First-Principles Calculation for the Half Metallic Properties of La2NbMnO6

La2 VMnO6 is measured to be insulating and ferrimagnetic experimentally. In this study, by substituting V with Nb, La2NbMnO6 is investigated using the density functional theory. The calculated results indicate that La2 NbMnO6 is also ferrimagnetic and exhibits the half metallic properties due to the strong electron correlation of Mn. The valence states of Nb and Mn are assigned to be 4-4 and ＋2 in La2NbMn06, respectively, which are different from V3＋/Mn3＋ in La2 VMnO6.

Half-metallic ferromagneticWeyl fermions related to dynamic correlations in the zinc-blende compound VAs

The realization of 100%polarized topologicalWeyl fermions in half-metallic ferromagnets is of particular importance for fundamental research and spintronic applications.Here,we theoretically investigate the electronic and topological properties of the zinc-blende compound VAs,which was deemed as a half-metallic ferromagnet related to dynamic correlations.Based on the combination of density functional theory and dynamical mean field theory,we uncover that the half-metallic ferromagnet VAs exhibits attractive Weyl semimetallic behaviors which are very close to the Fermi level in the DFT+U regime with effect U values ranging from 1.5 eV to 2.5 eV.Meanwhile,we also investigate the magnetization-dependent topological properties;the results show that the change of magnetization directions only slightly affects the positions of Weyl points,which is attributed to the weak spin–orbital coupling effects.The topological surface states of VAs projected on semi-infinite(001)and(111)surfaces are investigated.The Fermi arcs of all Weyl points are clearly visible on the projected Fermi surfaces.Our findings suggest that VAs is a fully spin-polarized Weyl semimetal with many-body correlated effects in the effective U values range from 1.5 eV to 2.5 eV.

Structural Stability and Half Metallic Features of Zn_(0.5)Cr_(0.5)S under Pressure

Spin-polarized first-principle was performed to study the structural stability and the electronic states of Cr doped ZnS with the Cr component of 50% in zincblende （ZB）, wurtzite （W） and rocksalt （RS） structures under pressure. The results show that the zincblende and wurtzite structures become unstable under low pressures of about 4.68 and 9.61 GPa, respectively, but the rocksalt structure can be maintained up to an extremely high pressure of about 32.92 GPa. Both zincblende and wurtzite Zno.sCro.5S display half metallic features under pressure, while rocksalt Zno.sCro.sS exhibits metallic feature. The half metallic features can be ascribed to the stronger interactions between S-3p and Cr-3d states and the metallic feature is due to the higher crystal symmetry of rocksalt Zn0.5Cr0.5S. These results can provide helpful guidance for Cr doped ZnS to be used in spintronic devices.

Hydroxylation-induced half-metallicity in graphitic ZnO sheet

The structural, electronic and magnetic properties of the hydroxylated graphitic Zinc oxide (ZnO) sheet were studied using the density functional theory. We found that the hydroxylation can induce a magnetic moment of 1.0 μB per unit cell and turn graphitic ZnO sheet from semiconductor into half metal for the three studied hydroxylated configurations with a half-metal gap up to 0.60 eV. The relative stability of each situation was also discussed and the structure for hydroxyl absorbed above the hexagonal ring of ZnO sheet was the most steady. The prominent electronic and magnetic properties may endow 2D ZnO sheet great opportunity in future spintronics.

Spin and valley half metal induced by staggered potential and magnetization in silicene

We investigate the electron transport in silicene with both staggered electric potential and magnetization; the latter comes from the magnetic proximity effect by depositing silicene on a magnetic insulator. It is shown that the silicene could be a spin and valley half metal under appropriate parameters when the spin–orbit interaction is considered; further, the filtered spin and valley could be controlled by modulating the staggered potential or magnetization. It is also found that in the spin-valve structure of silicene, not only can the antiparallel magnetization configuration significantly reduce the valve-structure conductance, but the reversing staggered electric potential can cause a high-performance magnetoresistance due to the spin and valley blocking effects. Our findings show that the silicene might be an ideal basis for the spin and valley filter analyzer devices.

