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We analyze the coexisting ordered phases that arise in the half-filled ε -t-U-V extended Hubbard Model on the square lattice when tackled within the Kotliar and Ruckenstein slave boson representation in the thermodynamical limit. Particular emphasis is put on the dependence of the quasi-particle dispersions, the gaps, the spin-resolved renormalization factors, and the distribution of double occupancy on the microscopical parameters of the model. Our calculations are performed in a parameter range that is most suitable for resistive switching. In particular, the main contributions to the gaps are shown to either arise from ε in the weak coupling regime, or from U and V when they are the largest scales. The gaps are thus from joint spin and charge origin, and so are the order parameters. [ABSTRACT FROM AUTHOR]

The study is devoted to the theoretical analysis of noncollinear magnetic structures of charge-ordered manganites with a doping level of x = 3/4, 4/5. The reasons for canted and perpendicular magnetic structures to form as a result of the competition between the orbitally dependent exchange interactions in different crystallographic directions and the influence of single-ion anisotropy are considered. The mechanism of formation of predominantly noncollinear magnetic structures is shown. Trimer stripe magnetic structures with ordering along pseudo-perovskite axes xp, yp, zp = b are predicted. The presence of magnetic structure components aligned with the b axis is assumed and methods for checking the presence of such components based on field dependencies of magnetization and antiferromagnetic resonance frequencies are proposed. [ABSTRACT FROM AUTHOR]

A great number of chemical and mechanical phenomena, ranging from catalysis to friction, are dictated by the atomic-scale structure and properties of material surfaces. Yet, the principal tools utilized to characterize surfaces at the atomic level rely on strict environmental conditions such as ultrahigh vacuum and low temperature. Results obtained under such well-controlled, pristine conditions bear little relevance to the great majority of processes and applications that often occur under ambient conditions. Here, we report true atomic-resolution surface imaging via conductive atomic force microscopy (C-AFM) under ambient conditions, performed at high scanning speeds. Our approach delivers atomic-resolution maps on a variety of material surfaces that comprise defects including single atomic vacancies. We hypothesize that atomic resolution can be enabled by either a confined, electrically conductive pathway or an individual, atomically sharp asperity at the tip-sample contact. Using our method, we report the capability of in situ charge state manipulation of defects on MoS2 and the observation of an exotic electronic effect: room-temperature charge ordering in a thin transition metal carbide (TMC) crystal (i.e., an MXene), α-Mo2C. Our findings demonstrate that C-AFM can be utilized as a powerful tool for atomic-resolution imaging and manipulation of surface structure and electronics under ambient conditions, with wide-ranging applicability.

In this research, we have tried to investigate the effect of the cationic disorder on charge ordering and magnetic phase separation in La 0.5-x Eu x Ca 0.5-y Ba y MnO 3 (x = 0, 0.05, and 0.1) compounds synthesized by using the sol-gel method. All the samples possess the same average ionic radius at A site and the same Mn3+/Mn4+ ratio. Our analysis confirmed the chemical composition by energy dispersive X-ray spectroscopy and verified the structural integrity and purity of the phase by X-ray diffraction, revealing an orthorhombic structure with Pnma space group, which is in agreement with the tolerance factor. The important mismatch effect observed in the substituted specimens induces drastic effects on the structural and microstructural properties. Magnetic measurements indicate a great reduction of Curie temperature for substituted samples (from 250 K for x = 0 to 90 K for x = 0.05 and 85 K for x = 0.1), which indicates a weakening of ferromagnetic double exchange interactions induced by cationic disorder. The Arrott plots and the magnetocaloric study of the Eu−based samples indicate the persistence of the antiferromagnetic charge-ordered state characterizing the pristine compound (x = 0) as well as the presence of a first-ordered metamagnetic transition for all the studied samples, which is ascribed to the presence of antiferromagnetic domains. Such transition induced the appearance of a shoulder peak near 100 K in the magnetic entropy change curves for high magnetic field values, resulting in an extra cooling efficiency. [ABSTRACT FROM AUTHOR]

To address the issues of superconducting and charge properties in hydrated sodium cobalt, we investigate an extended ionic Hubbard model on the triangular lattice, which includes off-site attractions between sites with minor charges. Our quantum Monte Carlo simulations show that close to quarter filling, the off-site attractions induce a significant enhancement of d-wave and extended s-wave pairing correlations. Simultaneously, they render an increase of the charge structure factor at most of wave vectors. A combination with charge correlations in real space indicates the development of short-range finite-q charge density waves on the sites with minor charges. Our findings provide a new perspective on the superconducting mechanism in hydrated sodium cobalt based on the electronic structure which explicitly takes the effect of sodium atoms into account.

