Magnetic Properties Of Monolayer Research Articles

Electronic and magnetic properties of 2D vanadium-based transition metal dichalcogenides

In this paper, electronic and magnetic properties of monolayers and bilayers of Vanadium-based transition metal dichalcogenides VX2 (X = S, Se, Te) in the H phase are investigated theoretically using methods based on DFT calculations as well as analytical methods based on effective spin Hamiltonians. The band structure has been computed for all systems, and then the results have been used to determine exchange parameters and magnetic anisotropy constants. These parameters are subsequently used for the determination of the Curie temperatures, hysteresis curves, and energy of spin-wave excitations. In the latter case, we compare analytical results based on effective spin Hamiltonian with those determined numerically by Quantum ATK software and find a good agreement. The determined Curie temperature for VTe2 monolayers and bilayers is below the room temperature (especially that for bilayers), while for the other two materials, i.e. for VS2 and VSe2, it is above the room temperature, in agreement with available experimental data.

Layer-dependent electronic and magnetic properties for Cr[formula omitted]NO[formula omitted] and Cr[formula omitted]CO[formula omitted

Using the first-principles calculations, we study the stability, electronic and magnetic properties of monolayer, bilayer and trilayer Cr2NO2 and Cr2CO2. Stability is estimated from the thermal, mechanical and dynamical perspectives. Calculations show that the monolayer, bilayer and trilayer Cr2NO2 and Cr2CO2 are ferromagnetic ground states, and Cr2CO2 are nearly half-metals, and Cr2NO2 are half-metals with an integer total magnetic moment. For the monolayer, bilayer and trilayer Cr2NO2 and Cr2CO2, the Z-axis direction is their easy magnetization axis, and their magnetic anisotropy energies are obviously increased with the increase of layered number, the improvement of magnetic anisotropy energy origins from the enhancement of spin–orbit coupling strength. In addition, we also discuss the origin of gaps for monolayer, bilayer and trilayer half-metallic Cr2NO2.

Ferromagnetism and structural deformation in monolayer alpha lead oxide induced by N and F doping: New insights from first principles

AbstractWe study the structural, electronic, and magnetic properties of monolayer α‐PbO0.875A0.125 (A = N, F), which are calculated using first principles. As a result, N doping induces local ferromagnetism centered at the N2− site, originating from the spin‐down N 2p valence states. On the other hand, F doping induces nonmagnetism and induces ab‐plane deformation, where F− receives one electron to its nearest‐neighboring Pb1.75+ ions. N doping redshifts the bandgap of the undoped system and transforms it to be indirect, while F doping blueshifts the bandgap through the Burstein‐Moss effect. The hybridization of Pb 6p and O 2p orbitals is stronger near the A site than that of the crystal structure edge. Our result shows new insights, predicting possible experimental results for future functional device applications.

Remarkably enhanced Curie temperature in monolayer CrI3 by hydrogen and oxygen adsorption: A first-principles calculations

Two-dimensional (2D) materials unique properties and their promising applications in post-silicon microelectronics have attracted significant attention in the past decade. Recently, ferromagnetic order with out-of-plane easy axis in a monolayer of CrI3 has been observed and reported, with a Curie temperature of 45 K. Here we study, using density functional theory (DFT) calculations, how hydrogen and oxygen adsorption affects the structural, electronic, and magnetic properties of a CrI3 monolayer. Our results show that while the structure remains almost unchanged by the adsorption of hydrogen, adsorption of oxygen completely distorts it. We have also found that both the adsorption of hydrogen and oxygen atoms significantly influences the electronic and magnetic properties of the monolayer. While hydrogen quenches the magnetic moments of Cr atoms, oxygen introduces an impurity band in the gap. Interestingly, we find a strong enhancement of the Curie temperature by full hydrogenation, while the results are not conclusive for O. This result suggests a simple and effective approach to manipulate the electronic and magnetic properties of 2D magnets for spintronics applications.

Electronic and Magnetic Properties of Monolayer and Bilayer Phosphorene Doped with Transition‐Metal Atoms

The structural, electronic, and magnetic properties of phosphorene doped with transition‐metal (TM) atoms have been investigated within the framework of density functional theory based on spin‐polarized first‐principles calculations. Strong orbital hybridization is exhibited between TM atoms and P atoms, where covalent bonds form in phosphorene. Except for the Ni atom, the other TM atoms still possess localized magnetic moments. Meanwhile, the TM doping also modulates the electronic structure of phosphorene. A spin‐polarized semiconducting state appears for Mn, Fe, Co, Ni atoms absorbed on monolayer phosphorene, while metallic states appear by doping with V and Cr. Also, in the Mn/Fe/Co doping systems the spin polarization is found to be 100% at the highest occupied molecular orbital (HOMO). In contrast, bilayer phosphorene doped with TM atoms retains its intrinsic semiconducting feature, and the systems with V and Mn interlayer doping show 100% spin polarization at the HOMO level. Whereas, both monolayer and bilayer phosphorene doped with Ni atom exhibit no spin polarization.

