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The lack of suitable channel semiconductor materials has been a limiting factor in the development of tunneling field-effect transistor (TFET) architectures due to the stringent criteria of both air stability and excellent gate-tunable electronic properties. Here, we report the performance limits of sub-10-nm double-gated monolayer (ML) BiN TFETs by utilizing first-principles quantum-transport simulations. We find that ML BiN possesses an indirect bandgap of 0.8 eV and effective masses of 0.24m0 and 2.24m0 for electrons and holes, respectively. The n-type BiN TFETs exhibit better performance than the p-type ones, and the on-state current can well satisfy the requirements of the International Roadmap for Devices and Systems for both high-performance and low-power standards. Notably, we find that the BiN TFETs exhibit distinguished gate controllability with an ultra-low subthreshold swing below 60 mV/decade even with a small gate length of 6 nm, which is superior to the existing field-effect transistors, such as black phosphorus TFETs, GeSe TFETs, and BiN metal–oxide–semiconductor field-effect transistors. Furthermore, the BiN TFETs are endowed with the potential to realize high switching speed and low-power consumption applications because of their extremely short delay time and ultra-low power-delay product. Our results reveal that the ML BiN is a highly competitive channel material for the next-generation TFETs. [ABSTRACT FROM AUTHOR]

First-principles calculations are performed to investigate the magnetic anisotropy and voltagecontrolled magnetic anisotropy (VCMA) in the strontium titanate (SrTiO3)-based structure. It is found that SrTiO3/Fe/Cu gives rise to an interfacial perpendicular magnetic anisotropy (PMA) of 1.3 mJ/m2. More importantly, the VCMA coefficient of this structure is 37% larger than that of the MgO-based counterpart. The microscopic mechanism is elucidated by resolving the VCMA effect to each atomic layer and each orbital hybridization. We demonstrate that the VCMA effect is not confined at the first Fe monolayer of the SrTiO3/Fe interface but extends into the second and third Fe monolayers. The origin of these phenomena can be explained with the changes of contributions to PMA from each orbital hybridization induced by redistributions of orbital occupancy under an electric field. [ABSTRACT FROM AUTHOR]

We introduce enhanced hybridization of Ti 3d-O 2p electronic states by applying an inhomogeneous electric field to a perovskite oxide, SrTiO3, which leads to lattice deformation through electrostriction and the converse flexoelectric effect. However, unlike most studies revealing lattice responses to dipolar polarization, the enhanced electronic hybridization introduced in SrTiO3 is not strong enough to compensate local repulsions and gives rise to the off-centered Ti displacement. This is consistent with the fact that SrTiO3 has a small vibronic coupling constant compared to other ferroelectric materials. In situ time-dependent X-ray diffraction studies reveal lattice relaxation. Band structures and electronic hybridization play important roles in lattice relaxation, which is different from the relaxation of metals where the carrier concentration may be dominant. Our results provide insight into the coupling behaviors between the lattice and electronic hybridization, considering both static and dynamic aspects. [ABSTRACT FROM AUTHOR]

We introduce enhanced hybridization of Ti 3d-O 2p electronic states by applying an inhomogeneous electric field to a perovskite oxide, SrTiO3, which leads to lattice deformation through electrostriction and the converse flexoelectric effect. However, unlike most studies revealing lattice responses to dipolar polarization, the enhanced electronic hybridization introduced in SrTiO3 is not strong enough to compensate local repulsions and gives rise to the off-centered Ti displacement. This is consistent with the fact that SrTiO3 has a small vibronic coupling constant compared to other ferroelectric materials. In situ time-dependent X-ray diffraction studies reveal lattice relaxation. Band structures and electronic hybridization play important roles in lattice relaxation, which is different from the relaxation of metals where the carrier concentration may be dominant. Our results provide insight into the coupling behaviors between the lattice and electronic hybridization, considering both static and dynamic aspects. [ABSTRACT FROM AUTHOR]

The anomalous Nernst effect in a perpendicularly magnetized Ir22Mn78/Co20Fe60B20/MgO thin film is measured using well-defined in-plane temperature gradients. The anomalous Nernst coefficient reaches 1.8 μV/K at room temperature, which is almost 50 times larger than that of a Ta/Co20Fe60B20/MgO thin film with perpendicular magnetic anisotropy. The anomalous Nernst and anomalous Hall results in different sample structures revealing that the large Nernst coefficient of the Ir22Mn78/Co20Fe60B20/MgO thin film is related to the interface between CoFeB and IrMn. [ABSTRACT FROM AUTHOR]

