Spin-up Electrons Research Articles

Electronic Structure Of Cobalt Phosphates Co1-xmxpo4 Doped With Iron And Nickel Atoms

In this research, the electronic states, band structures, and bond properties of the framework compounds of CoPO4, Co1-xFexPO4, and Co1–xNixPO4 were investigated by the density functional theory calculations. The potential capabilities of these systems in the photocatalytic water splitting to produce hydrogen were analyzed. The spin-up electron densities of states for the CoPO4, Co1–xFexPO4, and Co1–xNixPO4 systems have band gaps of 2.7, 3.4, and 3.45 eV, respectively. The band of spin-down electron states has several energy gaps above the Fermi level. The density of states of electron with spin up near the Fermi level is obviously greater than that of electrons with spin down. In this case, localized states of electrons appear in the band gap of doped semiconductors due to impurity atoms. The calculated value of the energy at the lower edge of the conduction band for CoPO4 was –0.7 eV, which is more negative than the energy required for water splitting. Meanwhile, the calculated value of the energy at the upper edge of the valence band was 2.01 eV, which is more positive than the oxygen evolution energy of 1.23 eV.

Lattice defects and surface adsorption properties of gold-bearing chalcopyrite: A theoretical study based on DFT

Chalcopyrite (CuFeS2), as one of the carrier minerals of gold, undergoes significant alterations in lattice and surface properties upon doping with gold impurities. These changes markedly influence its separation and purification techniques, especially flotation. Using Density Functional Theory (DFT) based on first-principles, we analyze the influence of gold impurities on the lattice defects and surface properties of chalcopyrite. We developed an adsorption model using prop-2-yn-1-yl diethylcarbamodithioate (PDEC), a sulfur ester collector with an ethynyl group, on gold-infused chalcopyrite to elucidate the adsorption mechanism. Our findings indicate that the Au atom primarily occupies interstitial sites within the chalcopyrite lattice, resulting in an expanded lattice structure. Despite the doping, the lattice remains a p-type semiconductor with increased conductivity, facilitated by Au 6 s orbitals contributing to impurity levels within the conduction band from 2 to 4 eV. Additionally, there is a marked rise in spin-up electrons, with Integrated |Spin Density| results showing greater electron localization in Cu15Fe16S32Au and Cu16Fe16S32Au compared to ideal chalcopyrite crystal (Cu16Fe16S32). The Au atom exhibits maximum stability when adsorbed onto the S-Fe bonds on chalcopyrite surfaces, primarily forming covalent bonds through electron acceptance from Fe 3d orbitals. The presence of gold impurities decreases the collector's adsorption energy on the chalcopyrite (112) surface. However, PDEC exhibits enhanced adsorption performance relative to Al-DECDT and Z-200, primarily due to the chelation between thiocarbonyl and ethynyl groups of PDEC and the gold-bearing chalcopyrite (112) surface. Electron donation from Fe 4p orbitals of surface to the S 3 s and 3p orbitals of collector forms a sigma bond, while the ethynyl group undergoes hybridization with the Au 5d orbitals from −5 to −2.5 eV, fostering stable electron transfer.

Magnetic bilayer qubits: A bipartite quantum system

An exfoliated monolayer CrI3 possessing the ferromagnetic (FM) nature of out-of-plane Ising spin-up (or spin-down) electrons can be considered as a qubit with a quantum state of |ѱ>=|↑>=|0> (or |ѱ>=|↓>=|1>) due to the theory of the Bloch sphere. Therefore, here a bipartite quantum system of the antiferromagnetic (AFM) and FM bilayer CrI3 is proposed for four fundamental two-qubit (2Q) quantum states (≡|ѱѱ>) of |↑↓>=|01>, |↓↑>=|10>, |↑↑>=|00> and |↓↓>=|11>, respectively. Energy-resolved magnetic circular dichroism (MCD) spectropolarimetry was used to detect d-d transitions of the FM and AFM bilayer CrI3 for the four fundamental quantum states. The obtained MCD spectra of the d-d transitions with spin-frustration and spin-parallelism possess quantum signals of the four fundamental 2Q quantum states at θB = 0, where θB is the angle between the magnetic field and the surface normal. Hence, the bilayer CrI3 is a potential candidate for use in quatum computer.

