Gate-tunable large spin polarization in a few-layer black phosphorus-based spintronic device

Multiconfiguration b-AsP-based doping systems with enriched elements (C and O): novel materials for spintronic devices

Black arsenical phosphorus (b-AsP), a derivative of black phosphorus, is a bimetallic alloy compound with the advantage of high carrier mobility, high stability, and tailorable configuration. However, lack of an effective tool to facilitate the application of AsP as a magnetic device. Herein, band gap modulation and the introduction of magnetism can be achieved by doping non-metallic atoms in three different AsP configurations. And the doping of the same atom will cause variation in the electronic structure depending on the configuration. Surprisingly, doping with both enriched elements C and O transforms AsP into a magnetic material. Furthermore, the source of the magnetic moment is explained by solving the wave function of the doped AsP, which is caused by the orbital coupling of the C and O atoms to AsP. To excavate the potentials of this magnetic AsP system for magnetic devices, field-effect transistors based on two doped armchair AsP3 nanoribbons are simulated. The devices show considerable negative differential conductivity effect and good spin filtering efficiency. These findings suggest that AsP doping with enriched elements C and O could be an excellent candidate for future spintronics applications.

Detection of extremely large magnetoresistance in a ring-shaped array of magnetic quantum dots with very high performance and controllable parameters

By means of Green’s function technique, we study the magnetoresistance (MR) effect in a ring-shaped array of magnetic quantum dots (QDs), with or without magnetic leads, while the magnetic QDs...

Substantial and stable magnetoresistance and spin conductance in phosphorene-based spintronic devices with Co electrodes

Designing devices with excellent spin-polarized properties has been a challenge in physics and materials science. In this work, we report a theoretical investigation of the spin injection and spin-polarized transport properties of monolayer and bilayer phosphorene devices with Co electrodes. Based on the analysis of transmission coefficients, spin-polarized current, magnetoresistance (MR) (or tunnel MR) ratio and spin injection efficiency (SIE), both devices show superior spin-polarized transport properties. As phosphorene in the device is changed from monolayer to bilayer, the charge carrier type can be tuned from n-type to p-type. For the monolayer phosphorene device, the tunnel MR ratio reaches about 210% and the SIE is about 80.7% at zero bias. Notably, the SIE and tunnel MR ratio maintain almost constant values against bias voltage and gate voltage, which makes it suitable for magnetic sensors. As for the bilayer phosphorene device, it not only exhibits a considerable tunnel MR ratio, but also shows significantly enhanced conductance, beneficial to the sensitivity of spintronic devices. Further analysis shows that the improvement of conductance is attributed to the low barrier height between the bilayer phosphorene channel and Co electrodes. According to our results, the studied phosphorene devices with Co electrodes demonstrate superior spin injection and transport properties. We believe that these theoretical findings will be a strong asset for future experimental works in spintronics.

Photovoltaic modulation of ferromagnetism within a FM metal/P-N junction Si heterostructure

Obtaining small, fast, and energy-efficient spintronic devices requires a new way of manipulating spin states in an effective manner. Here, a prototype photovoltaic spintronic device with a p-n junction Si wafer is proposed which generates photo-induced electrons and changes the ferromagnetism by interfacial charge doping. A ferromagnetic resonance field change of 48.965 mT and 11.306 mT is achieved in Co and CoFeB thin films under sunlight illumination, respectively. The transient reflection (TR) analysis and the first principles calculation reveal the photovoltaic electrons that are doped into the magnetic layer and alter its Fermi level, correspondingly. This finding provides a new method of magnetism modulation and demonstrates a solar-driven spintronic device with abundant energy supply, which may further expand the landscape of spintronics research.

Gate-controlled spin-valley-layer locking in bilayer transition-metal dichalcogenides

The interplay between various internal degrees of freedom of electrons is of fundamental importance for designing high performance electronic devices. A particular instance of this interplay can be observed in bilayer TMDs due to the combined effect of spin-orbit and interlayer couplings. We study the transport of spin, valley and layer pseudospin, generally, through a magnetoelectric barrier in AB-stacked bilayer TMDs and demonstrate an electrically controllable platform for multifunctional and ultra-high-speed logic devices. Perfect spin and valley polarizations as well as good layer localization of electrons occur in a rather large range of Fermi energies for moderate electric and magnetic fields. Any number of these polarizations can be inverted by adjusting the two potential gates on the two layers. Furthermore, the conditions for the excellent polarizations are determined for the spin, valley and layer degrees of freedom, in terms of the adjustable system parameters. We discuss the individual electric and magnetic barriers and show that the single electric barrier acts as a bipolar pseudospin semiconductor with opposite polarizations for the conduction and valence bands. The results of this study pave the way for multifunctional pseudospintronic applications based on 2D materials.

First principles modeling of pure black phosphorus devices under pressure

Black phosphorus (BP) has a pressure-dependent bandgap width and shows the potential for applications as a low-dimensional pressure sensor. We built two kinds of pure BP devices with zigzag or armchair conformation, and explored their pressure-dependent conductance in detail by using first principles calculations. The zigzag BP devices and the armchair BP devices exhibit different conductance-pressure relationships. For the zigzag BP devices conductance is robust against stress when the out-of-plane pressure ratio is less than 15%, and then increases rapidly until the conductive channels are fully opened. For the armchair pure BP devices conductance decreases at first by six orders of magnitude under increasing pressure and then increases quickly with further increase of pressure until the devices enter the on-state. This shows that the pure zigzag BP devices are more suitable for the application as flexible electronic devices with almost constant conductance under small pressure, while armchair BP devices can serve as bidirectional pressure sensors. Real-space distributions of band alignments were explored to understand the different pressure-related properties. We fitted a set of parameters based on the results from the empirical Wentzel-Kramers-Brillouin method, which provides an effortless approximation to quantitatively predict the pressure-related behaviors of large pure BP devices.