Spin Band Gap Research Articles

Half-metallic behavior in rare earth metal (Sm, Gd) co-doped zigzag Gallium Phosphide nanoribbons

Using first-principle calculations, we have studied the structural and electronic properties of the Gallium Phosphide (GaP) nanoribbon doped with rare earth (RE) metal elements. The substitution of Ga and P atoms with RE leads to the structural deformation in zigzag GaP nanoribbon. For every nanostructure under study, the binding energy (Eb), density of states (DOS), and electronic band structures have been computed. The bare and pristine undoped GaP show non-magnetic behavior. The bare z-GaPNR shows metallic nature while the pristine z-GaPNR exhibits band gap of 2.44 eV with indirect characteristics. With Samarium (Sm) and Gadolinium (Gd) doping in z-GaPNR, a transformation of the semiconducting nature of z-GaPNRs turns to half metallic one. The transport properties show that half-metal ferromagnetic behavior with 92%–98% spin polarization at the Fermi level is produced by RE (Gd, Sm) co-doped z-GaPNRs. The synergistic effect of the Gd and Sm impurities are seen to diminish energy band gaps. Conversely, we have the energy band gap in spin down energy levels results in semiconducting behavior, whereas in the spin up energy state, metallic behavior is observed. This could be caused by the 4f-states of the Sm and Gd dopants. Therefore, this work presents half-metallic (HM) properties for RE-doped z-GaPNRs. Our study depicts that the electrical, spin, and transport properties of z-GaPNRs could be altered magnificently by co-doping of Gd and Sm rare earth metals. Additionally, the current findings can be used to create a workable method of absolute fermi level shifting for spin energy levels, which is required for applications involving spintronic devices, spin filters, as well as for z-GaPNRs’ electrical characteristics modifications.

Above room-temperature two-dimensional ferromagnetic half-metals in Mn-based Janus magnets

Two-dimensional (2D) ferromagnets and their heterostructures offer fertile grounds for designing fascinating functionalities in ultra-thin spintronic devices. Here, by first-principles calculations, we report the discovery of energetically and thermodynamically stable 2D ferromagnets with very strong in-plane magnetic anisotropy in MnXY (X = S and Se; Y = Cl, Br, and I) monolayers. Remarkably, we find that the Curie temperatures of the ferromagnetic MnSBr, MnSI, MnSeCl, and MnSeI monolayers are as high as 271, 273, 231, and 418 K, respectively. In addition, we demonstrate that these ferromagnetic monolayers are intrinsic half-metals with large spin bandgaps ranging from 2.5 to 3.2 eV. When spin–orbit coupling is considered in these ferromagnetic monolayers, the nature of their half-metal is almost unaffected. Finally, the strong in-plane magnetic anisotropy of MnSY (Y = Br, I) and MnSeY (Y = Cl, I) monolayers originate mainly from halogen and chalcogen atoms, respectively. Our work shows that 2D Janus Mn-based ferromagnetic half-metals may have appealing functionalities in high-performance spintronic applications.

Janus tetragonal Mn2BN monolayer: A 2D polar half-metal with coexistent ferroelectricity and magnetism

The integration of ferroelectricity, ferromagnetism, and half-metallicity in two-dimensional (2D) materials is pivotal for advancing spintronic device technologies. However, the progress in identifying such materials is limited, and we here propose a compelling approach by constructing asymmetry structures (Janus) based on known 2D magnets, namely, the Janus tetragonal Mn2BN monolayer as a promising polar half-metal. The asymmetric arrangement of B and N atoms, coupled with comparable atomic sizes and evident electronegativity, ensures structural stability and inherent polarization, while the dominance of Mn atoms governs magnetism. The robust ferromagnetic order stems from a strong super-exchange interaction, evident in the significant hybridization between Mn d and B/N p orbitals. The Mn2BN monolayer exhibits a wide spin bandgap (1.09 eV), a substantial electric polarization (9.15 μC cm−2), and a sizable magnetic anisotropic energy (238 μeV/Mn) and maintains stable ferromagnetic order to ∼800 K. These properties position it as a promising candidate for next-generation multifunctional devices in spintronics.