Beyond memory and storage, future logic applications put forward higher requirements for electronic devices. All spin logic devices (ASLDs) have drawn exceptional interest as they utilize pure spin current instead of charge current, which could promise ultra-low power consumption. However, relatively low efficiencies of spin injection, transport, and detection actually impede high-speed magnetization switching and challenge perspectives of ASLD. In this work, we study partial spin absorption induced magnetization switching in asymmetrical ASLD at the mesoscopic scale, in which the injector and detector have the nano-fabrication compatible device size (>100 nm) and their contact areas are different. The enlarged contact area of the detector is conducive to the spin current absorption, and the contact resistance difference between the injector and the detector can decrease the spin current backflow. Rigorous spin circuit modeling and micromagnetic simulations have been carried out to analyze the electrical and magnetic features. The results show that, at the fabrication-oriented technology scale, the ferromagnetic layer can hardly be switched by geometrically partial spin current absorption. The voltage-controlled magnetic anisotropy (VCMA) effect has been applied on the detector to accelerate the magnetization switching by modulating magnetic anisotropy of the ferromagnetic layer. With a relatively high VCMA coefficient measured experimentally, a voltage of 1.68V can assist the whole magnetization switching within 2.8 ns. This analysis and improving approach will be of significance for future low-power, high-speed logic applications. [ABSTRACT FROM AUTHOR]

We report the observation of the Quantum Hall effect from the topological surface states in both the Dirac electron and Dirac hole regions in a 4 quintuple layer (Bi0.53Sb0.47)2Te3 film grown on GaAs (111)B substrates. The Fermi level is sitting within the enlarged bulk band gap due to the quantum confinement of the ultra-thin film and can be tuned through the Dirac point by gate biases. Furthermore, the Hall resistance Rxy shows even denominator plateaus, which could be fractional Quantum Hall states. This may be due to the hybridization between the top and bottom surface states and suggests the possible way to manipulate the interaction of two surfaces for potential spintronic devices. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junction based on the CoFeB/MgO/CoFeB structures is of great interest due to its application in the spin-transfer-torque magnetic random access memory (STT-MRAM). Large interfacial perpendicular magnetic anisotropy (PMA) is required to achieve high thermal stability. Here, we use the first-principles calculations to investigate the magnetic anisotropy energy (MAE) of the MgO/CoFe/capping layer structures, where the capping materials include 5d metals Hf, Ta, Re, Os, Ir, Pt, and Au and 6p metals Tl, Pb, and Bi. We demonstrate that it is feasible to enhance PMA by using proper capping materials. Relatively large PMA is found in the structures with the capping materials of Hf, Ta, Os, Ir, and Pb. More importantly, the MgO/CoFe/Bi structure gives rise to giant PMA (6.09 mJ/m2), which is about three times larger than that of the MgO/CoFe/Ta structure. The origin of the MAE is elucidated by examining the contributions to MAE from each atomic layer and orbital. These findings provide a comprehensive understanding of the PMA and point towards the possibility to achieve the advanced-node STT-MRAM with high thermal stability. [ABSTRACT FROM AUTHOR]

We studied the impact of different insertion layers (Ta, Pt, and Mg) at the CoFeB∣MgO interface on voltage-controlled magnetic anisotropy (VCMA) effect and other magnetic properties. Inserting a very thin Mg layer of 0.1-0.3 nm yielded a VCMA coefficient of 100 fJ/V-m, more than 3 times higher than the average values of around 30 fJ/V-m reported in Ta∣CoFeB∣MgO-based structures. Ta and Pt insertion layers also showed a small improvement, yielding VCMA coefficients around 40 fJ/V-m. Electrical, magnetic, and X-ray diffraction results reveal that a Mg insertion layer of around 1.2 nm gives rise to the highest perpendicular magnetic anisotropy, saturation magnetization, as well as the best CoFe and MgO crystallinity. Other Mg insertion thicknesses give rise to either under- or over-oxidation of the CoFe∣MgO interface; a strong over-oxidation of the CoFe layer leads to the maximum VCMA effect. These results show that precise control over the Mg insertion thickness and CoFe oxidation level at the CoFeB∣MgO interface is crucial for the development of electric-field-controlled perpendicular magnetic tunnel junctions with low write voltage. [ABSTRACT FROM AUTHOR]

The current-induced spin-orbit torques (SOTs) in the perpendicularly magnetized Ir22Mn78/Co20Fe60B20/MgO structures are investigated. The damping- and field-like torques are characterized using a harmonic technique. The spin Hall angle of Ir22Mn78 is determined to be θSHE = +0.057 ± 0.002. The SOT-driven magnetization switching is also demonstrated with the assistance of an external in-plane field. Furthermore, the magneto-optical Kerr effect imaging experiments show that the magnetization switching is realized through domain nucleation and domain wall motion. These results may promise potential practical applications in high-performance SOT devices based on the antiferromagnetic materials. [ABSTRACT FROM AUTHOR]

We study the magnetic properties of W/Co40Fe40B20 (CoFeB)/MgO films using the spin-torque ferromagnetic resonance (ST-FMR) technique. This study takes the advantage of the spin Hall magnetoresistance (SMR) for generating an oscillating resistance, which is one of the necessary requirements for obtaining mixing voltage in the ST-FMR technique. We have measured both the as-grown and the annealed samples with different CoFeB layer thicknesses, which include the in-plane and out-of-plane magnetic anisotropies. The spectra for these two types of anisotropies show distinct signatures. By analyzing the ST-FMR spectra, we extract the effective anisotropy field for both types of samples. In addition, we investigate the influence of CoFeB thickness and annealing on the Gilbert damping constant. Our experiments show that by taking advantage of SMR, the ST-FMR measurement acts as an effective tool with high sensitivity for studying the magnetic properties of ultrathin magnetic films. [ABSTRACT FROM AUTHOR]