Mn-doped Monolayer Research Articles

Tunable room-temperature ferromagnetism in the SiC monolayer

It is essential to explore two-dimensional (2D) material with magnetic ordering in new generation spintronic devices. Particularly, the seeking of room-temperature 2D ferromagnetic (FM) materials is a hot topic of current research. Here, we study magnetism of the Mn-doped and electron-doped SiC monolayer using first-principle calculations. For the Mn-doped SiC monolayer, we find that either electron or hole could mediate the ferromagnetism in the system and the Curie temperature (TC) can be improved by appropriate carrier doping. The codoping strategy is also discussed on improving TC. The transition between antiferromagnetic and FM phase can be found by strain engineering. The TC is improved above room temperature (RT) under the strain larger than 0.06. Moreover, the Mn-doped SiC monolayer develops half-metal at the strain range of 0.05-0.1. On the other hand, the direct electron doping can induce ferromagnetism due to the van Hove singularity in density of states of the conduction band edge of the SiC monolayer. The TC is found to be around RT. These fascinating controllable electronic and magnetic properties are desired for spintronic applications.

Enhanced magnetic properties and tunable Dirac point of graphene/Mn-doped monolayer MoS2 heterostructures

Graphene is one of the most promising spintronic materials due to its high carrier mobility. However, the absence of a band gap and ferromagnetic order in graphene seriously limit its applications in spintronics. How to utilize its high carrier mobility as well as mediate its electronic structure remains a challenge. Herein, we design a novel composite, which is composed of graphene and Mn-doped monolayer MoS2. The magnetic properties and electronic structures of graphene/Mn-doped monolayer MoS2 heterostructures were studied by using density functional theory (DFT) with the van der Waals (vdW) correlations (DFT-D). We found that the heterostructures show increased magnetic moments and more stable ferromagnetic (FM) states compared with that of isolated Mn-doped MoS2 monolayer. Our further studies show that many electrons are transferred to Mn-doped MoS2 monolayer from graphene, which causes the Fermi level to shift down below the Dirac cone about 0.59 eV. The transfered electrons also enhance the FM coupling between Mn ions. Graphene is partially spin polarized because of the magnetic proximity effect, which leads to the spin-dependent gaps for spin-up (16.1 meV) and spin-down (5 meV) at Dirac point, respectively. The introduction of sulfur (S) vacancy to the interface results in a much more stable FM structure and a higher total magnetic moment of the FM state; furthermore, it raises the spin polarization of graphene π orbitals and opens up a small band gap of about 7 meV. These findings propose a new route to facilitate the design of spintronic devices which both need stable ferromagnetism and finite band gap.

Tunable magnetic coupling in Mn-doped monolayer MoS2 under lattice strain

First-principles calculations are conducted to study the electronic and magnetic states of Mn-doped monolayer MoS2 under lattice strain. Mn-doped MoS2 exhibits half-metallic and ferromagnetic (FM) characteristics in which the majority spin channel exhibits metallic features but there is a bandgap in the minority spin channel. The FM state and the total magnetic moment of 1 µB are always maintained for the larger supercells of monolayer MoS2 with only one doped Mn, no matter under tensile or compressive strain. Furthermore, the FM state will be enhanced by the tensile strain if two Mo atoms are substituted by Mn atoms in the monolayer MoS2. The magnetic moment increases up to 0.50 µB per unit cell at a tensile strain of 7%. However, the Mn-doped MoS2 changes to metallic and antiferromagnetic under compressive strain. The spin polarization of Mn 3d orbitals disappears gradually with increasing compressive strain, and the superexchange interaction between Mn atoms increases gradually. The results suggest that the electronic and magnetic properties of Mn-doped monolayer MoS2 can be effectively modulated by strain engineering providing insight into application to electronic and spintronic devices.

Strain-mediated electronic properties of pristine and Mn-doped GaN monolayers

Graphene-like two-dimensional (2D) monolayer structures GaN has gained enormous amount of interest due to high thermal stability and inherent energy band gap for practical applications. First principles calculations are performed to investigate the electronic structure and strain-mediated electronic properties of pristine and Mn-doped GaN monolayer. Binding energy of Mn dopant at various adsorption site is found to be nearly same indicating these sites to be equally favorable for adsorption of foreign atom. Depending on the adsorption site, GaN monolayer can act as p-type or n-type magnetic semiconductor. The tensile strength of both pristine and doped GaN monolayer (∼24 GPa) at ultimate tensile strain of 34% is comparable with the tensile strength of graphene. The in-plane biaxial strain modulate the energy band gap of both pristine and doped-monolayer from direct to indirect gap semiconductor and finally retendered theme into metal at critical value of applied strain. These characteristics make GaN monolayer to be potential candidate for the future applications in tunable optoelectronics.

