Showing papers on "Half-metal published in 2021"

Cr2NX2 MXene (X = O, F, OH): A 2D ferromagnetic half-metal

Abstract: Using the spin-polarized first-principles calculations, we revealed that two-dimensional transition metal nitride MXenes Cr2NX2 (X = O, F, OH) are excellent two-dimensional half-metallic ferromagnetic materials. Their structures and ferromagnetic ground states are stable well above room temperature. In addition, their large half-metal bandgaps are enough to prevent spin reversal and ensure high spin filtering efficiency and large spin mean free paths. The half-metallic property of these functionalized Cr2NX2 systems is robust and can be maintained under tensile strains up to 10%. These predictions suggest that the functionalized Cr2NX2 is of great significance for the development of highly efficient spintronic devices for room temperature applications.

1T-CrO2 monolayer: a high-temperature Dirac half-metal for high-speed spintronics

Abstract: Two-dimensional (2D) materials with complete spin-polarization, high-speed conduction electrons, large Curie temperatures and robust ferromagnetic ground states are desirable for spintronic applications. Based on first-principles calculations, we demonstrate that the 1T-CrO2 monolayer is an intrinsic 3d ferromagnetic Dirac half metal (DHM) with two symmetry protected Dirac cones near the Fermi level. The Fermi velocities (3.21 × 105 m s−1 and 4.85 × 105 m s−1) of the Dirac cones are in the same order as that of graphene, indicating its excellent transport properties. Its 2.48 eV half-metallic gap is large enough to prevent the spin-flip transition. Moreover, the two Dirac cones are robust against biaxial strain of up to ±4%. The robust ferromagnetism is mainly contributed by the 3d states of Cr and its Curie temperature is up to 507 K. Our results indicate that the ferromagnetic 1T-CrO2 monolayer is a promising candidate for high temperature, high efficiency spintronics applications.

Theoretical study of tunable magnetism of two-dimensional MnSe 2 through strain, charge, and defect.

Abstract: Two-dimensional transition metal dichalcogenide MnSe2(2D-MnSe2) with Curie temperature approximate to 300 K has a significant spintronic application on thin-film devices. We demonstrate theoretically a tunable magnetic transition of 2D-MnSe2between anti-ferromagnetic (AFM) metal and ferromagnetic (FM) half metal as strain increasing. Mechanism of that transition involves a competition betweend-p-dthrough-bond andd-ddirect interaction in 2D-MnSe2. Hole doping is an alternative way to enhance the stability of FM coupling. Adsorption (including Li, Na, Cl and F) and vacancy (Mn and Se) studies confirm that the controllable magnetism of 2D-MnSe2is related to both interaction competition and charge doping. Tensile strains can greatly amplify through-bond interaction and exchange parameters, resulting in a sharp increase of Curie temperature.

First-Principles Study of the Physical Properties of the New Quaternary Heusler Alloy CoMnVZ (Z = Sn and Sb)

Abstract: The physical properties of two new quaternary Heusler alloys CoMnVSn and CoMnVSb were systematically studied by using first-principles calculation. The results show that the type-1 structures of ferromagnetic phase for these two alloys are the most stable. They all exhibit half-metallic behavior at equilibrium, and their half-metallic characteristics are maintained in the lattice region of 5.73–6.19 A for CoMnVSn and 5.82–6.18 A for CoMnVSb. The calculated magnetic moment Mt of each molecular unit in the half-metal lattice region strictly follows the Slater–Pauling empirical rule Mt = Zt – 24, where Zt is the number of valence electrons. The elastic constants show that the mechanical properties of the two compounds are stable at equilibrium, and the anisotropy factor and three-dimensional Young’s modulus confirm that they have anisotropy. It is expected that the CoMnVSn and CoMnVSb alloys are promising candidates in spintronics.

Generation of terahertz transients from Co 2 Fe 0.4 Mn 0.6 Si -Heusler-alloy/normal-metal nanobilayers excited by femtosecond optical pulses

Abstract: We generated pulses of electromagnetic radiation in the terahertz (THz) frequency range by optical excitation of ${\mathrm{Co}}_{2}{\mathrm{Fe}}_{0.4}{\mathrm{Mn}}_{0.6}\mathrm{Si}$ (CFMS)/normal-metal (NM) bilayer structures. The CFMS is a Heusler alloy showing a band gap in one spin channel and is therefore a half metal. We compared the THz emission efficiency in a systematic manner for four different CFMS/NM bilayers, where NM was either Pt, Ta, Cr, or Al. Our measurements show that the THz intensity is highest for a Pt capping. We also demonstrate the tunability of the THz amplitude by varying the magnetic field for all four bilayers. We attribute the THz generation to the inverse spin Hall effect. In order to investigate the role of the interface in THz generation, we measured the spin mixing conductance for each CFMS/NM bilayer using a ferromagnetic resonance method. We found that the spin-orbit coupling cannot completely describe the THz generation in the bilayers and that the spin transmission efficiency of the CFMS/NM interface and the spin diffusion length, as well as the oxidation of the NM layer, play crucial roles in the THz emission process.