Magnetosonic shock waves in degenerate electron–positron–ion plasma with separated spin densities

This study investigates magnetosonic shock waves in a spin-polarized three-component quantum plasma using the quantum magnetic hydrodynamic model. We explore the influence of spin effects, specifically spin magnetization current and spin pressure, on shock wave behavior. Numerical analysis of the linear dispersion relation under varying parameters such as positron imbalance, spin polarization ratio, plasma beta, quantum diffraction, and magnetic diffusivity reveals differential impacts, with diffusion exerting significant influence on the plasma frequency. Our findings highlight the sensitivity discrepancy between the real and imaginary parts of the dispersion relation. Furthermore, nonlinear behavior of magnetosonic shock waves is examined via the Korteweg–de Vries–Burgers equation, showcasing transitions between oscillatory and monotonic wave patterns based on changes in dimensionless parameters. Notably, we observe the combined effects of spin-up and spin-down positrons with spin-up and spin-down electrons on shock wave dynamics, contributing to a deeper understanding of spin-plasma interactions with implications across various fields.

Quantum Transport through a Quantum Dot Coupled to Majorana Nanowire and Two Ferromagnets with Noncollinear Magnetizations.

We study the electron tunneling (ET) and local Andreev reflection (AR) processes in a quantum dot (QD) coupled to the left and right ferromagnetic leads with noncollinear ferromagnetisms. In particular, we consider that the QD is also side-coupled to a nanowire hosting Majorana bound states (MBSs) at its ends. Our results show that when one mode of the MBSs is coupled simultaneously to both spin-up and spin-down electrons on the QD, the height of the central peak is different from that if the MBS is coupled to only one spin component electrons. The ET and AR conductances, which are mediated by the dot-MBS hybridization, strongly depend on the angle between the left and right magnetic moments in the leads. Interaction between the QD and the MBSs will result in sign change of the angle-dependent tunnel magnetoresistance. This is very different from the case when the QD is coupled to regular fermonic mode, and can be used for detecting the existence of MBSs, a current challenge in condensed matter physics under extensive investigations.

Controllable pure spin currents in bilayer graphene grown on monolayer Cr2X2Te6 hybrid structures: Layer-dependent magnetism

We investigate the spin transport properties of bilayer graphene grown on a monolayer Cr2X2Te6 hybrid structure. Here, X can be Ge, Si, or Sn, all of which are van der Waals layered materials with magnetic properties. Our results show that the magnetism in bilayer graphene is layer-dependent, affecting the spin-dependent energy gap and Fermi level. Focusing specifically on the X = Ge case, we reveal that pure spin currents can be precisely controlled by applying gate voltage and a perpendicular electric field across the barrier. By varying these parameters, we achieve perfect switching of pure spin current from spin-down to spin-up due to the system’s layer-dependent magnetism. Moreover, due to differing gaps between spin-up and spin-down electrons, spin polarization can sharply jump from 0 % to 100 % with changes in gate voltage. The splitting of spin conductance curves, creating a fully functional spin-filtering junction, is also predicted under a varying perpendicular electric field. This model can be extended to cases where X is Si or Sn due to their similar electronic band structures. Our research demonstrates the potential of bilayer graphene on Cr2X2Te6 hybrid structures, which exhibit distinctive layer-dependent magnetism ideal for spintronic applications.

Electron Spin Broken-Symmetry of Fe-Co Diatomic Pairs to Promote Kinetics of Bifunctional Oxygen Electrocatalysis for Zinc-Air Batteries.

