Strong Spin Polarization Research Articles

N-doped coralline Co9S8−xNx for inducing Amitriptyline decontamination in Electro-Fenton Process: Degradation scheme Elucidation, nitrogen activating catalyst delocalized electron and enhancing 2-Electron oxygen reduction reaction mechanism investigation

Improving the recalcitrant emergent contaminant removal in electron-Fenton (EF) has been one of the focal problems. Here, a N-doped coralline Co9S8−xNx catalyst was synthesized with high electronegativity and strong spin polarization for promoting the H2O2 generation efficiency and Amitriptyline (AMT) removal. After doping nitrogen, catalytic performance of Co9S8−xNx has increased ∼10 % on AMT decay and the treatment time was shortened ∼40 min. Co9S8−xNx induced 2-electron oxygen reduction reaction (ORR) mechanism has also been investigated. According to electronic structure analysis, electrons surrounding the cobalt atoms were redistributed and the π* orbitals of *O2 were occupied asymmetrically forcing *O2 to be of radical nature active for hydrogenation, which significantly reduced required absorption energy in the rate-determining step (RDS). This work clarifies the mediate role of N-doped activating delocalized electron of adjacent atoms on the surface of Co9S8−xNx and also gives new insights into the rational design of catalyst for refractory pollutant degradation in wastewater.

Ab initio prediction of half-metallicity in the NaMnZ2 (Z = S, Se, Te) ternary layered compounds

Motivated by recent theoretical studies predicting half-metallicity in some ternary manganese chalcogenides, first-principles calculations based on spin-polarized density functional theory (DFT) are applied to investigate the structural, elastic, electronic and magnetic properties of the ternary layered compounds NaMnZ2 (Z = S, Se, Te). We assume for all compounds the experimentally determined, in the case of NaMnSe2 and NaMnTe2 compounds, noncentrosymmetric trigonal structure (space group P3m1; no. 156). The analysis of spin-polarized band structures and of the diagrams of density of states reveals the half-metallic character of the considered materials. We find that the strong spin polarization of the d orbitals of the manganese atoms is at the origin of the ferromagnetism of these compounds with a total magnetic moment per formula unit of 4μB. The studied compounds show a Slater-Pauling behavior and the total spin magnetic moment per cell (Mt) evolves with the total number of valence electrons (Zt) according to the lawMt=(Zt−22)μB. The calculated values of the minority-spin energy gap (Eg) and of the half-metallic gap (EHM) for the explored materials show that they are promising compounds for spintronic applications.

Dynamical correlations in single-layer CrI3

Chromium triiodide is an intrinsically magnetic van der Waals material down to the single-layer limit. Here, we provide a first-principles description of finite-temperature magnetic and spectral properties of monolayer (ML) ${\mathrm{CrI}}_{3}$ based on fully charge self-consistent density functional theory (DFT) combined with dynamical mean-field theory, revealing a formation of local moments on Cr from strong local Coulomb interactions. We show that the presence of local dynamical correlations leads to a modification of the electronic structure of ferromagnetically ordered ${\mathrm{CrI}}_{3}$. In contrast to conventional $\mathrm{DFT}+U$ calculations, we find that the top of the valence band in ML ${\mathrm{CrI}}_{3}$ demonstrates essentially different orbital character for minority and majority spin states, which is closer to the standard DFT results. This leads to a strong spin polarization of the optical conductivity upon hole doping, which could be verified experimentally.

Spin Polarization of Mn Could Enhance Grain Boundary Sliding in Mg.

Segregation of rare earth alloying elements are known to segregate to grain boundaries in Mg and suppress grain boundary sliding via strong chemical bonds. Segregation of Mn, however, has recently been found to enhance grain boundary sliding in Mg, thereby boosting its ductility. Taking the Mg (114) twin boundary as an example, we performed a first-principles comparative study on the segregation and chemical bonding of Y, Zn, and Mn at this boundary. We found that both Y-4d and Mn-3d states hybridized with the Mg-3sp states, while Zn–Mg bonding was characterized by charge transfer only. Strong spin-polarization of Mn pushed the up-spin 3d states down, leading to less anisotropic Mn–Mg bonds with more delocalized charge distribution at the twin boundary, and thus promotes grain boundary plasticity, e.g., grain boundary sliding.

