High $ZT$ value and large Seebeck coefficient have been reported in the nanostructured Fe-doped Si-Ge alloys. In this work, the large Seebeck coefficient in Fe-doped Si-Ge systems is qualitatively reproduced from the computed electronic density of states, where a hybrid functional, HSE06, is used for an exchange-correlation functional, as well as a special quasi-random structure (SQS) for a disordered atomic configuration. Furthermore, by replacing Fe with other transition metals, such as Mn, Co, Ni, Cu, Zn, and Au, a better dopant that produces a larger Seebeck coefficient in Si-Ge alloy systems is explored.
A new approach is developed to calculate temperature dependent Seebeck coefficient of heavily doped systems by using Boltzmann transport theory and electron density of states (DOS) obtained from density functional calculations. This approach is applied to heavily doped La:STO with DOS from tetrahedral method and Fermi energy using Fermi integrals. The calculated Seebeck coefficient agrees with the experimental data nearly quantitatively, which proved the accuracy of this approach. The influence of the Fermi energy and asymmetry of DOS on the Seebeck coefficient is analyzed.
In this work, we introduce models for deriving lower limits for the key parameters doping efficiency, charge carrier concentration, and charge carrier mobility from conductivity data of doped organic semiconductors. The models are applied to data of thin layers of Fullerene C60 n-doped by four different n-dopants. Combining these findings with thermoelectric Seebeck data, the energetic position of the transport level can be narrowed down and trends for the absolute values are derived.
We study the origin of the large Seebeck coefficient despite the metallic conductivity in the La-doped SrTiO$_3$ and Ba-doped KTaO$_3$. We calculate the band structure of SrTiO$_3$ and KTaO$_3$, from which the Seebeck coefficient is obtained using the Boltzmann's equation. We conclude that the multiplicity of the $t_{2g}$ bands in these materials is one major origin of the good thermoelectric property in that when compared at a fixed total number of doped electrons, the Seebeck coefficient and thus the power factor are larger in multiple band systems than in single band ones because the number…
Half-Heusler alloys have been one of the benchmark high temperature thermoelectric materials owing to their thermal stability and promising figure of merit ZT. Simonson et al. early showed that small amounts of vanadium doped in Hf0.75Zr0.25NiSn enhanced the Seebeck coefficient and correlated the change with the increased density of states near the Fermi level. We herein report a systematic study on the role of vanadium (V), niobium (Nb), and tantalum (Ta) as prospective resonant dopants in enhancing the ZT of n-type half-Heusler alloys based on Hf0.6Zr0.4NiSn0.995Sb0.005. The V doping was fou…
Graphene halfly doped with H or F possesses local magnetization at the undoped C sites. Thus the Seebeck coefficient is different for each spin channel and its sign also changes depending on the spin polarization. Deposition of doped graphene on the C-face 4H-SiC(0001) with two buffer layers substantially varies the electronic and thermoelectric properties. These properties are efficiently calculated from the semiclassical Boltzmann equations, using the maximally-localized Wannier-functions interpolation of the band structures obtained with the density-functional theory. Our results indicate l…
Based on first-principles calculations, we study the origin of the large thermopower in Ni-doped LaRhO3 and Mg-doped CuRhO2. We calculate the band structure and construct the maximally localized Wannier functions from which a tight binding Hamiltonian is obtained. The Seebeck coefficient is calculated within the Boltzmann's equation approach using this effective Hamiltonian. For LaRhO3, we find that the Seebeck coefficient remains nearly constant within a large hole concentration range, which is consistent with the experimental observation. For CuRhO2, the overall temperature dependence of the…
We present a first-principles study of the magnetotransport phenomena in p-doped diamond via the exact solution of the linearized Boltzmann transport equation, in which the materials' parameters, including electron-phonon and phonon-phonon interactions, are obtained from density functional theory. This approach gives results in very good agreement with experimental data for Hall and drift mobilities, low- and high-field magnetoresistance and Seebeck coefficient, including the phonon-drag effect, in a range of temperatures and carrier concentrations. In particular, our results provide a detaile…