Designing bifunctional catalysts to reduce the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) reaction barriers while accelerating the reaction kinetics is perceived to be a promising strategy to improve the performance of Zinc-air batteries. Unsymmetric configuration in single-atom catalysts has attracted attention due to its unique advantages in regulating electron orbitals. In this work, a seesaw effect in unsymmetric Fe-Co bimetallic monoatomic configurations is proposed, which can effectively improve the OER/ORR bifunctional activity of the catalyst. Compared with the symmetrical model of Fe-Co, a strong charge polarization between Co and Fe atoms in the unsymmetric model is detected, in whom the spin-down electrons around Co atoms are much higher than those spin-up electrons. The seesaw effect occurred between Co atoms and Fe atoms, resulting in a negative shift of the d-band center, which means that the adsorption of oxygen intermediates is weakened and more conducive to their dissociation. The optimized reaction kinetics of the catalyst leads to excellent performance in ZABs, with a peak power density of 215mW cm-2 and stable cycling for >1300 h and >4000 cycles. Flexible Zinc-air batteries have also gained excellent performance to demonstrate their potential in the field of flexible wearables.

Magnetic topological phases in the double exchange model with spin–orbit coupling

The double exchange model with the spin–orbit coupling is studied by the dynamical mean field theory. It reveals a competition between the magnetic, charge orderings and the non-trivial topology of the ground state. The spin exchange tends to maintain the magnetic ordering, and at the same time it tries to suppress the charge ordering. The spin–orbit coupling maintains nontrivial topology of the ground state, whereas the magnetic ordering tries to destroy it. As a result, a rich phase diagram is obtained. The competition leads to a half topological ground state, where spin-up electrons form a nontrivial topological state, while spin-down electrons are in the topological trivial insulating state.

Efficient spin filtering through Fe4GeTe2-based van der Waals heterostructures.

Utilizing ab initio simulations, we study the spin-dependent electronic transport characteristics within Fe4GeTe2-based van der Waals heterostructures. The electronic density of states for both free-standing and device-configured Fe4GeTe2 (F4GT) confirms its ferromagnetic metallic nature and reveals a weak interface interaction between F4GT and PtTe2 electrodes, enabling efficient spin filtering. The ballistic transport through a double-layer F4GT with a ferromagnetic configuration sandwiched between two PtTe2 electrodes is predicted to exhibit an impressive spin polarization of 97% with spin-up electrons exhibiting higher transmission probability than spin-down electrons. Moreover, we investigate the spin transport properties of Fe4GeTe2/GaTe/Fe4GeTe2 van der Waals heterostructures sandwiched between PtTe2 electrodes to explore their potential as magnetic tunnel junctions in spintronic devices. The inclusion of monolayer GaTe as a 2D semiconducting spacer between F4GT layers results in a tunnel magnetoresistance of 487% at a low bias and decreases with increasing bias voltage. Overall, our findings underscore the potential of F4GT/GaTe/F4GT heterostructures in advancing spintronic devices based on van der Waals materials.

Efficient Thermo-Spin Conversion in van der Waals Ferromagnet FeGaTe.

Recent discovery of 2D van der Waals magnetic materials has spurred progress in developing advanced spintronic devices. A central challenge lies in enhancing the spin-conversion efficiency for building spin-logic or spin-memory devices. Here, the anomalous Hall and Nernst effects are systematically investigated to uncover significant spin-conversion effects in above-room-temperature van der Waals ferromagnet FeGaTe with perpendicular magnetic anisotropy. The anomalous Hall effect demonstrates an efficient electric spin-charge conversion with a notable spin Hall angle of over 6%. In addition, the anomalous Nernst effect produces a significant transverse voltage at room temperature without a magnetic field, displaying unique temperature dependence with a maximum transverse Seebeck coefficient of 440 nVK-1 and a Nernst angle of ≈62%. Such an innovative thermoelectric signal arises from the efficient thermo-spin conversion effect, where the up-spin and down-spin electrons move in opposite directions under a temperature gradient. The present study highlights the potential of FeGaTe to enhance thermoelectric devices through efficient thermo-spin conversion without the need for a magneticfield.

