Structural defects are important for both solid-state chemistry and physics, as they can have a significant impact on chemical stability and physical properties. Here, we identify a vacancyinduced pseudo-gap formation in antiferromagnetic Cr$_{0.86}$ZnSb. Cr$_{1-x}$ZnSb alloys were studied combining efforts of density functional theory (DFT) calculations and experimental methods to elucidate the effect of vacancies. Detailed analyses (X-ray powder and single crystal diffraction, transmission and secondary scanning electron microscopy) of Cr$_{1-x}$ZnSb, $0<x<0.20$, prompts Cr$_{0.86}$ZnSb as the only stable compound, crystallizing with the MnAlGe-type structure. From DFT calculations, an antiferromagnetic spin configuration of Cr local magnetic moments was found to be favorable for both, the perfectly stoichiometric compound CrZnSb, as well as for Cr$_{0.875}$ZnSb. Magnetic order is observed experimentally for Cr$_{0.86}$ZnSb by temperature- and field-dependent magnetization measurements, revealing a magnetic phase transition near 220 K, which is corroborated by zero-field muon spin relaxation studies. Thermoelectric transport properties exhibit distinct maxima in the temperature-dependent Seebeck coefficient and electrical resistivity at around 190 K. Analyzing the measured data on the basis of a triple parabolic band model and DFT simulations, their characteristic features are traced back to a pseudo-gap in the electronic structure arising from a particular vacancy arrangement. These findings offer valuable insights into the role of vacancies in defected materials, contributing to the broader understanding of structural defects and their impact on the electronic structure.
The power factor of pure p-type ZnSb has been calculated via ab initio simulations assuming that the carrier concentrations are due to the doping effect of intrinsic zinc vacancies. With a vacancy concentration close to the experimental solubility limit we were able to perfectly reproduce the Power Factor measured in polycrystalline ZnSb samples. The methodology has then been successfully extended for predicting the effect of extrinsic doping elements on the thermoelectric properties of ZnSb. Germanium and tin seem to be promising p-type doping elements. In addition, we give, for the first tim…
One intriguing finding in graphene is the vacancy-induced magnetism that highlights the interesting interaction between local magnetic moments and conduction electrons. Within density functional theory, the current understanding of the ground state is that a Stoner instability gives rise to ferromagnetism of $π$ electrons aligned with the localized moment of a $σ$ dangling bond and the induced $π$ magnetic moments vanish at low vacancy concentrations. However, the observed Kondo effect suggests that $π$ electrons around the vacancy should antiferromagnetically couple to the local moment and ca…
We study the magnetic and electronic properties of defects in SnO$_{2}$ using pseudopotential and all electron methods. Our calculations show that bulk SnO$_{2}$ is non-magnetic, but it shows magnetism with a magnetic moment around 4.00 $μ_{B}$ due to Sn vacancy (V$_\mathrm{Sn}$). The magnetic moment comes mainly from O atoms surrounding V$_\mathrm{Sn}$ and Sn atoms, which couple antiferromagnetically with the O atoms in the presence of V$_\mathrm{Sn}$. The coupling between different Sn vacancies is also studied and we find that these defects not only couple ferromagnetically but also antiferr…
We have studied the electronic, magnetic and linear phonon dispersion behavior of Phosphorene monolayer using rst principle based ab initio method. Phosphorene monolayer is a semiconducting system with a dimensional dependent variable range of band gap. Vacancy has been done to study the geometry and physical behavior of the monolayer system. Pristine, vacancy induced monolayer and vacancy induced doped monolayer are included in the calculation. Dopant concentration has been well checked via optimization algorithm to maintain the dilute magnetic semiconducting behavior of the monolayer system.…
A group-theoretical framework to describe vacancy ordering and magnetism in the Fe$_{1-x}$S system is developed. This framework is used to determine the sequence of crystal structures consistent with the observed magnetic structures of troilite (FeS), and to determine the crystallographic nature of the low-temperature Besnus transition in Fe$_{0.875}$S. We conclude that the Besnus transition is a magnetically driven transition characterised by the rotation of the moments out of the ac-plane, accompanied by small atomic displacements that lower the symmetry to triclinic at low temperatures. Bas…
