Bipolar Magnetic Semiconductor Research Articles

Electronic structures, field effect transistor and bipolar field-effect spin filtering behaviors of functionalized hexagonal graphene nanoflakes

We report first-principles calculations on the electronic properties, spin magnetism, and potential applications of the functionalized hexagonal armchair graphene nanoflakes (GNFs). It is found that the gap of the GNF changes in an obvious oscillating manner with the size of its hexagonal defect (antidot), and when the antidot is large enough, it will lead to a prominent splitting of the α-spin and β-spin orbitals and the intriguing property of bipolar magnetic semiconductors for the GNF. And also shown is that the electronic structures of the GNF can be tuned from semiconducting to metallic properties by different edge modifications. More importantly, based on the suitable hexagonal defective GNFs, we design a field effect transistor (FET) and a bipolar field-effect spin-filtering (BFESF) device, and find that they all exhibit extremely high performances. For this FET, its ON/OFF ratio reaches ∼105, subthreshold swing ∼90meV per decade, and the transconductance ∼103S/m, and for this BFESF device, the spin polarization nearly reaches 100% with different spin directions only by altering signs of gate voltages.

Enhanced half-metallicity in carbon-chain–linked trigonal graphene

The spin polarization property of a zigzag-edge trigonal graphene (ZTG) linked with different-length carbon chains Cn is investigated theoretically. It has been found that the enhancement of such a property completely depends on that the number of carbon atoms in a chain being odd or even. If it is an even number, the spin polarization is only changed slightly due to the nearly nonmagnetic property of these carbon chains. In contrast, while it is an odd number, the spin polarization is enhanced significantly to a larger energy range, i.e., showing a prominent half-metallicity and perfect spin-filter effects, owing to interactions of the ZTG and carbon chains with the strong ferromagnetism property. Deepgoing analyses show that these results are intimately related to a polyyne-like configuration for carbon chains in nanojunctions and the transition from the bipolar magnetic semiconductor to half-metallicity. Our findings suggest that this simple structure might promise importantly potential applications for developing nano-scale spintronics devices.

Electronic structures of zigzag silicene nanoribbons with asymmetric sp2−sp3 edges

The nanomaterials with peculiar spintronic characteristics, such as half-metals, spin gapless semiconductors [X. L. Wang, Phys. Rev. Lett. 100, 156404 (2008)], and bipolar magnetic semiconductors [Li et al., Nanoscale 4, 5680 (2012)], play the crucial role in nano-electronics and spintronics. Here, we report the zigzag silicene nanoribbons (ZSiNRs) with asymmetric sp2−sp3 edges are bipolar magnetic semiconductors due to the incorporation of Klein and zigzag edge states. With the bipolar feature, these asymmetric ZSiNRs can be altered to half-metals with opposite conductive spin channels by p-type and n-type dopings. Moreover, the semiconducting properties can also be tailored by the strain, which makes the nanoribbons into spin gapless semiconductors or ferromagnetic metals.

Ab initio search for novel bipolar magnetic semiconductors: Layered YZnAsO doped with Fe and Mn

Very recently, the newest class of spintronic materials, where reversible spin polarization can be controlled by applying gate voltage: so-called bipolar magnetic semiconductors (Xingxing Li et al., arXiv:1208.1355) was proposed. In this work, a novel way to creation of bipolar magnetic semiconductors by doping of non-magnetic semiconducting 1111 phases with magnetic dn < 10 atoms is discussed using ab initio calculations of layered YZnAsO doped with Fe and Mn. In addition, more complex materials with several spectral intervals with opposite 100% spin polarization where multiple gate-controlled spin-polarization can be expected are proposed.

Hydrogenated bilayer wurtzite SiC nanofilms: a two-dimensional bipolar magnetic semiconductor material

Recently, a new kind of spintronics material, bipolar magnetic semiconductors (BMS), has been proposed. The spin polarization of BMS can be conveniently controlled by a gate voltage, which makes it very attractive in device engineering. Now, the main challenge is finding more BMS materials. In this article, we propose that hydrogenated wurtzite SiC nanofilm is a two-dimensional BMS material. Its BMS character is very robust under the effect of strain, substrate or even a strong electric field. The proposed two-dimensional BMS material paves the way to use this promising new material in an integrated circuit.

Control of spin in a La(Mn,Zn)AsO alloy by carrier doping

The control of spin without magnetic field is one of challenges in developing spintronic devices. In an attempt to solve this problem, we proposed a novel hypothetic LaMn0.5Zn0.5AsO alloy from two experimentally synthesized rare earth element transition metal arsenide oxides, i.e. LaMnAsO and LaZnAsO. On the basis of the first-principles calculations with strong-correlated correction, we found that the LaMn0.5Zn0.5AsO alloy is an antiferromagnetic semiconductor at ground state, while bipolar magnetic semiconductor at ferromagnetic state. Both electron and hole doping in the LaMn0.5Zn0.5AsO alloy induces the transition from antiferromagnetic to ferromagnetic, as well as semiconductor to half metal. In particular, the spin-polarization direction is switchable depending on the doped carrier's type. As carrier doping can be realized easily in experiment by applying a gate voltage, the LaMn0.5Zn0.5AsO alloy stands for a promising spintronic material to generate and control the spin-polarized carriers with electric field.

Bipolar magnetic materials for electrical manipulation of spin-polarization orientation

In spintronics, both the charge and spin of the electrons are exploited for information processing. Developing simple methods to manipulate and detect the carriers' spin orientation is among the key issues for spintronics applications. Electrical field has the advantage that it can be easily applied locally in contrast with a conventionally used magnetic field, thus it is more convenient and efficient. Bipolar magnetic materials, characterized by a unique electronic structure where the valence band and conduction band possess opposite spin polarization around the Fermi level, serve as a new class of materials for spintronics through which electrical control of spin-polarization direction can be realized simply by applying a gate voltage. This article reviews a range of materials that have bipolar spin polarization, including bipolar half metals and bipolar magnetic semiconductors, and their potential applications for creating, manipulating, and detecting spin-polarized carriers. These materials provide a promising future for electrically controllable spintronics devices.

Bipolar magnetic semiconductors: a new class of spintronics materials

Electrical control of spin polarization is very desirable in spintronics, since electric fields can be easily applied locally, in contrast to magnetic fields. Here, we propose a new concept of bipolar magnetic semiconductors (BMS) in which completely spin-polarized currents with reversible spin polarization can be created and controlled simply by applying a gate voltage. This is a result of the unique electronic structure of BMS, where the valence and conduction bands possess opposite spin polarization when approaching the Fermi level. BMS is thus expected to have potential for various applications. Our band structure and spin-polarized electronic transport calculations on semi-hydrogenated single-walled carbon nanotubes confirm the existence of BMS materials and demonstrate the electrical control of spin-polarization in them.