We investigate the thermoelectric propeties of the electron-doped FeAs$_2$ both experimentally and theoretically. Electrons are doped by partially substituting Se for As, which leads to a metallic behavior in the resistivity. A Seebeck coefficient of about $-$200 $μ$V/K is reached at 300 K for 1% doping, and about $-$120 $μ$V/K even at 5% doping. The origin of this large Seebeck coefficient despite the metallic conductivity is analyzed from a band structure point of view. The first-principles band calculation reveals the presence of a pudding-mold type band just above the band gap, somewhat si…
The net entropy change corresponding to the charge carriers in a Ni-doped FeRh bulk polycrystal was experimentally evaluated in a single sample using low temperature heat capacity experiments with applied magnetic field, and using Seebeck effect and Hall coefficient measurements at high temperatures across the first order transition. From the heat capacity data a value for the electronic entropy change \(ΔS_{el}\approx8.9\) J\ kg\(^{-1}\)K\(^{-1}\) was extracted, whereas a value of up to 4 J\ kg\(^{-1}\)K\(^{-1}\) was obtained form the Seebeck coefficient. Additionally, the analysis of the See…
We have performed first-principles investigations on the native defects in the full Heusler alloys Co$_2$Ti$Z$ ($Z$ one of the group IV elements Si, Ge, Sn), determining their formation energies and how they influence the transport properties. We find that Co vacancies (Vc) in all compounds and the Ti$_\text{Sn}$ anti-site exhibit negative formation energies. The smallest positive values occur for Co in excess on anti-sites (Co$_Z$ or Co$_\text{Ti}$) and for Ti$_Z$. The most abundant native defects were modeled as dilute alloys, treated with the coherent potential approximation in combination …
The crystal structure and magnetoresponsive properties of Fe-doped MnCoGe alloys have been investigated using x-ray diffraction (XRD) and magnetic measurements. By alloying the Fe-containing isostructure compounds into MnCoGe, a magnetostructural transition from paramagnetic austenite to ferromagnetic martensite with large magnetization difference can be realized in a temperature window between the Curie temperatures of the austenite and martensite, resulting in magnetic-field-induced martensitic transformations and large magnetic-entropy changes. A structural and magnetic phase diagram of Fe-…
The structure, magnetic and martensitic properties of Fe doped Ni-Mn-In magnetic shape memory alloys have been studied by differential scanning calorimetry, magnetization, resistivity, X-ray diffraction (XRD) and EXAFS. While Ni$_{2}$MnIn$_{1-x}$Fe$_{x}$ ($0 \le x \le 0.6$) alloys are ferromagnetic and non martensitic, the martensitic transformation temperature in Ni$_{2}$Mn$_{1.5} $In$_{1-y}$Fe$_{y}$ and Ni$_{2}$Mn$ _{1.6} $In$_{1-y}$Fe$_{y}$ increases for lower Fe concentrations ($y \le 0.05$) before decreasing sharply for higher Fe concentrations. XRD analysis reveals presence of cubic and …
The origin of the recently discovered large thermopower in hole-doped PtSb$_2$ is theoretically analyzed based on a model constructed from first principles band calculation. It is found that the valence band dispersion has an overall flatness combined with some local ups and downs, which gives small Fermi surfaces scattered over the entire Brillouin zone. The Seebeck coefficient is calculated using this model, which gives good agreement with the experiment. We conclude that the good thermoelectric property originates from this "corrugated flat band", where the coexistence of large Seebeck coef…
Present work reports a detailed investigation on the magnetoresistance and magnetocaloric behavior of Ni and Cr-doped Mn$_5$Si$_3$ alloys with general formula Mn$_{5-x}$A$_x$Si$_3$ (where A = Ni/Cr; $x$ = 0, 0.05, 0.1 and 0.2). Both pure (undoped) and doped alloys show a reasonably large amount of magnetoresistance (MR). Doping at Mn-site, both by Ni and Cr, results in a monotonic decrease in MR values. Magnetocaloric effect (MCE), on the other hand, is found to be interesting, and all the alloys show both conventional and inverse MCE around the magneto-structural transition temperature. Among…
