Communications in Physics

In this paper, the density functional theory (DFT) study on nano-thin films of the most typical ferroelectric compound BaTiO$_3$ was presented. The results showed that the convergence of the film model using for DFT calculation were obtained for the thickness of the vacuum slabs as large as ten times of the BaTiO$_3$ slabs within the total energy error $\bsim$ 0.01 eV. The lattice contraction was observed in the surface region of the material. The difference in atomic layer termination, between BaO terminated and TiO$_2$ terminated films, gives rise to the difference in lattice reconstruction at the surface region which, in turn, leads to the difference in surface electric dipoles. The surface effect acts on the electronic structure of thin films in the manner of the asymmetry of atomic sites and the structural reconstruction due to the surface relaxation. Our results indicated that the termination also decides how and how much these two manners take effects on the electronic structure of the material.

To date semiconductor nanowire (NW) heterostructures (HS) have attracted extensive attention as important components of electronic and optoelectronic nanodevices. Further NWs also show promising potency to enhance the solar energy harvesting, e.g. improving both light trapping, photo-carrier collection, and contacting surface area. In this work we show theoretically that the \(d^{0}\)-ferromagnetism and NW HS bandgap can be turned by engineering the HS interfaces in non-magnetic ZnO/GaN core/shell NW HS. In that NW HS the incorporation of one compound into the other leads to the bandgap narrowing in the nonisovalent alloy because of the type II band alignment betwwen ZnO and GaN. The \(d^{0}\)-ferromagnetic interface can be developed by creating \(p\)-type defect with \(N\) and/or \(n\)-type defect with Zn in Ga--O interface bonds due to the defect-induced polar discontinuity. It's noted that the GaN/ZnO NW HS itself without defect or with same number defects of both types are not ferromagnetic. So that the induced magnetic moment is suggested to be related to the missing charge introduced at these defects. In our study we focused on the effects of GaN/ZnO interfaces on the electronic and magnetic properties, e.g. interface states within the bandgap and interface-induced ferromagnetism and impact of surface reconstruction and quantum confinement. The origin of this \(d^{0}\)-FM is revealed by analyses of spin-polarized bandstructure indicated by the asymmetrical spin-up and spin-down states near the Fermi level, the projected densities of states (PDOSs) and the spin-polarized mulliken charge differences, indicated that most spin-polarized states are dominated by the interface defect site N$p$ electrons. The calculated GaN/ZnO interface magnetism, have been compared with FM at the LaAlO\(-SrTiO\(_{3}\) interface which are theoretically predicted [30] and experimentally confirmed [31], where the magnetic moments also arise from the polar discontinuity.

In this paper, we report results on the fabrication and magnetic properties of spinel ferrite Mn1-xZnxFe2O4 (0 ≤ x ≤ 0.8) nanoparticles. The nanoparticles were synthesized by a co-precipitation method. The effects of substituting Zn for Mn on the magnetic properties and particles size were focused. It was found that the phase-formation temperature is 90OC and the average particle size decreases from 40 nm to 10 nm when increased Zn concentration from zero to 0.8. The Curie temperature TC strongly decreases from 585 K (x = 0) to 320 K (x = 0.8) concomitantly with a decrease of the saturation magnetization MS. With a TC of 320 K and MS of 17 emu/g, the x=0.8 sample could be a promising candidate for some biomedical applications.

Magnetic properties and giant magnetocaloric effect (GMCE) of Mn-based Heusler compounds such as Co-Mn-Si, Ni-Mn-Sn, Ni-Mn-Sb have been investigated. The results show that the structure strongly influences on magnetic properties and GMCE of these alloys. The coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) orders is observed. The magnetic phase transitions can be controlled by changing composition and annealing condition of the alloys. GMCEs with large magnitude and wide working temperature range have been obtained on these alloys showing their application potential for magnetic refrigeration technology.

This paper discusses about Robertson-Walker space-time with quadratic equation of state and dynamical cosmological parameter Λ . Some exact solutions of Einstein’s field equations for three cases have been obtained. Physical behaviors of the models are discussed in detail.