Metal-to-insulator transitions (MITs), which are achieved in 3d-band correlated transitional metal oxides, trigger abrupt variations in electrical, optical, and/or magnetic properties beyond those of conventional semiconductors. Among such material families, iron (Fe: 3d64s2)-containing oxides pique interest owing to their widely tunable MIT properties, which are associated with the various valence states of Fe. Their potential electronic applications also show promise, given the large abundance of Fe on Earth. Representative MIT properties triggered by critical temperature (TMIT) were reported for ReFe2O4 (Fe2.5+), ReBaFe2O5 (Fe2.5+), Fe3O4 (Fe2.67+), Re1/3Sr2/3FeO3 (Fe3.67+), ReCu3Fe4O12 (Fe3.75+), and Ca1−xSrxFeO3 (Fe4+) (where Re represents rare-earth elements). The common feature of MITs of these Fe-containing oxides is that they are usually accompanied by charge ordering transitions or disproportionation associated with the valence states of Fe. Herein, we review the material family of Fe-containing MIT oxides, their MIT functionalities, and their respective mechanisms. From the perspective of potentially correlated electronic applications, the tunability of the TMIT and its resultant resistive change in Fe-containing oxides are summarized and further compared with those of other materials exhibiting MIT functionality. In particular, we highlight the abrupt MIT and wide tunability of TMIT of Fe-containing quadruple perovskites, such as ReCu3Fe4O12. However, their effective material synthesis still needs to be further explored to cater to potential applications. [ABSTRACT FROM AUTHOR]

The mixed-valent spinel LiV2O4 is known as the first oxide heavy-fermion system. There is a general consensus that a subtle interplay of charge, spin, and orbital degrees of freedom of correlated electrons plays a crucial role in the enhancement of quasi-particle mass, but the specific mechanism has remained yet elusive. A charge-ordering (CO) instability of V3+ and V4+ ions that is geometrically frustrated by the V pyrochlore sublattice from forming a long-range CO down to T = 0 K has been proposed as a prime candidate for the mechanism. Here, we uncover the hidden CO instability by applying epitaxial strain on single-crystalline LiV2O4 thin films. We find a crystallization of heavy fermions in a LiV2O4 film on MgO, where a charge-ordered insulator comprising of a stack of V3+ and V4+ layers along [001], the historical Verwey-type ordering, is stabilized by the in-plane tensile and out-of-plane compressive strains from the substrate. Our discovery of the [001] Verwey-type CO, together with previous realizations of a distinct [111] CO, evidence the close proximity of the heavy-fermion state to degenerate CO states mirroring the geometrical frustration of the V pyrochlore lattice, which supports the CO instability scenario for the mechanism behind the heavy-fermion formation. [ABSTRACT FROM AUTHOR]

Charge-order-driven ferroelectrics are an emerging class of functional materials, distinct from conventional ferroelectrics, where electron-dominated switching can occur at high frequency. Despite their promise, only a few systems exhibiting this behavior have been experimentally realized thus far, motivating the need for new materials. Here, we use density-functional theory to study the effect of artificial structuring on mixed-valence solid-solution La1/3Sr2/3FeO3 (LSFO), a system well studied experimentally. Our calculations show that A-site cation (111)-layered LSFO exhibits a ferroelectric charge-ordered phase in which inversion symmetry is broken by changing the registry of the charge order with respect to the superlattice layering. The phase is energetically degenerate with a ground-state centrosymmetric phase, and the computed switching polarization is 39 μC/[Formula: see text], a significant value arising from electron transfer between [Formula: see text] octahedra. Our calculations reveal that artificial structuring of LSFO and other mixed valence oxides with robust charge ordering in the solid solution phase can lead to charge-order-induced ferroelectricity.