We present a study of the thermoelectric (Seebeck and Nernst) response in heavily overdoped, non-superconducting La$_{1.67}$Sr$_{0.33}$CuO$_4$. In spite of the electron-like curvature of the Fermi surface, the Seebeck coefficient is positive at low temperatures. Such a feature, previously observed in copper, silver, gold and lithium, is caused by a non-trivial energy dependence of the scattering time. We argue that this feature implies a strong asymmetry between the lifetime of occupied and unoccupied states along the zone diagonals and such an electron-hole asymmetry impedes formation of Coop…
We perform a systematical analysis of the spin Hall effect (SHE) in the Cu alloys doped with a series of 5d elements, by the combined approach of density functional theory and Hartree-Fock approximation. We find that not only the spin orbit interactions (SOI) in both the 5d and 6p orbitals, but also the local correlations in the 5d orbitals of the impurities, are decisive on the sign of the spin Hall angle (SHA). Including all of these three factors properly, we predict the SHA for each alloy in the series. The signs of CuIr and CuPt are sensitive to perturbation of the local correlations. Thi…
Mn doping in dilute III-V alloys has been examined as a route to enhance ferromagnetic stability. Strong valence band bowing is expected at the dilute limit, implying a strong modification of the ferromagnetic stability upon alloying, with even an increase in some cases. Using first principle electronic structure calculations we show that while codoping with a group V anion enhances the ferromagnetic stability in some cases when the effects of relaxation of the lattice are not considered, strong impurity scattering in the relaxed structure result in a reduction of the ferromagnetic stability.
One of the most remarkable characteristics of topological materials is that they have special surface states, which are determined by the topological properties of their bulk materials. The angle resolved photoemission spectroscopy (ARPES) is a powerful tool to explore the surface states, which allows to further investigate the topological phase transitions. However, it is very difficult to compare the first-principle calculated band structures to the ARPES results,when the systems are doped or alloyed, because the band structures are heavily folded.We develop an efficient band unfolding metho…
We have applied extended X-ray absorption fine structure (EXAFS) analyses and ab-initio molecular dynamics (AIMD) simulations to study the atomic structure of Ag-doped (up to 42%) Ge1Sb2Te4 alloys. Analysis of the models that are consistent with the EXAFS experiment reveals that the Ge environment is significantly modified by Ag doping whereas those of Sb and Te are barely affected (except for high Ag concentrations), and suggests that Ag prefers bonding with Te to Ge or Sb. Doping with Ag promotes the conversion of tetrahedral Ge sites to octahedral Ge sites and enhances the speed of crystall…
We have investigated the detailed magnetic structure of a Fe-doped MnNiGe alloy of nominal composition MnNi$_{0.75}$Fe$_{0.25}$Ge by ambient and high pressure (6 kbar) neutron powder diffraction study. The alloy undergoes a martensitic phase transition between 230 K and 275 K. The low-temperature martensite phase orders antiferromagnetically with helical modulation of Mn-spins. At 1.5 K, the incommensurate propagation vector $\bf k$ is found to be (0.1790(1),0,0), and it remains almost unchanged with temperature under ambient condition. The Application of external pressure ($P$) reduces the ma…
Structural and electronic properties of hypothetical zinc blende Tl(x)Ga(1-x)N alloys have been investigated from first principles. The structural relaxation, preformed within the LDA approach, leads to a linear dependence of the lattice parameter a on the Tl content x. In turn, band structures obtained by MBJLDA calculations are significantly different from the corresponding LDA results. The decrease of the band-gap in Tl-doped GaN materials (for x<0.25) is predicted to be a linear function of x, i.e. 0.08 eV per atomic % of thallium. The semimetallic character is expected for materials with …
