Insulating-metallic transition mediated by substitutional atoms is predicted in a series of two-dimensional carbon-based structures. Introducing Si atoms in selected sites of tetrahexcarbon [Carbon 137 (2018) 266] according to rational chemical rules, metallicity by trivial band inversion without band gap opening is induced. Additional substitution of remaining C atoms by BN dimers introduces no changes in the metallic properties. A series of isomorphous two-dimensional materials with isoelectronic structures derived by exchanging group IV elements exhibiting various band gaps is obtained. Dynamical stability is verified with phonon analysis and beyond the harmonic approximation with molecular dynamics up to room temperature. The semi-metallic compounds have well-nested pockets of carriers and are good candidates for the formation of an excitonic insulator.
Employing {\it ab initio} electronic structure calculations we extensively study ternary Heusler compounds having the chemical formula X$_2$X$^\prime$Z, where X = Mn, Fe or Co; Z = Al or Si; and X$^\prime$ changes along the row of 4$d$ transition metals. A comprehensive overview of these compounds, addressing the trends in structural, electronic, magnetic properties and Curie temperature is presented here along with the search for new materials for spintronics applications. A simple picture of hybridization of the $d$ orbitals of the neighboring atoms is used to explain the origin of the half-…
Half-Heusler compounds with 18 valence electrons per unit cell are well-known non-magnetic semiconductors. Employing first-principles electronic band structure calculations, we study the interface properties of the half-Heusler heterojunctions based on FeVSb, CoTiSb, CoVSn, and NiTiSn compounds, which belong to this category of materials. Our results show that several of these heterojunction interfaces become not only metallic but also magnetic. The emergence of spin-polarization is accompanied by the formation of two-dimensional electron gas (2DEG) or hole gas (2DHG) at the interface. We qual…
This paper presents a detailed investigation of FeCr-based quaternary Heusler alloys. By using ultrasoft pseudopotential, electronic and magnetic properties of the compounds are studied within the framework of Density Functional Theory (DFT) by using the Quantum Espresso package. The thermodynamic, mechanical, and dynamical stability of the compounds is established through the comprehensive study of different mechanical parameters and phonon dispersion curves. The meticulous study of elastic parameters such as bulk, Young's, shear moduli, etc. is done to understand different mechanical propert…
First principles studies were performed in order to find out the possibility of inducing half-metallicity in Heusler Compound CoFeMnSb, by means of alloying it with 3d-transition metal elements. Proper alloying element is selected through the calculations of formation energies. These calculations were tested with different concentrations of alloying elements at different atomic sites. Among the selected transition metal elements Sc and Ti are proposed to be excellent alloying elements particularly at Mn site. By using these alloying elements complete half metallic behaviour is obtained in CoFe…
Here, we systematically investigate the structure, phase stability, half-metallicity, and topological electronic structure for a new topological spintronic material NaV2O4. The material has a tetragonal structure with excellent dynamical and thermal stabilities. It shows a half-metallic ground state, where only the spin-up bands present near the Fermi level. These bands form a Weyl nodal line close to the Fermi level, locating in the kz = 0 plane. The nodal line is robust against SOC, under the protection of the mirror symmetry. The nodal line band structure is very clean, thus the drumhead su…
Atomistic simulations of liquid alloys face the challenge of correctly modeling basic thermodynamic properties. In this work we present an interatomic potential for the Li-Pb system, as well as a study of physical properties of Li-Pb alloys. Despite the complexity due to Li-Pb being a compound forming system where charge transfer is expected, we show here how the empirical EAM formalism is able to satisfactorily describe several physical properties in a wide range of Li concentration. Application of our potential to Li-Pb eutectic allows us to correctly predict many physical properties observe…
Charged nitrogen dimers are ubiquitous in high-pressure binary metal-nitrogen systems. They are known to possess integer formal charges x varying from one through four. Here, we present the investigation of the binary alkali- and alkaline earth metal-nitrogen systems, Na-N, Ca-N, Sr-N, Ba-N to 70 GPa. We report on compounds-Na3(N2)4, Ca3(N2)4, Sr3(N2)4, and Ba(N2)3-featuring charged nitrogen dimers with paradigm-breaking non-integer charges, x = 0.67, 0.75 and 1.5. The metallic nature of all four compounds is deduced from ab initio calculations. The conduction electrons occupy the pi* antibond…
Molecule oxygen resembles 3d and 4f metals in exhibiting long-range spin ordering and electron strong correlated behaviors in compounds. The ferromagnetic spin ordering and half-metallicity, however, are quite elusive and have not been well acknowl-edged. In this article, we address this issue to study how spins will interact each other if the oxygen dimers are arranged in a dif-ferent way from that in the known super- and per-oxides by first principles calculations. Based on the results of structure search, thermodynamic study and lattice dynamics, we show that tetragonal α-BaNaO4 is a stable…
While the role of the free energy barrier during nucleation is a text-book subject the importance of the kinetic factor is frequently underestimated. We obtained both quantities from molecular dynamics (MD) simulations for the pure Ni and B2 phases in the Ni50Al50 and Cu50Zr50 alloys. The free-energy barrier was found to be higher in Ni but the nucleation rate is much lower in the Ni50Al50 alloy which was attributed to the ordered nature of the B2 phase. Since the Cu50Zr50 B2 phase can has even smaller fraction of the anti-site defects its nucleation is never observed in the MD simulation.
