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Traditional thermoelectric materials often face a trade-off between efficient power generation (high ZT) and cooling performance. Here, we explore the potential of achieving simultaneous thermoelectric power generation and cooling capability in the recently fabricated bulk ZrSeTe Janus structure using first-principles density functional theory (DFT). The layered ZrSeTe Janus structure exhibits a semimetal character with anisotropic transport properties along the in-plane and out-of-plane directions. Our DFT calculations, including the explicit calculation of relaxation time, reveal a maximum ZT of ~0.065 in the out-of-plane direction at 300 K which is one order of magnitude larger than that in the in-plane direction (ZT~0.006). Furthermore, the thermoelectric cooling performance is also investigated. The in-plane direction shows a cooling performance of 13 W/m·K and a coefficient of performance (COPmax) of ~90 with a temperature difference (ΔT) of 30 K, while the out-of-plane direction has a cooling performance of 2.5 W/m·K and COPmax of ~2.5. Thus, the out-of-plane current from the thermoelectric power generation can be utilized as an in-plane current source for active heat pumping. Consequently, we propose that the semimetal ZrSeTe Janus structure can display bifunctional thermoelectric properties for simultaneous thermoelectric power generation and active cooling. [ABSTRACT FROM AUTHOR]

Valleytronics is receiving extensive research efforts. Thus, we investigated the electric field-induced valley polarization in the WSe2/CrSnSe3 heterostructures by varying the stacking order. The heterostructure shows indirect band gaps of 270 and 330 meV in the two most stable structures. The WSe2/CrSnSe3 heterostructure displays a ferromagnetic ground state with out-of-plane anisotropy (0.02 meV) in one stable stacking (S-1) while a small in-plane anisotropy (−0.01 meV) is found in other stacking (S-2). The Curie temperature is slightly enhanced to 73 K compared to the monolayer CrSnSe3. We have found the valley splitting of 4 meV in S-1 whereas it became 9 meV in the S-2 system. The valley splitting is further enhanced if an electric field is applied from CrSnSe3 to the WSe2 layer whereas it is suppressed in the reversed electric field. Particularly, the S-2 structure shows a giant valley splitting of 67 meV at an electric field of 0.6 V Å−1. We attribute this electric field-dependency to the dipolar effect. Overall, we propose that the WSe2/CrSnSe3 heterostructure can be a potential structure for obtaining a giant valley splitting. [ABSTRACT FROM AUTHOR]

Using the full-potential, linearized, augmented plane wave method, we have investigated the magnetic properties of body-centered-cubic Mn(2 monolayers [ML])/Fe(001), Mn(2 ML)/ Ag(1 ML)/Fe(001), and Mn(2 ML)/Ag(2 ML)/Fe(001). We find that the Mn overlayers have a layered antiferromagnetic ground state. However, the Ag spacer layer induces an oscillatory magnetic behavior in Mn film, because the relative direction of magnetization in Mn film is changed with increasing Ag layer thickness. In addition, we have realized that the optimized structure is a crucial factor to determine magnetic ground state of an ultrathin Mn/Fe(001) system. It is achieved that both Mn/Fe and Mn/Ag/Fe(001) systems manifest perpendicular magnetocrystalline anisotropy (MCA). Interestingly, the Ag spacer layer greatly enhances perpendicular magnetic anisotropy energy. The MCA energy in Mn(2 ML)/Fe(001) is about 137 μeV/cell, and it becomes 920 μeV in Mn(2 ML)/Ag(2 ML)/Fe(001). Therefore, we report that the large perpendicular magnetic anisotropy system can be materialized in the Mn/Ag/Fe(001) structure. In addition, we also present the calculated x ray absorption spectroscopy and x ray magnetic circular dichroism of Fe and Mn layers. [ABSTRACT FROM AUTHOR]

Using the full potential linearized augmented plane wave method, we have explored the magnetic properties of one dimensional (1D) Ti atomic chain. Interestingly, we have observed that the 1D Ti atomic chain has ferromagnetic ground state even on NiAl(110) surface. In addition, it has been found that the magnetic dipole interaction is a key factor in the study of magnetic anisotropy, not the magnetocrystalline anisotropy arising from spin-orbit interaction. [ABSTRACT FROM AUTHOR]