Structural, Electronic, and Magnetic Properties of Sr\(_{1-x}\)Mn\(_{x}\)F\(_{2}\) Alloys Studied by First-principles Calculations

In this work, the structural, electronic, and magnetic properties of the Sr\(_{1-x}\)Mn\(_{x}\)F\(_{2}\) (x = 0, 0.25, 0.5, 0.75, and 1) compounds are investigated using first-principles calculations. Crystallizing in fluorite structure, SrF\(_{2}\) is a magnetism-free indirect gap insulator with band gap of 11.61 eV as determined by the reliable mBJK functional. Mn substitution induces the magnetic insulator behavior as both spin configurations exhibit large band gaps with a strong spin-polarization. Specifically, spin-up energy gaps of 8.554, 7.605, 6.902, and 6.154 eV are obtained for Sr\(_{0.75}\)Mn\(_{0.25}\)F\(_{2}\), Sr\(_{0.5}\)Mn\(_{0.5}\)F\(_{2}\), Sr\(_{0.25}\)Mn\(_{0.75}\)F\(_{2}\), and MnF\(_{2}\), respectively. Whereas, the spin-down state shows larger values of 8.569, 8.864, 9.307, and 9.837 eV, respectively. Consequently, significant magnetization is induced and an integer total spin magnetic moment of 5 \(\mu_{B}\) is obtained, being produced mainly by the spin-up Mn-3d state. Finally, the formation enthalpy and cohesive energy are determined, which indicate good thermodynamic and structural stability of the studied materials. Results suggest that Mn substitution at the Sr-sites of SrF\(_{2}\) compound may be an efficient approach to create new magnetic materials to be used in the spintronic devices.

Dynamic spin polarization in organic semiconductors with intermolecular exchange interaction

It is shown that in organic semiconductors where organic magnetoresistance (OMAR) is observed, the exchange interaction between electrons and holes localized at different molecules leads to dynamic spin polarization in the direction of the applied magnetic field. The polarization appears even at room temperature due to the non-equilibrium conditions. The strong spin polarization requires exchange energy to be comparable with Zeeman energy in the external field and be larger or comparable with the energy of hyperfine interaction of electron and nuclear spins. The exchange interaction also modifies the lineshape of OMAR.

Highly efficient, field-assisted water splitting enabled by a bifunctional Ni3Fe magnetized wood carbon

Various strategies have been used to improve the performance of non-noble catalysts, such as alloying, doping, and fine structure modulations. Herein, we reported a magnetic field-enhanced, bifunctional Ni3Fe/wood carbon electrode (Ni3Fe-CW) for efficient overall water splitting. Wood with numerous porous channels allows high loading of metal ions via the hydrothermal method, while the following high-temperature calcination leads to well-dispersed and uniform Ni3Fe nanoparticles, which are both electrocatalytically and magnetically active. As a result, the Ni3Fe-CW shows low overpotentials of 237 mV and 76 mV at 10 mA cm−2 for both oxygen and hydrogen evolutions under magnetic field (300 mT by a permanent magnet). Density functional theory calculations demonstrate that the Ni3Fe exhibits strong spin polarization under magnetic field with accelerated electron transfer, leading to lower reaction energy barrier and enhanced catalytic activities. Importantly, the electrolytic cell constructed by the bifunctional Ni3Fe-CWs as both cathode and anode displays a low cell voltage of 1.54 V at 10 mA cm−2 with an appropriate stability over 50 h (with a passive magnet). Considering the ubiquitous application of magnetic Fe, Co, Ni in catalytic reactions and the passive-radiation role of magnet, our strategy is promising for many energy conversion technologies toward highly efficient catalysis.

Synergistic Effect of Chiral Nanofibers Amplifying the Orbit Angular Momentum To Enhance Optomagnetic Coupling.

Manipulating magnetic bits by photon in spintronics, opto-magnetic coupling, is lagging far behind what we could expect. To investigate the issue, one should face the problem to find photon dependence of spin dynamics and spin manipulation. In this work, through introducing chiral orbit in organic crystals, circularly polarized photon can manipulate spin via the channel of photon-orbit-spin interactions. Under the stimulus of the magnetic field, strong spin polarization will feed back to the change in polarized state of light. Moreover, twisting several chiral nanofibers into a thick one, a more pronounced opto-magnetic coupling is clearly observed due to the chirality generated larger chiral orbit. Meanwhile, spin dynamics (or spin response times) inside the aggregated thick chiral fiber can be further tuned by circularly polarized light. Hopefully, this study can deepen the understanding of organic chiral spin-photonics and enhance the application of organic functional crystals in the future.