Photoinduced Electronic and Spin Topological Phase Transitions in Monolayer Bismuth.

Ultrathin bismuth exhibits rich physics including strong spin-orbit coupling, ferroelectricity, nontrivial topology, and light-induced structural dynamics. We use abinitio calculations to show that light can induce structural transitions to four transient phases in bismuth monolayers. These light-induced phases exhibit nontrivial topological character, which we illustrate using the recently introduced concept of spin bands and spin-resolved Wilson loops. Specifically, we find that the topology changes via the closing of the electron and spin band gaps during photoinduced structural phase transitions, leading to distinct edge states. Our study provides strategies to tailor electronic and spin topology via ultrafast control of photoexcited carriers and associated structural dynamics.

Sb surface terminated MnSb devices in the niccolite phase

The magneto-electronic properties of ferromagnetic MnSb grown by molecular beam epitaxy can be dominated by the presence of a surface state in the minority spin bandgap when the surface is Sb-terminated. The material resistivity is 120 µΩ.cm at 295 K, and although this is determined by the majority spin population, the anisotropic magnetoresistance, dependent on minority spins, is ∼0.24% for the Sb-terminated devices with Mn-terminated devices showing ∼0.02%. At 295 K, the extraordinary Hall constant is 0.5 Ω/T for the Sb-terminated surface and 1.5 Ω/T for the Mn-terminated surface with the extraordinary Hall constant and anisotropic magnetoresistance behaving with an anomalous temperature dependence between 295 and 1.5 K. The dominant MnSb structural phase on the GaAs (001) orientation is naturally doped p-type with a carrier density ∼1 × 1022 cm−3 determined by the normal Hall effect after the extraordinary Hall effect has saturated at higher fields than ∼2 T. Spintronic device possibilities are discussed, particularly the spin-light emitting diode and magnetic nano-structures. A natural p-type doping in MnSb limits the devices to dominant hole carrier effects although there is compatibility with both III–V and Si–Ge materials for hybrid device possibilities.

An Ab Initio Study of Monolayer Mn2Mg2X5 (X = S, Se), a Novel Family of 2D Half‐Metallic Ferromagnets

The recent advances in the synthesis of 2D magnetic materials have raised hopes for their potential use in next‐generation spintronics devices. These candidates, however, still possess relatively low magnetic transition temperatures and small magnetic anisotropy energies to achieve efficient functionality. Aiming to find high‐performance 2D magnetic crystals, the authors predict (X = S, Se) as a novel family of 2D ferromagnets with half‐metallic electronic properties. A single‐channel spin bandgap of ≈2 eV makes them suitable for spin‐filtering applications. Their easy‐plane magnetic anisotropy is relatively high, especially in the case of (MAE = 1.46 meV/Mn). Furthermore, the magnetic transition temperature of these compounds is relatively high ( ≈ 200 K) compared to those of most synthesized 2D magnetic compounds. The existence of nonmagnetic van der Waals analogs of these compounds, such as , accompanied by their energy, dynamic, thermal, and mechanical stability, suggest that they have a good probability of being synthesized.

First-principles study of two-dimensional half-metallic ferromagnetism in CrSiSe4 monolayer

Two-dimensional (2D) ferromagnetic (FM) half-metallic materials have attracted intensive attention due to their unique electronic and magnetic properties and potential applications in spintronic devices. In this study, we predicted a stable 2D half-metallic material monolayer CrSiSe4 using first-principles density functional theory. The structure, electronic and magnetic properties were systematically studied. The calculations show that the monolayer CrSiSe4 is a dynamically stable FM half-metallic material. The spin-dependent transport properties and the Curie temperature up to 239 K are demonstrated. The spin band gap of monolayer CrSiSe4 was about 0.83 eV by the the Heyd–Scuseria–Ernzerhof function calculation. The magnetic anisotropy energy of each Cr atom in the monolayer of CrSiSe4 is eV. When the applied biaxial tensile strain is greater than 2%, monolayer CrSiSe4 spin-up conduction band and valence band will show a band gap at the Fermi level, and the electronic properties change from a half-metal to a semiconductor. Thus, the monolayer CrSiSe4 can provide an ideal candidate material for exploring 2D magnetic and spintronics experiments.

