Regulating the dopant clustering in LiZnAs-based diluted magnetic semiconductor

Tuning of the magnetic interaction plays the vital role in reducing the clustering of magnetic dopant in diluted magnetic semiconductors(DMS).Due to the not well understood magnetic mechanism and the interplay between different magnetic mechanisms,no efficient and universal tuning strategy is proposed at present.Here,the magnetic interactions and formation energies of isovalent-doped(Mn) and aliovalent(Cr)-doped LiZnAs are studied based on density functional theory(DFT).It is found that the dopant–dopant distance-dependent magnetic interaction is highly sensitive to the carrier concentration and carrier type and can only be explained by the interplay between two magnetic mechanisms,i.e.,superexchange and Zener’s p–d exchange model.Thus,the magnetic behavior and clustering of magnetic dopant can be tuned by the interplay between two magnetic mechanisms.The insensitivity of the tuning effect to U parameter suggests that our strategy could be universal to other DMS.

First-Principle Study on the Electronic Structure and Optical Property of New Diluted Magnetic Semiconductor(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO

The band structure,DOSs,and optical properties of(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO,including dielectric function,absorption function,reflection function,and energy loss spectrum were studied by using the first-principles calculation.The calculation results indicate that(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO is a direct bandgap semiconductor with a bandgap of 1.1 eV.The Fermi surface is asymmetric and exhibits spin splitting phenomenon.The new type of dilute magnetic semiconductor(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO exhibits significant light loss around 70 eV,with light reflection gradually increasing after 30 eV,and light absorption mainly occurring around 8-30 eV.These results also provide a basis for the discovery of more types of 1111 phase new dilute magnetic semiconductors in the future.

Development of 400-μW cryogen-free dilution refrigerators for quantum experiments

We have successfully developed cryogen-free dilution refrigerators with medium cooling power that can be applied to quantum experiments. Breakthroughs have been made in some key technologies and components of heat switches and dilution units. Our prototype has been running continuously and stably for more than 100 hours below 10 m K, with a minimum temperature of 7.6 m K and a cooling power of 450 μW at 100 m K. At the same time, we have also made progress in the application of dilution refrigerators, such as quantum computing, low-temperature detector, and magnet integration. These indicators and test results indicate good prospects for application in physics, astronomy, and quantum information.

Correlation of work function and stacking fault energy through Kelvin probe force microscopy and nanohardness in diluteα-magnesium

Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca,Mg-Sr and Mg-Ba systems.This investigation incorporated the difference in the‘Work Function'(ΔWF)measured via Kelvin Probe Force Microscopy(KPFM),as a property directly affected by interatomic bond types,i.e.the electronic structure,nanoindentation measurements,and Stacking Fault Energy values reported in the literature.It was shown that the nano-hardness of the solid-solutionα-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba.Thus,it was shown,by also considering the nano-hardness levels,that SFE of a solid-solution is closely correlated with its‘Work Function'level.Nano-hardness measurements on the eutectics andΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys.Correlation withΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree,relatively simple atomic models and a number of assumptions.As asserted by this investigation,if the results of measurement techniques can be qualitatively correlated with those of the computational methods,it can be possible to evaluate the electronic structures in alloys,starting from binary systems,going to ternary and then multi-elemental systems.Our investigation has shown that such a qualitative correlation is possible.After all,the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level,that is,free electron density distributions.Our study indicated that the principles of‘electronic metallurgy'in developing multi-elemental alloy systems can be followed via practical experimental methods,i.e.ΔWF measurements using KPFM and nanoindentation.

Magnetism and Stability of Diluted Magnetic Semiconductor (Ga_(1-x)Fe_x)As

Magnetism and the stability of (Ga 1-xFe x)As are investigated using the first principles LMTO-ASA band calculation by assuming supercell structures.Four concentrations of the 3d impurities are studied (x=1,1/2,1/4,and 1/8).The results show the effect of varying Fe concentration on the magnetic and stable properties.

Double Covalency Factors and DoubleξModel in Study on Optical and Magnetic Properties of Diluted Magnetic Semiconductors ZnX∶Co~ 2+

The optical absorption spectra of the covalent crystals ZnX(X=S,Se) doped with Co 2+ are studied using the double covalency factors,which considers the anisotropic distortion of e g and t 2g orbits for d electron.When the paramagnetic g factor is calculated,the contributions of the spin orbit coupling from the ligand ions are taken into account besides that from the central ion,which is the double ξ model.The calculated results indicate that the theoretical values coincide with the experimental values very well.This suggests that the method presented in this paper could be more valid to some strongly covalent crystals.