Multiferroics in which giant ferroelectric polarization and magnetism coexist are of tremendous potential for engineering disruptive applications in information storage and energy conversion. Yet the functional properties of multiferroics are thought to be affected detrimentally by the presence of point defects, which may be abundant due to the volatile nature of some constituent atoms and high temperatures involved in materials preparation. Here, we demonstrate with theoretical methods that oxygen vacancies may enhance the functionality of multiferroics by radically changing their magnetic in…
Oxygen vacancies (VOs) effects on magnetic ordering in Eu0.5Ba0.5TiO3-δ (EBTO3-δ) thin films have been investigated using a combination of experimental measurements and first-principles density-functional calculations. Two kinds of EBTO3-δthin films with different oxygen deficiency have been fabricated. A nuclear resonance backscattering spectrometry technique has been used to quantitatively measure contents of the VOs. Eu0.5Ba0.5TiO3 ceramics have been known to exhibit ferroelectric (FE) and G-type antiferromagnetic (AFM) properties. While, a ferromagnetic (FM) behavior with a Curie temperatu…
Magnetic quantum defects in a uniaxial antiferromagnetic insulator
Rutgers University（罗格斯大学）；Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）；National Institute of Chemical Physics and Biophysics（化学物理与生物物理学国立研究所）；University of South Carolina（南卡罗来纳大学）
We study from first principles the magnetism in graphene induced by single carbon atom defects. For two types of defects considered in our study, the hydrogen chemisorption defect and the vacancy defect, the itinerant magnetism due to the defect-induced extended states has been observed. Calculated magnetic moments are equal to 1 $μ_B$ per hydrogen chemisorption defect and 1.12$-$1.53 $μ_B$ per vacancy defect depending on the defect concentration. The coupling between the magnetic moments is either ferromagnetic or antiferromagnetic, depending on whether the defects correspond to the same or t…
Antiferromagnetic (AF) spintronics is merit on ultra-high operator speed and stability in the presence of magnetic field. To fully use the merit, the device should be pure rather than hybrid with ferromagnet or ferrimagnet. For the magnetism in the antiferromagnet is canceled by that of different sublattices, breaking the symmetry in the material can revive the native magnetism, which can be detected by the magnetoresistance (MR) effect. Achieving noticeable MR effect in the pure AF device is diffcult but essential for the AF spintronic applications. Here, we study the tunnel magnetoresistance…
MnBi$_2$Te$_4$ is an antiferromagnetic topological insulator which stimulates intense interests due to the exotic quantum phenomena and promising device applications. Surface structure is a determinant factor to understand the novel magnetic and topological behavior of MnBi2Te4, yet its precise atomic structure remains elusive. Here, we discovered a spontaneous surface collapse and reconstruction in few-layer MnBi2Te4 exfoliated under delicate protection. Instead of the ideal septuple-layer structure in the bulk, the collapsed surface is shown to reconstruct as Mn-doped Bi$_2$Te$_3$ quintuple-…
The roles of oxygen vacancies on the electronic and magnetic properties of Ni doped In$_2$O$_3$ have been studied by first-principles calculations based on hybrid functional theory. Our results predict that the Ni-doped In$_2$O$_3$ system displays a ferromagnetic semiconducting character. However, the presence of oxygen vacancies results in antiferromagnetic coupling between the neighboring Ni pair bridged by an oxygen vacancy. The antiferromagnetic coupling is found to arise from the predominant role of superexchange due to the strong Ni 3d-O 2p hybridization. Consequently, the oxygen vacanci…
Layered-antiferromagnetic compound CuCrS2 has been prepared by different methods. The analysis of X-ray diffraction patterns of different samples gave significant amount of vacancy-disorder of Cr-atoms within the layers. Extended period of sintering above 9000C increases the transfer of Cr-atoms to the interstitial sites between the layers. This disorder has marginal effect on the Antiferromagnetic properties. The electrical conductivity is increased and the thermoelectric power remains positive and quite high between 150-400\muV/K in the paramagnetic state around room temperature with increas…
