Modern Physics Letters B

A closed-loop high-precision front-end interface circuit in a standard 0.35 $\mu$m CMOS technology for a tunneling magneto-resistance (TMR) sensor is presented in this paper. In consideration of processing a low frequency and weak geomagnetic signal, a low-noise front-end detection circuit is proposed with chopper technique to eliminate the 1/f noise and offset of operational amplifier. A novel ripple suppression loop is proposed for eliminating the ripple in a tunneling magneto-resistance sensor interface circuit. Even harmonics is eliminated by fully differential structure. The interface is fabricated in a standard 0.35 $\mu$m CMOS process and the active circuit area is about $4.6\times 3.7{\mathrm{\text{mm}}}^2$. The interface chip consumes 7 mW at a 5 V supply and the 1/f noise corner frequency is lower than 1 Hz. The interface circuit of TMR sensors can achieve a better noise level of $16.7\mathrm{\text{nV}}/{\mathrm{\text{Hz}}}^{1/2}$. The ripple can be suppressed to less than 10 $\mu$V by ripple suppression loop.

In this paper, we report the structural, magnetic, and magnetocaloric properties of Ge-doped ${\mathrm{\text{Nd}}}_6{\mathrm{\text{Fe}}}_{13}{\mathrm{\text{Pd}}}_{1-x}{\mathrm{\text{Ge}}}_x$ (x = 0.1, 0.2) compounds. Rietveld refinement of X-ray powder diffraction shows that all the investigated samples are single phase and crystallize in a tetragonal ${\mathrm{\text{Nd}}}_6{\mathrm{\text{Fe}}}_{13}\mathrm{\text{Si}}$-type structure with the space group $I4$/mcm. The magnetic properties of the intermetallic ${\mathrm{\text{Nd}}}_6{\mathrm{\text{Fe}}}_{13}{\mathrm{\text{Pd}}}_{1-x}{\mathrm{\text{Ge}}}_x$ compounds have been investigated by the physical property measurement system (PPMS). The magnetic transition temperatures $(T_{\mathrm{\text{tr}}})$ from the ferromagnetic (FM) to the antiferromagnetic (AFM) states are determined to be 123 and 111 K for x = 0.1, 0.2, respectively, which shifted to lower temperatures compared with the ${\mathrm{\text{Nd}}}_6{\mathrm{\text{Fe}}}_{13}\mathrm{\text{Pd}}$ compound. For a field change of 5 T, the peak values of $\left|\mathrm{\Delta }{S}_M\right|$ for the ${\mathrm{\text{Nd}}}_6{\mathrm{\text{Fe}}}_{13}{\mathrm{\text{Pd}}}_{0.9}{\mathrm{\text{Ge}}}_{0.1}$ and ${\mathrm{\text{Nd}}}_6{\mathrm{\text{Fe}}}_{13}{\mathrm{\text{Pd}}}_{0.8}{\mathrm{\text{Ge}}}_{0.2}$ compounds are estimated to be 3.73 and $1.92{\mathrm{\text{J kg}}}^{-1}{\mathrm{\text{K}}}^{-1}$ with the corresponding refrigeration capability (RC) values of 271.7 and $184.5{\mathrm{\text{J kg}}}^{-1}$, respectively.

The inhomogeneous nonlinear Hirota equation is more realistic than the nonlinear Schrödinger equation when approximating the wave propagation in the ocean and optical fibers. In this paper, the inhomogeneous nonlinear Hirota equation with a self-consistent source and its Lax pair are presented. The high-order rogue-wave solutions are worked out by the generalized Darboux transformation and their evolution dynamics is analyzed.

Through the silicon modulation-doping (MD) growth method, the electrical performance of AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs) is improved by replacing the commonly uniform-doped (UD) method of n-AlGaN layer. The electroluminescence characterisic measurements demonstrate the MD growth method could effectively enhance the light emission intensity. Both the forward voltage and reverse leakage current of the MD samples are obviously reduced compared to those of the UD sample. Due to the existence of periodic Si-MD superlattices in n-AlGaN layers, which may behave like a series of capacitors, the built-in electric fields are formed. Both the measured capacitance–voltage (C–V) characteristics, and related photoluminescence (PL) intensity with the Si-MD growth method are enhanced. In detail, the effects of these capacitors can enhance the peak internal capacitance up to 370 pF in the MD sample, whereas the UD sample is only 180 pF. The results also mean that with better current spreading ability in the MD sample, the MD processes can effectively enhance the efficiency and reliability of DUV-LEDs. Thus, the investigations of the Si-MD growth methods may be useful for improving the electrical performance of DUV-LEDs in future works. Meanwhile, this investigation may partly suggest the minor crystalline quality improvements in the epi-layers succeeding the MD n-AlGaN layer.