Energy Stabilities, Magnetic Properties, and Electronic Structures of Diluted Magnetic Semiconductor Zn1-xMnxS（001） Thin Films

We investigate the electronic and magnetic properties of the diluted magnetic semiconductors Zn1-xMnxS（001） thin films with different Mn doping concentrations using the total energy density functional theory. The energy stability and density of states of a single Mn atom and two Mn atoms at various doped configurations and different magnetic coupling state were calculated. Different doping configurations have different degrees of p-d hybridization, and because Mn atoms are located in different crystal-field environment, the 3d projected densities of states peak splitting of different Mn doping configurations are quite different. In the two Mn atoms doped, the calculated ground states of three kinds of stable configurations are anti-ferromagnetic state. We analyzed the 3d density of states diagram of three kinds of energy stability configurations with the two Mn atoms in different magnetic coupling state. When the two Mn atoms are ferromagnetic coupling, due to d-d electron interactions, density of states of anti-bonding state have significant broadening peaks. As the concentration of Mn atoms increases, there is a tendency for Mn atoms to form nearest neighbors and cluster around S. For such these configurations, the antiferromagnetic coupling between Mn atoms is energetically more favorable.

A preliminary study of variations of the Changjiang Diluted Water between August of 1999 and 2006

A large area hypoxia has been already reported respectively by two interdisciplinary surveys off the Changjiang Estuary since summer of 1999 and 2006. The bypoxic zone shows distinct year-to-year variations. Observed oceanographic data are first analysized and reveal a big difference for the Changjiang Diluted Water （CDW） between these two periods. These great changes are related to the tremendous reduction of the freshwater discharge and variations of wind fields between these two years. It is also found that the monthly mean intrusion of Kuroshio and its branches has increased in the northern East China Sea （ECS）, but decreased in the southern ECS in August of 2006 as compared with 1999 on the base of general circulation models. Then, the Regional Ocean Modelling Systems is applied to the East China Sea to evaluate the contributions and relative importance of impacts from the river discharge, wind forcing and open boundary data. Our simulations reproduce the phenomena that more fresh water extends northeastward in 2006 and forms a negative SSS anomaly to the northeast of the river mouth as compared with 1999, which is consistent with observations. The five group numerical tests suggest that the wind forcing dominates the CDW variations followed by the Kuroshio and its branches. The study implies important roles played by hydrodynamic processes on the variability of hypoxic zone in the study areas.

A numerical study of summertime expansion pattern of Changjiang (Yangtze) River diluted water

Observations show that during summer especially in August, the northward expansion of the Changjiang（Yangtze） River diluted water （CRDW） is blocked in the vicinity of the Changjiang Estuary. To explain this phenomenon, Princeton ocean model （POM） is applied to simulate the summertime expansion pattern of CRDW. Numerical experiments show that to the north of the Changjiang Estuary, a tide-induced temperature front of a cold water centered at （34°N, I22.5°E） plays the key role in determining the expansion pattern of CRDW. This front splits the CRDW into two parts： the main part expands northeastward, and the other small part expands northwestward off the coast of Jiangsu Province, China.

A New Hybrid Vertical Coordinate Ocean Model and Its Application in the Simulation of the Changjiang Diluted Water

Based on the analysis of the advantages and disadvantages of some vertical coordinates applied in the calculation of the Changjiang diluted water （CDW）, a new hybrid vertical coordinate is designed, which uses σ coordinate for current and σ-z coordinate for salinity. To combine the current and salinity, the Eulerian-Lagrangian method is used for the salinity calculation, and the baroclinic pressure gradient （BPG） is calculated on the salinity sited layers. The new hybrid vertical coordinate is introduced to the widely used model of POM （Princeton Ocean Model） to make a new model of POM-σ-z. The BPG calculations of an ideal case show that POM-σ-z model brings smaller error than POM model does. The simulations of CDW also show that POM-σ-z model is better than POM model on simulating the salinity and its front.