Enhancement of the thermoelectric performance of half-metallic full-Heusler Mn_(2)VAl alloys via antisite defect engineering and Si partial substitution

A half-metallic full-Heusler Mn_(2)VAl alloy is a potential p-type thermoelectric material that can directly generate electricity from waste heat via the Seebeck effect.For practical use,the Seebeck coefficient S of Mn_(2)VAl should be increased while maintaining a high electrical conductivity s from its half-metallic character.Herein,we achieved this objective through antisite defect engineering.Theoretically,it was predicted that the S was maximized by regulating partial density of states of majority-spin sp-electrons through the control of the fraction of antisite defect,f_(AD),between V and Al atoms in Mn_(2)VAl.Experi-mentally,a significant increase in S and a slight decrease in s were observed for an Mn_(2)VAl sample with an optimal fAD=33%,enhancing the thermoelectric power factor PF by 2.7 times from an Mn_(2)VAl sample with fAD=14%.Furthermore,we combined the antisite defect engineering with a partial substitution method.An Mn_(2)V(Al_(0.96)Si_(0.04))sample with fAD=33%exhibited the highest PF=4.5×10^(-4)W·m^(-1)·K^(-2)at 767 K among the samples.The maximum dimensionless figure-of-merit zT of the Mn_(2)V(Al_(0.96)Si_(0.04))sample with f_(AD)=33%was measured to be 3.4×10^(-2)at 767 K,which is the highest among the p-type half-metallic full-Heusler alloys.

Optimization of biliary drainage in inoperable distal malignant strictures

BACKGROUND Given most patients with distal malignant biliary obstruction present in the nonresectable stage,palliative endoscopic biliary drainage with fully covered metal stent(FCMS)or uncovered metal stent(UCMS)is the only available measure to improve patients’quality of life.Half covered metal stent(HCMS)has been recently introduced commercially.The adverse effects and stent function between FCMS and UCMS have been extensively discussed.AIM To study the duration of stent patency of HCMS and compare it with FCMS and UCMS to optimize biliary drainage in inoperable patients with distal malignant obstruction.Secondary aims in our study included evaluation of patients’survival and the rates of adverse events for each type of stent.METHODS We studied 210 patients and randomized them into three equal groups;HCMS,FCMS and UCMS were inserted endoscopically.RESULTS Stent occlusion occurred in(18.6%,17.1%and 15.7%in HCMS,FCMS and UCMS groups,respectively,P=0.9).Stent migration occurred only in patients with FCMS(8.6%of patients).Cholangitis and cholecystitis occurred in 11.4%and 5.7%of patients,respectively,in FCMS.Tumor growth occurred only in 10 cases among patients with UCMS after a median of 140 d,sludge occurred in nine,seven and one patients in HCMS,FCMS and UCMS,respectively(P=0.04).CONCLUSION Given the prolonged stent functioning time,the use of HCMS is preferred over the use of UCMS and FCMS for optimizing biliary drainage in patients with distal malignant biliary obstruction.

Spin transport in epitaxial Fe3O4/GaAs lateral structured devices

Research in the spintronics community has been intensively stimulated by the proposal of the spin field-effect transistor(SFET),which has the potential for combining the data storage and process in a single device.Here we report the spin dependent transport on a Fe_(3)O_(4)/GaAs based lateral structured device.Parallel and antiparallel states of two Fe_(3)O_(4) electrodes are achieved.A clear MR loop shows the perfect butterfly shape at room temperature,of which the intensity decreases with the reducing current,showing the strong bias dependence.Understanding the spin-dependent transport properties in this architecture has strong implication in further development of the spintronic devices for room-temperature SFETs.