The temperature dependence of the Seebeck coefficient of homoepitaxial metal organic vapor phase (MOVPE) grown, silicon doped $β$-Ga$_2$O$_3$ thin films was measured relative to aluminum. For room temperature we found the relative Seebeck coefficient of $S_{β\text{-Ga}_2\text{O}_3\text{-Al}}=(-300\pm20)\;μ$V/K. At high bath temperatures $T>240$ K, the scattering is determined by electron-phonon-interaction. At lower bath temperatures between $T=100$ K and $T=300$ K, an increase in the magnitude of the Seebeck coefficient is explained in the frame of Strattons formula. The influence of the diff…
We have studied magnetic properties of heavily Mn-doped [(In0.44Ga0.56)0.79Mn0.21]As thin films grown by low-temperature molecular-beam epitaxy (LT-MBE) on InP substrates. The (InGaMn)As with high Mn content (21%) was obtained by decreasing the growth temperature to 190 degC. When the thickness of the [(In0.44Ga0.56)0.79Mn0.21]As layer is equal or thinner than 10 nm, the reflection high-energy electron diffraction (RHEED) pattern and transmission electron microscopy (TEM) show no MnAs clustering, indicating that a homogeneous single crystal with good quality was grown. In the magnetic circular…
High entropy alloy(HEA) films of CrFeCoNiCu were prepared by sputtering, their structure was characterized, and their electric properties measured by temperature dependent Hall and Seebeck measurement. The HEA films show a solid solution with fcc structure, and a 111 texture with columnar grains of widths 15-30 nm extending through film thickness with very many twins. The residual electrical resistivity of the films is around 140 μΩcm and the temperature dependence of the resistivity is metal-like. The temperature coefficient of resistivity (TCR) is small (2 ppm/K). The Hall coefficient is pos…
Motivated by a recent observation of good thermoelectric properties in %a %pyrite material PtSb$_2$, we theoretically study related pyrites %materials in an attempt to %find a %better thermoelectric material. %Our aim is to seek for a material which overcomes the suppression of the Seebeck coefficient at high temperatures.% in PtSb$_2$. We find that PtAs$_2$ and PtP$_2$ are good candidates, where a larger band gap than in PtSb$_2$ combined with the overall flatness of the band top gives rise to a monotonically increasing Seebeck coefficient up to high temperatures. This expectation has been co…
Alloying effects by T=Mn,Co,Ni-substitution on FeS$_2$ have been investigated using density-functional calculations. The ferromagnetic alloys Fe$_{1-x}$T$_x$S$_2$ have been investigated for concentrations $x=\frac{1}{4},\frac{1}{2},\frac{3}{4}$ together with the ground states of the pure compounds. The electronic structure is discussed with the goal to identify candidates for half metals, which are of interest for spintronics applications. We find interesting candidates at high concentration of the Mn-doped FeS$_2$ and at low concentrations for Ni-doped materials. For the Mn alloys we also not…
Ge with a quasi-direct band gap can be realized by strain engineering, alloying with Sn, or ultrahigh n-type doping. In this work, we use all three approaches together to fabricate direct-band-gap Ge-Sn alloys. The heavily doped n-type Ge-Sn is realized with CMOS-compatible nonequilibrium material processing. P is used to form highly doped n-type Ge-Sn layers and to modify the lattice parameter of P-doped Ge-Sn alloys. The strain engineering in heavily-P-doped Ge-Sn films is confirmed by x-ray diffraction and micro Raman spectroscopy. The change of the band gap in P-doped Ge-Sn alloy as a func…
We investigate the spin-dependent electric and thermoelectric properties of ferromagnetic zigzag-graphyne nanoribbons (ZGNRs) using the density-functional theory combined with the non-equilibrium Green's function method. A giant magnetoresistance is obtained in the pristine even-width ZGNRs and can be as high as 10e6 %. However, for the doped systems, a large magnetoresistance behavior may appear in the odd-width ZGNRs rather than the even-width ones. This suggests that the magnetoresistance can be manipulated in a wide range by the dopants on edges of ZGNRs. Another interesting phenomenon is …
We found a giant Seebeck effect in semiconducting single-wall carbon nanotube (SWCNT) films, which exhibited a performance comparable to that of commercial Bi2Te3 alloys. Carrier doping of semiconducting SWCNT films further improved the thermoelectric performance. These results were reproduced well by first-principles transport simulations based on a simple SWCNT junction model. These findings suggest strategies that pave the way for emerging printed, all-carbon, flexible thermoelectric devices.