A High-Efficiency Fiber-to-Waveguide Coupler with Low Polarization Dependence Using a Diluted Waveguide in InP Substrate with a 1.55μm Wavelength

We propose a fiber-to-waveguide coupler for side-illuminated p-i-n photodiodes to obtain high responsivity and low polarization dependence that is grown on InP substrate and is suitable for surface hybrid integration in low cost modules. The fiber-to-waveguide coupler is based on a diluted waveguide,which is composed of ten periods of undoped 120nm InP/80nm InGaAsP （1.05μm bandgap） multiple layers. Using the semi-vectorial three dimensional beam propagation method （BPM） with the central difference scheme,the coupling efficiency of fiber-to-waveguide under different conditions is simulated and studied,and the optimized conditions for fiber-to-waveguide coupling are obtained. For TE-like and TM-like modes,the calculated maximum coupling efficiency is higher than 94% and 92% ,respectively. The calculated polarization dependence is less than 0. ldB,showing good polarization independence.

Advances in new generation diluted magnetic semiconductors with independent spin and charge doping

As one branch of spintronics, diluted magnetic semiconductors (DMSs) are extensively investigated due to their fundamental significance and potential application in modern information society. The classical materials (Ga,Mn)As of III-V group based DMSs has been well studied for its high compatibility with the high-mobility semiconductor GaAs. But the Curie temperature in (Ga,Mn)As film is still far below room temperature because the spin & charge doping is bundled to the same element that makes the fabrication very difficult. Alternatively, the discovery of a new generation DMSs with independent spin and charge doping, such as (Ba,K)(Zn,Mn)2As2 (briefly named BZA), attracted considerable attention due to their unique advantages in physical properties and heterojunction fabrication. In this review we focus on this series of new DMSs including (I) materials in terms of three types of new DMSs, i.e. the "111","122" and "1111" system;(II) the physical properties of BZA;(III) single crystals & prototype device based on BZA. The prospective of new type of DMSs with independent spin and charge doping is briefly discussed.

Progress on microscopic properties of diluted magnetic semiconductors by NMR and μSR

Diluted magnetic semiconductors (DMSs) that possess both properties of semiconductors and ferromagnetism, have attracted a lot of attentions due to its potential applications for spin-sensitive electronic devices. Recently, a series of bulk form DMSs isostructural to iron-based superconductors have been reported, which can be readily investigated by microscopic experimental techniques such as nuclear magnetic resonance (NMR) and muon spin rotation (μSR). The measurements have demonstrated that homogeneous ferromagnetism is achieved in these DMSs. In this review article, we summarize experimental evidences from both NMR and μSR measurements. NMR results have shown that carriers facilitate the interactions between distant Mn atoms, while μSR results indicate that these bulk form DMSs and (Ga,Mn)As share a common mechanism for the ferromagnetic exchange interactions.

Progress of novel diluted ferromagnetic semiconductors with decoupled spin and charge doping: Counterparts of Fe-based superconductors

Diluted ferromagnetic semiconductors（DMSs） that combine the properties of semiconductors with ferromagnetism have potential application in spin-sensitive electronic（spintronic） devices. The search for DMS materials exploded after the observation of ferromagnetic ordering in Ⅲ-Ⅴ（Ga,Mn）As films. Recently, a series of DMS compounds isostructural to iron-based superconductors have been reported. Among them, the highest Curie temperature TCo f 230 K has been achieved in（Ba,K）（Zn,Mn）2As2. However, most DMSs, including（Ga,Mn）As, are p-type, i.e., the carriers that mediate the ferromagnetism are holes. For practical applications, DMSs with n-type carriers are also advantageous. Very recently,a new DMS Ba（Zn,Co）2As2 with n-type carriers has been synthesized. Here we summarize the recent progress on this research stream. We will show that the homogeneous ferromagnetism in these bulk form DMSs has been confirmed by microscopic techniques, i.e., nuclear magnetic resonance（NMR） and muon spin rotation（μSR）.

First principles study on the structural, electronic and optical properties of diluted magnetic semiconductors Zn1-xCoxX （X=S, Se, Te）

The electronic and optical properties of zincblende ZnX（X=S, Se, Te） and ZnX：Co are studied from density functional theory （DFT） based first principles calculations. The local crystal structure changes around the Co atoms in the lattice are studied after Co atoms are doped. It is shown that the Co-doped materials have smaller lattice constant （about 0.6%-0.9%）. This is mainly due to the shortened Co-X bond length. The （partial） density of states （DOS） is calculated and differences between the pure and doped materials are studied. Results show that for the Co-doped materials, the valence bands are moving upward due to the existence of Co 3d electron states while the conductance bands are moving downward due to the reduced lattice constants. This results in the narrowed band gap of the doped materials. The complex dielectric indices and the absorption coefficients are calculated to examine the influences of the Co atoms on the optical properties. Results show that for the Co-doped materials, the absorption peaks in the high wavelength region are not as sharp and distinct as the undoped materials, and the absorption ranges are extended to even higher wavelength region.