Magnetization relaxation, ac susceptibility, dc magnetization and magnetoelectrical transport measurements have been carried out on Al3+-doped manganites La 0.5 Ca 0.5 Mn 1- x Al x O 3- δ (x = 0.05, 0.07, 0.09, 0.10, 0.15). Experimental results suggest that nonmagnetic Al3+ substituting Mn suppresses the ferromagnetic phase and induces a charge ordered antiferromagnetic phase. The coexistence and competition of these two kinds of interactions result in a spin-glass like state in x = 0.1 and 0.15 system. Obvious hysteresis was observed in both magnetization and resistivity versus temperature and magnetic field curves, suggesting an inhomogeneous metastable phase transition. Upon applying a magnetic field of H C A-F, the Al3+-doped samples undergo an irreversible metamagnetic transition from the charge ordering antiferromagnetic insulating to ferromagnetic metallic phase in the low temperature region. Phase diagram in the H C - T plane has been determined according to the magnetization and magnetoelectric transport measurements. The magnetic disorders and antiferromagnetic matrix produced by Al3+ dopants and spontaneous oxygen vacancies play an important role in the pinning of the FM phase. [ABSTRACT FROM AUTHOR]

Consequences of the variation of the particle size and external magnetic field on the magnetic and transport characteristics have been investigated in the perovskite manganite of composition Nd0.50Ca0.50MnO3. The size of the crystallites (particles) enhances from ~ 17 nm (144 nm) to ~ 25 nm (600 nm) as TS enhances from 900 to 1300 ℃, with a simultaneous increase in the orthorhombic lattice parameters. The ZFC–FC magnetization-temperature (M-T) data recorded at H = 500 Oe show the coexistence of ferromagnetic (FM) and antiferromagnetic charge–ordered (AFM-CO) phases, and the accompanying ZFC–FC divergence gives signature of a cluster glass-like phase in the lower temperature regime. The FM region close to the Curie temperature (TC) exhibits scaling of the type M = M O (T C - T) β . The value of exponent β is found to be ~ 0.491 and 0.548 at 144 nm and 600 nm particle size, respectively. The value of β is found to increase as the M-T measurement field increases; e.g., for 600 nm particle size, its value increases from 0.5484 to 0.7551. In the absence of a magnetic field, all the samples remain insulators. A zero-field insulator–metal transition (IMT) is conspicuously absent. The application of a magnetic field induces IMT in all the samples, and it occurs at H = 60 kOe for 900 ℃, 40 kOe for 1100 ℃, and 20 kOe for 1300 ℃ sintered samples. Such behavior brings out the softening of the AFM-CO phase with an increase in particle size. [ABSTRACT FROM AUTHOR]

Consequences of the variation of the particle size and external magnetic field on the magnetic and transport characteristics have been investigated in the perovskite manganite of composition Nd0.50Ca0.50MnO3. The size of the crystallites (particles) enhances from ~ 17 nm (144 nm) to ~ 25 nm (600 nm) as TS enhances from 900 to 1300 ℃, with a simultaneous increase in the orthorhombic lattice parameters. The ZFC–FC magnetization-temperature (M-T) data recorded at H = 500 Oe show the coexistence of ferromagnetic (FM) and antiferromagnetic charge–ordered (AFM-CO) phases, and the accompanying ZFC–FC divergence gives signature of a cluster glass-like phase in the lower temperature regime. The FM region close to the Curie temperature (TC) exhibits scaling of the type M = M O (T C - T) β . The value of exponent β is found to be ~ 0.491 and 0.548 at 144 nm and 600 nm particle size, respectively. The value of β is found to increase as the M-T measurement field increases; e.g., for 600 nm particle size, its value increases from 0.5484 to 0.7551. In the absence of a magnetic field, all the samples remain insulators. A zero-field insulator–metal transition (IMT) is conspicuously absent. The application of a magnetic field induces IMT in all the samples, and it occurs at H = 60 kOe for 900 ℃, 40 kOe for 1100 ℃, and 20 kOe for 1300 ℃ sintered samples. Such behavior brings out the softening of the AFM-CO phase with an increase in particle size. [ABSTRACT FROM AUTHOR]