Abstract: Using the full potential linearized augmented plane wave (FLAPW) method, we have investigated the thickness dependent magnetic properties of rare earth free exchange spring magnet FeCo/FePt(001). The FeCo adlayer thickness is increased from one monolayer (ML) to four ML coverage. It is observed that the FeCo adlayers and Fe atoms in FePt substrate show almost half metallic behavior, while an ordinary metallic feature is found in Pt atoms. The average magnetization increases with FeCo thickness and the estimated maximum energy product reaches 66MGOe in FeCo(4ML)/FePt(001). A giant perpendicular magnetocrystalline anisotropy (MCA) energy of 18.20meV/cell is found in pure FePt(001) and it becomes 17.35meV/cell even in FeCo(4ML)/FePt(001). In addition, we find very large coercivity field in FeCo/FePt(001) systems. For instance, the calculated maximum coercivity field in FeCo(4ML)/FePt(001) is about 188kOe. Both energy product and coercivity field calculations may imply that the FeCo/FePt can be utilized for potential rare earth free exchange spring magnet material. [Copyright &y& Elsevier]

Abstract: Using the full potential linearized augmented plane wave (FLAPW) method, thickness dependent magnetic anisotropy of ultrathin FeCo alloy films in the range of 1 monolayer (ML) to 5ML coverage on Pd(001) surface has been explored. We have found that the FeCo alloy films have close to half metallic state and well-known surface enhancement in thin film magnetism is observed in Fe atom, whereas the Co has rather stable magnetic moment. However, the largest magnetic moment in Fe and Co is found at 1ML thickness. Interestingly, it has been observed that the interface magnetic moments of Fe and Co are almost the same as those of surface elements. The similar trend exists in orbital magnetic moment. This indicates that the strong hybridization between interface FeCo alloy and Pd gives rise to the large magnetic moment. Theoretically calculated magnetic anisotropy shows that the 1ML FeCo alloy has in-plane magnetization, but the spin reorientation transition (SRT) from in-plane to perpendicular magnetization is observed above 2ML thickness with huge magnetic anisotropy energy. The maximum magnetic anisotropy energy for perpendicular magnetization is as large as 0.3meV/atom at 3ML film thickness with saturation magnetization of . Besides, the calculated X-ray magnetic circular dichroism (XMCD) has been presented. [Copyright &y& Elsevier]

Abstract: Using the full potential linearized augmented plane wave method (FLAPW), the magnetic properties of ultrathin Fe/Ni films grown on Cu(001) surface have been investigated. We have varied both Ni and Fe film thicknesses and also have explored the strain effect on the magnetic anisotropy. For surface Fe atom, a typical surface enhancement of spin magnetic moment has been observed while the magnetic moments of other constituents are rather insensitive to the strain effect. Nonetheless, we have realized that the direction of magnetization is significantly affected by the strain factor. For instance, the Fe/Ni films always have perpendicular magnetization provided that they are grown on Cu(001) lattice constant. However, we have obtained a spin reorientation transition (SRT) phenomenon in the presence of strain effect. [Copyright &y& Elsevier]

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]

We have calculated magnetic anisotropy energies of several free standing Co nanoclusters consisting of one, two, three, and six Co atoms with the full potential linearized augmented plane wave method. The magnetic moments are found to be aligned perpendicular to the Co -- Co bond. The results show that the spin magnetic moments are suppressed by roughly 10% compared to Co monolayer or Co nanowire. Orbital magnetic moments and anisotropy energies depend sensitively on the size and shape of clusters. [ABSTRACT FROM AUTHOR]

Phosphorene is receiving great research interests because of its peculiar physical properties. Nonetheless, no systematic studies on the transport properties modified due to defects have been performed. Here, we present the electronic band structure, defect formation energy and bias dependent transport property of various defective systems. We found that the defect formation energy is much less than that in graphene. The defect configuration strongly affects the electronic structure. The band gap vanishes in single vacancy layers, but the band gap reappears in divacancy layers. Interestingly, a single vacancy defect behaves like a p-type impurity for transport property. Unlike the common belief, we observe that the vacancy defect can contribute to greatly increasing the current. Along the zigzag direction, the current in the most stable single vacancy structure was significantly increased as compared with that found in the pristine layer. In addition, the current along the armchair direction was always greater than along the zigzag direction and we observed a strong anisotropic current ratio of armchair to zigzag direction. [ABSTRACT FROM AUTHOR]