Investigation of the dynamic interaction between dopants and oxygen vacancies in amorphous Nb2O5: Simulation and experimental study

Resistive random-access memory can potentially be used to construct high-speed, low-power, and high-density data-storage drives. Managing oxygen flow at the electrode-oxide interface is vital for improving endurance. Dopant-oxygen interactions govern ion diffusion and vacancy creation. The interactions between multivalent dopants and oxygen vacancies in Nb2O5 have been investigated in previous studies. In this study, we simulated the relationship between a multivalent dopant Mn and oxygen vacancies in amorphous Nb2O5. We introduced oxygen vacancies and Mn ions with different oxidation states to determine the effects of spin densities and band gaps. Experimental results obtained from deposited amorphous thin films validated the simulation results, demonstrating a close agreement between the experimentally obtained (1.11 eV) and predicted bandgaps (0.93 eV). The results of study illuminate the amorphous structure of Nb2O5, the interactions between multivalent Mn dopants and oxygen vacancies, and the resulting electronic properties, offering the potential for designing and optimizing functional materials.

Prediction of Interesting Ferromagnetism in Janus Semiconducting Cr2AsP Monolayer

Abstract2D half‐metallic materials that have sparked intense interest in advanced spintronic applications are essential to the developing next‐generation nanospintronic devices. This study has adopted a first‐principles calculation method to predict the magnetic properties of intrinsic, Se‐doped, and biaxial strain tuning Cr2AsP monolayer. The Janus Cr2AsP monolayer is proven to be an intrinsic ferromagnetic (FM) semiconductor with an exchange splitting bandgap of 0.15 eV at the PBE+U level. Concentration‐dependent Se doping, such as Cr2AsSexP (x = 0.25, 0.50, 0.75), can regulate Cr2AsP from FM semiconductor to FM half‐metallicity. Specifically, the spin‐up channel crosses the Fermi level, while the spin‐down channel has a bandgap. More interestingly, the wide half‐metallic bandgaps and spin bandgaps make them have important implications for the preparation of spintronic devices. At last, it also explore the effect of biaxial strain from ‐14% to 10% on the magnetism of the Cr2AsP monolayer. There appears a transition from FM to antiferromagnetic (AFM) at a compressive strain of ‐10.7%, originating from the competition between the indirect FM superexchange interaction and the direct AFM interaction between the nearest neighboring Cr atoms. Additionally, when the compressive strain is ‐2% or the tensile strain is 6%, the semiconducting Cr2AsP becomes a half‐metallic material. These charming properties render the Janus Cr2AsP monolayer with great potential for applications in spintronic devices.

Antiferromagnetic Spin-Ordered Topology of Surface Functionalized Sb and Bi Monolayer Nanoflakes

Abstract Scale effect and topological frustration have been found to induce magnetic ordering in graphene-like nanoflakes. Based on triangular nanoflakes, the chemically surface-modified Sb and Bi monolayer nanotopological structures are proposed as spintronic logic gates, and their first-principles spin-polarized electron-structure calculations are performed to provide a theoretical basis for developing a new generation of ultrafast spin devices. The net spin of surface-functionalized Sb and Bi monolayer triangular nanoflakes mainly originates from the topological edge-states, exhibiting a sufficiently large spin bandgap, thus enabling stable large spin magnetic moments even under conditions of internal or edge defects and room-temperature electron excitation. The double-triangular nanoflakes of surface-functionalized Sb and Bi monolayers exhibit two stable spin configurations: ferromagnetic coupling and antiferromagnetic coupling. These configurations can serve as elementary variables for spin logic gates. Even at a linear scale as small as 2 nm, the spin coupling energy remains greater than 120 meV, and the error rate decreases below 1×10-5 at room temperature, demonstrating the spin logic gates of triple triangular nanoflakes protected by scattering-prohibited topology.