Quantum materials are amenable to nonequilibrium manipulation with light, enabling modification and control of macroscopic properties. Light-based augmentation of superconductivity is particularly intriguing. Copper-oxide superconductors exhibit complex interplay between spin order, charge order, and superconductivity, offering the prospect of enhanced coherence by altering the balance between competing orders. We utilize terahertz time-domain spectroscopy to monitor the c-axis Josephson plasma resonance (JPR) in La2-xBaxCuO4 (x = 0.115) as a direct probe of superconductivity dynamics following excitation with near-infrared pulses. Starting from the superconducting state, c-axis polarized excitation with a fluence of 100 μJ/cm2 results in an increase of the far-infrared spectral weight by more than an order of magnitude as evidenced by a blueshift of the JPR, interpreted as resulting from nonthermal collapse of the charge order. The photoinduced signal persists well beyond our measurement window of 300 ps and exhibits signatures of spatial inhomogeneity. The electrodynamic response of this metastable state is consistent with enhanced superconducting fluctuations. Our results reveal that La2-xBaxCuO4 is highly sensitive to nonequilibrium excitation over a wide fluence range, providing an unambiguous example of photoinduced modification of order-parameter competition.

Present communication reports the possible origin of the colossal magnetodielectric (MD) effect observed at room temperature in La 0.4 Re 0.1 Ca 0.5 MnO 3 (with Re = Eu, Gd, and Dy) polycrystalline manganites. This study reveals that all the samples are half–doped (% Mn3+ = % Mn4+ = 50 %) and room temperature X-ray absorption measurement at Mn L-edges confirms the presence of both Mn3+ and Mn4+ ions in these oxides. All these specimens are paramagnetic at room temperature with the presence of metastable charge–ordered domains. The application of a low constant magnetic field of 0.6 T and 1.2 T collapses some of the charge-ordered domains that lead to the charge delocalization and colossal values of the MD effect. The Dy–based sample exhibits the strongest charge ordering state, ascribed to the important cationic mismatch effect. [Display omitted] • La 0.4 Re 0.1 Ca 0.5 MnO 3 (Re = Eu, Gd, and Dy) manganites possess colossal magnetodielectric effect at room temperature. • The magnetodielectric effect can be linked to the presence of charge ordering. • Cationic mismatch plays a key role in the physical properties of the studied samples. [ABSTRACT FROM AUTHOR]

The multifunctionality concept is the trend in recent materials science research due to the need for the reduction of functional device size. Perovskite manganites characterized by magnetic phase separation phenomenon are potential candidates for multifunctional devices. The unconventional control of the physical properties of such systems by several parameters (magnetic and electric field, temperature, light) gives limitless possibilities of new technological devices with multifunctional applications and helps to achieve energy efficiency. The fractions of the coexisting magnetic phases need to be well calibrated in order to guarantee a good performance. [ABSTRACT FROM AUTHOR]

This study of nonmagnetic Zn-substitution effect on the charge-ordered behavior of Pr 0.5 Ca 0.5 Mn 1- x Zn x O 3 (x = 0.0, 0.1) compounds reveal the weakening of strong charge-ordered antiferromagnetic state of the parent compound (x = 0.0). Magnetocaloric effect (MCE) has been calculated using a Python package from isothermal M-H data for these samples. A prominent ferromagnetic contribution in the antiferromagnetic matrix for Mn-site doping is observed, which removes the inverse MCE observed in the pristine sample below the charge ordering temperature T CO. Development of ferromagnetism in the doped system exhibits a metal-insulator transition at T MI = 90 K under 7 T magnetic field and large magnetoresistance (> 99 %), which is not observed in parent compound. Magnetic field-dependent hysteresis at low temperature reveals the ferromagnetic metastability and first-order nature of magnetic phase transition. Random occupation of Zn at the Mn-site of the parent compound disrupts 1:1 Mn3+/Mn4+ charge-ordered superstructure of the parent compound which weakens the charge-ordered antiferromagnetic strength promoting ferromagnetism and double-exchange interaction through an enhanced 2 p -3 d hybridization between Mn and O ions. [Display omitted] • Substitution of Zn in Pr0.5Ca0.5Mn1-xZnxO3 compounds affects their charge-ordered behavior. • Strong charge-ordered antiferromagnetic state in the parent compound weakens with Zn substitution. • MCE was calculated using a Python package from isothermal M-H data. • Mn-site doping removes the inverse MCE observed in the parent sample below the charge ordering temperature. • Metal-insulator transition at TMI = 90 K under a 7 T magnetic field and large magnetoresistance (> 99 %) is observed. [ABSTRACT FROM AUTHOR]

