Catálogo de publicaciones - revistas

<jats:p>Via structural searching methodology and first-principles calculations, we predicted two new BC<jats:sub>6</jats:sub>N allotropes, a C-centered monoclinic BC<jats:sub>6</jats:sub>N (Cm-BC<jats:sub>6</jats:sub>N) and a primitive-centered monoclinic BC<jats:sub>6</jats:sub>N (Pm-BC<jats:sub>6</jats:sub>N). The lattice vibrations, elastic properties, ideal strength, theoretical hardness, and electronic structure of the predicted BC<jats:sub>6</jats:sub>N were investigated systematically. Our results reveal that Cm-BC<jats:sub>6</jats:sub>N is more favorable energetically than graphite-like g-BC<jats:sub>6</jats:sub>N above 20.6 GPa, which is lower than the transition pressures of r-BC<jats:sub>6</jats:sub>N, t-BC<jats:sub>6</jats:sub>N, and Pm-BC<jats:sub>6</jats:sub>N. Both Cm-BC<jats:sub>6</jats:sub>N and Pm-BC<jats:sub>6</jats:sub>N are indirect semiconductors with band gaps of 2.66 eV and 0.36 eV, respectively. Cm-BC<jats:sub>6</jats:sub>N exhibits the excellent ideal shear strength of 53.9 GPa in (011)[01 <jats:inline-formula> <jats:tex-math><?CDATA $\bar{1}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_096201_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>], much greater than that of Pm-BC<jats:sub>6</jats:sub>N (25.0 GPa in (010)[101] shear direction), and Cm-BC<jats:sub>6</jats:sub>N shows a much lower anisotropy in shear strength than Pm-BC<jats:sub>6</jats:sub>N. The Vickers hardness of Cm-BC<jats:sub>6</jats:sub>N is estimated to be above 80 GPa, which is more outstanding than those of t-BC<jats:sub>6</jats:sub>N and r-BC<jats:sub>6</jats:sub>N.</jats:p>

<jats:p>Multiple phase transitions are detected in sodium amide (NaNH<jats:sub>2</jats:sub>), an important hydrogen storage material, upon compression in diamond anvil cells (DAC) by using Raman spectroscopy and x-ray diffraction (XRD) measurements. Additional Bragg reflections appear on lower and higher angle sides of the original ones at ∼ 1.07 GPa and 1.84 GPa, accompanied by obvious changes in Raman spectroscopy, respectively. It reveals that NaNH<jats:sub>2</jats:sub> undergoes the high-pressure phase sequence (<jats:italic>α</jats:italic>–<jats:italic>β</jats:italic>–<jats:italic>γ</jats:italic>) up to 20 GPa at room temperature. Spectral analysis indicates an orthorhombic structure with <jats:italic>PBAN</jats:italic> space group for the <jats:italic>γ</jats:italic> phase. We also experimentally observe high pressure induced recrystallization in alkaline amide compounds for the first time.</jats:p>

<jats:p>The interfacial magnetoelectric interaction originating from multi-orbital hopping processes with ferroelectric-associated vector potential is theoretically investigated for complex-oxide composite structures. Large mismatch in the electrical permittivity of the ferroelectric and ferromagnetic materials gives rise to giant anisotropic magnetoelectric effects at their interface. Our study reveals a strong linear dynamic magnetoelectric coupling which genuinely results in electric control of magnetic susceptibility. The constitutive conditions for negative refractive index of multiferroic composites are determined by the analysis of light propagation.</jats:p>

<jats:p>Uniform precession dynamics and its magnetic damping are investigated in epitaxial Co<jats:sub>2</jats:sub>Fe<jats:sub>1−<jats:italic>x</jats:italic> </jats:sub>Mn<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Al films by using the time-resolved magneto–optical Kerr effect under out-of-plane configuration. The decay time of uniform precession mode decreases, and thus the magnetic damping increases with the increase of external field. Moreover, the decay time decreases as <jats:italic>x</jats:italic> decreases, so that the enhancement of magnetic damping occurs in Fe-rich sample. Furthermore, the decay time decreases as the excitation fluence increases, which drops rapidly at low magnetic field comparing with the slow reduction at high magnetic field. This unique magnetic damping enhancement is attributed to the enhancement of homogeneous magnetization.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the magnetic properties of the double perovskite ruthenate compound Sr<jats:sub>2</jats:sub>YRuO<jats:sub>6</jats:sub> using Monte Carlo simulations (MCS). We elaborate the ground state phase diagrams for all possible and stable configurations. The magnetizations and the susceptibilities as a function of temperature for the studied system are also reported. The effects of the exchange coupling interactions and the crystal field are examined and discussed. On the other hand, since the compound Sr<jats:sub>2</jats:sub>YRuO<jats:sub>6</jats:sub> exhibits an antiferromagnetic behavior, we find its Néel temperature, <jats:inline-formula> <jats:tex-math> <?CDATA ${T}_{{\rm{N}}}\approx 31\,{\rm{K}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">N</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>31</mml:mn> <mml:mspace width="0.25em" /> <mml:mi mathvariant="normal">K</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_097503_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, which is in good agreement with the experimental results in the literature. To complete this study, the hysteresis loops and the coercive field as a function of the external magnetic field are also obtained for fixed values of the physical parameters.</jats:p>