DFT studies on electronic, magnetic and thermoelectric properties of half Heusler alloys XCaB (X = Li, Na, K and Rb)

In this work, the results of first principles calculations of structural, electronics, magnetic and thermoelectric properties of half Heusler alloys XCaB (X = Li, Na, K and Rb) are presented. The pseudopotential method as implemented in the Quantum Espresso package has been used with the exchange correlation functional of Perdew, Burke and Ernzerhof (PBE). The total energy calculations show that the proposed alloys are in stable ferromagnetic phase and the calculated equilibrium lattice constant are in good agreement with the earlier reported results. All the alloys show strong spin polarisation of energy states near the Fermi level confirming ferromagnetic nature and also semiconducting for majority spin channel and metallic for down spin channel exhibiting half metallic property. The calculated magnetic moment of all the alloys XCaB (X = Li, Na, K and Rb) is around 2.00 µB mainly arises from the np electrons of B atom with partial involvement of nd electrons of Ca atom. The thermoelectric properties of the materials are calculated using the BoltzTrap code. The calculated transport properties like electrical conductivity, thermal conductivity and power factor increases with temperature which is a perfect fit for thermoelectric applications. The half metallic gap, strong spin polarization and high figure of merit (ZT) values shows that these studied materials can be used for both spintronics and thermoelectric device applications.

Magnetotransport in ferromagnetic Fe2Ge semimetallic thin films

Thin films of ferromagnet Fe2Ge were grown via molecular beam epitaxy, and their electrical and magneto-transport properties were measured for the first time. X-ray diffraction and vibrating sample magnetometry measurements confirmed the crystalline ferromagnetic Fe2Ge phase. The observed high-temperature maximum in the longitudinal resistivity, as well as the observed suppression of electron–magnon scattering at low temperatures, points to the presence of strong spin polarization in this material. Measurements of the Hall resistivity, ρxy, show contributions from both the ordinary Hall effect and the anomalous Hall effect, ρxyAH, from which we determined the charge carrier concentration and mobility. Measurements also show a small negative magnetoresistance in both the longitudinal and transverse geometries. Fe2Ge holds promise as a useful spintronic material, especially for its semiconductor compatibility.

First principle calculation of electronic, optical and magnetic properties of Zn1−xFexSe compound

By employing the first principles method within the generalized gradient approximation for the exchange and correlation potential, the electronic, optical and magnetic properties of pure and Fe-doped zinc-blende ZnSe are investigated. According to the obtained band structure, density of state and optical spectrum the electronic origin of the maxima in the optical spectrum has been observed. The optical spectrum peak is generated mainly from the charge transfer between the Se(4[Formula: see text] and Zn(3[Formula: see text] states. Our results reveal that the strong spin polarization of the 3[Formula: see text] states of the Fe atoms is the origin of antiferromagnetism in Zn[Formula: see text]Fe[Formula: see text]Se. A decrease in the concentration of iron atoms in the supercell does not affect the stability of the AFM phase.

Kitkaite NiTeSe, an Ambient‐Stable Layered Dirac Semimetal with Low‐Energy Type‐II Fermions with Application Capabilities in Spintronics and Optoelectronics

AbstractThe emergence of Dirac semimetals has stimulated growing attention, owing to the considerable technological potential arising from their peculiar exotic quantum transport related to their nontrivial topological states. Especially, materials showing type‐II Dirac fermions afford novel device functionalities enabled by anisotropic optical and magnetotransport properties. Nevertheless, real technological implementation has remained elusive so far. Definitely, in most Dirac semimetals, the Dirac point lies deep below the Fermi level, limiting technological exploitation. Here, it is shown that kitkaite (NiTeSe) represents an ideal platform for type‐II Dirac fermiology based on spin‐resolved angle‐resolved photoemission spectroscopy and density functional theory. Precisely, the existence of type‐II bulk Dirac fermions is discovered in NiTeSe around the Fermi level and the presence of topological surface states with strong (≈50%) spin polarization. By means of surface‐science experiments in near‐ambient pressure conditions, chemical inertness towards ambient gases (oxygen and water) is also demonstrated. Correspondingly, NiTeSe‐based devices without encapsulation afford long‐term efficiency, as demonstrated by the direct implementation of a NiTeSe‐based microwave receiver with a room‐temperature photocurrent of 2.8 µA at 28 GHz and more than two orders of magnitude linear dynamic range. The findings are essential to bringing to fruition type‐II Dirac fermions in photonics, spintronics, and optoelectronics.