Spin-valley switch and conductance oscillations in antiferromagnetic transition metal dichalcogenides

Antiferromagnetic materials are regarded as the outstanding candidates for the next generation of spintronics applications thanks to the numerous interesting features. We theoretically study the spin and valley transport in transition metal dichalcogenides in the present of antiferromagnetic exchange field. It is found that the spin and valley dependent band gap can be controlled by the exchange field. The system could become a spin-valley half metal, where a certain spin-valley electron is metallic state and other electrons are insulating states. The normal/antiferromagnetic/normal junction could work as an effective spin-valley switch controlled by the gate voltage. In the normal/antiferromagnetic/normal/ferromagnetic/normal junction, quantum beats occur in the oscillations of total conductance. The beat phenomenon results from the interference of two different spin-valley dependent conductances with similar frequencies. In addition, the junction can also work as a magnetoresistance device.

First-principles calculations to investigate electronic, magnetic and half-metallic ferromagnetic properties of full-Heusler Mn2OsSn

ABSTRACT The structural, electrical, magnetic, and elastic characteristics of the Mn2OsSn full-Heusler compound have all been studied using the full potential linearised augmented plane (FP-LAPW) method. The study's exchange and correlation potentials are calculated using the generalised gradient approach (GGA) developed by Burke, Perdew, and Ernzerhof; the GGA with the Tran-Blaha-modified Becke–Johnson approximations; and the GGA with the correlated Hubbard parameter (GGA +U). Our calculations show that the formation energy of the compound is negative for the two-type structure, which means the crystal may persist indefinitely. Our chemical has a convex hull distance at 0 K for cubic regular and inverse-type structures, indicating that it will likely be synthesised via equilibrium processing. The electronic band structures, densities of states, and 100 spin-polarisation at the Fermi level in the typical cubic AlCu2Mn-type structure show Mn2OsSn in its complete Heusler ferromagnetic state has a half-metallic feature with an indirect band gap in the minority spin. Alternatively, in the CuHg2Ti-type ferromagnetic state, with its inverse cubic structure, this material exhibits metallic ferromagnetic behaviour with a polarisation of 96,325. The half metallicity of the AlCu2Mn-type combination is preserved at 1 GPa of hydrostatic pressure. Thus, Mn2OsSn, with the appropriate correction option for the Hubbard-Coulomb parameter U, will be a promising contender for spintronic applications.

Cobalt-based full Heusler compounds Co2FeZ (Z = Al, Si, and Ga): A comprehensive study of competition between XA and L21 atomic ordering with ab initio calculation

To study the structural properties of Co2FeZ (Z = Al, Si, Ga) (CFZ) alloys, we will use the approximation method GGA-PBE based on the method of plane waves increased by linear waves at full potential using the theory of functional density in both the Hg2CuTi and Cu2MnAl-type structures. From the most stable state we determine the other properties such as the magnetic, elastic and thermoelectric properties. The band structure calculation reveals indirect band gap in spin down channel and zero band gap in spin up channel of valence and conduction bands confirming the spin gapless semiconducting nature of these compounds. Calculated Seebeck coefficient in spin up and spin down channel reveals that the CFZ behaves as both n and p type thermoelectric materials with better output efficiency. The transport properties of these materials are discussed on the basis of Seebeck coefficient, electrical conductivity coefficient, thermal conductivity and figure-of-merit coefficient. By analyzing the nature of the bonding between the different atoms that form CFZ that each of them has a strong covalent character.