Numerical Investigation of Fuel Dilution Effects on the Performance of the Conventional and the Highly Preheated and Diluted Air Combustion Furnaces

This numerical study investigates the effects of using a diluted fuel （50% natural gas and 50% N2） in an industrial furnace under several cases of conventional combustion （air with 21% O2 at 300 and 1273 K） and the highly preheated and diluted air （1273 K with 10% O2 and 90% N2） combustion （HPDAC） conditions using an in-house computer program. It was found that by applying a combined diluted fuel and oxidant instead of their uncombined and/or undiluted states, the best condition is obtained for the establishment of HPDAC＇s main unique features. These features are low mean and maximum gas temperature and high radiation/total heat transfer to gas and tubes; as well as more uniformity of theirs distributions which results in decrease in NOx pollutant formation and increase in furnace efficiency or energy saving. Moreover, a variety of chemical flame shape, the process fluid and tubes walls temperatures profiles, the required regenerator efficiency and finally the concentration and velocity patterns have been also qualitatively/quantitatively studied.

Buoyancy leads to high productivity of the Changjiang diluted water:a note

Being the mightiest river emptying into the East China Sea （ECS） and the Pacific Ocean, compounded with the large increase of nitrogen and phosphorus input due to anthropogenic activities, the Changjiang River （Yangtze River） has become a dominating source of these nutrients to the estuary. The high nutrient concentrations notwithstanding, however, outside of the estuary the high biological productivity of the Changjiang diluted water （CDW） are most probably fueled mainly by nutrient-rich subsurface waters originating from the upwelled Kuroshio waters. This is because while the buoyancy of the CDW spreads it out on the ECS continen- tal shelf, the CDW entrains subsurface waters along with the nutrients. Nutrients thus supplied are several times more than those supplied by the Changjiang River.

Magnetic properties of Mn-doped ZnO diluted magnetic semiconductors

A series of Mn-doped ZnO films have been prepared in different sputtering plasmas by using the inductively coupled plasma enhanced physical vapour deposition. The films show paramagnetic behaviour when they are deposited in an argon plasma. The Hall measurement indicates that ferromagnetism cannot be realized by increasing the electron concentration. However, the room-temperature ferromagnetism is obtained when the films are deposited in a mixed argon-nitrogen plasma. The first-principles calculations reveal that antiferromagnetic ordering is favoured in the case of the substitution of Mn^2＋ for Zn^2＋ without additional acceptor doping. The substitution of N for O （NO^-） is necessary to induce ferromagnetic couplings in the Zn-Mn-O system. The hybridization between N 2p and Mn 3d provides an empty orbit around the Fermi level. The hopping of Mn 3d electrons through the empty orbit can induce the ferromagnetic coupling. The ferromagnetism in the N-doped Zn-Mn-O system possibly originates from the charge transfer between Mn^2＋ and Mn^3＋ via NO^-, The key factor is the empty orbit provided by substituting N for O, rather than the conductivity type or the carrier concentration.

Theoretical prediction and experimental realization of transition metal doped rutiles as diluted magnetic semiconductors

First principle calculations have been performed to study the electron structures and magnetic properties of transition metal doped ruilles in order to predict room temperature diluted magnetic semiconductors. Different doping configurailons have been calculated to find the preferred doping site. The ground state energies of both FM and AFM states have been calculated to study the magnetic coupling between the dopants. The calculation results show the Co doped mutile has a Curie temperature of 1438 K. Co doped mille films have been prepared on Si substrate by magnetron sputtering. X-ray diffraction results show that the deposited film is ruille. Hysteresis loop curves measured by vibration sample magnetization show that the film is ferromagnetic at root temperature.

Room-temperature anomalous Hall effect and magnetroresistance in(Ga,Co)-codoped ZnO diluted magnetic semiconductor films

This paper reports that the （Ga, Co）-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition. Room-temperature ferromagnetism is observed for the as-grown thin films. The x-ray absorption fine structure characterization reveals that Co2＋ and Ga3＋ ions substitute for Zn2＋ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin. The ferromagnetic （Ga, Co）-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room tempera- ture. The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed.