphology of primary α-Al phase in the feedstock of both the alloy and composite. A fine distribution of eutectic Si phase within the matrix was observed in the composite feedstock. The rheocast billets of both the alloy and composite were then thixoformed successfully at 50 % solid fraction temperatures of 580 and 585 °C respectively. Further, tensile properties of thixoformed alloy and composite were measured and compared with those of gravity-cast samples. It was observed that the % increase in yield strength and tensile strength of thixoformed alloy increased by 43 and 36 % respectively with respect to the gravity-cast alloy. The thixoformed composite attained the highest ultimate tensile strength of 211 MPa which is about 40 % higher as compared to gravity-cast alloy. Interestingly, the ductility of the composites is comparable to that of alloy after thixoforming.

The present article investigates the age hardening behavior of thixoformed A356–5TiB 2 in-situ composite prepared by a salt-metal reaction. The non-dendritic feedstock for thixoforming was prepared by a cooling slope casting technique. The results show that the thixoformed A356–5TiB 2 composite attains the peak hardness in only four hours. The detailed microstructural analysis of thixoformed composite shows that enhanced ageing can be attributed to high dislocation density generated in α-Al matrix due to thermal mismatch and the thixoforming process itself. Furthermore, it was found that thixoforming not only increases the tensile strength of thixoformed composite in peak-aged condition but also increases the ductility by ~7.4%.

It is widely accepted that phonon-mediated high-temperature superconductivity is impossible at ambient pressure, because of the very large effective masses of polarons/bipolarons at strong electron-phonon coupling. Here we challenge this belief by showing that strongly bound yet very light bipolarons appear for strong Peierls/Su-Schrieffer-Heeger interaction. These bipolarons also exhibit many other unconventional properties, e.g. at strong coupling there are two low-energy bipolaron bands that are stable against strong on-site Hubbard repulsion. Using numerical simulations and analytical arguments, we show that these properties result from the specific form of the phonon-mediated interaction, which is of "pair-hopping" instead of regular density-density type. This unusual effective interaction is bound to have non-trivial consequences for the superconducting state expected to arise at finite carrier concentrations, and should favor a large critical temperature., Comment: 6 pages, 5 figures

We study two identical fermions, or two hard-core bosons, in an infinite chain and coupled to phonons by interactions that modulate their hopping as described by the Peierls/Su-Schrieffer-Heeger (SSH) model. We show that exchange of phonons generates effective nearest-neighbor repulsion between particles and also gives rise to interactions that move the pair as a whole. The two-polaron phase diagram exhibits two sharp transitions, leading to light dimers at strong coupling and the flattening of the dimer dispersion at some critical values of the parameters. This dimer (quasi)self-trapping occurs at coupling strengths where single polarons are mobile. This illustrates that, depending on the strength of the phonon-mediated interactions, the coupling to phonons may completely suppress or strongly enhance quantum transport of correlated particles., 6 pages main text + 8 pages supplementary material, 3 figures main text + 1 figure supplementary material

High conductivity and the absence of ferromagnetism in pristine graphene fail to satisfy primary criteria for possible technological application in spintronics. Opening of the bandgap in graphene is primarily desirable for such applications. We report a simplified and novel approach of controlled grafting of a magnetic alloy on reduced graphene oxide. This eventually leads to ferromagnetism of the stable hybrid material at room temperature, with a large moment (∼1.2 μB) and a remarkable decrease in conductivity (∼10 times) compared to highly ordered pyrolytic graphite. Our model band-structure calculation indicates that the combined effect of controlled vacancies and impurities attributed to the nanocrystalline alloy grafting leads to a promising step toward band gap engineering.

