Narrow Results

In comparison with silicon (100) we argue that the silicon (111) surface is a surface with higher mobility and stronger Coulomb interaction effects. For the resistance of the two-dimensional electron gas we discuss the effects of a magnetic field parallel to the surface: for zero temperature we present theoretical results for the magnetoresistance of an electron gas at the surface of silicon (111) with a six-fold valley degeneracy. Impurity scattering and interface roughness scattering are taken into account. A recent study of a hydrogen-passivated silicon (111) surface showed a mobility proportional to the electron density. We present, using a model for neutral impurities, predictions for the magnetoresistance of this sample in a parallel magnetic field.

The Goos–Hänchen (GH) shift and the spin polarization are theoretically investigated under the anti-parallel double $\delta$-magnetic-barrier nanostructure model by applying a bias using Airy’s function formalism and transfer-matrix technique, which is an improvement on previous calculation. The results show the magnitude and sign of GH shift and spin polarization can be easily changed by modulating the applied bias. The closer the applied bias to the critical value is, the more intensive GH shift and spin polarization will be. Furthermore, two critical values come through modulating the strength of magnetic fields, and an intensive GH shift and a spin polarization also exist near each critical value. These findings can provide a practical approach to designing and fabricating spin beam filters or splitters modulated by applied bias.

A model of small polaron hopping being dependent on spin-polarization is suggested to describe the transport and the colossal magnetoresistance behaviors in manganese perovskites R-A-Mn-O (R: rear earth; A: alkali earth or transition metals). Being different from the theory of simple small polarons, the double exchange interaction and some empirical rules related to lattice effect induced by an external magnetic field and changing concentration have been taken into account. Based on this, a simple formula of resistivity versus temperature, concentration and normalized magnetization has been obtained for the hole-doped perovskite. From the formula, most of the transport behaviors including the colossal magnetoresistive observed in the perovskite have been successfully illustrated.

We investigate the occurrence of a ferromagnetic phase transition in high density hadronic matter (e.g., in the interior of a neutron star). This could be induced by a four-fermion interaction analogous to the one which is responsible for chiral symmetry breaking in the Nambu–Jona-Lasinio model, to which it is related through a Fierz transformation. Flavor SU(2) and flavor SU(3) quark matter are considered. A second-order phase transition is predicted at densities about 5 times the normal nuclear matter density. It is also found that in flavor SU(3) quark matter, a first-order transition from the so-called 2 flavor super-conducting phase to the ferromagnetic phase arises. The color-flavor-locked phase may be completely hidden by the FP.

Nanoscale characterization is a key field in nanoscience and technology as it provides fundamental understanding of the properties and functionalities of materials down to the atomic and molecular scale. In this article, we review the development and application of scanning tunneling microscope (STM) techniques in nanoscale characterization. We will discuss the working principle, experimental setup, operational modes, and tip preparation methods of scanning tunneling microscope. Selected examples are provided to illustrate the application of STM in the nanocharacterization of semiconductors. In addition, new developments in STM techniques including spin-polarized STM (SP-STM) and multi-probe STM (MP-STM) are discussed in comparison with conventional non-magnetic and single tip STM methods.

A systematic investigation on magnetism and spin-resolved electronic properties in double perovskite Ca₂CoMoO₆ compound was performed by using the full-potential augmented plane wave plus local orbitals (APW$+lo$) method within the generalized gradient approximation (GGA-PBE) and GGA-PBE$+U$ scheme. The stability of monoclinic phase ($P{2}_1∕n$ #14) relative to the tetragonal ($I4∕m$#87) and cubic ($Fm\bar{3}m$ #225) phase is evaluated. We investigate the effect of Hubbard parameter $U$on the ground-state structural and electronic properties of Ca₂CoMoO₆ compound. We found that the ferromagnetic ground state is the most stable magnetic configuration. The calculated spin-polarized band structures and densities of states indicate that the Ca₂CoMoO₆ compound is half-metallic (HM) and half-semiconductor (HSC) ferromagnetic (FM) semiconductor with a total magnetic moment of 6.0 using GGA-PBE and GGA-PBE$+U$, respectively. The Hubbard $U$ parameter provides better description of the electronic structure. Using the Vampire code, an estimation of exchange couplings and magnetic Curie temperature is calculated. Further, our results regarding the magnetic properties of this compound reveal their ferromagnetic nature. The GGA-PBE$+U$ approach provides better band gap results as compared to GGA-PBE approximation. These results imply that Ca₂CoMoO₆ could be a promising magnetic semiconductor for application in spintronic devices.