Prediction of a Heusler alloy with switchable metal-to-half-metal behavior

Abstract: We propose a ferromagnetic Heusler alloy that can switch between a metal and a half-metal. This effect can provide tunable spintronics properties. Using the density functional theory with reliable implementations of the electron correlation effects, we find ${\mathrm{Mn}}_{2}\mathrm{ScSi}$ total energy curves consisting of distinct branches with a very small energy difference. The phase at low lattice crystal volume is a low magnetic half-metallic state while the phase at high lattice crystal volume is a high magnetic metallic state. We suggest that the transition between half-metallic and metallic states can be triggered by a triaxial contraction/expansion of the crystal lattice or by an external magnetic field if we assume that the lattice is cubic and remains cubic under expansion/contraction. However, the phase at high volume can also undergo an austenite-martensite phase transition because of the presence of Jahn-Teller active $3d$ electrons on the Mn atoms.

Transition of spin gapless semiconductor to semiconductor and half-metal in ferromagnetic Ba2MnTeO6

Abstract: A novel spin gapless semiconductor material Ba2MnTeO6 is found and reported by first-principles calculations. In this paper, we study the influence of spin orbit coupling, strain and Coulomb interaction on the properties of ferromagnetic Ba2MnTeO6 in order to test the stability of physical properties. It turns out that the spin orbit coupling has no significant effect on the electronic structures of the Ba2MnTeO6 at equilibrium state. Under the action of uniform compressive strain and tensile strain, Ba2MnTeO6 transforms from spin gapless semiconductor to semiconductor and half-metal respectively. At the same time, as the strain increases, the semiconductor band gap gradually widens, and the half-metallic gap gradually narrows. After considering Coulomb interaction, Ba2MnTeO6 will also be transformed into a semiconductor, and the semiconductor band gap will increase with the increasing of U values. Furthermore, the mechanical performance studies show that Ba2MnTeO6 is an anisotropic material with stable structure. As the first pure double perovskite type spin gapless semiconductor, the high spin polarization and accurately adjustable physical properties of ferromagnetic Ba2MnTeO6 indicate that it has broad application prospects in the fields of spintronics and optoelectronic materials and devices.

Topological metal phases in irradiated graphene sandwiched by asymmetric ferromagnets

Abstract: The ill-defined Chern number and disappearing topological edge states make it difficult to characterize the topological properties of a metal. In this work, we investigate the abundant topological phases of monolayer graphene, which is sandwiched by asymmetric ferromagnets and irradiated by off-resonant light. In this system, there exist some rarely noticed metal phases, which are spin-valley polarized metal, topological spin metal (TSM), spin half metal, and topological spin half metal (TSHM). Particularly, for the TSM, the subband with spin up or spin down is topological, but the whole state becomes a metal. For the TSHM, a subband with one spin is topological, while the other subband with the opposite spin is insulated, and the whole state is a spin half metal. As a consequence, one topological protected spin current flows on the edge and the other spin propagates in the bulk. Further calculations indicate that the Berry curvatures for the metal phases are nonzero. We propose to probe the topological properties of the metal states with the anomalous Nernst effect. For these topological phases, spin and valley splitting and flip can be obtained by modulating the Fermi level. An electrically or magnetically controlled switch is designed by a two-terminal TSHM junction. It is expected that these topological metal phases can broaden the band engineering in monolayer graphene and support a promising platform for the studies of spin and valley caloritronics.

Robust half-metallicity in CoZrMnZ (Z = P, As and Sb) quaternary Heusler alloys

Abstract: The spin-polarized full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT) and the exchange and correlation potential is treated with the genera...

Proximity Effect in Heterostructures Based on a Superconductor/Half-Metal System

Abstract: We have demonstrated that with increasing the exchange splitting of the conduction band of a ferromagnet and, respectively, of the degree of the spin polarization, the probability of transmission of the superconducting Cooper pairs through the S/F interface decreases. We have concluded that the spin imbalance plays a key role in the processes taking place at the interface between a superconductor and a ferromagnet with spin-polarized conduction electrons. We have studied the superconducting spin-valve effect in F1/F2/S heterostructures containing the Heusler alloy Co2Cr1 – xFexAly as one of two ferromagnetic (F1 or F2) layers. We have used the Heusler alloy layer in two roles: as a weak ferromagnet on the place of the F2 layer and as a half-metal on the place of the F1 layer. In the first case, we have obtained the full switching between the normal and superconducting states is realized with the dominant aid of the long-range triplet component of the superconducting pair condensate which occurs at the perpendicular mutual orientation of magnetizations. In the second case, we have observed separation between the superconducting transitions for perpendicular and parallel configurations of magnetizations reaching 0.5 K. We have also found good agreement between our experimental data and theoretical results.