We perform ab initio investigations of the bulk and surface band structures of LaSb and LaBi and resolve the existing disagreements about the topological property of LaSb, considering LaBi as a reference. We examine the bulk band structure for band inversion, along with the stability of surface Dirac cones (if any) to time-reversal-preserving perturbations, as a strong diagnostic test for determining the topological character of LaSb, LaBi and LaSb-LaBi multilayer. A detailed ab initio investigation of a multilayer consisting of alternating unit cells of LaSb and LaBi shows the presence of band inversion in the bulk and a massless Dirac cone on the (001) surface, which remains stable under the influence of time-reversal-preserving perturbations, thus confirming the topologically non-trivial nature of the multilayer in which the electronic properties can be tailored as per requirement. A detailed $${{\mathbb{Z}}}_{2}$$ Z 2 invariant calculation is performed to arrive at a holistic conclusion.

We investigate the electronic structure of CMR manganite Pr1-xCaxMnO3 at x = 0 and 0.25, within density functional theory (DFT). We find that the Pr atoms in PrMnO3 do not posses any magnetic moment whereas in Pr0.75Ca0.25MnO3, the Pr moment changes to the high spin value of −1.95μB per formula unit. The appearance of the moment in Pr site, noticed experimentally long back, is an outstanding problem. Our ab initio electronic structure investigation leads us to the conclusion that the modified crystal ambience resulting from Ca doping holds the key to the origin of large Pr magnetic moment in Pr0.75Ca0.25MnO3.

We study the ground state of 1D Holstein single polaron with next nearest neighbour electron hopping (NNN), employing a variational approximation based on exact diagonalization. Our investigation reveals that, depending upon the sign and magnitude of the NNN hopping integral with respect to nearest neighbour hopping, the polaron band minima may occur at non-zero kGS. We compare the present scenario with the SSH polarons, where a similar feature is also observed, albeit, due to very different mechanism. Our initial investigation of triplet bipolarons, in presence of an attractive extended Hubbard interactions, further substantiates the differences between the present model and the SSH model., Comment: 4

Herein, we report the graded electronic band gap along the axis of individual heterostructured WZ-ZB InAs/InSb

We investigate the orbital effects of strong external magnetic field on the ground state properties of a two dimensional holstein polaron, employing variational approaches based on the exact diagonalization (VAED). From the ground state energy and the wave function we calculate electron-phonon correlation function, the average phonon number and the Drude weight and investigate the evolution of a 2D holstein polaron as a function of the magnetic flux. Although the external magnetic field affects the polaron throughout the parameter regime, we show that the magnetic field has a stronger effect on a loosely bound (spatially extended) polaron. We also find that the magnetic field can be used as a tuning parameter, particularly for weakly coupled polaron, to reduce the spatial extent of a large polaron.

We report a detailed ab initio study of two superlattice heterostructures, one component of which is a unit cell of CuPt ordered InSb_(0.5)As_(0.5). This alloy part of the heterostructures is a topological semimetal. The other component of each system is a semiconductor, zincblende-InSb, and wurtzite-InAs. Both heterostructures are semiconductors. Our theoretical analysis predicts that the variation in the thickness of the InSb layer in InSb/InSb_(0.5)As_(0.5) heterostructure renders altered band gaps with different characteristics (i.e. direct or indirect). The study holds promise for fabricating heterostructures, in which the modulation of the thickness of the layers changes the number of carrier pockets in these systems., Title changed, this is a replacement and major revision of arXiv:1801.03392

We have developed an interface between the all-electron density functional theory code WIEN2k, and the MIT Ab-initio Phase Stability (MAPS) code of the Alloy-Theoretic Automated Toolkit (ATAT). WIEN2k is an implementation of the full-potential linearized augmented planewave method which yields highly accurate total energies and optimized geometries for any given structure. The ATAT package consists of two parts. The first one is the MAPS code, which constructs a cluster expansion (CE) in conjunction with a first-principles code. These results form the basis for the second part, which computes the thermodynamic properties of the alloy. The main task of the CE is to calculate the many-body potentials or effective cluster interactions (ECIs) from the first-principles total energies of different structures or supercells using the structure-inversion technique. By linking MAPS seamlessly with WIEN2k we have created a tool to obtain the ECIs for any lattice type of an alloy. We have chosen fcc Al–Ti and bcc W–Re to evaluate our implementation. Our calculated ECIs exhibit all features of a converged CE and compare well with literature results.