Theoretical study of the effect of hydrogen adsorption on the stability and electronic properties of hybrid monolayers

We have applied first-principle calculations, based on the density functional theory, to analyze the stability, electronic and magnetic properties of monolayers of graphene with a nanodomain of boron nitride (h-BN) with different geometries. To this end, we have investigated the effects of the adsorption of one and two hydrogen atoms by different atoms at the edge of the h-BN nanodomain, where we used the GGA approximation for the functional exchange and correlation. Specifically, we found that the structures with triangular-shaped nanodomains are the most stable and have a non-integer magnetic moment upon adsorption of the hydrogen atoms. We have also shown that both the electronic and magnetic properties can be influenced by the type of atom which adsorbs the hydrogen at the edge of the nanodomain. Additionally, we have demonstrated that some structures can quench the spin that would be generated by the adsorption of the hydrogen atoms.

Electronic and Magnetic Properties Modulated by Adsorption of 3d Transition Metal Atoms in Monolayer and Bilayer MoS2 Sheets

The adsorption effects of 3d transitional metal (TM) adatoms on electronic and magnetic properties of monolayer and bilayer MoS2 sheets have been investigated by using first-principle calculations based on the density functional theory. The calculated results suggest that both monolayer and bilayer MoS2 sheets have power abilities of absorbing 3d TM atoms. The interlayer adsorption of bilayer MoS2 is relatively more stable than the surface adsorption of monolayer MoS2. The 3d TM adatoms and the neighboring S atoms behave a clear covalent-binding character. It was found that TM adatoms induce certain impurity states within the band gap of the pristine MoS2 sheet which result in the systems magnetically semiconducting or half metallic. The adsorbed systems for Cr and Co on the surface of monolayer MoS2 sheet, as well as Sc, Cr and Fe in the interlayer of bilayer MoS2 sheet exhibit half-metallic behavior. And the other 3d TM-adsorbed systems are magnetic semiconductor except for Ni species.

First-principles study of magnetic frustration in FeSe epitaxial films onSrTiO3

The effects of electron doping and phonon vibrations on the magnetic properties of monolayer and bilayer FeSe epitaxial films on SrTiO$_3$ have been studied, respectively, using first-principles calculations with van der Waals correction. For monolayer FeSe epitaxial film, the combined effect of electron doping and phonon vibrations readily leads to magnetic frustration between the collinear antiferromagnetic state and the checkerboard antiferromagnetic N\'eel state. For bilayer FeSe epitaxial film, such magnetic frustration is much more easily induced by electron doping in its bottom layer than its top layer. The underlying physics is that the doped electrons are accumulated at the interface between the FeSe layers and the substrate. These results are consistent with existing experimental studies.

Characterization of Metallo-porphine Monolayer and Bilayer on Ag(111): Screening of Substrate Effects

The structures and magnetic properties of monolayer and bilayer of transitional metallo-porphine (MP) species (M = Mn, Fe, Co, Ni, Cu) on the Ag (111) substrate are investigated by DFT based first-principle method. The MP monolayer has a distortion about 10° towards the substrate due to strong interaction between adsorbed molecule and substrate. The molecule-substrate interaction could quench the magnetic moment of the adsorbed molecule. For MP bilayer adsorption on the Ag (111), the top layer remains its planar structure and magnetic moment due to the screening of substrate effects by bottom layer, meanwhile the bottom layer has strong structural distortions and obvious variations of magnetic moment.