This work presents results for the magnetic properties of the compound GeTe doped with 3d transition metals V, Cr and Mn from the viewpoint of potential application in spintronics. We report a systematic density-functional study of the electronic structure, magnetic and cohesive properties of these ternary compounds in both rock salt and zinc blende structures. In both cases, it is the Ge sublattice that is doped with the three transition metals. Some of these compounds are found to be half-metallic at their optimized cell volumes. For these particular cases, we calculate both exchange interac…
Results of Co and Ni substituted AlN in the zinc blende phase are presented. For spin up states the hybridized N-2p and Co/Ni-3d states form the valance bands with a bandgap around the Fermi level for both materials, while in the case of the spin down states the hybridized states cross the Fermi level and hence show metallic nature. It is found that, Al0.75Co0.25N and Al0.75Ni0.25N are ferromagnetic materials with magnetic moments of 4 μB and 3 μB respectively. The integer magnetic moments and the full spin polarization at the Fermi level make these compounds half-metallic semiconductors. Furt…
The half-metallic properties of a new and promising full-Heusler compound, Zr2CoSn, are investigated by means of ab initio calculations within the Density Functional Theory framework. The ferromagnetic ordered Hg2CuTi-type crystal structure is energetically favorable and the optimized lattice parameter is 6.76 A. The total magnetic moment calculated is 3 uB/f.u. and follows a typical Slater-Pauling dependence. The half metallicity disappears if the unit cell volume is contracted by 5 %.
Influence of mixing the low-valent transition metal atoms (Y,Y$^*$=Cr,Mn,Fe) on the properties of the quaternary Co$_2$[Y$_{1-x}$Y$^*_x$]Z (Z=Al,Ga,Si,Ge,Sn) Heusler compounds
我们补充了我们对Co-$_2$-MnZ化合物的掺杂和无序的研究[I. Galanakis \textit{et al.}，Appl. Phys. Lett. \textbf{89}，042502（2006）和K.Özdogan \textit{et al.}，Phys. Rev. B \textbf{74}，（2006）]，以还涵盖四元钴$_2$ [Y $_{1-x}$ Y $^*_x$ ]Z化合物，其中低价过渡金属Y、Y $^*$为Cr、Mn或Fe，且sp原子Z为Al、Ga、Si、Ge、Sn中的一种。这项研究给出了这些化合物的磁性和电子性质的全局概述，因为我们改变了Y和Z元素。我们的研究结果表明，对于实际应用中，最合适的化合物是那些属于家庭的Co $_2$ [Mn $_{1-x}$ Cr $_x$ ]Z与$x>0.5$的$sp$原子的性质无关，因为它们结合了高值的大多数DOS在费米能级由于Cr的存在下，和半金属性与大的带隙。另一方面，Fe的存在大大降低了费米能级处的多数态密度，并且当与属于Si柱的元素结合时，它甚至可以破坏半金属性。
Using three correlated band approaches, namely the conventional band approach plus on-site Coulomb repulsion $U$, the modified Becke-Johnson functional, and hybrid functional, we have investigated inverse-Heusler ferrimagnets Cr$_2$Co${\cal Z}$ (${\cal Z}$=Al, Ga, In). These approaches commonly indicate that the Cr$_2$CoAl synthesized recently is a precise compensated half-metal (CHM), whereas Cr$_2$CoGa and Cr$_2$CoIn are ferrimagnets with a small moment. This is also confirmed by the fixed spin moment approach. Analysis of the Bader charge decomposition and the radial charge densities indica…
Herbertsmithite and Zn-doped barlowite are two compounds for experimental realization of twodimensional gapped kagome spin liquid. Theoretically, it has been proposed that charge doping a quantum spin liquid gives rise to exotic metallic states, such as high-temperature superconductivity. However, one recent experiment about herbertsmithite with successful Li-doping shows surprisingly the insulating state even under the heavy doped scenario, which can hardly be explained by many-body physics. Using first-principles calculation, we performed a comprehensive study about the Li intercalated dopin…
A triangular lattice selenide series of rare earth (RE), CsRESe2, were synthesized as large single crystals using a flux growth method. This series stabilized in either trigonal (R-3m) or hexagonal (P63/mmc) crystal systems. Physical properties of CsRESe2 were explored by magnetic susceptibility and heat capacity measurements down to 0.4 K. Antiferromagnetic interaction was observed in all magnetic compounds, while no long-range magnetic order was found, indicating the frustrated magnetism. CsDySe2 presents spin freezing at 0.7 K, revealing a spin-glass state. CsCeSe2 and CsYbSe2 present broad…
Heusler alloys with Mn and Co have been found to exhibit interesting electronic and magnetic properties. Mn$_2$CoAl is well known SGS compound while Mn$_2$CoGa has weak half metallic character. By using plane wave pseudo-potential method, we studied the effect of Fe and Cr doping on half-metalicity and magnetism of these compounds. The doping destroys the SGS nature of Mn$_2$CoAl while the small-scale doping enhance the half-metallicity of Mn$_2$CoGa making it perfect half-metal. In case of Mn$_2$CoAl, the doping decrease the band gap while increase in band width is noticed for Mn$_2$CoGa. The…