The present study has examined the thermodynamics of MgAl2O4 and MgO formations in Al–Mg alloy/quartz (>99% crystalline silica) through differential thermal analysis (DTA). The formation of MgAl2O4 and MgO is detected as exothermic peaks in the heat flow curve and the reaction is confirmed by the Si dissolution peaks observed during the reheating of samples and SEM analysis of the reacted sample. The presence of MgAl2O4 and MgO is confirmed in the XRD analysis of the reacted sample. The study has enabled the production of nano sized MgAl2O4 and MgO crystals at the interface of Al–Mg alloy and quartz. The reaction between them is found to be influenced by the oxidation of Mg, which is reduced by increasing heating rates.

Equal channel angular pressing (ECAP) of in situ Al-5 wt% TiB2 composite was successfully carried out at room temperature up to four passes. Large particle free zones of about 50-100 ?m size present in as cast condition have been reduced to 20-30 ?m by ECA pressing. The initially clustered distribution of TiB2 has become homogeneous after four ECAP passes. A significant grain refinement down to ?500 nm has been achieved by ECA pressing but the average particulates size remains unchanged at 0.5-0.6 ?m. � 2007 Elsevier B.V. All rights reserved.

Aluminium matrix composites reinforced with molybdenum aluminide nanoparticles were synthesized by ball milling and reactive sintering of the mixture of aluminium and 10 wt% hydrated molybdenum oxide powders. Sintering the as milled powder in air below 750 °C produced MoAl12 intermetallic compound nanoparticles, at 750 °C produced a mixture of MoAl5 and MoAl4 nanoparticles and at 800 °C under Argon atmosphere produced predominantly MoAl4 intermetallic nano-particles in the Al matrix. The powder compacts sintered in air below 750 °C produced MoAl12 whereas at 750 °C or above formed the Al matrix composite reinforced with the MoAl5 nanoparticles. These nanoparticles become agglomerated to take up some irregular shaped flakes in the metal matrix. The reaction between Al and hydrated Mo oxide powders was found to be a favorable way to produce predominantly a particular Mo–Al intermetallic compound at a particular temperature. The Al2O3 particles formed as another reaction product, in all the above reactions, remain distributed in these composites. The composites thus formed were characterized by SEM-EDS, DTA, XRD and TEM analysis.

The formation of Al2O3, MgAl2O4, and MgO has been widely studied in different Al base metal matrix composites, but the studies on thermodynamic aspects of the Al2O3/ MgAl2O4/MgO phase equilibria have been limited to few systems such as Al/Al2O3 and Al/SiC. The present study analyzes the Al2O3/MgAl2O4 and MgAl2O4/MgO equilibria with respect to the temperature and the Mg content in Al/SiO2 system using an extended Miedema model. There is a linear and parabolic variation in Mg with respect to the temperature for MgAl2O4/MgO and Al2O3/MgAl2O4 equilibria, respectively, and the influence of Si and Cu in the two equilibria is not appreciable. The experimental verification has been limited to MgAl2O4/MgO equilibria due to the high Mg content (≥0.5 wt pct) required for composite processing. The study has been carried out on two varieties of Al/SiO2 composites, i.e., Al/Silica gel and Al/Micro silica processed by liquid metallurgy route (stir casting route). MgO is found to be more stable compared to MgAl2O4 at Mg levels ≥5 and 1 wt pct in Al/Silica gel and Al/Micro silica composites, respectively, at 1073 K. MgO is also found to be more stable at lower Mg content (3 wt pct) in Al/Silica gel composite with decreasing particle size of silica gel from 180 micron to submicron and nanolevels. The MgO to MgAl2O4 transformation has taken place through a series of transition phases influenced by the different thermodynamic and kinetic parameters such as holding temperature, Mg concentration in the alloy, holding time, and silica particle size.