<jats:p>We review the microwave methods to characterize the material properties, including the established and the emerging techniques in material characterization, especially the permeability spectra of the magnetic thin films. Almost all aspects of the microwave techniques for characterizing the permeability of thin films at microwave frequencies, including the new methods developed by our group, are presented. Firstly, the introduction part is presented. Secondly, the coaxial-line with transmission/reflection methods and the pickup coil with electromagnetic induction method are presented. Thirdly, the most widely used shorted microstrip technique is discussed in detail by the equivalent circuit method, transmission line method, and electromagnetic induction method. Fourthly, the coplanar waveguide method and the near-field probe method are also introduced. Finally, the high temperature permeability characterization by using the shorted microstrip line, the near-field microwave probe, and the shorted microstrip line probe are described in detail. This paper may be useful for researchers or engineers who will build up such measurement fixture to make full use of the existing methods or to develop original methods to meet the requirements for ever-rising measurements.</jats:p>

<jats:p>Na<jats:sub>0.5</jats:sub>Sm<jats:sub>0.5</jats:sub>Cu<jats:sub>3</jats:sub>Ti<jats:sub>4</jats:sub>O<jats:sub>12</jats:sub> (NSCTO) ceramics have been prepared by reactive sintering of amorphous powder. Spark plasma sintering (SPS) for 10 min at 1025 °C and conventional sintering (CS) for 10 h at 1090 °C have been employed. X-ray diffraction measurements confirmed the pure CCTO-like phase for SPS and CS NSCTO ceramics. The SPS ceramic showed an average grain size of 500 nm, which is much smaller than that of the CS (<jats:inline-formula> <jats:tex-math><?CDATA $\sim 5\,{\rm{\mu }}{\rm{m}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mn>5</mml:mn> <mml:mspace width="0.25em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_098202_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) sample. The impedance spectroscopy measurements revealed an electrically inhomogeneous structure in the prepared ceramics. While the resistivities of grains of both ceramic samples were in the same order of magnitude, the resistivity of grain-boundaries of the CS ceramic was three orders of magnitude greater than that of the SPS ceramic. Both of the samples showed giant dielectric constant (<jats:inline-formula> <jats:tex-math><?CDATA $\gt {10}^{3}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>&gt;</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_098202_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>) over wide ranges of temperatures and frequencies. Nevertheless, the room-temperature dielectric loss of the SPS NSCTO (3.2 at 1.1 kHz) ceramic sample was higher than that of the CS NSCTO (0.08 at 1.1 kHz) ceramic sample due to the reduced grain-boundary resistivity of the former. Two dielectric relaxations were detected for each sample and attributed to the relaxations in grains and grain-boundaries. The dielectric behavior of the SPS and CS NSCTO ceramics could be interpreted in terms of the internal barrier layer capacitor (IBLC) model.</jats:p>

<jats:p>We investigate the <jats:italic>XY</jats:italic> control and manipulation of the superconducting qubit state using direct digital synthesis (DDS) for the microwave pulse signal generation. The decoherence time, gate fidelity, and other qubit properties are measured and carefully characterized, and compared with the results obtained by using the traditional mixing technique for the microwave pulse generation. In particular, the qubit performance in the state manipulation with respect to the sampling rate of DDS is studied. Our results demonstrate that the present technique provides a simple and effective method for the <jats:italic>XY</jats:italic> control and manipulation of the superconducting qubit state. Realistic applications of the technique for the possible future scalable superconducting quantum computation are discussed.</jats:p>

<jats:p>Magnetic oxide semiconductors are significant spintronics materials. In this article, we review recent advances for homogeneous and inhomogeneous magnetic oxide semiconductors. In the homogeneous magnetic oxide semiconductors, we focus on the various doping techniques including choosing different transition metals, codoping, non-magnetic doping, and even un-doping to realize homogeneous substitution and the clear magnetic origin. And the enhancement of the ferromagnetism is achieved by nanodot arrays engineering, which is accompanied by the tunable optical properties. In the inhomogeneous magnetic oxide semiconductors, we review some heterostructures and their magnetic and transport properties, especially magnetoresistance, which are dramatically modulated by electric field in the constructed devices. And the related mechanisms are discussed in details. Finally, we provide an overview and possible potential applications of magnetic oxide semiconductors.</jats:p>

<jats:p>The mechanism of terahertz (THz) pulse coherent detection via two-color laser pulses of various frequency ratios in gas plasma is theoretically investigated. Our investigations demonstrate that except for the commonly used frequency ratio of 2, other uncommon frequency ratios can also be utilized to detect THz pulse, such as 2<jats:italic>n</jats:italic>, <jats:italic>n</jats:italic>+1/2 (<jats:inline-formula> <jats:tex-math> <?CDATA $n\le 3$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>n</mml:mi> <mml:mo>≤</mml:mo> <mml:mn>3</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_098701_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:italic>n</jats:italic> is a positive integer). The well-developed transient photocurrent model is extended to our terahertz detection process. Based on this model, our simulation results can be explained by analyzing the process of asymmetric electron ionization and electron acceleration.</jats:p>