The realization of the stable structure of Heusler compounds and the study of different properties is an important step for their potential application in spintronics and magnetoelectronic devices. In this paper, using the plane-wave pseudopotential method within the framework of density functional theory (DFT), we investigate 25 Quaternary Heusler compounds for their electronic, magnetic, and mechanical properties. The Open Quantum Materials Database (OQMD) is used to screen a large number of compounds to narrow down the possible synthesizable materials. The convex-hull distance and elastic c…
We present extensive first-principles calculations on the inverse full-Heusler compounds having the chemical formula X$_2$YZ where (X = Sc, Ti, V, Cr or Mn), (Z = Al, Si or As) and the Y ranges from Ti to Zn. Several of these alloys are identified to be half-metallic magnets. We show that the appearance of half-metallicity is associated in all cases to a Slater-Pauling behavior of the total spin-magnetic moment. There are three different variants of this rule for the inverse Heusler alloys depending on the chemical type of the constituent transition-metal atoms. Simple arguments regarding the …
Polycrystalline samples of NaYbO$_2$ are investigated by bulk magnetization and specific-heat measurements, as well as by nuclear magnetic resonance (NMR) and electron spin resonance (ESR) as local probes. No signatures of long-range magnetic order are found down to 0.3~K, evidencing a highly frustrated spin-liquid-like ground state in zero field. Above 2\,T, signatures of magnetic order are observed in thermodynamic measurements, suggesting the possibility of a field-induced quantum phase transition. The $^{23}$Na NMR relaxation rates reveal the absence of magnetic order and persistent fluctu…
Spin freezing in the $A$-site spinel FeAl$_2$O$_4$ which is a spin liquid candidate is studied using remnant magnetization and nonlinear magnetic susceptibility and isofield cooling and heating protocols. The remnant magnetization behavior of FeAl$_2$O$_4$ differs significantly from that of a canonical spin glass which is also supported by analysis of the nonlinear magnetic susceptibility term $χ_3 (T)$. Through the power-law analysis of $χ_3 (T)$, a spin-freezing temperature, $T_g$ = 11.4$\pm$0.9~K and critical exponent, $γ$ = 1.48$\pm$0.59 are obtained. Cole-Cole analysis of magnetic suscept…
This paper is focused on the relationship between solidification and melt sates. An abnormal change which takes place at 744 C from 84 to 120 min indicated a liquid-liquid structure transition in pure Bi melt. Based on liquid-liquid structure transition, experiments of pure Bi were carried out. Cooling from different melt states, the solidification behaviors and structures changed a lot, such as undercooling, solidification time, grain sizes and the number of twins and pedestal sits. Especially, as a semi-metal, a liquid-liquid structure transition greatly increases the metallicity of Bi, and …
Computational Investigation of Reactivity Parameters, UV-Vis and IR Spectra, NLO Properties, and Temperature-Dependent Thermodynamic Characteristics of Schiff-Based Interdigitated 5O.m (m=14,16) Liquid Crystalline Compounds: A DFT Analysis
We search for new fully compensated half metals, in which only one electronic spin channel is conducting and there exists no net magnetic moment. We focus on half Heusler alloys and we examine the physical consequence of different crystal structures found in the literature for these compounds, XMnZ, with a transition metal element, such as Cr, Mn, and Fe for X and a nonmetallic element, such as P, Sb and Si for Z. The structures differ in the placement of voids in the L2$_1$ structure of the full Heulser alloy. One structure has the void at (1/4, 3/4, 1/4)a and the other places the void at (0.…
The Cr2Ge2Te6 (CGT) compound is an intrinsic ferromagnetic material with a van der Waals layered structure that shows great promise in spintronics applications. In this work, we investigated the edge effect in the formation of CGT nanoribbons with different terminations as well as the change in electronic and magnetic properties considering spin-orbit effects on the calculations. We studied the thermodynamic stability of the nanoribbon employing the surface formation energy formalism. According to the calculations, in regions of Ge-rich, Te-rich, and Ge-poor, Te-poor of chemical potential the …