Magnetocrystalline anisotropy (MCA) in doped Ce$_{2}$Co$_{17}$ and other competing structures was investigated using density functional theory. We confirmed that the MCA contribution from dumbbell Co sites is very negative. Replacing Co dumbbell atoms with a pair of Fe or Mn atoms greatly enhance the uniaxial anisotropy, which agrees quantitatively with experiment, and this enhancement arises from electronic-structure features near the Fermi level, mostly associated with dumbbell sites. With Co dumbbell atoms replaced by other elements, the variation of anisotropy is generally a collective eff…
We have studied the effect of Fe addition on the structural and magnetic transitions in the magnetic shape memory alloy Ni-Mn-Ga by substituting systematically each atomic species by Fe. Calorimetric and AC susceptibility measurements have been carried out in order to study the magnetic and structural transformation properties. We find that the addition of Fe modifies the structural and magnetic transformation temperatures. Magnetic transition temperatures are displaced to higher values when Fe is substituted into Ni-Mn-Ga, while martensitic and premartensitic transformation temperatures shift…
The structural and magnetic behavior of Mn-site doped intermetallic manganese silicide alloys of nominal compositions Mn$_{5-x}$A$_x$Si$_3$ ($x$ = 0.05, 0.1, 0.2 and A = Ni, Cr) have been investigated with a focus to the inverted hysteresis behavior and thermomagnetic irreversibility. Room temperature x-ray powder diffraction data confirm that all the doped alloys crystallize in hexagonal $D8_8$ type structure with space group $P6_3/mcm$. The doped alloys are found to show paramagnetic (PM) - collinear antiferromagnetic (AFM2) - noncollinear antiferromagnetic (AFM1) transitions during cooling …
The electric and thermo-magneto-electric transport of the prototypical ferromagnetic transition-metal alloy system fcc-Co$_x$Pd$_{1-x}$ has been investigated on the basis of Kubo's linear response formalism. The results for the full electric conductivity tensor allow to discuss the spin-orbit induced anisotropic magneto-resistance (AMR) and the anomalous Hall effect (AHE). These are complemented by results for the corresponding thermo-magneto-electric transport properties anisotropy of the Seebeck effect (ASE) and anomalous Nernst effect (ANE). The relation between the respective response coef…
By using a multiscale approach based on first-principles density functional theory combined with atomistic spin dynamics, we investigate the electronic structure and magnetization dynamics of an inverse Heusler and a Heusler compound and their alloys, i. e. Mn$_{2-x}Z_x$CoAl and Mn$_{2-x}Z_x$VAl, where $Z$ = Mo, W, Os and Ru, respectively. A signature of the ferrimagnetic ordering of Mn$_{2}$CoAl and Mn$_{2}$VAl Heusler alloys is reflected in the calculated Heisenberg exchange constants. They decay very rapidly with the interatomic distance and have short range, which is a consequence of the e…
For simultaneously achieving the high-power factor and low lattice thermal conductivity of Si-Ge based thermoelectric materials, we employed, in this study, constructively modifying the electronic structure near the chemical potential and nano-structuring by low temperature and high-pressure sintering on nano-crystalline powders. Nickel was doped to create the impurity states near the edge of the valence band for enhancing the power factor with boron for tuning the carrier concentration. The nanostructured samples with the nominal composition of Si0.65-xGe0.32Ni0.03Bx (x = 0.01, 0.02, 0.03, an…
Very sharp magnetization step is observed across the field induced antiferromagnetic to ferromagnetic transition in various doped-CeFe$_2$ alloys, when the measurement is performed below 5K. In the higher temperature regime (T$>$5K) this transition is quite smooth in nature. Comparing with the recently observed similar behaviour in manganites showing colossal magnetoresistance and magnetocaloric material Gd$_5$Ge$_4$ we argue that such magnetization step is a generalized feature of a disorder influenced first order phase transition.