Polaron assisted electrical transport and fertile field emission response in polycrystalline LiNi0.33Co0.33Mn0.33O2 with theoretical insight by density functional theory

Polycrystalline LiCo0.33Ni0.33Mn0.33O2 compounds were prepared via a sol-gel auto combustion synthesis route to examine its conduction mechanism with thermal assessment and a new window of its application as a field emitter is explored. The structural modules and molecular footmarks have been confirmed by XRD, Raman, FTIR, XPS and FESEM techniques. The Nyquist plots (Z′vs.Z′′) exhibits significant contribution of electrode solid interface effect with compared to intra and inter granular contribution. The variation of real and imaginary impedance, modulus, and conductivity spectra with thermal evolution is attributed with the creation of a quasi-particle called “polaron” and the migration of small polaron by tunneling/hopping creates localized state in high temperature. However, a weak crossover between small polaron hopping (SPH) and Mott’s variable range hopping (VRH) is observed near 323 K. The colossal dielectric permittivity (ɛr′)~5 × 106 is originated from inhomogeneous electronic conduction process in LiNi0.33Co0.33Mn0.33O2 due to the creation of absorption current in the flimsy grain boundary which leads to the stockpile of charge carriers in the external-electrode sample interface and induces Maxwell-Wagner electrode interfacial polarization. The exquisite field emission properties were discovered in LiNi0.33Co0.33Mn0.33O2 with low turn-on field@ 1 µA/cm2~2.75 V/µm and threshold field@ 10 µA/cm2~4.39 V/µm with field enhancement factor (β)~4251. The structural and electronic properties of LiNi0.33Co0.33Mn0.33O2 and the local work function (φ)~4.94 eV is computed employing the Density functional theory (DFT). It further supports the conduction mechanism due to self-trapping electrons and strong spin polarization of the O-2p state under applied electric field.

Room temperature short-range ferromagnetic order in Ni-doped tetragonal perovskite niobate

Here, we report a strong room-temperature magnetism in Ni-doped BaNbO3. The tetragonal BaNixNb(1-x)O3-δ nano-powders are prepared by the composite-hydroxide-mediated method. The as-prepared BaNixNb(1-x)O3-δ has a saturation magnetization (Msat) of 2.54 emu/g, a remnant magnetization (Mr) of 0.228 emu/g, and a small coercive field (Hc) of 99.14 Oe at room temperature, presenting as a short-range magnetic order. The Ni-doping leads to an incommensurate valence state of Nb, and the oxidation state of Ni in the matrix is + 2. It brings not only strong local spin polarization to the matrix, but also balances the oxygen defects and gives rise to a more doping content. The strong magnetism originated from the existence of short-range magnetic order and the strong local net spin polarization at the Fermi level (EF), which are proved by the first-principle calculations.

Mitrofanovite Pt3Te4: A Topological Metal with Termination-Dependent Surface Band Structure and Strong Spin Polarization

Due to their peculiar quasiparticle excitations, topological metals have high potential for applications in the fields of spintronics, catalysis, and superconductivity. Here, by combining spin- and angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and density functional theory, we discover surface-termination-dependent topological electronic states in the recently discovered mitrofanovite Pt3Te4. Mitrofanovite crystal is formed by alternating, van der Waals bound layers of Pt2Te2 and PtTe2. Our results demonstrate that mitrofanovite is a topological metal with termination-dependent (i) electronic band structure and (ii) spin texture. Despite their distinct electronic character, both surface terminations are characterized by electronic states exhibiting strong spin polarization with a node at the Γ point and sign reversal across the Γ point, indicating their topological nature and the possibility of realizing two distinct electronic configurations (both of them with topological features) on the surface of the same material.

Hydrodeoxygenation of aliphatic acid over NiFe intermetallic compounds: Insights into the mechanism via model compound study

Hydrodeoxygenation (HDO) is a promising way to produce the second generation bio-diesel from aliphatic acid based biomass. Compared with the monometallic Ni/SiO2, appropriate introduction of Fe results in the complete conversion of lauric acid and nearly 100% yield of alkane as well as satisfactory stability on conversion. Further study on mechanism shows that the NiFe intermetallic compounds (IMC) catalyst promotes the ratedetermining step, i.e., C11H23COOH → C11H23CHO, which is attributed to the synergistic effect of Ni-Fe bimetallic sites according to the characterization and calculation. For one thing, strong spin polarization enhances the interaction between Fe sites and aliphatic acid, and the subsequent dissociation of C-OH bond indicated by the DOS and transition state analysis. For another, dissociation of H2 on Ni site is promoted because of the higher charge density around Ni in the IMC according to the in-suit FTIR and Bader analysis. However, with the repeated use of the catalyst, the selectivity to alkane decreased gradually, which is ascribed to the oxidation of metal Ni-Fe bimetallic sites. This demonstrates that the reduced Ni-Fe bimetallic sites rather than the oxidized ones are the active phases in the HDO of aliphatic acid to produce alkanes with the NiFe IMC.

