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Bipolar magnetic semiconductor (BMS) has special electronic structures; i.e., its conduction band minimum (CBM) and valence band maximum (VBM) are completely spin-polarized in opposite directions. In this work, the band structures of 2H-VX2 (X = S, Se, and Te) are examined through first-principles calculations, and the results show that both 2H-VS2 and 2H-VSe2 are BMSs, while 2H-VTe2 is a unipolar magnetic semiconductor (UMS); i.e., its CBM and VBM show the same spin direction. Most interestingly, we find that electronic orbitals near the Fermi level of 2H-VX2 are occupied by d z 2 and d x y orbitals, which can be effectively modulated by the biaxial strain. With appropriate strain modulations, 2H-VX2 can be BMS, UMS, or half-metal (HM). Our investigation reveals strain effects on the band structure of 2H-VX2, which greatly enhances their significance in spintronics. [ABSTRACT FROM AUTHOR]

Herein, in order to overcome the poor conductivity and pH limitation of MoS2 in electrocatalytic applications, a MoS2/Nb2CTx heterostructure was synthesized for the first time via an easy hydrothermal method and first-principles investigation was further carried out. The MoS2/Nb2CTx contact shows a metallic property, which guarantees excellent conductivity. Meanwhile, the low p-type Schottky barrier contact on the interface leads to efficient charge transfer from Nb2CTx to MoS2 and further improves its ability to adsorb hydrogen. As a result, the composite showed a low overpotential of 127 mV at 10 mA cm−2, Tafel slope of 56.3 mV dec−1 in acidic solution and an overpotential of 138.8 mV at 10 mA cm−2, and Tafel slope of 93.4 mV dec−1 in alkaline solution. In both solutions, it showed outstanding stability after 3000 cycles. Both experimental and theoretical investigation in our work revealed the potential of this composite for hydrogen evolution reaction in both acidic and alkaline media and provided an effective route to design high-performance MoS2-based catalysts. [ABSTRACT FROM AUTHOR]

Manipulating magnetic properties by purely electrical means is a key challenge to improve information technology. In the three-dimensional ferromagnetic (FM) metal thin films, for example, the 3d-transitonal metal thin films Fe, Co, and Ni, the electric-field effect is restricted within the surface around 2–3 Å due to the screening effect, and it is hard to separate the bulk and surface states. In the present investigation, through first-principles calculations, we explore the electric-field effect on the two-dimensional (2D) FM metal monolayers Fe3GeTe2, Fe3GeSe2, and Fe3GeTeSe. It is found that magnetic anisotropy energy (MAE) of these three materials follows the sequence: Fe3GeTe2 > Fe3GeTeSe > Fe3GeSe2, because the atomic spin–orbital coupling of Te is much stronger than that of Se. The most interesting finding is that the electric-field effect on MAE is obviously enhanced in Fe3GeTeSe, which is nearly ten times of Fe3GeTe2 and Fe3GeSe2, and we find the large difference results from its asymmetric structure. Our investigation reveals the magnetoelectric (ME) mechanism and obtains the large ME effect, which is of great significance in the 2D magnetoelectronics. [ABSTRACT FROM AUTHOR]

We report a systematic study on the structural, electronic, magnetic, and ferroelectric properties of [111]-oriented BiFeO3/BiAlO3 (BFO/BAO) superlattice using density-functional calculations. It is found that the Fe-O-Fe superexchange interactions in BFO/BAO superlattice are greatly suppressed by the inserted BAO layers, with the antiferromagnetic-ferromagnetic transition energy decreasing from around 280 meV per BFO formula unit (five atoms) to 11.6 meV per BFO/BAO formula unit (ten atoms). The tensile strain can further decrease this energy, making the magnetic transition more plausible. In addition, we find that BFO/BAO superlattice preserves the large ferroelectric polarization as well as energy gap of bulk BFO. Therefore, BAO may be a good candidate for constructing the BFO-based superlattice with improved multiferroicity. [ABSTRACT FROM AUTHOR]

Multiferroic and magnetoelectric materials are considered as major candidates for next-generation information storage technologies due to their simultaneous presence and interplay of two or more ferroic orders. In this paper, we briefly review our theoretical progress relating to the all-electric spintronics, i.e., spin manipulation via an electric means rather than a magnetic field. Special focus is given to interface/surface magnetoelectric effect, electric field control of magnetocrystalline anisotropy, Rashba spin–orbit coupling, spin transport, and other generalized all-electric modulation of magnetism. Our recently developed method, i.e., the orbital selective external potential method, is also expounded. This method might be a powerful tool in finding the mechanisms responsible for the intriguing phenomena occurred in multiferroics or magnetoelectric materials. [ABSTRACT FROM AUTHOR]

Multiferroics are materials where two or more ferroic orders coexist owing to the interplay between spin, charge, lattice and orbital degrees of freedom. The explosive expansion of multiferroics literature in recent years demonstrates the fast growing interest in this field. In these studies, the first-principles calculation has played a pioneer role in the experiment explanation, mechanism discovery and prediction of novel multiferroics or magnetoelectric materials. In this review, we discuss, by no means comprehensively, the extensive applications and successful achievements of first-principles approach in the study of multiferroicity, magnetoelectric effect and tunnel junctions. In particular, we introduce some our recently developed methods, e.g., the orbital selective external potential method, which prove to be powerful tools in the finding of mechanisms responsible for the intriguing phenomena occurred in multiferroics or magnetoelectric materials. We also summarize first-principles studies on three types of electric control of magnetism, which is the common goal of both spintronics and multiferroics. Our review offers in depth understanding on the origin of ferroelectricity in transition metal oxides, and the coexistence of ferroelectricity and ordered magnetism, and might be helpful to explore novel multiferroic or magnetoelectric materials in the future. [ABSTRACT FROM AUTHOR]

Review: 293 refs. [ABSTRACT FROM AUTHOR]