SEM micrographs of the synthesized compounds and the probability distribution (%) as a function of average particles size (nm) calculated via ImageJ software. [Display omitted] • Sm 0.5 Ca 0.5 MnO 3 manganite doped with Na and K ions were prepared by the Pechini method. • At room–temperature, all the prepared samples crystallized in orthorhombic symmetry. • Hysteresis loops of all samples measured at 5 K show exchange bias effect. • Undoped and Na − doped samples show both normal and inverse magnetocaloric effect. • K − doped sample presents |ΔS M | = 1.1 J.kg−1.K−1 and RCP = 55.75 J.kg−1 at μ 0 ΔH = 5 T. Undoped Sm 0.5 Ca 0.5 MnO 3 and doped Sm 0.5 Ca 0.4 A 0.1 MnO 3 (A = Na and K) compounds were prepared via the sol–gel chemistry route and the composition was verified using X–ray and EDAX measurements. Results from X–ray powder diffraction reveal an orthorhombic structure with Pnma space group. Particle size calculated using the SEM images confirmed a successful synthesis of nanomaterials in the range of 76 and 136 nm. The temperature dependence magnetization curve of the Sm 0.5 Ca 0.5 MnO 3 compound shows three distinct points at 45 K, 65 K and 270 K corresponding to the nonhomogeneous magnetic clusters, weak ferromagnetic and charged ordered antiferromagnetic transitions, respectively. The experimental results confirm that Na substituted sample undergoes a charge ordering transition, while K substitution suppresses the charge ordering phase and leads to Griffiths phase formation. In addition, zero–field–cooled and field–cooled magnetization curves bifurcate and the complex coexistence of magnetic phases at the lower temperature is supposed. Such phase coexistence at low temperature may be responsible for the exchange bias effect. Our study also highlights the efficacy of magnetocaloric effect as a tool to discern between the different magnetic states. Undoped and Na − doped samples show both normal and inverse magnetocaloric effect which is interesting for magnetic refrigeration applications. The maximum value of magnetic entropy change was found to be − ΔS M = 1.1 J.kg−1.K−1 for K − doped sample upon an applied magnetic field change of 5 T. Meanwhile, this sample exhibits a net relative cooling power of 55.75 J.kg−1 at μ 0 ΔH = 5 T. [ABSTRACT FROM AUTHOR]

To address the issues of superconducting and charge properties in hydrated sodium cobalt, we investigate an extended ionic Hubbard model on the triangular lattice, which includes off-site attractions between sites with minor charges. Our quantum Monte Carlo simulations show that close to quarter filling, the off-site attractions induce a significant enhancement of d -wave and extended s -wave pairing correlations. Simultaneously, they render an increase of the charge structure factor at most of wave vectors. A combination with charge correlations in real space indicates the development of short-range finite- q charge density waves on the sites with minor charges. Our findings provide a new perspective on the superconducting mechanism in hydrated sodium cobalt based on the electronic structure which explicitly takes the effect of sodium atoms into account. • The hydrated sodium cobalt is studied based on an extended ionic Hubbard model. • Unconventional superconductivity is enhanced by the off-site attractions. • Short-range charge density wave is induced by the off-site attractions. [ABSTRACT FROM AUTHOR]

In insulating compounds R1-xAxMnO3, the role of orbital ordering in magnetic competition is emphasized. The conditions of ordered state's destruction are estimated. The ranges of orbital structure mixing angles to form frustrated or low-dimensional magnetic structures are determined. The influence of nonlinear and nonlocal terms of vibronic interaction on orbital ordering and magnetic structure are discussed. The possible magnetic structures are described. [ABSTRACT FROM AUTHOR]