The crystal and magnetic structures of the superconducting iron based chalcogenides RbyFe2-xSe2 have been studied by means of single crystal synchrotron x-ray and high resolution neutron powder diffraction in the temperature range 2-570 K. The ground state of the crystal is an intrinsically phase separated state with two distinct by symmetry phases. The main phase has the iron vacancy ordered \surd5x\surd5 superstructure (I4/m space group) with AFM ordered Fe spins. The minority phase does not have \surd5x\surd5-type of ordering and has smaller in plane lattice constant a and larger tetragonal…
We address the electronic structure and magnetic properties of vacancies and voids both in graphene and graphene ribbons. Using a mean field Hubbard model, we study the appearance of magnetic textures associated to removing a single atom (vacancy) and multiple adjacent atoms (voids) as well as the magnetic interactions between them. A simple set of rules, based upon Lieb theorem, link the atomic structure and the spatial arrangement of the defects to the emerging magnetic order. The total spin $S$ of a given defect depends on its sublattice imbalance, but some defects with S=0 can still have l…
\textit{Ab-initio} calculations based on density functional theory with local spin density approximation are used to study defects-driven magnetism in bulk $α$-Li$ _{3}$N. Our calculations show that bulk Li$ _{3} $N is a non-magnetic semiconductor. Two types of Li vacancies (Li-I and Li-II) are considered, and Li-vacancies (either Li-I or Li-II type) can induce magnetism in Li$ _{3}$N with a total magnetic moment of 1.0 $μ_{\rm B}$ which arises mainly due to partially occupied N-$p$-orbitals around the Li vacancies. The defect formation energies dictate that Li-II vacancy, which is in the Li$ …
We report direct imaging of boundary magnetization associated with antiferromagnetic domains in magnetoelectric epitaxial Cr2O3 thin films using diamond nitrogen vacancy microscopy. We found a correlation between magnetic domain size and structural grain size which we associate with the domain formation process. We performed field cooling, i.e., cooling from above to below the Néel temperature in the presence of magnetic field, which resulted in the selection of one of the two otherwise degenerate 180 degree domains. Lifting of such a degeneracy is achievable with a magnetic field alone due to…
We use first-principles calculations based on density functional theory to investigate the interplay between oxygen vacancies, A-site cation size / tolerance factor, epitaxial strain, ferroelectricity and magnetism in the perovskite manganite series, AMnO3 (A=Ca2+, Sr2+, Ba2+). We find that, as expected, increasing the volume through either chemical pressure or tensile strain generally lowers the formation energy of neutral oxygen vacancies consistent with their established tendency to expand the lattice. Increased volume also favors polar distortions, both because competing rotations of the o…
The electronic structure of the vacancy-ordered K$_{0.5}$Fe$_{1.75}$Se$_2$ iron-selenide compound (278 phase) is studied using the first-principles density functional method. The ground state of the 278 phase is stripe-like antiferromagnetic, and its bare electron susceptibility shows a large peak around $(π, π)$ in the folded Brillouin zone. Near Fermi level, the density of states are dominated by the Fe-3d orbitals, and both electron-like and hole-like Fermi surfaces appear in the Brillouin zone. Unfolded band structure shows limited similarities to a hole doped 122 phase. With 0.1e electron…
We report the synthesis of MnO2−delta microspheres using hydrothermal and conventional chemical reaction methods. The microspheres of MnO2−delta consist of nanowires having a diameter of 20-50 nm and a length of 2-8 micro m. The value of the oxygen vacancy delta estimated from the x-ray photoelectron spectrum (XPS) is 0.3. The magnetization versus temperature curve indicates a magnetic transition at about 13 K. It is found that a parasitic ferromagnetic component is imposed on the antiferromagnetic structure of MnO2−delta, which might result from distortion of the lattice str…
We recently demonstrated that the superconductor-to-insulator transition induced by ionic liquid gating of the high temperature superconductor YBa2Cu3O7 (YBCO) is accompanied by a deoxygenation of the sample [Perez-Munoz et al., PNAS 114, 215 (2017)]. DFT calculations helped establish that the pronounced changes in the spectral features of the Cu K-edge absorption spectra measured in situ during the gating experiment arise from a decrease of the Cu coordination within the CuO chains. In this work, we provide a detailed analysis of the electronic structure origin of the changes in the spectra r…