Topological-edge-state spin transport in asymmetric three-terminal silicenelike nanodevice

We theoretically investigate the topological-edge-state spin transport in asymmetric three-terminal silicene-like nanodevice. Since silicene-like materials are honeycomb structures with considerable spin-orbit interaction (SOI), they possess both Dirac electron and topology insulator behaviors. In the three-terminal silicene-like nanodevice, the SOI realizes helical edge state and brings fully spin polarization selectively without external field. Firstly, we find that the spin degeneracy breaking gives rise to spin-polarized transport, i.e., up-spin electron and down-spin electron propagating to different leads from the top lead. The distribution of edge-state spin-dependent current in the real space indicates that an up-/down-spin channel to the left/right lead is opened at the interface of the present nanodevice. Secondly, the spin-polarized transport behavior has a competition with the effect of asymmetric transport, which prefers propagating the up- and down-electrons from top lead to the same (right) lead. Interestingly, as the geometric size variation is considered, the results show that the width increase of the horizontal armchair (top vertical zigzag) lead reinforces the spin-polarized (asymmetric) transport. However, when both the armchair and zigzag leads increase simultaneously, the spin-polarized transport becomes the dominant effect. Therefore, this edge-state spin-polarized transport behavior is topologically protected and very robust as the whole geometric size of the nanodevice increases. These properties of the topological-edge-state spin transport enable the asymmetric three-terminal silicene-like nanodevice a spin filter or a spin valve, and might contribute to the silicene-like nanocircuit engineering and spintronics application.

Unravelling the Effect of Acid-Driven Electron Transfer in High-Valent FeIV =O/MnIV =O Species and Its Implications for Reactivity.

The electron transfer (ET) step is one of the crucial processes in biochemical redox reactions that occur in nature and has been established as a key step in dictating the reactivity of high-valent metal-oxo species. Although metalloenzymes possessing metal-oxo units at their active site are typically associated with outer-sphere electron transfer (OSET) processes, biomimetic models, in contrast, have been found to manifest either an inner-sphere electron transfer (ISET) or OSET mechanism. This distinction is clearly illustrated through the behaviour of [(N4Py)MnIV (O)]2+ (1) and [(N4Py)FeIV (O)]2+ (2) complexes, where complex 1 showcases an OSET mechanism, while complex 2 exhibits an ISET mechanism, especially evident in their reactions involving C-H bond activation and oxygen atom transfer reactions in the presence of a Lewis/Bronsted acid. However, the precise reason for this puzzling difference remains elusive. This work unveils the origin of the perplexing inner-sphere vs outer-sphere electron transfer process (ISET vs OSET) in [(N4Py)MnIV (O)]2+ (1) and [(N4Py)FeIV (O)]2+ (2) species in the presence of Bronsted acid. The calculations indicate that when the substrate (toluene) approaches both 1 and 2 that is hydrogen bonded with two HOTf molecules (denoted as 1-HOTf and 2-HOTf, respectively), proton transfer from one of the HOTf molecules to the metal-oxo unit is triggered and a simultaneous electron transfer occurs from toluene to the metal centre. Interestingly, the preference for OSET by 1-HOTf is found to originate from the choice of MnIV =O centre to abstract spin-down (β) electron from toluene to its δ(dxy ) orbital. On the other hand, in 2-HOTf, a spin state inversion from triplet to quintet state takes place during the proton (from HOTf) coupled electron transfer (from toluene) preferring a spin-up (α) electron abstraction to its σ* (dz 2 ) orbital mediated by HOTf giving rise to ISET. In addition, 2-HOTf was calculated to possess a larger reorganisation energy, which facilitates the ISET process via the acid. The absence of spin-inversion and smaller reorganisation energy switch the mechanism to OSET for 1-HOTf. Therefore, for the first time, the significance of spin-state and spin-inversion in the electron transfer process has been identified and demonstrated within the realm of high-valent metal-oxo chemistry. This discovery holds implications for the potential involvement of high-valent Mn-oxo species in performing similar transformative processes within Photosystem II.

First-Principles Study of Structural, Electronic and Magnetic Properties of Lithium Doped Hexa]gonal Boron Nitride Monolayer (h-BN)

We examine the structural, electronic, and magnetic properties of pure and lithium doped hexagonal boron nitride (h-BN) monolayer using density functional theory (DFT) based on first-principles calculations. LiB site is more conducive to doping than LiN site, according to the values of formation energy, which are found to be 13.06 eV and 18.50 eV, respectively. Metallic behavior may be seen in the band structures for both the LiB site and LiN in nature. At both sites, the density of states (DOS) is asymmetric for spin-up and spin-down electrons. This suggests that systems with Li doping on h-BN are magnetic.