We study the structural, electronic, and magnetic properties of Co$_2$ZAl compounds employing a pseudopotential electronic bandstructure method. The stability of the compounds is established through the formation and cohesive energy calculations. The effect of the lattice parameter variation on the electronic and magnetic properties of the compounds is investigated and meticulous explanation is provided for the observed behavior. The variation of the individual spin magnetic moments and the stability of the total spin magnetic moment during the expansion and contraction of the lattice paramete…
We investigate the electronic structure and magnetism of half-Heusler compounds XYZ (X, Y=V, Cr, Mn, Fe, Co and Ni; Z=Al, Ga, In, Si, Ge, Sn, P, As, and Sb) using the ab initio density functional theory calculations. Nine half-metals with half-Heusler structure have been predicted with the half-metallic gap of 0.07-0.67 eV. The calculations show that the formation energies for these nine half-Heusler compounds range from -1.32 to -0.12 eV/f.u., and for CoCrSi, CoCrGe, CoFeGe, CoMnSi, CoMnGe, FeMnGe and FeMnAs, the total energy differences between the half-Heusler structure and the correspondin…
Compound semiconducting nanowires are promising building blocks for several nanoelectronic devices yet the inability to reliably control their growth morphology is a major challenge. Here, we report the Au-catalyzed vapor-liquid-solid (VLS) growth of GaN nanowires with controlled growth direction, surface polarity and surface roughness. We develop a theoretical model that relates the growth form to the kinetic frustration induced by variations in the V(N)/III(Ga) ratio across the growing nanowire front. The model predictions are validated by the trends in the as-grown morphologies induced by s…
Non-Fermi-liquid behavior in Ce(Ru$_{1-x}$Fe$_x$)$_2$Ge$_2$: cause and effect
本文报道了金属间化合物Ce（Ru $_{1-x}$ Fe $_x$）$_2$ Ge $_2$（$x$ = 0.65，0.76和0.87）的非弹性中子散射测量。这些化合物分别代表磁有序相、量子临界点和重费米子相的样品。我们表明，在高温下的三种组合物具有相同的本地时刻系统的响应。然而，在低温下，临界组成中的自旋涨落由非费米液体动力学给出，而重费米子系统中的自旋涨落则随时间呈简单的指数衰减。在这两种组合物中，波动的寿命仅由到量子临界点的距离决定。我们讨论了这些意见的影响，在这个系统中的非费米液体行为的可能起源。
Novel liquid crystalline (LC) compositions are suggested and studied as elements of LC-nose. This allows for optical detection of several volatile organic compounds (VOCs). Ethanol, toluene, pyridine and acetic acid were detected by means of colorimetric and spectroscopic techniques during their diffusion inside chiral elements of LC-nose. Selectivity to different VOCs is enhanced by means of components of liquid crystal matrix with different viscosity, affinities to the solvents, and abilities to form hydrogen bonding.
Cooling oxygen-deficient strontium titanate to liquid-helium temperature leads to a decrease in its electrical resistivity by several orders of magnitude. The temperature dependence of resistivity follows a rough T$^{3}$ behavior before becoming T$^{2}$ in the low-temperature limit, as expected in a Fermi liquid. Here, we show that the roughly cubic resistivity above 100K corresponds to a regime where the quasi-particle mean-free-path is shorter than the electron wave-length and the interatomic distance. These criteria define the Mott-Ioffe-Regel limit. Exceeding this limit is the hallmark of …
Reduced dimensionality offers a crucial information in deciding the type of the quantum ground state in heavy fermion materials. Here we have examined stoichiometric CeCo$_{2}$Ga$_{8}$ compound, which crystallizes in a quasi-one-dimensional crystal structure with Ga-Ce-Co chains along the $c$-axis. The low-temperature behavior of magnetic susceptibility ($χ\sim-\ln T$), heat capacity ($C_p/T\sim-\ln T$), and resistivity ($ρ\sim T^{n}$) firmly confirm the non-Fermi liquid ground state of CeCo$_{2}$Ga$_{8}$. We studied the low-energy spin dynamics of CeCo$_{2}$Ga$_{8}$ compound utilizing zero fi…
The interplay of non-local Coulomb repulsion and Hund's coupling in the d-orbital manifold in frustrated triangular lattices is analyzed by a mutliband extended Hubbard model. We find a rich phase diagram with several competing phases, including a robust pinball liquid phase, which is an unconventional metal characterized by threefold charge order, bad metallic behavior and the emergence of high spin local moments. Our results naturally explain the anomalous charge-ordered metallic state observed in the triangular layered compound AgNiO2. The potential relevance to other triangular transition …
