Search

In spintronics, transverse anomalous transport properties have emerged as a highly promising avenue surpassing the conventional longitudinal transport behaviors. Here, we explore the transverse transport properties of monolayer and bilayer Fe3−xCoxGaTe2 (x = 0.083, 0.167, 0.250, and 0.330) systems. All the systems exhibit ferromagnetic ground states with metallic features and also have perpendicular magnetic anisotropy. Besides, the magnetic anisotropy is substantially enhanced with increasing Co-doping concentration. However, unlike magnetic anisotropy, the Curie temperature is suppressed by increasing the Co-doping concentration. For instance, the monolayer and bilayer Fe2.917Co0.083GaTe2 hold a Curie temperature of 253 K and 269 K, which decreases to 163 K and 173 K in monolayer and bilayer Fe2.67Co0.33GaTe2 systems, respectively. We find a giant anomalous Nernst conductivity (ANC) of 6.03 A/(K·m) in the monolayer Fe2.917Co0.083GaTe2 at −30 meV, and this is further enhanced to 11.30 A/(K·m) in the bilayer Fe2.917Co0.083GaTe2 at −20 meV. Moreover, the bilayer Fe2.917Co0.083GaTe2 structure has a large anomalous thermal Hall conductivity (ATHC) of −0.14 W/(K·m) at 100 K. Overall, we find that the Fe3−xCoxGaTe2 (x = 0.083, 0.167, 0.250, and 0.330) structures have better anomalous transverse transport performance than the pristine Fe3GaTe2 system and can be used for potential spintronics and spin caloritronics applications. [ABSTRACT FROM AUTHOR]

Through the full potential linearized augmented plane wave method, we have explored the vacancy defect induced magnetism in wurtize ZnO. It has been found that the Zn vacancy defect brings a spin polarized state in the nearest neighbor oxygen atoms, whereas the oxygen vacancy defect has no influence on the magnetism. However, it is found that the lattice distortion is a crucial factor for the Zn vacancy induced ferromagnetism because the ferromagnetic ground state cannot be achieved if there is no lattice distortion due to Zn vacancy defect. The magnetic moment of oxygen atom in the nearest neighbor from the Zn vacancy site is ranged from 0.10 to 0.19 μB and the spin polarized oxygen atoms have metallic feature in both spin states. These results are quite different from those found in other calculation [Q. Wang et al., Phys. Rev. B 77, 205411 (2008)]. In addition, we have found that the ferromagnetic exchange interaction among oxygen atoms is mediated by Zn 3d state. Along with these, the theoretically calculated x-ray absorption spectroscopy and x-ray magnetic circular dichroism are presented. [ABSTRACT FROM AUTHOR]

[Display omitted] • The origin of the ferromagnetism in the 2D Co doped ZnO system was investigated. • The graphene/Co doped ZnO/graphene multilayer structure was also considered. • The hydrogen effect was found to be the origin of the ferromagnetism in both systems. • High Curie temperature (∼500 K) was found in both systems using the Heisenberg model. • Both systems showed optical transparency in the visible spectrum. Despite extensive efforts to find room temperature ferromagnetic (FM) two-dimensional (2D) materials, only a few 2D FM materials have been experimentally synthesized. Particularly, it is a still challenging task to find optically transparent room temperature 2D FM systems. Recently, room temperature ferromagnetism was confirmed in 2D graphene/Co doped ZnO/graphene multilayer structure. However, in our calculations, the Co doped ZnO (ZCO) monolayer showed an antiferromagnetic (AFM) ground state. Moreover, both ZCO/graphene bilayer and graphene/ZCO/graphene trilayer systems also exhibited an AFM state. Thus, we investigated the possibility of hydrogen-induced ferromagnetism. After the introduction of the H atom (H-ZCO), we found a ferromagnetic (FM) ground state in both H-ZCO monolayer and graphene/H-ZCO/graphene trilayer systems. We obtained that the FM state appeared only when the H atom stayed on the same ZCO layer. Thus, we propose that the ferromagnetism in the graphene/ZCO/graphene originates from the H effect. Also, we obtained a Curie temperature (T C) of 500 K in H-ZCO and graphene/H-ZCO/graphene trilayer systems. Moreover, we find that the graphene/H-ZCO/graphene shows optically transparent behavior in the visible frequencies. [ABSTRACT FROM AUTHOR]