The atlas of ferroicity in two-dimensional MGeX_(3) family:Room-temperature ferromagnetic half metals and unexpected ferroelectricity and ferroelasticity

Two-dimensional(2D)ferromagnetic and ferroelectric materials attract unprecedented attention due to the spontaneous-symmetry-breaking induced novel properties and multifarious potential applications.Here we systematically investigate a large family(148)of 2D MGeX3(M=metal elements,X=O/S/Se/Te)by means of the high-throughput first-principles calculations,and focus on their possible ferroic properties including ferromagnetism,ferroelectricity,and ferroelasticity.We discover eight stable 2D ferromagnets including five semiconductors and three half-metals,212D antiferromagnets,and 11 stable 2D ferroelectric semiconductors including two multiferroic materials.Particularly,MnGeSe3 and MnGeTe3 are predicted to be room-temperature 2D ferromagnetic half metals with Tc of 490 and 308 K,respectively.It is probably for the first time that ferroelectricity is uncovered in 2D MGeX3 family,which derives from the spontaneous symmetry breaking induced by unexpected displacements of Ge-Ge atomic pairs,and we also reveal that the electric polarizations are in proportion to the ratio of electronegativity of X and M atoms,and IVB group metal elements are highly favored for 2D ferroelectricity.Magnetic tunnel junction and water-splitting photocatalyst based on 2D ferroic MGeX3 are proposed as examples of wide potential applications.The atlas of ferroicity in 2D MGeX3 materials will spur great interest in experimental studies and would lead to diverse applications.

Room-temperature ferrimagnetism and size-modulated electronic structures in two-dimensional cluster-based metal-organic frameworks

Cluster-assembled materials have attracted particular attention for their complex hierarchical structures and unique properties.However,the majority of cluster-based assemblies developed so far are either non-magnetic or only exhibit magnetic ordering with a relatively low Curie temperature,limiting their applications in spintronics.Thus,two-dimensional(2D)cluster-assembled materials with room-temperature magnetism remain highly desirable.For this purpose,based on first principles calculations,we design a series of thermodynamically stable 2D cluster-based metal-organic frameworks(MOFs)Fe_(n)-(pyz)(n=1-6)by utilizing Fenmetal clusters as nodes and nitrogen-containing pyrazine ligands as organic linkers.These 2D cluster-based MOFs exhibit robust ferrimagnetic ordering due to the strong d-p direct exchange interaction between d-electron spin of Fe_(n)(n=1-6)clusters and charge transfer-induced p-electron spin of pyrazine ligands.In particular,the ferrimagnetic Curie temperatures are well above room temperature(up to 836 K).Additionally,altering the size of Fe_(n)clusters in Fe_(n)-(pyz)(n=1-6)MOFs results in diverse functional spintronic properties,including bipolar magnetic semiconductors,half semiconductors and Dirac half metals.Moreover,these 2D assembled MOFs possess sizable magnetic anisotropy energies,up to 9.16 me V per formula.

Two-dimensional bipolar magnetic semiconductors with high Curie-temperature and electrically controllable spin polarization realized in exfoliated Cr(pyrazine)_(2) monolayers

Exploring two-dimensional(2D)magnetic semiconductors with room-temperature magnetic ordering and electrically controllable spin-polarization is a highly desirable but challenging task for nano-spintronics.Here,through first-principles calculations,we propose to realize such a material by exfoliating the recently synthesized organometallic layered crystal Li0.7[Cr(pyz)_(2)]Cl0.7·0.25(THF)(pyz=pyrazine,THF=tetrahydrofuran).The feasibility of exfoliation is confirmed by the rather low exfoliation energy of 0.27 J m^(−2),even smaller than that of graphite.In exfoliated Cr(pyz)_(2)monolayers,each pyrazine ring grabs one electron from the Cr atom to become a radical anion,and then a strong d-p direct-exchange magnetic interaction emerges between Cr cations and pyrazine radicals,resulting in room-temperature ferrimagnetism with a Curie temperature of 342 K.Moreover,the Cr(pyz)_(2)monolayer is revealed to be an intrinsic bipolar magnetic semiconductor where electrical doping can induce half-metallic conduction with controllable spin-polarization direction.