Herein, we report the graded electronic band gap along the axis of individual heterostructured WZ-ZB InAs/InSb0.12As0.88 nanowires. Resonance Raman imaging has been exploited to map the axial variation in the second excitation gap energy (E1) at the high symmetry point (L point) of the Brillouin zone. We relate the origin of the observed evolution of the gap energy to the fine tuning of the alloy composition from the tip towards the interface of the nanowire. The electronic band structures of InAs, InSb and InSbxAs1−x alloy systems at x = 0.125, 0.25, 0.50, 0.75 and 0.875, using the all electron density functional theory code Wien2k, are reported. The measured band gap along the axis of the InAs/InSb0.12As0.88 nanowire is correlated with the calculated gap energy at the A point and the L point of the Brillouin zone for InAs and InSb0.125As0.875, respectively. We draw a one-to-one correspondence between the variation of the E1 gap and the fundamental E0 gap in the calculated electronic band structure and propose the graded fundamental gap energy across the axis of the nanowire.

Employing a self-consistent (optimized) variational diagonalization scheme, we investigate the formation of polaronic quasiparticles in a spinless fermion-boson transport model that couples the movement of charge carriers to fluctuations and correlations of a background medium. The background is parameterized by bosonic degrees of freedom. The variational fermion-boson Hilbert space is constructed to achieve high accuracy in one to three spatial dimensions with modest computational requirements. To characterize the ground-state properties of the Edwards model in the single-particle sector, we present exact numerical results for the polaron band dispersion, quasiparticle weight, Drude weight, mass enhancement, and the particle-boson correlations in a wide parameter regime. In the Edwards model, transport will be quasifree, diffusive or boson-assisted in the weakly fermion-boson coupled, fluctuation-dominated or strongly correlated regimes, respectively. Thereby correlated transport is not only assisted but also limited by the bosonic excitations. As a result, the Drude weight remains finite even in the limit of very small boson frequencies. For a strongly correlated background, closed loops are important, in any dimension, to generate a finite effective particle mass even when the free fermion has an infinite mass., Comment: 9 pages 13 figures

Fluidity behavior of the A356 Al alloy and A356 Al–SiCp composites has been theoretically predicted using the Flemings model after incorporating (1) the solidification behavior of the alloy; (2) the decrease in flow velocity due to surface tension and friction losses; and (3) the increase in viscosity of composite slurries due to size, shape, and volume fraction of the reinforcement. It is observed that the fluidity values of A356 Al alloy and A356 Al–10 vol pct SiCp composite predicted by the modified Flemings model are in good agreement with the experimental values reported in the literature. On the other hand, the theoretically calculated fluidity length of A356 Al–15 and 20 vol pct SiCp composites using the modified Flemings model agrees well with the experimental results only up to 750 °C and 710 °C, respectively. However, above these respective temperatures, the experimental spiral length decreases with pouring temperature, whereas the theoretically calculated spiral length increases linearly as a function of pouring temperature. Incorporation of experimentally calculated interfacial reaction terms in the modified Fleming model makes the predicted and experimental values of fluidity of A356 Al–15 and 20 vol pct SiCp composites closer in the entire temperature range. Thus, the high dependence of the fluidity of A356 Al–SiCp composites on the morphology of the interfacial reaction product is demonstrated.

In this communication we present a study of the electronic structure of partially disordered bulk and (1 0 0) thin film of quaternary pseudo-Heusler alloy Co 2 Fe 0.4 Cr 0.6 Al in the L2 1 phase using the augmented space recursion (ASR) on a scalar-relativistic tight binding linear muffin-tin orbitals (TB-LMTO) basis. We study the orbital resolved magnetic moment contributions of the constituents of the alloy. Our theoretical predictions match well with the available experimental observations for the magnetic moments of Fe and Co but they overestimate that of Cr. For a (1 0 0) thin film, layer as well as orbital resolved properties have been studied.