The calcium intercalated graphite $({\mathrm{\text{CaC}}}_6)$ is considered to be a representative material of the graphite intercalated superconductors, which exhibits sizable anisotropy of the Fermi surface (FS). Herein, the influence of the FS anisotropy on the critical magnetic field $(H_C)$ in ${\mathrm{\text{CaC}}}_6$ superconductor is comprehensively analyzed within the Migdal–Eliashberg (M–E) formalism. To precisely account for the mentioned anisotropy effects, the analysis is conducted in the framework of the six-band approximation, hitherto not employed for calculations of the $H_C$ function in ${\mathrm{\text{CaC}}}_6$ material. For convenience, the obtained results are compared with the available one- and three-band estimates reported by using the M–E theory. A notable signature of the increased number of bands is observed for the temperature-dependent $H_C$ functions. In particular, the $H_C$ function decreases at T = 0 K as the number of the considered bands is higher. Moreover, it is argued that the six-band formalism yields the most physically relevant shape of the $H_C$ function among all considered approximations. Therefore, the six-band model introduces not only quantitative but also qualitative changes to the results, in comparison to the other discussed FS approximations. This observation supports postulate that the six-band model constitutes minimal structure for FS of ${\mathrm{\text{CaC}}}_6$, but also magnifies importance of anisotropy effects for the critical magnetic field calculations.

Lattices are used in such fields as electricity, optics and magnetism. Under investigation in this paper is an inhomogeneous discrete nonlinear Schrödinger equation, which models the wave propagation in a lattice. Employing the Kadomtsev–Petviashvili (KP) hierarchy reduction, we obtain the rogue-wave solutions, and see that the rogue waves are affected by the coefficient of the on-site external potential. We see (1) the first-order rogue wave with one peak and two hollows; (2) the second-order rogue waves, each of which is with one peak or three humps; (3) the third-order rogue waves, each of which is with one peak or six humps, and those humps exhibit the triangular pattern, anti-triangular pattern and circular pattern. When the coefficient of the on-site external potential is a constant, the rogue waves periodically appear. When the coefficient of the on-site external potential monotonously changes, oscillations emerge on the constant background.

We designed and fabricated a new micro-needle-column discharge chip by Lithographie, Galvanoformung and Abformung technology to meet sterilization requirements. The dimensions of the chip are 11.6 mm × 11.7 mm × 3 mm. The micro-discharge structure is composed of a needle electrode and two cylinder electrodes. We employed a needle with a tip diameter of 20 $\mu$m and a thickness of 20 $\mu$m as the discharge cathode. We used a cylinder with a thickness of 1 mm and diameter of 0.4 mm as the anode. We carried out the gas discharge experiments in ambient air and at room temperature, without external air flow. In the experiments, a corona and glow discharge with applied voltages of −2.1 kV and −3.8 kV were realized. We carried out the sterilization experiments for six different discharge times (15, 30, 60, 90, 120 and 180 s) with an applied voltage of −3.8 kV. The inactivation efficiency of Escherichia coli and Staphylococcus aureus reached 100% for sterilization times of 120 s and 180 s. This indicates that the micro-needle-column discharge chip may be suitable as a portable sterilizer.

Aiming at the problem of poor reliability of beam membrane fabrication in silicon microstructure processing technology, a technique for preparing microbeams using porous silicon sacrificial layer is proposed. The comparison of different porosity, different depths of porous silicon to beam membrane release and the comparison of different beam structures to beam membrane release were studied. The experiment was carried out by selecting different process parameters and testing the prepared beam membrane. According to the test results, the appropriate electrochemical corrosion process parameters were selected to prepare the porous silicon layer with appropriate porosity, large depth, good support effect and fast release speed, which can realize the release of the beam membrane and improve the reliability of the beam membrane. The field of application of microsensors and microactuators has been greatly increased.

In this study, thermo-elastic and lattice dynamic properties of XMgAl (X = Li, Na) half-Heusler compounds are investigated using density functional theory implemented in WIEN2k and Quantum ESPRESSO codes. Generalized gradient approximation (GGA) as an exchange correlation function has been used in Kohn–Sham equations. Firstly, the structure of these Heusler compounds is optimized and then these optimized parameters are used to find three elastic constants $C_{11}$, $C_{12}$ and $C_{44}$ for $C_{1b}$ type structures. Three elastic constants are then used to determine different elastic moduli like bulk modulus, shear modulus, Young’s modulus and other mechanical parameters like Pugh’s ratio, Poisson’s ratio, anisotropic ratio, sound velocities, Debye temperature and melting temperature. On behalf of these mechanical parameters, the brittle/ductile nature and isotropic/anisotropic behavior of the materials has been studied. Different regions of vibrational modes in the materials are also discussed on behalf of Debye temperature calculations. The vibrational properties of the half-Heusler compounds are computed using Martins–Troullier pseudo potentials implemented in Quantum ESPRESSO. The phonon dispersion curves and phonon density of states in first Brillion zone are obtained and discussed. Reststrahlen band of LiMgAl is found greater than NaMgAl.