Using the full potential linearized augmented plane wave method, we explored the structural and magnetic properties of hybrid bilayer FeCo/FePt. The effect of interface hybridization and strain induced in FeCo by FePt buffer layer was studied. We found a tetragonal distortion in FeCo structure due to the lattice mismatch between FePt buffer layer and ferromagnetic FeCo layer. The magnetic moments of Fe and Co were insensitive to the strain effect, but the suppression in the magnetic moments of Fe and Co at the interface was observed because of the interface hybridization. The magnetocrystalline anisotropy energy of FeCo film was enhanced almost twice due to the strain. In FeCo/FePt structure, the uniaxial anisotropy constants of 9.96 and 8.78 MJ/m 3 were obtained for 2 and 5 ML FeCo/FePt hybrid systems respectively. Additionally, we found that the coercive field is decreased from 146 to 119 kOe while maximum energy product increases from 74 to 85 MGOe with increase in FeCo soft layer from 2 to 5 ML. These high values of coercive field and maximum energy product may insure the basic requirement of designing rare-earth free permanent magnets. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic properties of MnNi surface alloy grown on fcc Co(001) surface have been explored through the full potential linearized augmented plane wave (FLAPW) method. It has been found that one monolayer (ML) of Mn0.5Ni0.5 alloy on Co(001) surface has a ferromagnetic (FM) ground state. We suggest that the direct exchange coupling between Mn and Ni plays an essential role for the ferromagnetism. The vertical position of Mn is higher by 0.26Å than that of Ni, i.e., the surface has a buckling geometry. In contrast to pure fcc Co(001) film which has in-plane magnetization, we have obtained that the magnetocrystalline anisotropy of MnNi/Co(001) due to spin–orbit interaction is perpendicular to the film surface and the magnetic anisotropy energy is 146μeV/cell. In addition, the theoretically calculated X-ray magnetic circular dichroism (XMCD) is presented. [Copyright &y& Elsevier]

Abstract: Based on the full-potential linearized augmented plane wave (FLAPW) calculations, various magnetic properties of ultra thin face centered cubic (fcc) Co(001) film and V adsorbed systems on Co(001) surface are explored. It was found that the V film grown on fcc Co(001) surface has large induced magnetic moment and the direction of magnetization is antiparallel to that of Co atom in the submonolayer coverage. Very interestingly, we found that the surface alloy and 0.5ML adsorbed V/Co(001) systems have perpendicular magnetocrystalline anisotropy and the magnitude of anisotropy energy in 0.5ML V on fcc Co(001) surface is greatly larger than that of surface alloy, while we observed in-plane magnetization in pure fcc Co(001) film. It was found that the spin–orbit interaction through spin–flip process cannot be ignored, therefore the simple relation with orbital anisotropy is not applicable in the interpretation of magnetocrystalline anisotropy. [Copyright &y& Elsevier]

Spin Seebeck effect has been mostly explored in bulk magnetic materials, but the efficiency is not large enough for device application. Recently, we have found that the 2D ferromagnetic CrPbTe3 layer has rather a high Curie temperature of 110 K. Thus, we have investigated the spin dependent Seebeck effect using the Boltzmann transport approach. We have found the largest carrier mobility and relaxation time in the minority spin electron carrier system due to the spin dependent effective mass and deformation potential constant. The onset energy of the electrical conductivity shows spin and carrier type dependency. Thus, both effective spin and effective charge Seebeck coefficients are originated from the majority spin carrier in the hole doped system whereas the minority spin carrier controls the effective spin and effective charge Seebeck coefficient in the electron doped system. We have obtained the maximum spin Seebeck coefficient of 1320 μV/K at 50 K. This value is suppressed at 100 K, but we still find a large spin Seebeck coefficient of 715 μV/K. • We investigated the spin dependent thermoelectric properties of the 2D CrPbTe3 monolayer system. • We obtained a large spin Seebeck effect of 1320 μV/K at 50 K. • The spin Seebeck effect has a magnitude of 715 μV/K at 100 K. • The spin and charge Seebeck effect exhibited similar behavior. • This find may lead to various spin dependent thermoelectric applications. [ABSTRACT FROM AUTHOR]

Abstract Using the first principles calculations, we investigated the physical properties of hydrogenated black phosphorene layer. For a single H adsorption, the P top site became the most stable adsorption position and this impurity adsorption created a broken P P bond. Due to this broken bond, the adsorption of a single hydrogen atom on a phosphorene layer induced a total magnetic moment at about 1.0 μ B and that the spin-polarized state was mainly localized around the dangling phosphorus atom. In the hydrogenated system, the hydrogen atoms preferred the different sublattice adsorption at rather short H H inter-atomic distance (∼3.5 Å) while the sublattice dependent formation energy was greatly suppressed at larger than H H distance of 3.5 Å. We obtained that the hydrogenated phosphorene layer displayed an antiferromagnetic state until the H H inter-atomic distance became around 8 Å and the energy difference between ferromagnetic (FM) and antiferromagnetic (AFM) states almost vanished beyond this interatomic distance. This result may suggest that the hydrogenated phosphorene layer system shows an antiferromagnetic state at high H concentration while the exchange coupling is greatly suppressed at low H concentration. Thus, it will be possible to manipulate the magnetic property by applying even small magnetic field at low H concentration and this can feature can be utilized for spintronics applications. Highlights • The hydrogen adored on the top site over phosphorene layer. • The adsorption of single H atom induced a local magnetic moment around 1 μ B. • The adsorption of 2H atoms displayed an antiferromagnetic state over phosphorene. • The energy difference between FM and AFM states almost vanished at d H-H > 8 Å. [ABSTRACT FROM AUTHOR]