In this study, a surface-enhanced Raman scattering (SERS) substrate based on an octahedral cuprous oxide (Cu2O) nanostructure to probe methylene blue (MB) molecules as an analyte chemical has been implemented. Octahedral Cu2O nanocrystals were synthesized by a novel hydrothermal process using only ethylene glycol as both a reductant and organic solvent. The characteristics of Cu2O nanocrystals were well recognized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), FTIR, and Raman spectroscopy. The mechanism of the SERS surface has been thoroughly investigated and has been shown to involve the contributions of both surface plasmon resonance and charge transfer effects. Using a simple collection rule for SERS bands, the portion of charge transfer processes was estimated to be about 46%.

Possible contributions to neutrinoless double beta (ββ)0ν decay in the economical 3-3-1 model are discussed. We show that the (ββ)0ν decay in this model is due to both sources—Majorana L and Dirac D neutrino masses. If the mixing angle between charged gauge bosons, the standard model W and bilepton Y , is in range of the ratio of neutrino masses L/D, both the Majorana and Dirac masses simultaneously give contributions dominant to the decay. As results, constraints on the bilepton mass are also given.

In this paper, we present \(\mathcal{O}(\alpha^3)\) QED corrections due to initial-state photon radiation (ISR) to processes \(e^{−} e^{+} \to f \bar{f} H\) with \(f = e, \mu_e, \nu_{\mu}, \nu_{\tau}\) at future lepton colliders. The impact of the ISR corrections on the total cross sections are studied. We find that the corrections vary from ∼ −30% to −10% in the range of center-of-mass energies from 200 GeV to 700 GeV. The ISR corrections to some realistic distributions of experimental interest for searching the properties of the Higgs boson are also evaluated and they are order of \(\sim −10\)% contributions at \(s = 250\) GeV. The corrections are massive contributions and they must be taken into account for matching high precision data at future lepton colliders.

The natural radioactivity due to presence of 226Ra, 232Th and 40K radionuclides in Lao PDR cements was measured for first time using a gamma-spectrometry with HPGe detector. Two different types of cement produced by 4 local cement companies in Lao PDR have been investigated.  The specific radioactivity of 226Ra, 232Th and 40K in the investigated samples ranged from 24.83 ± 1.18  to 54.39 ± 5.90  Bq kg-1 with a mean of 37.76 ± 10.71 Bq kg-1, 6.63 ± 1.59 to 21.17 ± 0.48 Bq kg-1 with a mean of 13.77 ± 5.85 Bq kg-1 and 43.28 ± 7.68 to 168.70 ± 3.34 Bq kg-1 with a mean of 116.07 ± 47.50 Bq kg-1, respectively. The radium equivalent activity (Raeq), the gamma-index, the external and internal hazard indices, Absorb Dose Rate in Air (D) and Annual Effective Dose Equivalent (AEDE) were estimated for the radiation hazard of the natural radioactivity in all cement samples. The obtained results were compared with the corresponding values for cement of different countries. The calculated Raeq values of Lao PDR samples are lower than the limit of 370 Bq kg-1 set fo building materials. The mean indoor absorbed dose rate is slightly lower than the population-weighted average of 84 nGy h-1 while the corresponding effective dose was 79% less than the dose ft of 1 mSv y-1. The results obtained in this study show no significant radiological hazards arising from using Lao PDR cement for construction of houses.

Noise is unavoidable in practice and its presence makes quantum protocols imperfect. In this paper we consider a way to cope with typical types of noise in joint remote preparation of an arbitrary 2-qubit state. The idea is to use nonmaximally (in stead of maximally) entangled states as the initial quantum channel. Because noise changes the initial quantum channel we can beforehand tailor it to be nonmaximally entangled by introducing free parameters which, depending on given types of noise, can be controlled so that due to the affect of noise the initial quantum channel becomes closest to the maximally entangled one, thus optimizing the performance of the joint remote state preparation protocol. The dependence of the optimal averaged fidelities on the strength of various types of noise is represented by phase diagrams that clearly separate the quantum domain from the classical one.