Magnetism and Optical Property of Mn-Doped Monolayer CrSi2 by First-Principle Study

We investigate magnetism and optical properties of intrinsic and Mn-doped monolayer CrSi2 using the first-principle methods based on density functional theory. The results show that both monolayer CrSi2 sheets are metallic and ferromagnetic (FM) that hold promise in future 2D magnetic devices. In spite the slight reduction of the total magnetic moment of system after Mn doping in monolayer CrSi2, the formation energies of ferromagnetic CrSi2 are also reduced. So, Mn doping in monolayer CrSi2 can have more promising applications in spintronics and magnetic storage. The optical properties of monolayer CrSi2, including the absorption spectra, reflectivity, refractive index, loss function and dielectric function are also calculated. The intensity of reflectivity in far-infrared ranges is enhanced and real part n of refractive index decreases after Mn doping. The real part n of the refractive index is nearly constant (˜1) beyond 13 eV indicating that monolayer CrSi2 is vacuum like and fully transparent.

Ferromagnetic properties of Mn-doped HfS2 monolayer under strain

Using the first-principles calculations, we investigated electronic and magnetic properties of Mn-doped HfS2 monolayer for 4% and 8% Mn concentration. We study the strain tuning of electronic and magnetic properties of 4% Mn-doped HfS2 monolayer firstly. Our results show that the Mn-doped HfS2 monolayer is magnetic nanomaterial without strain. It keeps this character until the compressive strain comes to −8%, and the magnetism disappear with lager compressive strain. With the increasing tensile strain, the doped system transforms from semiconductor to half-metallic when the tensile strain is equivalent to or greater than 5%. The largest half-metallic gap is 1.307eV at 5% tensile strain and the magnetic moment always keeps about 3μB, which indicates that Mn-doped HfS2 monolayer can be a candidate for superior half-metallic namomaterial. Furthermore, we find two Mn dopants couple ferromagnetically via antiferromagnetic (AFM) p-d exchange interaction at the environment of 8% concentration. It keeps the properties of magnetic semiconductor under two Mn-doped configurations with different Mn-Mn separations. Our studies predict Mn-doped HfS2 monolayer under strain to be candidates for dilute magnetic semiconductors.

The structure, electronic, magnetic and optical properties of the Mn doped and Mn-X (X = F, Cl, Br, I and At) co-doped monolayer WS2: A first-principles study

The spin-polarized first-principles calculations are performed to study the structure, electronic, magnetic and optical properties of the pure, Mn doped and Mn-X (X = F, Cl, Br, I and At) co-doped monolayer WS2 systems. Although the pure monolayer WS2 system is a nonmagnetic semiconductor with a direct band gap of 1.820 eV, the Mn doped (Mn-Br co-doped) monolayer WS2 systems change to half-metal (HM) ferromagnet with a total magnetic moment Mtot of 1 μB (-2 μB) and the spin-down band gap Eg↓ of 1.262 eV (spin-up band gap Eg↑ of 1.321 eV) and thus useable in the spintronic devices. The Mn-F, Mn-Cl, Mn-I and Mn-At co-doped monolayer WS2 systems remain the nonmagnetic semiconducting character with the smaller band gaps Eg of 0.667, 0.578, 0.558, and 0.564 eV, respectively. Comparing the formation energies Eform, we find that it is the lowest for the Mn-F co-doped monolayer WS2 system and increases for the Mn-F, Mn-Cl, Mn-Br, Mn-I and Mn-At co-doped cases successively, indicating the Mn-F co-doped monolayer WS2 system is the most stable. The Mn doped monolayer WS2 system has the highest static dielectric constants ε1(0) and ε2(0), refractive indices n(0) and k(0). The absorption coefficients α(ω) show the pure monolayer WS2 system has the highest transmittance in low energy region. Meanwhile, the pure monolayer WS2 system has larger absorption from 6 to 9.5 eV and thus is more suitable to make a near-ultraviolet (6–9.5 eV) photodetector, while all doped monolayer WS2 systems are more suitable to make an infrared photodetector due to their red-shift phenomenon.

Electronic and magnetic properties of Mn-doped WSe2 monolayer under strain

Electronic and magnetic properties of Mn-doped WSe2 monolyer subject to isotropic strain are investigated using the first-principles methods based on the density functional theory. Our results indicate that Mn-doped WSe2 monolayer is a magnetic semiconductor nanomaterial with strong spontaneous magnetism without strain and the total magnetic moment of Mn-doped system is 1.038μB. We applied strain to Mn-doped WSe2 monolayer from -10% to 10%. The doped system transforms from magnetic semiconductor to half-metallic material from −10% to −2% compressive strain and from 2% to 6% tensile strain. The largest half-metallic gap is 0.450eV at −2% compressive strain. The doped system shows metal property from 7% to 10%. Its maximum magnetic moment comes to 1.181μB at 6% tensile strain. However, the magnetic moment of system decreases to zero sharply when tensile strain arrived at 7%. Strain changes the redistribution of charges and arises to the magnetic effect. The coupling between the 3d orbital of Mn atom, 5d orbital of W atom and 4p orbital of Se atom is analyzed to explain the strong strain effect on the magnetic properties. Our studies predict Mn-doped WSe2 monolayers under strain to be candidates for thin dilute magnetic semiconductors, which is important for application in semiconductor spintronics.