Local photo-excitation of spin current generation in a one-dimensional system

We investigate the dynamics of spin current generation in a one-dimensional system under light illumination by using the time-dependent nonequilibrium Green’s function formalism. To demonstrate the mechanism of spin current generation, we first consider a spinless system with an asymmetric on-site potential. Thus, the system under light irradiating exhibits a DC particle current, which is an odd function of the parameter to characterize the asymmetric potential. Based on that, we design a model, in which the asymmetric potential experienced by the spin-up electrons is opposite to that for the spin-down electrons. Consequently, the DC polarized currents from the spin-up electrons and from the spin-down ones may travel along opposite directions, and thus a pure DC spin current is realized. The spin current as a function of the light frequency is also discussed briefly. These results could be useful for the design of spin devices based on electronic materials.

Structural, electronic and optical properties of the YVO4:Eu3+ red phosphor

The structural, electronic and optical properties of the YVO4:Eu3+ compound have been discussed in terms of the results of the first-principles calculations on the density functional theory level. The emphasis has been given to the analysis of the Eu contribution to these properties. The calculations have been performed in a frame of the mBJ + SO + U approach, i.e. applying modified Becke-Johnson (mBJ) potential for exchange-correlation effects, spin-orbit (SO) coupling, and Hubbard correction U for the Eu 4f-shell treatment. The electronic structure of the pure YVO4 is found to be similar to previously published ones, with the O 2p- and the V 3d-states dominating the valence and the conduction band respectively, but with the improved bandgap description (3.7 eV compared to the experimentally determined 3.8 eV). In the case of the YVO4:Eu3+, different U values have been tested in order to obtain the best agreement between calculated and experimental optical absorption (OA) spectra. The value of U = 2.5 eV fulfilled this condition. The bandgap is found to be 3.6 eV, independently of the applied U value. The basic features of the electronic structure did not change with respect to the pure compound. The Eu spin-up 4f-states (accommodating 6 electrons) are found to be spread out within the valence band, with a very narrow empty band (accommodating 1 spin-up electron) localized inside the bandgap, around 2 eV measured from the valence band top. A rich structure of various sharp peaks in the energy interval 2–3 eV of the OA spectrum, observed experimentally, has been reproduced and explained in terms of electron transitions to the empty Eu 4f band inside the gap. The calculated OA spectrum is found to be very anisotropic, with dominating absorption of light polarized parallel to the tetragonal c-axis.

Mirroring and reversible fine-tuning of the transport spin-polarization in PC3 nanoribbons based on an electrical method

The electrical approach is favored over the conventional magnetic approach for its low energy consumption and continuously variable control of spin polarization. Inspired by the recently reported PC3 monolayer, we investigate its spin-dependent electron transmission characteristics through the first-principles calculations. The results show that the transmission peaks with opposite spin directions at the Fermi level have precisely opposite responses to the gate voltage, which leads to the system being able to alter between spin-polarized and unpolarized states, and as well as achieving any ratio between − 100 % and 100 % for spin-up and spin-down electrons. Notably, this regulation is also reversible and mirror-symmetric. Further research demonstrates that the crux lies in the particular transmission peak contributed by the edge sp2-hybridized C atoms. This study sheds new light on the potential of PC3 as a novel nanoelectronic material for spintronics applications, suggesting that it can be used to create bipolar spin filters with tunable filtering effects.

On the Possible Half-Metallic Properties of Fe2RhZ (Z = Al, Si, Ga, Ge, In, Sn) Ferromagnetic Heusler Alloys

The possible presence of half-metallic properties in Fe2RhZ (Z = Al, Si, Ga, Ge, In, Sn) ferromagnetic Heusler alloys is ab initio studied. The calculation is carried out taking into account the exchange correlation effects using the generalized and meta-generalized gradient approximations. It is shown that the ground state of most investigated alloys is ferromagnetic ordering in the Тр model lattice. An analysis of the phase stability of the alloys showed that, in the considered approximations, most of them are stable in both the regular and inverse lattice, as well as in the three model lattices belonging to inverse-type Heusler structures with different atomic orders. It was predicted using the strongly constrained and appropriately normed (SCAN) functional that the Fe2RhSi alloy can exhibit the properties of half-metals, since it has an integer magnetic moment, a fairly high degree of polarization, and an energy gap at the Fermi level of spinup electrons.