In this work, ${\mathrm{\text{BiFeO}}}_3$ and Eu-doped ${\mathrm{\text{BiFeO}}}_3({\mathrm{\text{Bi}}}_{0.9}{\mathrm{\text{Eu}}}_{0.1}{\mathrm{\text{FeO}}}_3)$ samples were prepared by a simple solid-phase sintering method and the structure and magnetic properties were studied. The results of X-ray diffraction show that ${\mathrm{\text{Bi}}}_{0.9}{\mathrm{\text{Eu}}}_{0.1}{\mathrm{\text{FeO}}}_3$ sample maintains the same rhombohedral R3c structure as ${\mathrm{\text{BiFeO}}}_3$ sample but with a slight lattice distortion due to the Eu substitution for Bi. Compared with ${\mathrm{\text{BiFeO}}}_3$, the ${\mathrm{\text{Bi}}}_{0.9}{\mathrm{\text{Eu}}}_{0.1}{\mathrm{\text{FeO}}}_3$ sample exhibits a larger remnant magnetization and a higher Curie–Weiss temperature. These results indicate that appropriate doping with Eu is effective in improving the magnetic properties of ${\mathrm{\text{BiFeO}}}_3$ and the solid-phase sintering method used in this study is a simple and good solid-phase sintering method to prepare ${\mathrm{\text{BiFeO}}}_3$.

We have performed a density functional theory (DFT) study of the electronic structure in ceria $({\mathrm{\text{CeO}}}_2)$ and gadolinium-doped ceria (GDC) system using VASP code in the generalized gradient approximation (GGA) with DFT+U. The band structures in GDC and thin film GDC are calculated and compared to that of bulk ceria. Doping of gadolinium significantly decreases the band gap of ceria, while the thin film structure of GDC raises the band gap greatly. The results help explain the electronic conductivity behavior of GDC and suggest that thin film-structured GDC could be used as a possible way to overcome the current leakage disadvantage of GDC.

Relieving complete congestion in a traffic system is an important problem. We propose a strategy to realize this, in which the packets on nodes shared by many shortest paths are dropped preferentially. A simple scale-free network is chosen to demonstrate the importance of the degree heterogeneity to the congestion problem, though this network structure cannot mimic a real traffic network. Two traffic models are simulated: in one of which, all the nodes are identical, and in the other, the delivering capacity and storing ability for each node are both proportional to its degree. Both models can give a phase transition between free-flow and congested states, while the latter model has significant strong transportation performance (a larger critical value of the packet generation rate). The strategy of preferentially dropping packets on nodes shared by many shortest paths, as proposed in this paper, can realize remarkably better transportation performance measured by the fraction of congested nodes and the average arrival rate compared with the random packet dropping strategy in the literature.

A new method was used to predict the surface energies of three low-index surfaces for intermetallic compound B₂-AgMg. The results show that Ag-terminal and Mg-terminal are the two kinds of surface models for (1 0 0) and (1 1 1) surfaces which are non-stoichiometry. (1 1 0) surface has only one surface terminal, which is stoichiometry, and the smallest surface energy (about $0.862\mathrm{\text{J}}/{\mathrm{\text{m}}}^2)$ in three low-index surfaces. The surface energies are related to the chemical potential of Ag and Mg atoms for (1 0 0) and (1 1 1) surfaces, but it is of no concern to this factor for stoichiometry (1 1 0) surface. Analysis of electronic properties is coincident with the calculated surface energies.

Lithium-rich manganese-based layered oxides are of great interest as cathode materials for lithium ion batteries due to their high energy density. The voltage decay and capacity fading during prolonged charge/discharge cycling are the key obstacles for their practical usage. In this work, using density functional theory, we investigated the origin of the Ni surface segregation by calculating the defect formation energies of antisite defects, including Ni cation substituting a Li cation $({\mathrm{\text{Ni}}}_{\mathrm{\text{Li}}})$ and pairs of Ni cation swapping with Li cation (${\mathrm{\text{Ni}}}_{\mathrm{\text{Li}}}$–${\mathrm{\text{Li}}}_{\mathrm{\text{Ni}}}$) in ${\mathrm{\text{LiMnO}}}_2$, ${\mathrm{\text{LiNi}}}_{1/3}{\mathrm{\text{Mn}}}_{1/3}{\mathrm{\text{Co}}}_{1/3}{\mathrm{\text{O}}}_2$ and ${\mathrm{\text{LiNiO}}}_2$ to represent the Mn-rich, Mn–Ni equivalence and Ni-rich conditions, respectively. Results show that ${\mathrm{\text{Ni}}}_{\mathrm{\text{Li}}}$–${\mathrm{\text{Li}}}_{\mathrm{\text{Ni}}}$ defect is of energy favorable in Li-rich and Mn-rich layered oxide cathode. Al-doping is beneficial for improving the structure stability and preventing the surface segregation, thus Al-doping can improve cycle ability and rate capability of Li-rich and Mn-rich layered cathodes. This work provides deep insights for the design of layered cathode materials with both high capacity and voltage stability during cycling.