Engineering the electronic and magnetic properties of nitrogene monolayer and bilayer by doping: A first-principles study

The (N) nitrogen monolayer (nitrogene) has been predicted to be stable in the buckled hexagonal structure. However the non-magnetic nature and large band-gap may restrict its practical applications. In this paper, the electronic and magnetic properties of the nitrogene monolayer and bilayer doped with carbon (C) and boron (B) are investigated using first-principles calculations. Nitrogene monolayer is a non-magnetic two-dimensional (2D) material with an indirect band-gap of 4.185(6.023) eV determined by the PBE(HSE06) functional. Nitrogene bilayers with different stacking shaps are examined. Results reveal dynamical stability of the AA-, AA′-, and AB-stacked bilayers. Such atomic arrangements depict an energy gap reduction as compared to that of the monolayer. C doping causes strong spin polarization at the vicinities of the Fermi level, giving place to magnetic semiconductor nature. The magnetic properties are produced mainly by the C dopants (0.7 μB), and also proximity induced small contributions on the N atoms (0.07 μB). In contrast, B doping produces non-magnetic materials with band-gap reduction (∼12% and 20.5%) for all considered systems. When the co-doping is treated, the effect on the electronic and magnetic properties can be considered as the combined effects of the separated C doping and B doping. Results presented herein may propose an efficient method to functionalize the nitrogene monolayer and bilayer for practical applications in optoelectronic and spintronic nano devices.

Interplay between friction and spin-orbit coupling as a source of spin polarization

We study an effective one-dimensional quantum model that includes friction and spin-orbit coupling (SOC), and show that the model exhibits spin polarization when both terms are finite. Most important, strong spin polarization can be observed even for moderate SOC, provided that the friction is strong. Our findings might help to explain the pronounced effect of chirality on spin distribution and transport in chiral molecules. In particular, our model implies static magnetic properties of a chiral molecule, which lead to Shiba-like states when a molecule is placed on a superconductor, in accordance with recent experimental data.

Spin Polarization of Mn Enhances Grain Boundary Sliding in Mg

Segregation of rare earth alloying elements are known to segregate to grain boundaries in Mg and suppress grain boundary sliding via strong chemical bonds. Segregation of Mn, however, has recently been found to enhance grain boundary sliding in Mg and thereby boosting its ductility. Taking the Mg (-2114) twin boundary as an example, we have performed a first-principles comparative study on the segregation and chemical bonding of Y, Zn, and Mn at this boundary. We find that both Y-4d and Mn-3d states hybridize with the Mg-3sp states, while Zn-Mg bonding is characterized by charge transfer only. Strong spin-polarization of Mn pushes the up-spin 3d states down, leading to less anisotropic Mn-Mg bonds with more delocalized charge distribution at the twin boundary, and thus promotes grain boundary plasticity, e.g., grain boundary sliding.

Bipolar magnetic semiconductor materials based on 2D Fe2O3 lattice

Bipolar magnetic materials play an important role in spintronics. Its unique electronic structure allows the materials to easily regulate fully spin-polarized currents with different spin polarization directions by a gate voltage. It is predicted that 2D monolayer Fe2O3 is a new class of bipolar magnetic semiconductor (BMS) materials by first-principles calculations. The valence band (VB) and the conduction band (CB) have opposite spin polarizations near the Fermi level, and a direct band gap of 0.28 eV between the conduction band bottom (CBM) and the valence band top (VBM). At the same time, the two spin channels have relatively large spin-conserved gaps of 1.05 eV and 2.40 eV. The ground state of the Fe2O3 lattice is a ferromagnetic (FM) state. It has strong intrinsic spin polarization and has a magnetic moment of 10.0 μB per unit cell, and the spin polarization is mainly derived from the transition metal Fe atom. The Bader analysis find that the local magnetic moment of each Fe atom is 4.2 μB, and the local magnetic moment of each O atom is only 0.5 μB. The mechanism of magnetism could be understood by the direct exchange between the orbitals of Fe atom. The Curie temperature (TC) of the Fe2O3 calculated based on Monte Carlo (MC) simulation up to 110 K, which is much larger than the 45 K of CrI3. The characteristics of electrically-controlled polarization currents in bipolar magnetic semiconductor materials have broadened application prospects in the development of spintronics and the construction of bipolar magnetic electronic devices.