Design of a new two-dimensional diluted magnetic semiconductor: Mn-doped GaN monolayer

To meet the need of low-dimensional spintronic devices, we investigate the electronic structure and magnetic properties of Mn-doped GaN monolayer using first-principles method. We find the nonmagnetic GaN monolayer exhibits half-metallic ferromagnetism by Mn doping due to double-exchange mechanism. Interestingly, the ferromagnetic coupling in Mn-doped GaN monolayer is enhanced with tensile strain and weakened with compressive strain. What is more, the ferromagnetic–antiferromagnetic transformation occurs under compressive strain of −9.5%. These results provide a feasible approach for fabrication of a new GaN monolayer based diluted magnetic semiconductor.

A first-principles study on the magnetic properties of Sc, V, Cr and Mn-doped monolayer TiS3

Substitutional doping of V, Cr and Mn atoms can induce the magnetic moment in monolayer TiS3.

Effect of structural defects on electronic and magnetic properties of pristine and Mn-doped MoS2 monolayer

Abstract We investigate electronic and magnetic properties of pristine and Mn-doped MoS 2 monolayer with vacancy defects using the first-principles methods based on density functional theory. The results show that intrinsic two-Molybdenum vacancy ( V 2Mo ) and 1Mo+2S vacancy ( V 1Mo+2S ) can induce to total spin magnetic moment of 0.430 μ B and 1.076 μ B , respectively. One and two sulfurs vacancy show spin magnetic moment of 1.037 μ B and 1.146 μ B in Mn-doped MoS 2 monolayer. Total magnetic moment can be increased with the increasing of sulfur vacancy defects in Mn-doped MoS 2 monolayer. Several of the Mo atoms in the immediate vicinity of the Mn atom display antiferromagnetism in Mn-doped MoS 2 with sulfur vacancy defects. This finding is important for the achievement of spin devices on MoS 2 nanostructures.

Structural defects in pristine and Mn-doped monolayer WS2: A first-principles study

We investigate electronic and magnetic properties of pristine and Mn-doped monolayer WS2 with vacancy defects using the first-principles methods based on density functional theory. The results show that intrinsic three-tungsten vacancy (V3W), six-sulfur vacancy (V6S) and 1W+2S vacancy (V1W+2S) can induce to total spin magnetic moment of 0.169μB, 0.608μB and 0.981μB, respectively. One and two sulfurs vacancy show spin magnetic moment up to 1.048μB and 1.172μB in Mn-doped monolayer WS2. Sulfur vacancy defects (V1S and V2S) can induce to the increase of the total magnetic moment in Mn-doped monolayer WS2 system. Several of the W atoms in the immediate vicinity of the Mn atom display antiferromagnetic coupling to the dopant with the increase of sulfur vacancy defects. This finding indicates an immediate significance of pristine and Mn-doped 1L WS2 with vacancy defects for new spintronic applications.

Electronic and magnetic properties of Mn-doped monolayer WS2

Abstract We investigate the electronic and magnetic properties of Mn-doped monolayer WS 2 for 6.25% and 8% Mn concentration using the first-principles methods based on the density functional theory. Mn dopants are shown to couple ferromagnetically via a double-exchange mechanism. Our studies predict Mn-doped WS 2 monolayers to be candidates for thin dilute magnetic semiconductors. Moreover, the formation energy calculations also indicate that it is energy favorably and relatively easier to incorporate Mn atom into the WS 2 monolayer under S-rich experimental conditions. For all possible Mn-doped configurations, a possible Mn clustering behavior may be formed in the Mn-doped WS 2 monolayer systems.

Mn-doped monolayer MoS2: An atomically thin dilute magnetic semiconductor

We investigate the electronic and magnetic properties of Mn-doped monolayer MoS${}_{2}$ using a combination of first-principles density functional theory (DFT) calculations and Monte Carlo simulations. Mn dopants that are substitutionally inserted at Mo sites are shown to couple ferromagnetically via a double-exchange mechanism. This interaction is relatively short ranged, making percolation a key factor in controlling long-range magnetic order. The DFT results are parameterized using an empirical model to facilitate Monte Carlo studies of concentration- and temperature-dependent ordering in these systems, through which we obtain Curie temperatures in excess of room temperature for Mn doping in the range of 10--15$%$. Our studies demonstrate the potential for engineering a new class of atomically thin dilute magnetic semiconductors based on Mn-doped MoS${}_{2}$ monolayers.