The current work emphasizes Aluminum based metal matrix composites with TiB 2 as reinforcement are emerging materials because of their potential for applications in automotive and aerospace industries. The machining of these materials has become a very important subject for research. This paper presents the application of Design of Experiments and analysis of variance in optimizing the machining process parameters such as cutting speed, feed rate and depth of cut, during turning operation. The response considered for the analysis was surface roughness. The results indicated that A356-5TiB 2 composite produces higher tool wear, surface roughness and minimizes the cutting forces. Moreover, there was improvement in the quality of the machined surface in the A356-5TiB 2 composite compared to A356 alloy. The chips formed during turning were characterized by Scanning Electron Microscope and analyzed from the machinability point of view. Optimum machining parameters for minimizing the surface roughness were determined. Thus, this work is an attempt to study the machinability behavior of thixoformed A356-5TiB 2 in-situ composites.

In this paper we carry out a detailed orbital ( l – m – m s ) resolved study of the way in which the local magnetic moment changes as we go from the bulk to a planar or a rough surface. For a rough surfaces (FCC Ni (1 0 0) and BCC Fe (1 0 0) surfaces) we shall concentrate on specific structures on them and study the way in which local environment affects the local magnetic moment. Results will be shown for Fe, Co and Ni planar surfaces.

Isothermal rheocasting studies were carried out on Al–5.2Si alloy under different processing conditions. The parameters varied are the shear rate, time of stirring, addition of grain refiner and the cooling rate. The addition of grain refiner prior to stirring has been found to influence the size and morphology of the primary particles. The shear rate–time combination has found to have tremendous effect in deciding the primary particle morphology. By proper selection of the processing parameters, globular primary particles can be obtained by mechanical stirring with a radial flow impeller in the semisolid range. The observed particle growth with increasing isothermal shearing time could be understood with the available theories of particle growth.

We present calculations of the electronic and magnetic structure of thin films of Ni, using the recursion technique based on the tight-binding linearized muffin-tin orbitals basis. We find that the surface layers of free standing Ni thin films do carry enhanced magnetic moment.

27Al nuclear magnetic resonance (NMR) studies were performed in CeNiAl4, a fluctuating valence system with Kondo temperature T*≈99 K and showing heavy fermion behavior at low temperature. The temperature dependence of the lineshape and the spin lattice relaxation rate (1/T1) were measured in the range 75–300 K. The effect of Ce-4f electron moment on the lineshape was found to be less pronounced. Moreover, the contribution of the 4f electron spin fluctuation to the Al nuclear spin-lattice relaxation process was also found to be less effective in this temperature range compared to that of the contact interaction of the conduction electrons. This suggests a faster spin fluctuation rate of the Ce-4f electron compared to the NMR time scale.

We have developed a new self-consistent scheme of generating variational basis based on the exactdiagonalization, which can be applied efficiently to various types of electron-phonon systems. This scheme is quite general and brings down the size of the variational space by an order of magnitude or even more in some cases to reproduce the most precise ground state energies and correlation functions available in the literature. This method has enormous potential for application to systems with more electrons or in higher dimensions, which are still beyond the reach of exact-diagonalization just because of the sheer size of their variational space needed to get reasonably convergent results., 4 pages, 3 figures, submitted to PRB

Employing the recently developed self-consistent variational basis generation scheme, we have investigated the bipolaron-bipolaron interaction within the purview of Holstein-Hubbard and the extended-Holstein-Hubbard (F2H) model on a discrete one-dimensional lattice. The density-matrix renormalization group (DMRG) method has also been used for the Holstein-Hubbard model. We have shown that there exists no bipolaron-bipolaron attraction in the Holstein-Hubbard model. In contrast, we have obtained clear-cut bipolaron-bipolaron attraction in the F2H model. Composite bipolarons are formed above a critical electron-phonon coupling strength, which can survive the finite Hubbard $U$ effect. We have constructed the phase diagram of F2H polarons and bipolarons, and discussed the phase separation in terms of the formation of composite bipolarons., Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev. B

We present the effect of next-nearest-neighbor hopping on Holstein polarons. The energy and wavefunction of the ground state and first excited state are obtained by using a conjugate-gradient technique on the variational Hilbert space of the electron-phonon (e-ph) system. We increase the size of the variational space systematically to obtain high accuracy. With the converged wavefunction at our disposal we obtain various physical quantities and correlation functions to get a holistic insight into the physics of e-ph interaction. Our study reveals that the effect of next-nearest-neighbor hopping is most prominent at the physically interesting crossover regime of the e-ph coupling and in the adiabatic regime. We have also performed analytical strong coupling second order perturbation with a Lang-Firsov (LF) phonon basis to account for some features in the strong coupling regime.