The effect of different dopants and their positions on the magnetic properties of an armchair antimonene nanoribbon: comprehensive theoretical investigation

In this work, using density functional theory, we have studied the magnetic properties of an armchair antimonone nanoribbon doped with transition metal (TM) atoms (Mn, Fe, Co, Ni, V, Cr) in various positions and different number of impurity atoms. The results show that the investigated magnetic properties, such as spin band gap, spin polarization and magnetic moment vary with type and distance from the edge of the ribbon and the number of impurities. The obtained values of magnetic moment reveal, Mn-doped nanoribbons have greater magnetization than Fe, Cr, V, Ni and Co doped ones. Also, spin polarization with significant values is observed in Mn and Fe doped structures. Our calculated spin currents demonstrate that introducing of TM dopants leads to efficient separation of spin up and down currents. Interestingly, nanoribbons with Mn, Cr and V dopants show high spin filter efficiency in a wide range of voltages. Thus, it seems that our results prepare a promising way to nanoscale spintronic devices.

First principles study of 2D half-metallic ferromagnetism in Janus Mn2XSb (X = As, P) monolayers

Two-dimensional (2D) intrinsic magnetic materials have attracted much attention because of their fascinating physical properties. However, low Curie temperature TC and small magnetic anisotropy energy (MAE) limit their application prospects. Based on the density functional theory, we predict that Janus Mn2AsSb and Mn2PSb monolayers are 2D intrinsic ferromagnetic half-metals. Monte Carlo simulations suggest that the TC values of these monolayers are about 385 and 334 K, respectively. The Mn2AsSb and Mn2PSb monolayers exhibit large MAEs of 415.2 and 450.6 μeV per Mn, respectively. Their ferromagnetism is robust against biaxial strain in the range from −10% to 10%. An energy band calculation with the Heyd–Scuseria–Ernzerhof (HES06) functional indicates that the half-metallic spin bandgaps are about 1.00 and 0.81 eV and the bandgaps on the spin-down channel are 2.67 and 2.53 eV for Mn2AsSb and Mn2PSb monolayers, respectively. These exciting electronic and magnetic properties make Janus Mn2XSb (X = As, P) monolayers promising candidate materials for 2D spintronic devices.

The spin-state transition in ACo2O4 spinels (A = Be, Mg, Ca, Cd, Zn)

The magnetic and electronic properties of the Co-based spinel oxides ACo2O4 (A = Be, Mg, Ca, Zn, Cd) were studied within GGA + U approach. It was found that the Co3+ ion is in a low-spin state due to the effect of the crystal field of octahedral symmetry. It is shown that Co3+ ion undergoes a spin-state transition into the high-spin state under the critical pressure of P = −10 GPa – −20 GPa. This pressure-induced spin-state transition is caused by the redistribution of electrons between the t2g- and eg-orbitals arising with increasing interatomic distances. The role of interatomic distances between Co3+ ion and its ligands is discussed. Thin-film form also favors the appearance of a high-spin state of Co3+ ion. At the same critical pressure, there is a sharp increase in the majority spin bandgap and a sharp decrease in the minority spin bandgap. These findings allow manipulating the spin state of Co3+ ions and bandgap width through the pressure or strain arising in thin films.

Structural, electronic and optical properties of ternary rare-earth based GdPtSb half Heusler compound

We present a density functional theory (DFT) calculation for structural, electronic and optical properties of rare earth based GdPtSb half Heusler (HH) compound by using GGA + U approximation. Our calculated total density of states (DOS) and partial density of states (PDOS) of GdPtSb show that near Fermi energy (EF), the maximum contribution is due to the Gd-5d and Pt-5d states. The electronic band structure calculation shows the half-metallic nature of GdPtSb compound. We found a narrow energy band gap (86 meV) in majority spin, while in minority spin with electronic states of valence band crosses the Fermi level (EF). Optical response of GdPtSb compound is investigated by complex dielectric function, extinction coefficient, absorption coefficient, refractive index and reflectivity. From the best of our literature survey the electronic and optical properties are less explored in theoretical work. Our calculated structural and electronic properties are in agreement with other theoretical and experimental work, while the optical properties of GdPtSb compound are not explored experimentally till date.