Effect of oxygen off-stoichiometry on the structural and magnetic properties of La0.15Sr0.85MnO3-d (d = 0.02,0.14) has been studied employing low-temperature x-ray diffraction, calorimetry, electrical-transport and magnetization. The nearly stoichiometric composition under goesfirst order phase-transition from cubic to tetragonal P4/mmm at 238 K accompanied by magnetic and electrical phase-transitions. On the contrary the off-stoichiometric composition does not show any transition and remains cubic Pm-3m down to 80 K. Offstoichiometry induced oxygen-vacancy seems to suppress the cooperative JT…
Antiferromagnetic insulators (AFIs) are of significant interest due to their potential to develop next-generation spintronic devices. One major effort in this emerging field is to harness AFIs for long-range spin information communication and storage. Here, we report a non-invasive method to optically access the intrinsic spin transport properties of an archetypical AFI α-Fe2O3 via nitrogen-vacancy (NV) quantum spin sensors. By NV relaxometry measurements, we successfully detect the time-dependent fluctuations of the longitudinal spin density of α-Fe2O3. The observed frequency dependence of th…
Based on density functional theory (DFT), we performed first-principle studies on the electronic structure, magnetic state and optical properties of two-dimensional (2D) transition-metal phosphorous trichalcogenide MnPX$_3$ (X=S and Se). The calculated interlayer cleavage energies of MnPX$_3$ monolayers indicate the energetic possibility to be exfoliated from bulk phase, with good dynamical stability confirmed by the absence of the imaginary contributions in the phonon spectra. MnPX$_3$ monolayers are both Néel antiferromagnetic (AFM) semiconductors with direct band gaps falling into the visib…
Electrical switching of Néel order in an antiferromagnetic insulator is desirable as a basis for memory applications. Unlike electrically-driven switching of ferromagnetic order via spin-orbit torques, electrical switching of antiferromagnetic order remains poorly understood. Here we investigate the low-field magnetic properties of 30 nm thick, c-axis oriented $α$-Fe$_2$O$_3$ Hall devices using a diamond nitrogen-vacancy (NV) center scanning microscope. Using the canted moment of $α$-Fe$_2$O$_3$ as a magnetic handle on its Néel vector, we apply a saturating in-plane magnetic field to create a …
We studied structural, electronic and magnetic properties of a cubic perovskite BaFeO$_{3-δ}$ ($0 \le δ\le 0.5$) within the density functional theory using a generalized gradient approximation and a GGA+U method. According to our calculations, BaFeO$_3$ in its stoichiometric cubic structure should be half-metallic and strongly ferromagnetic, with extremely high Curie temperature ($T_C$) of 700 - 900 K. However, a such estimate of $T_C$ disagrees with all available experiments, which report that $T_C$ of the BaFeO$_3$ and undoped BaFeO$_{3-δ}$ films varies between 111 K and 235 K or, alternativ…
The magnetic properties and electronic structure of (K,Tl)y Fe1.6 Se2 is studied using first-principles calculations. The ground state is checkerboard antiferromagnetically coupled blocks of the minimal Fe4 squares, with a large block spin moment ~11.2μB . The magnetic interactions could be modelled with a simple spin model involving both the inter- and intra-block, as well as the n.n. and n.n.n. couplings. The calculations also suggest a metallic ground state except for y = 0.8 where a band gap ~400 - 550 meV opens, showing an antiferromagnetic insulator ground state for (K,Tl)0.8 Fe1.6 Se2 .…
The recently discovered K-Fe-Se high temperature superconductor has caused heated debate regarding the nature of its parent compound. Transport, angle-resolved photoemission spectroscopy, and STM measurements have suggested that its parent compound could be insulating, semiconducting or even metallic [M. H. Fang, H.-D. Wang, C.-H. Dong, Z.-J. Li, C.-M. Feng, J. Chen, and H. Q. Yuan, Europhys. Lett. 94, 27009 (2011); F. Chen et al. Phys. Rev. X 1, 021020 (2011); and W. Li et al.,Phys. Rev. Lett. 109, 057003 (2012)]. Because the magnetic ground states associated with these different phases have …
Motivated by the existence of superconductivity in pyrite-structure CuS$_2$, we explore the possibility of ionic-liquid-gating-induced superconductivity in the proximal antiferromagnetic Mott insulator NiS$_2$. A clear gating-induced transition from a two-dimensional insulating state to a three-dimensional metallic state is observed at positive gate bias on single crystal surfaces. No evidence for superconductivity is observed down to the lowest measured temperature of 0.45 K, however. Based on transport, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, atomic force micr…
