MnSb/GaSb(001)界面半金属特性的第一性原理研究

利用密度泛函理论计算六角NiAs型和立方闪锌矿型MnSb的电子和电磁特性,研究闪锌矿MnSb与GaSb(001)界面,并采用广义渐变近似计算了交换-相关项．闪锌矿结构的MnSb具有半金属铁磁特性,单分子磁矩4μB,MnSb/GaSb(001)界面同样具有半金属特性．界面中Mn原子的磁矩减小,界面中Sb原子磁矩等于两个相应界面磁矩的平均值．另外计算了能带排列在异质结中价带偏移大约1.25 eV.     

Robust half-metallicity at the zincblende CrTe(0 0 1) surfaces and its interface with ZnTe(0 0 1)

All electron full potential calculations based on spin density functional theory are performed to study cubic zincblende (ZB) and hexagonal NiAs structures of bulk CrTe, free (0 0 1) surfaces of ZB CrTe, and interface of ZB CrTe with ZnTe(0 0 1). The ferromagnetic NiAs structure is reported to be about 0.26 eV more stable than the ferromagnetic ZB phase while ZB CrTe is found to be a half-metallic ferromagnet with a half-metallic gap of about 2.90 eV. Thermodynamic stability of CrTe(0 0 1) surfaces are studied in the framework of ab-initio thermodynamic. The obtained phase diagram evidences more stability of the Te terminated surface compared with the Cr termination. We discuss that both Te and Cr ideal terminations of CrTe(0 0 1) retain bulk-like half-metallic property but with a reduced half-metallic gap compared with bulk value. The structural, electronic, magnetic, and band alignment properties of the ZB CrTe/ZnTe(0 0 1) interface are computed and a rather large minority valence band offset of about 1.09 eV is observed in this heterojunction.     

Quenching points of dimeric single-molecule magnets: Exchange interaction effects

We study the quenched energy-splitting (Δ_E) of a single-molecule magnet (SMM) conformed by two exchange coupled giant-spins. An assessment of two nontrivial characteristics of this quenching is presented: (i) The quenching-points of a strongly exchange-coupled dimer differ from the ones of their respective giant-spin modeled SMM and such a difference can be well described by using the Solari-Kochetov extra phase; (ii) the dependence on the exchange coupling of the magnetic field values at the quenching-points when Δ_E passes from monomeric to dimeric behavior. The physics behind these exchange-modified points, their relation with the Δ_E-oscillations experimentally obtained by the Landau-Zener method and with the diabolical-plane of a SMM, is discussed.     

Chemical Approach Towards Broadband Spintronics on Nanoscale Pyrene Films

The injection of pure spin current into the non-magnetic layer plays a crucial role in transmitting, processing, and storing data information in the realm of spintronics. To understand broadband molecular spintronics, pyrene oligomer film (≈20 nm thickness) was prepared using an electrochemical method forming indium tin oxide (ITO) electrode/pyrene covalent interfaces. Permalloy (Ni₈₀Fe₂₀) films with different nanoscale thicknesses were used as top contact over ITO/pyrene layers to estimate the spin pumping efficiency across the interfaces using broadband ferromagnetic resonance spectra. The spintronic devices are composed of permalloy/pyrene/ITO orthogonal configuration, showing remarkable spin pumping from permalloy to pyrene film. The large spin pumping is evident from the linewidth broadening of 5.4 mT at 9 GHz, which is direct proof of spin angular momentum transfer across the interface. A striking observation is made with the high spin-mixing conductance of ≈1.02×10¹⁸ m⁻², a value comparable to the conventional heavy metals. Large spin angular moment transfer was observed at the permalloy-pyrene interfaces, especially at the lower thickness of permalloy, indicating a strong spinterface effect. Pure spin current injection from ferromagnetic into electrochemically grown pyrene films ensures efficient broadband spin transport, which opens a new area in molecular broadband spintronics.     

Spin transport in graphene spin–orbit barrier structure

We studied spin-dependent transport in monolayer graphene with a spin–orbit barrier, a narrow strip in which the spin–orbit interaction is not zero. When the Fermi energy is between the two spin-split bands, the structure can be used to generate spin-polarized current. For a strong enough Rashba strength, a thick enough barrier or a low enough Fermi energy, highly spin-polarized current is generated (polarization ∼0.7–0.85$\sim 0.7\text{–}0.85$). Under these conditions, the spin direction of the transmitted electron is approximately perpendicular to the direction of motion. This shows that graphene spin–orbit nanostructures are useful for the development of graphene spintronic devices.     

Electronic and magnetic properties of semiconducting nanoclusters and large organic molecules: Features interesting for spintronics

Spin properties of single-doped and single-electron charged nano-systems having an odd number of electrons are studied. Starting from an expression for quasiparticle energies in the GW approximation, a simple analytical expression for the spin-splitting of an electron spectrum in such system is derived. First-principles calculations by the DFT–GGA, Hartree-Fock, GW- and hybrid functional methods, which were performed for the silicon clusters and metal phthalocyanine molecules of 1 nm diameter, support this analytical consideration. They show that the spin-splitting energy calculated by the DFT–GGA method is about one order lower, than the results obtained with the methods based on the many-electron theory. A large value of spin-splitting in investigated nano-systems, which is typically of several eV, has an origin in strong localization of electrons and weak screening of exchange interaction. A possible use of this effect in spintronic applications is discussed.     

岩盐结构SrC(111)表面和(111)界面的d~0半金属性

利用第一性原理方法,本文研究了岩盐结构的SrC块材、(111)表面和(111)界面的电子结构和磁性.块材的SrC被证实是一个良好的d~0半金属铁磁体.计算结果显示(111)方向的C表面和Sr表面都保持了块材的半金属性.对于(111)方向四个可能的界面,态密度的计算显示C-Pb界面呈现半金属特性.本文对岩盐结构SrC块材、(111)表面和(111)界面半金属性的研究结果,将为高性能自旋电子器件的实际应用提供一定的理论指导.     

First-principle investigation on multiferroicity and interfacial coupling of nonstoichiometric tetragonal La2/3Sr1/3MnO3/BiCoO3 interface

The energetically stable tetragonal nonstoichiometric La_2/3Sr_1/3MnO₃/BiCoO₃ (LSMO/BCO) interface, whose chemical formula is (BiO)₃(CoO₂)₄/(LaO)₃(SrO)₁(MnO₂)₃, was investigated by using first-principle calculations. A magnetoelectric coupling effect, i.e., an electric control of the magnetism, was approved by a maximum variation of 17.9% in magnetic moments tuned by the electric polarization reversal. The interfacial coupling was controlled by the polar shifts of the interfacial Co and/or O atoms. A huge variation in spin-polarization from 6.3% to 72.7% was achieved upon switching the electric polarization. These findings are useful for magnetoelectric coupled spintronic device applications.     

Mathematical modeling and numerical simulation of domain wall motion in magnetic nanostrips with crystallographic defects

We investigate field and current driven domain wall propagation in magnetic nanostrips in the framework of the modified Landau–Lifshitz–Gilbert equation including spin-torque effects. We focus our attention on a nonlinear “dry-friction” dissipation model useful for describing the effect of structural defects such as inclusions, impurities or dislocations. The analytical and numerical results herein obtained are compared and their physical implications are discussed.