The full-potential linearized augmented plane waves (FP-LAPW) method, within the density functional theory (DFT), has been used to investigate the structural and elastic properties of KRbAs, KNaAs and NaRbAs. The obtained results, utilizing the generalized gradient approximation (GGA), revealed that all compounds prefer their type-I structure ferromagnetic (FM) phase. However, only two among them, KRbAs and KNaAs, exhibit a mechanical stability thus the electronic and magnetic properties have been calculated for both compounds. In the electronic properties, we found that both compounds show a half-metallic character with direct gaps of 1.114$$eV and 1.514$$eV, in the spin-up channel, for KNaAs and KRbAs, respectively. Thus, they may be potential candidates for spin injection in the field of spintronic applications. Moreover, their integer calculated total magnetic moment of $1{\mu }_B$ agrees with the Slater–Pauling rule.

The structural, electronic, elastic and magnetic properties of CoCrScIn were investigated using first principle calculations with applying the full-potential linearized augmented plane waves (FP-LAPW) method, based totally on the density functional theory (DFT). After evaluating the results, the calculated structural parameters reveal that CoCrScIn compound is stable in its ferrimagnetic configuration of the type-III structure. The mechanical properties show its brittle and stiffer behavior. The formation energy value showed that CoCrScIn can be experimentally synthesized. Additionally, the obtained band structures and density of states (DOS) reflect the half-metallic behavior of CoCrScIn, with an indirect bandgap of 0.43$$eV. The total magnetic moment of 3$$${\mu }_B$ and half-metallic ferrimagnetic state are maintained in the range 5.73–6,79 Å. The magnetic moment especially issues from the Cr-$d$ and Co-$d$ spin-polarizations. Furthermore, the calculations of Curie temperature reveal that CoCrScIn has high magnetic transition temperature of 836.7$$K.

Using first-principle calculations within the framework of density functional theory (DFT), the full-potential linearized augmented plane-wave (FP-LAPW) method have been performed to investigate structural, electronic and magnetic properties of the Ca₂MnMoO₆ double perovskite. Different spin configurations (ferromagnetic (FM), ferrimagnetic (FiM), and anti-ferromagnetic AFM1, and AFM2) within both generalized gradient approximation (GGA) and $\mathrm{\text{GGA}}+U$ (Hubbard Coulomb onsite correction) were considered. The value of the Hubbard−Coulomb $U$ parameter was varied in the range of $1-4$$$eV. The ground state is found to be AFM and insulating with the AFM1 state which is the most favorable. In the AFM1 spin configuration, Ca₂MnMoO₆ compound has a semiconductor nature, with the fully spin-polarized valence and conduction bands in the same spin channel. Within the $\mathrm{\text{GGA}}+U$ approximation, the FM phase has a half-metallic character with a net magnetic moment of $5.0{\mu }_{\mathrm{\text{B}}}$ while in the anti-ferromagnetic phase it has an insulating character with zero net magnetic moment which was found at $U\ge 2$$$eV. We found that in the AFM phase within the GGA approximation, a metallic character is obtained for Ca₂MnMoO₆ and also for $U=1$$$eV. In particular, for Hubbard $U$ of 3.6$$eV, a small energy gap of 0.20$$eV is observed. The main features shown by the density of states curves motivate further experimental exploration in the double perovskite Ca₂MnMoO₆ for spintronic applications.

Nanoscale characterization is a key field in nanoscience and technology as it provides fundamental understanding of the properties and functionalities of materials down to the atomic and molecular scale. In this article, we review the development and application of scanning tunneling microscope (STM) techniques in nanoscale characterization. We will discuss the working principle, experimental setup, operational modes, and tip preparation methods of scanning tunneling microscope. Selected examples are provided to illustrate the application of STM in the nanocharacterization of semiconductors. In addition, new developments in STM techniques including spin-polarized STM (SP-STM) and multiprobe STM (MP-STM) are discussed in comparison with conventional non-magnetic and single tip STM methods.