A DFT+U study of the effect of transition metal replacements on optoelectronic and elastic properties of TmCu3S4 (Tm = V, Ta, Nb)

One of the main goals of researchers is to develop renewable, ecologic and efficient energy sources to meet energy needs in the near future. In this context, chalcogenide materials are the most promising candidates for the production of clean energy from solar radiations using a new generation of technologically advanced solar cells. In this paper, we use first-principles GGA+U calculations to study the optoelectronic and elastic properties of TmCu3S4 (Tm = V, Ta, Nb) in terms of their potential applications in optoelectronic devices. Our calculations show that VCu3S4 is a half-metallic compound, showing metallic properties in the spin up channel and semiconducting properties in the spin down channel. On the other hand, NbCu3S4 and TaCu3S4 are semiconductors. VCu3S4 has a direct bandgap in spin down channel as the CBM (conduction band minima) and VBM (valence band maxima) occur at the same point Γ. However, NbCu3Se4 and TaCu3Se4 are indirect bandgap semiconductors. The values of bandgaps for above-mentioned materials are increased by replacing Nb with Ta and V. The prospect of TmCu3S4 (Tm = V, Ta, Nb) for optoelectronic applications is demonstrated by detailed examination of optical parameters. This study reveals that TmCu3S4 (Tm = V, Ta, Nb) are week reflectors of incoming photons, and a maximum of 50% reflection of incoming photo radiations is depicted by these materials in the upper UV region for both spins. In the elastic properties, the values of Zener anisotropy factor A indicate that the cubic materials mentioned above are anisotropic and have covalent bonds. The material will be brittle if value of the Pugh’s ratio (B/G) is less than 1.75, otherwise it will be substantially plastic. In this study, values of Pugh’s ratio (B/G) TmCu3S4 (Tm = V, Ta, Nb) are below 1.75. Therefore, these cubic chalcogenides are fragile.

Half-metallicity in Fe2MnSi and Mn2FeSi heusler compounds: A comparative ab initio study

First-principles calculations of the structural, electronic, and magnetic properties of full-Heusler compounds Fe2MnSi and Mn2FeSi in regular L21 and inverse XA structures have been performed using density functional theory (DFT) within generalized gradient approximation (GGA) and SCAN functionals. All compounds indicate half-metallic properties with the minority spin bandgap. The causes for the appearance of half-metallic bandgap and the difference in the electronic and magnetic properties of Heusler compounds were studied and analyzed in terms of the local environment. It is shown, that the half-metallic bandgap determines by the behavior of the t2g-electrons of A- and C-sites atoms. The behavior of the compounds under pressure was also considered. The high sensitivity of the magnetic moments on atoms A, C and the bandgap to pressure is discussed. The transition from regular to inverse structure is predicted at the negative pressure.

A Theoretical Analysis of Physical Properties and Half-Metallic Stability under Pressure Effect of the ScNiCrZ (Z=Ga, Al, In) Heusler Alloys

The aim purpose of this study is to investigate the structural, elastic, magnetic, electronic properties and half-metallic stability under pressure of ScNiCrZ ([Formula: see text], Ga and In) quaternary Heusler alloys using full-potential linear muffin-tin orbital (FP-LMTO) method within the gradient generalized approximation (GGA) for exchange, and correlation potential. In order to evaluate the stability of our compounds, the formation energy, and elastic constants have been evaluated. The results showed that our compounds have ferromagnetic ground states and are energetically more stable in type-[Formula: see text] configuration. True half-metallic ferromagnetic behavior with 100% spin polarization at Fermi level [Formula: see text] with high Curie temperature [Formula: see text], and very interesting bandgap in the minority spin are obtained for the three alloys. The calculated total magnetic moment [Formula: see text] for all three alloys is consistent with Slater[Formula: see text]Pauling rule. The half-metallicity is maintained over a wide range of lattice constants making these alloys promising for spintronic, and magneto-electronics applications.