The alloy A356 was reinforced with in-situ TiB2 particles via salt-metal reaction, i.e., the reaction of K2TiF6 and KBF4 salts with the molten alloy. The study was undertaken to investigate the ageing response of the alloy when dispersed with TiB2 particles. The results indicated that the ageing time comes down from 12 h in the base alloy to 4 h in the composite with 10 wt.% TiB2. It was also observed that different amounts of TiB2 significantly alter the particle size distribution of Si which consequently affect the mechanical properties. Further, it was also noted that thermal modification plays an important role in retaining the ductility of composites. � 2008 Elsevier B.V. All rights reserved.

In this study, we report the observation of a pseudogap associated with the insulator-metal transition in compositions of ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ system with no charge ordering. Our valence-band photoemission study shows that the observed shifts in the near Fermi level density of states are abrupt at the Curie transition and occur over an energy scale of $\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, strongly suggesting that the charge-ordering gap observed earlier in other manganites and the pseudogap observed here may indeed have the same origin. These results could be understood within the framework of models based on electronic phase separation where it has been shown that the pseudogap is a generic feature of the mixed-phase compositions. Also, our band-structure calculations on ${\mathrm{Pr}}_{0.75}{\mathrm{Sr}}_{0.25}\mathrm{Mn}{\mathrm{O}}_{3}$ show the possible existence of half metallicity in this system.

Cooling Slope casting process has gained significant importance for manufacturing of semi-solid feedstock Al alloys and composites which find applications in automotive and aerospace industries. The primary objective of this research is to generate the semi-solid feedstock suitable for thixoforming process. The current work discusses the phenomena involved in the evolution of microstructure of the semi-solid feed stock by Cooling Slope casting process and the effect of various parameters. The process parameters like the angle and length of inclined plate affect the size and morphology of α-Al phase. The Cooling slope process resulted in the formation of fine grain size of about 38 μm of α-Al phase, compared to that of 98 μm processed conventionally. Further, the pouring temperature played a crucial role in the generation of semi-solid microstructures in case of both the alloy and composites. Moreover, fine TiB2 particles of size 0.2-0.5 μm are uniformly distributed in the almost spherical α-Al grains and at the grain boundaries in the composite feed stock. Cooling slope casting route is a suitable and economical route for semi-solid slurry generation by effectively varying the process parameters.

A new formalism using the ideas of the augmented space recursion (introduced by one of us) has been proposed to study the ground state properties of ordered and disordered one-dimensional Holstein model. For ordered case our method works equally well in all parametric regime and matches with the existing exact diagonalization and DMRG results. On the other hand the quenched substitutionally disordered model works in low and intermediate regime of electron phonon coupling. Effect of phononic and substitutional disorder are treated on equal footing., Accepted for publication in Physica B

Rapidly solidified Ni54Fe27−2xGa19+2x (x=0, 1, 2, 3, and 4) ferromagnetic shape memory alloys were made by melt-spinning with variation of Fe and Ga contents to report on the martensitic phase transformation, microstructures, and magnetic properties. Rapid solidification produced pure L21 phase by preventing the formation of γ-phase. To study the effect of heat treatment on the phase transitions, microstructures, and the magnetic properties, the melt-spun ribbons were partly heat treated at different temperatures of 800, 900, 1000, 1100, and 1200 K with holding times of 5, 10, and 15 min followed by either water quenching or air cooling. The microstructures of the as-spun ribbons as revealed by electron microscopy studies exhibited a gradual transition from cellular to dendritic structure with increasing Ga concentration and with the presence of some internal martensitic twin bands at higher Ga content. The ribbons exhibited very low coercivity with high saturation magnetization, as high as ∼87 emu/g (dec...