Metal Cyclopropenylidene Sandwich Cluster and Nanowire: Structural, Electronic, and Magnetic Properties

Abstract: Organometallic sandwich clusters and nanowires can offer prototypes for molecular ferromagnet and nanoscale spintronic devices due to the strong coupling of local magnetic moments in the nanowires direction and experimental feasibility. Here, on the basis of first-principles calculations, we reportTMn(c-C3H2)n+1(TM= Ti, Mn;n= 1-4) sandwich clusters and 1D [TM(c-C3H2)]∞sandwich nanowires building from transitional metal and the smallest aromatic carbene of cyclopropenylidene (c-C3H2). Based on the results of lattice dynamic and thermodynamic studies, we show that the magnetic moment of Mnn(c-C3H2)n+1clusters increases linearly with the number ofn, and 1D [Mn(c-C3H2)]∞nanowire is a stable ferromagnetic semiconductor, which can be converted into half metal with carrier doping. In contrary, both Tin(c-C3H2)n+1and 1D [Ti(c-C3H2)]∞nanowire are nonmagnetic materials. This study reveals the potential application of the [TM(c-C3H2)]∞nanowire in spintronics.

Half metallicity and long-range magnetic order in graphene/hematene van der Waals heterostructure

Abstract: Graphene/hematene heterostructure is an interesting 2D van der Waals material with exciting and valuable features of both graphene and hematene. Our density functional theory calculations reveal that the resulting heterostructure preserves a long-range ferromagnetic character of pristine hematene monolayer and behaves as a half metal with 100% spin polarization unlike individual graphene and hematene monolayers which act like non-magnetic semi-metal and ferrimagnetic semiconductor, respectively. This transition to the half metal mainly arises due to charge transfer from C atoms of graphene to O atoms of hematene monolayer. These results manifest that the proposed heterostructure will attract the experimentalists highly and serve as a powerful candidate in spintronics and magnetic memory-based storage devices in near future.

Improvement electronic and magnetic properties of Cr impurity doped PbSe for optoelectronic devices applications: a first-principles proposal

Abstract: To produce innovative spintronics components, we are now looking for ferromagnetic semiconductors at room temperature. The aim of this work is to study the electronic structures and the magnetic properties is to trigger ferromagnetism and to improve the band gap of PbSe The study of the electronic structure and the magnetic properties of diluted magnetic semiconductors (DMS) type IV–VI PbSe doped Cr is investigated in detail. Our results are as follows. We then calculated the sp-d exchange couplings between electrons (holes) of the conduction (valence) band and magnetic impurities. The topology of the band structure shows that our material is half metal, which has a direct gap in the minority channel due to the nature of sp–d coupling. The values of N $$\alpha $$ ferromagnetic and N $$\beta $$ antiferromagnetic obtained in the mean-field approximation are of the order of 0.551 and $$-0.445$$ eV respectively. The Thermoelectric Conversion Efficiency focuses on a single dimension parameter, the figure of merit ZT. We have seen that doping with Cr can also have a beneficial effect on thermal conductivity and consequently on ZT. This leads our material among the best compounds to thermoelectric applications.

Prediction of spin-dependent electronic structures of 3d transition metals doped Hittorf's violet phosphorene towards spintronics

Abstract: Modulation of spin-dependent properties in semiconductor is of importance in exploring the potential application in spintronics. Here, we theoretically investigated the structural deformation, electronic characters, and magnetic properties of the single-layered Hittorf's violet phosphorene nanosheet with 3d transition metal atoms (ranging from Sc to Ni) doping and under external electric field. The electronic band structures and magnetic properties was found to be obviously modulated by the dopants: the existence of a large spin splitting of the dopant 3d states tailors the semiconducting phosphorene into simple magnetic semiconductor or bipolar magnetic semiconductor, except for the case of Sc. The application of an appropriate electric field to V-doped system could induce a transition from bipolar magnetic semiconductor to half metal with the carriers fully spin-polarized in alternative spin channel. Moreover, Hittorf's violet phosphorene-based field-effect transistor was proposed with the aim of realizing gate-voltage control on the carriers' spin orientation. Our findings pointed out the possibilities for realizing spin-dependent field-effect transistor in doped Hittorf's violet phosphorene nanosheet and opened a window for the burgeoning field of multifunctional 2D nanoelectronics and spintronics devices.

Emergent Half Metal at Finite Temperatures in a Mott Insulator

Abstract: Sustaining quantum mechanical phenomena at high temperatures is a long standing goal of condensed matter physics. Half metals, with the technological promise of providing 100$\%$ spin polarised currents sources, typically are low temperature phases that lose spin polarisation with temperature increase. Here we predict a novel half metal that emerges up on heating a Mott insulator, whose onset temperature is characterised by 100\% spin polarisation. We demonstrate strong dependence of the onset temperature on electron correlation strength offering easy tunability of temperature regime of half metallicity and discuss possible scenarios for experimental realisation.