Electronic structure and magnetic properties for iron deficient TlFe$_{2-x}$Se$_2$ compounds are studied by first-principles calculations. We find that for the case of $x=0.5$ with a Fe-vacancy ordered orthorhombic superstructure, the ground state exhibits a stripe-like antiferromagnetic ordering and opens a sizable band gap if the short-ranged Coulomb interaction of Fe-3d electrons is moderately strong, manifesting a possible Mott insulating state. While increasing Fe-vacancies from the $x=0$ side, where the band structure is similar to that of a heavily electron-doped FeSe system, the Mott l…
Highly oriented polycrystalline SSMO thin films deposited on single crystal substrates by ultrasonic nebulized spray pyrolysis have been studied. The film on LAO is under compressive strain while LSAT and STO are under tensile strain. The presence of a metamagnetic state akin to cluster glass formed due to coexisting FM and antiferromagnetic/charge order (AFM/CO) clusters. All the films show colossal magnetoresistance but its temperature and magnetic field dependence are drastically different. In the lower temperature region the magnetic field dependent isothermal resistivity also shows signat…
Magnetism in lanthanum cobaltite (LCO, LaCoO$_3$) appears to be strongly dependent on strain, defects, and nanostructuring. LCO on strontium titanate (STO, SrTiO$_3$) is a ferromagnet with an interesting strain relaxation mechanism that yields a lattice modulation. However, the driving force of the ferromagnetism is still controversial. Experiments debate between a vacancy-driven or strain-driven mechanism for the ferromagnetism of epitaxial LCO. We found that a weak lateral modulation of the superstructure is sufficient to promote ferromagnetism. We find that ferromagnetism appears under unia…
Point defects in body-centred cubic Fe, Cr and concentrated random magnetic Fe-Cr are investigated using density functional theory and theory of elasticity. The volume of a substitutional Cr atom in ferromagnetic bcc Fe is approximately 18\% larger than the volume of a host Fe atom, whereas the volume of a substitutional Fe atom in antiferromagnetic bcc Cr is 5\% smaller than the volume of a host Cr atom. Elastic dipole $\boldsymbol{P}$ and relaxation volume $\boldsymbolΩ$ tensors of vacancies and self-interstitial atom (SIA) defects exhibit large fluctuations, with vacancies having negative a…
The role of Cr incorporation into the ZnO were probed through investigations into the structural, optical and magnetic properties. Zn1-xCrxO with x = 0, 0.01, 0.03 and 0.05, nanoparticles were prepared by solution combustion method. Powder x-ray diffraction (XRD) results reveal, all the synthesized samples are in single hexagonal wurtzite crystal structures, indicating that Cr3+ ions substitute the Zn2+ ions without altering the structure. The crystallite size and microstrain were calculated using the Willamson-Hall method and found to be 36 +- 2 nm for ZnO and it reduced with the increase of …
The effect of different surface defects on the atomic and electronic structures of cubic $β$-SiC(110) surface are studied by means of a first principles calculation based on Density Functional Theory using the SIESTA code. In the calculations, the possibility of different spin population at each atom is allowed. We find that while adsorption of oxygen or nitrogen and adsorption of hydrogen at the C surface carbon atoms do not induce magnetic moments on SiC(110); Si vacancies, substitutional C at the Si site and H or F adsorbed at the silicon surface sites induce localized magnetic moments as l…
The structural, magnetic, vibrational and electronic properties of single layer aluminum oxide (AlO2) are investigated by performing state-of-the-art first-principles calculations. Total energy optimization and phonon calculations reveal that aluminum oxide forms a distorted octahedral structure (1T'-AlO2) in its single layer limit. It is also shown that surfaces of 1T'-AlO2 display magnetic behavior originating from the O atoms. While the ferromagnetic (FM) state is the most favorable magnetic order for 1T'-AlO2, transformation to a dynamically stable antiferromagnetic (AFM) state upon a slig…
Institute of Solid State and Semiconductor Physics（固体态与半导体物理研究所）；CNRS, Université de Bordeaux, Bordeaux INP, ICMB UMR 5026（法国国家科学研究中心，波尔多大学，波尔多理工学院，ICMB UMR 5026）；Institut Laue-Langevin（朗之万研究所）；Joint Institute for Nuclear Research（联合核研究所）；Kant Baltic Federal University（康特波罗的海联邦大学）；Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；State Key Laboratory of Solidification Processing（凝固技术国家重点实验室）