Spin-Resolved Band Structure of Hoffman Clathrate [Fe(pz)2Pt(CN)4] as an Essential Tool to Predict Optical Spectra of Metal–Organic Frameworks

Paramount spin-crossover properties of the 3D-Hoffman metalorganic framework (MOF) [Fe(pz)2Pt(CN)4] are generally described on the basis of the ligand field theory, which provides adequate insight into theoretical and simulation analysis of spintronic complexes. However, the ligand field approximation does not take into account the 3D periodicity of the actual complex lattice and surface effects and therefore cannot predict a full-scale periodic structure without utilizing more advanced methods. Therefore, in this paper, the electronic properties of the exemplar MOF were analyzed from the band structure perspective in low-spin (LS) and high-spin (HS) states. The density-of-states spectra determined for both spin-up and spin-down electrons of Fe d6 orbitals indicate spin-orbital splitting and delocalization for HS due to spin polarization in the iron atom ligand field. Presence of the surface states in the real crystal causes a red shift of the metal-metal charge transfer (MMCT) and metal-ligand charge transfer (MLCT) peaks for both HS and LS states. The addition of residual water molecules and disorder among the pyrazine rings reveal additional influences on the positions of the pyrazine band and, therefore, on the absorption spectra of the crystal. The results show a magnification of the peak correlated with the MLCT in the HS state and a significant red shift of the LS characteristic absorption band. The presented approach involving band structure analysis delivers a more complete image of the electronic properties of the [Fe(pz)2Pt(CN)4] crystalline network and can be a landmark for insightful studies of other MOFs.

Density polarization effect of spin-up and spin-down electrons on magnetosonic solitons in a dense plasma with oblique magnetic field

Nonlinear wave propagation of fast and slow magnetosonic waves is investigated in a magnetized quantum plasma with spin polarization effects of degenerate electrons. The multi-fluid quantum magnetohydrodynamic model is considered and two separate fluid dynamic equations for degenerate electrons i.e. spin-up and spin-down states (Pauli paramagnetism) with their different Fermi pressures. The ions are assumed to be classical and external magnetic field lies in a plane. The magnetization energy and current density of electrons due to the spin-1/2 effects are included in the momentum equation of the degenerate electrons and Maxwell equations, respectively. A Korteweg-de-Vries (KdV) equation is derived for nonlinear magnetosonic waves in a dense magnetized plasma with the inclusion of electron spin effects and oblique external magnetic field. The electron inertial effect (which causes wave dispersion) of both spin-up and spin-down state electrons is also included in the model. It is found that electron spin polarization density has significant effects on the phase speed and soliton structures (i.e. its width and amplitude) of fast (hump) and slow (dip) magnetosonic waves in a dense magnetized plasma. The present theoretical study along with the obtained numerical results may have possible applications towards many realistic astrophysical scenarios.

Instability of magnetosonic waves in magnetized degenerate half-spin-polarized quantum plasma

Shock and solitary waves in plasmas are the main focus of many current studies of localized disturbances in both laboratory and astrophysical plasmas. Here, the linear and the nonlinear properties evolving in three dimensions quantum magnetized spin-1/2 plasma formed of spin up (↑) and spin down (↓), nonrelativistic degenerate inertialess electrons, and classical ions, are considered. The nonlinear propagation is governed by a quantum Zakharov–Kuznetsov–Burger (QZKB) and QZK equations which are derived by using the multiple scales perturbation technique. The shock and solitary wave structures are dependent on the spin polarization parameter, Bohm potential, Zeeman energy, and dissipative parameter. The first, and the second, orders instability growth rates are also derived by using the small-k perturbation expansion method. The previous parameters affect also the instability growth rates. There is a critical angle below which the first order becomes positive while the second order is negative, and over which the first order disappears and the second order becomes positive. Our present results may be useful in understanding the dynamics in the magnetic pulsars, and also in the magnetic white dwarfs and neutron stars systems where degenerate spin-up and spin-down electrons with dissipative effects can exist.