Microstructural origin of the simultaneous enhancements in strength and ductility of a nitrogen-doped high-entropy alloy
Soochow University（苏州大学）；Research Institute of Aero-Engine, Beihang University（北京航空航天大学发动机研究院）；Center for Advancing Materials Performance from the Nanoscale (CAMP-Nano) and Hysitron Applied Research Center in China (HARCC), and Center for Alloy Innovation and Design (CAID), State Key Lab for Mechanical Behavior of Materials, Xi’an Jiaotong University（西安交通大学材料行为科技重点实验室、纳米尺度材料性能提升中心（CAMP-Nano）、海塞特中国应用研究中心（HARCC）及合金创新与设计中心（CAID））；Max Planck Institute for Sustainable Materials（马普可持续材料研究所）；Institute for Materials Science, University of Stuttgart（斯图加特大学材料科学研究所）；ICAMS, Ruhr-Universität Bochum（波鸿鲁尔大学综合材料与结构科学研究所）；State Key Laboratory of Powder Metallurgy, School of Materials Science and Engineering, Central South University（中南大学材料科学与工程学院粉末冶金国家重点实验室）；Department of Materials, Royal School of Mine, Imperial College London（帝国理工学院皇家矿业学院材料系）
Giant magnetostriction is achieved in the slightly Tb-doped Fe83Ga17 melt-spun ribbons. The tested average perpendicular magnetostriction is -886 ppm along the melt-spun ribbon direction in the Fe82.89Ga16.88Tb0.23 alloy. The calculated parallel magnetostriction is 1772 ppm, more than 4 times as large as that of binary Fe83Ga17 alloy. The enhanced magnetostriction should be attributed to a small amount of Tb solution into the A2 matrix phase during rapid solidification. The localized strong magnetocrystalline anisotropy of Tb element is suggested to cause the giant magnetostriction.
While the thermoelectric figure of merit zT above 300K has seen significant improvement recently, the progress at lower temperatures has been slow, mainly limited by the relatively low Seebeck coefficient and high thermal conductivity. Here we report, for the first time, success in first-principles computation of the phonon drag effect - a coupling phenomenon between electrons and non-equilibrium phonons - in heavily doped region and its optimization to enhance the Seebeck coefficient while reducing the phonon thermal conductivity by nanostructuring. Our simulation quantitatively identifies th…
Here, we report the successful synthesis of electron- (Ni) and hole- (K) doped bulk BaFe2As2 compounds by means of mechanical alloying (MA) process. The MA technique allows one to obtain amorphous phase BaFe2As2 with a homogeneous distribution of doping atoms at room temperature without continuous heating. We found the optimum time for high-energy milling is in the range between 1-1.5 hours. Using pre-synthesised FeAs and NiAs precursors, we successfully obtained BaFe2-xNixAs2 and Ba1-xKxFe2As2 superconducting bulk samples after short-range heat treatment. This method can be easily scaled acco…
Upon chemical substitution of oxygen with fluor, LaMnAsO has been electron-doped in experiments, resulting in samples with remarkably high Seebeck coefficients of around -300$μVK^{-1}$ at room temperature and 3% doping. Within the framework of density functional theory plus dynamical mean-field theory we are not only able to reproduce these experimental observations, but can also provide a thorough investigation of the underlying mechanisms. By considering electronic correlations in the half-filled Mn-3d shells, we trace the high Seebeck coefficient back to an asymmetry in the spectral functio…
Investigation of Seebeck coefficient in ultra-wide bandgap materials presents a challenge in measurement, nevertheless, it is essential for understanding fundamental transport mechanisms involved in electrical and thermal conduction. \b{eta}-Ga2O3 is a strategic material for high power optoelectronic applications. Present work reports Seebeck coefficient measurement for single crystal Sn doped \b{eta}-Ga2O3 in a wide temperature range (80-630 K). The non-monotonic trend with large magnitude and negative sign in the entire temperature range shows electrons are dominant carriers. The structural …