Magnetic Properties of Mono- and Multilayer Assemblies of Iron Oxide Nanoparticles Promoted by SAMs

Owing to the wide scope of applications of magnetic nanoparticle assembling, the aim of this study is to evaluate the influence of nanoparticle aggregates on the magnetic properties of 2D assemblies. Magnetic iron oxide nanoparticles (NPs) have been synthesized by the coprecipitation (NPcop) and thermal decomposition (NPdec@OA) methods, and were assembled on self-assembled monolayers of organic molecules decorated by a phosphonic acid terminal group at their surface (SAM-PO3H2). The nanostructure and magnetic properties of assemblies depend directly on the aggregation of NP suspensions. NPcop result in an unstable suspension and were assembled into a non-homogeneous monolayer of aggregates. The post-functionalization of NPcop with oleic acid after synthesis (NPcop@OA) favors a better stability of the suspension and enhances the nanostructure of the assembly, although smaller NP aggregates remain. In contrast, NPdec@OA which are functionalized in situ by oleic acid during the synthesis step were assembled as individual nanomagnets and result in a dense monolayer. Multilayer assemblies were also prepared from NPcop@OA and NPdec@OA by performing the alternative deposition of these NPs with (1,4-phenylene)bisphosphonic acid. The nanostructure of assemblies has been studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The magnetic properties of monolayer and multilayer assemblies have been studied by using a SQUID magnetometer. While assemblies of individual NPs enhance dipolar interactions in-plane as a result of shape anisotropy, assemblies of NP aggregates favor stronger dipolar interactions with random orientation. The magnetic properties of monolayer and multilayer assemblies have also been compared. The dimensionality (2D vs 3D) has a strong effect on the dipolar interactions when individual NPs are considered in contrast to aggregated nanoparticles.

Preparation of CuCr2Se4/ZnSe layered films on glass substrates by laser ablation

Films of chalcogenide spinel CuCr2Se4 were prepared by laser ablation. Targets were synthesized by melting in silica tubes and connected to a rotating drum. The targets were then evaporated by a XeCl eximer laser (wavelength, 308 nm; pulse duration, 20 ns; pulse power, 10 mJ). The target and the substrate during deposition were rotated at a rate of 150 rpm in a vacuum chamber. The deposition of CuCr2Se4/ZnSe multilayer films was studied, their thickness was controlled, and their morphology was examined by scanning electron microscopy. The crystal structure and magnetic properties of monolayer and multilayer films were investigated.

Magnetic Anisotropies and Coupling Mechanisms inFe/Mo(110)Nanostripes

Using low-temperature (5 K) spin-polarized scanning tunneling microscopy, we have studied the morphology and magnetic properties of monolayer (ML) and double layer (DL) thick Fe nanowires grown by step flow on a Mo(110) single crystal. Magnetic contrast has been obtained using tungsten tips covered by Au/Co thin films. We find that the DL Fe nanowires, similarly to ML Fe nanowires, are perpendicularly magnetized. Because of the dipolar coupling, separated DL Fe nanowires are antiferromagnetically coupled. DL wires that are touching at step edges are ferromagnetically ordered due to direct exchange coupling. We measured the widths of the magnetic domain walls in the ML and DL Fe nanowires. The domain wall width increases with the thickness of Fe.

Magnetism of Fe on W(001) and the effects of oxygen adsorption

Structural, electronic and magnetic properties of monolayer and bilayer Fe on W(001), denoted by 1Fe/W(001), and 2Fe/W(001), and oxygen on 2Fe/W(001) have been calculated using the full potential linearized augmented plane wave method. The ferromagnetism of the Fe monolayer is found to be removed by the W(001) substrate (even as a metastable state) for the monolayer Fe/W(001) system; the AFM coupling becomes the ground state. Interestingly, an additional Fe overlayer can activate the ferromagnetism of the ‘dead’ Fe layer — which indicates the sensitivity of the magnetism to the overlayer thickness for Fe/W(001) especially around monolayer coverages. The bilayer Fe adopts a tetragonal (rather than bcc) structure on W(001), which keeps the interatomic distance between two Fe layers identical to that in bulk bcc Fe (4.69 a.u.). Oxygen adsorption induces a large change of the atomic structure and the Fe magnetic moment (an increase in the top layer and a reduction in the underlayer). Magnetic Fe overlayers induce a large magnetic moment of 0.19–0.22μB on the interfacial W atoms and a very large magnetic hyperfine interaction. The spin density at EF, m(r,EF), is negative in the surface-vacuum region for the bilayer Fe/W(001) system, but becomes positive on oxygen adsorption.

Magnetic Properties of Monolayers with Modified Gaussian Distribution of Exchange Integrals

AbstractMagnetic properties of a monolayer with a Gaussian‐type distribution of exchange integrals are investigated within the Ising model. The Gaussian distribution is modified in order to omit the range of negative exchange interactions as well as extreme positive values. The obtained results concern phase diagrams, magnetization, and correlation functions. A comparison with analogous results obtained for an ordinary Gaussian distribution is also made.