To clarify the origin of the nontrivial thermoelectric properties observed in the delafossite oxide CuRhO$_2$ polycrystals, we have performed the systematic transport measurements on the single-crystalline CuRhO$_2$ samples. In the parent compound, we find a pronounced peak structure due to a phonon-drag effect in the temperature dependence of the Seebeck coefficient, which is also confirmed by the size effect experiments. In the Mg-substituted crystals, in contrast to the results of the polycrystals, both the resistivity and the Seebeck coefficient decrease with increasing Mg content $y$. In …
We present a general coupled electron-phonon Boltzmann transport equations (BTEs) scheme designed to capture the mutual drag of the two interacting systems. By combining density functional theory based first principles calculations of anharmonic phonon-phonon interactions with physical models of electron-phonon interactions, we apply our implementation of the coupled BTEs to calculate the thermal conductivity, mobility, Seebeck and Peltier coefficients of n-doped gallium arsenide. The measured low temperature enhancement in the Seebeck coefficient is captured using the solution of the fully co…
Dispersion corrected density functional theory ($ω$B97X-D DFT) method is used to study the molecular hydrogen adsorption in $Ni_nMg_m$ $(1\geq n\geq 3,1\geq m\geq9)$ clusters. All these clusters can effectively adsorb multiple $H_2$ in the preferred binding energy (BE) range between physisorption and chemisorption, i.e., $0.1 eV\geq BE \geq0.8 $eV. $H_2$ adsorption on $Ni_kMg_k$ (Ni:Mg=1:1), $Ni_kMg_{2k}$ (Ni:Mg=1:2) and $Ni_kMg_{3k}$ (Ni:Mg=1:3) (k=1-3) clusters shows fascinating behaviours in terms of Ni:Mg alloying ratio and cluster size. In each Ni:Mg ratio, the number of adsorbed $H_2$ in…
The ground state properties of the ferromagnetic shape memory alloy of nominal composition Ni2Mn1.36Sn0.64 have been studied by dc magnetization and ac susceptibility measurements. Like few other Ni-Mn based alloys, this sample exhibits exchange bias phenomenon. The observed exchange bias pinning was found to originate right from the temperature where a step-like anomaly is present in the zero-field-cooled magnetization data. The ac susceptibility study indicates the onset of spin glass freezing near this step-like anomaly with clear frequency shift. The sample can be identified as a reentrant…
We present evidence of strong Shubnikov-de-Haas magnetoresistance oscillations in a polarization-doped degenerate three-dimensional electron slab in an Al$_{x}$Ga$_{1-x}$N semiconductor system. The degenerate free carriers are generated by a novel technique by grading a polar alloy semiconductor with spatially changing polarization. Analysis of the magnetotransport data enables us to extract an effective mass of $m^{\star}=0.19 m_{0}$ and a quantum scattering time of $τ_{q}= 0.3 ps$. Analysis of scattering processes helps us extract an alloy scattering parameter for the Al$_{x}$Ga$_{1-x}$N mat…
The Seebeck coefficients, electrical resistivities, total thermal conductivities, and magnetization are reported for temperatures between 5 and 350 K for n-type Bi0.88Sb0.12 nano-composite alloys made by Ho-doping at the 0, 1 and 3% atomic levels. The alloys were prepared using a dc hot-pressing method, and are shown to be single phase for both Ho contents with grain sizes on the average of 900 nm. We find the parent compound has a maximum of ZT = 0.28 at 231 K, while doping 1% Ho increases the maximum ZT to 0.31 at 221 K and the 3% doped sample suppresses the maximum ZT = 0.24 at a temperatur…
We study the Seebeck effect in the three-dimensional Dirac electron system based on the linear response theory with Luttinger's gravitational potential. The Seebeck coefficient $S$ is defined by $S = L_{12} / L_{11} T$, where $T$ is the temperature, and $L_{11}$ and $L_{12}$ are the longitudinal response coefficients of the charge current to the electric field and to the temperature gradient, respectively; $L_{11}$ is the electric conductivity and $L_{12}$ is the thermo-electric conductivity. We consider randomly-distributed impurity potentials as the source of the momentum relaxation of elect…