Hole-doped cuprates exhibit partially coexisting pseudogap (PG), charge ordering (CO) and superconductivity; we show that there exists a class of systems in which they have a single nature as it has recently been supposed. Since the charge-ordered phase exhibits large frozen deformation of the lattice, we develop a method for calculating the phase diagram of a system with strong long-range (Fröhlich) electron-phonon interaction. Using a variational approach, we calculate the free energy of a two-liquid system of carriers with cuprate-like dispersion comprising a liquid of autolocalized carriers (large polarons and bipolarons) and Fermi liquid of delocalized carriers. Comparing it with the free energy of pure Fermi liquid and calculating (with standard methods of Bose liquid theory) a temperature of the superfluid transition in the large-bipolaron liquid we identify regions in the phase diagram with the presence of PG (caused by the impact of the (bi)polarons potential on delocalized quasiparticles), CO and superconductivity. They are located in the same places in the diagram as in hole-doped cuprates, and, as in the latter, the shape of the calculated phase diagram is resistant to wide-range changes in the characteristics of the system. As in cuprates, the calculated temperature of the superconducting transition increases with the number of conducting planes in the unit cell, the superfluid density decreases with doping at overdoping, the bipolaron density (and bipolaronic plasmon energy) saturates at optimal doping. Thus, the similarity of the considered system with hole-doped cuprates is not limited to the phase diagram. The results obtained allow us to discuss ways of increasing the temperature of the superfluid transition in the large-bipolaron liquid and open up the possibility of studying the current-carrying state and properties of the bipolaron condensate., (© 2024 IOP Publishing Ltd.)

Magnetotransport properties of La0.5−xHoxCa0.5MnO3 (x = 0.05 and 0.1) polycrystalline samples were investigated in order to study the effect of magnetic Ho3+ ions on the stability of the charge ordering (CO) and magnetic phase coexistence in pristine La0.5Ca0.5MnO3. Our samples were synthesized by using solgel method. Temperature dependence of resistivity shows an insulating behavior with high resistivity values, confirming the presence of long-range CO. The application of 7 T magnetic field slightly reduces resistivity values and demonstrates relatively small magnetoresistance (MR) values (−MR(T) did not exceed 14% under 7 T applied field). This observation indicates that the CO in the Ho-based specimens is strong, which indicates that Ho substitution for La in La0.5Ca0.5MnO3 gives more strength to the CO. [ABSTRACT FROM AUTHOR]

The simple model that can describe structure and charge ordering in complex doped organic crystals is proposed. We consider the quasione-dimensional model of a crystal with chains (stacks) of flat BEDT-TTF molecules. In a chain of large molecules, small molecules fill every space between large molecules. The interaction between all molecules is described by the Lennard-Jones potential. It is shown that the small dopant molecules are in the double-well potential. It is shown that in case of the electrically neutral molecules at low temperatures, there is a fluctuating structural ordering: the small molecules group in pairs near a large molecule, and the lattice period in the fluctuation domain doubles. The structure of the boundary between the fluctuation domains is defined. In case of the charged molecules, correction to electric dipole interaction makes the system essentially three-dimensional, and there is ferroelectric ordering in a chain and an antiferroelectric one between the chains. Structure of the charge domains and domain boundaries are described. [ABSTRACT FROM AUTHOR]

The interplay of the inter-site Coulomb repulsion which induces charge ordering, and the correlated hopping of electrons, which causes peculiar dependence of energy characteristics on a doping, is studied in a model of BEDT-TTF organic conductor electronic subsystem. By applying the projection method in the Green function equation of motion approach the single-particle energy spectrum, sublattice magnetization in charge-ordered phase, and the transition temperature have been calculated. Dependence of Verwey temperature on the band filling shows that inter-site Coulomb correlation significantly influences the width of the concentration interval in which a charge order stabilizes. The correlated hopping causes the decrease of the critical value of electron concentration and increase of Verwey temperature in whole concentration interval of charge ordering stability. [ABSTRACT FROM AUTHOR]

In this work, we were interested in the Ca2−xNdxMnO4 compounds when (0.1 ≤ x ≤ 0.4). These oxides are synthesized through the solid-state method. In this study, we investigated the evolution of the structure, the magnetic properties and the Mn3+/Mn4+ ratio with the Nd content. The morphological study shows a decrease in the size of the grain in relation to x. The X-ray diffraction reveals a transition from the tetragonal phase to the orthorhombic phase when x = 0.4. Magnetic measurements have been taken for all the compounds in the temperature range between 2 and 300 K. The temperature-dependent magnetic susceptibility shows the presence of three transitions TN, TC and TCO. A dramatic difference in magnetic susceptibility between ZFC and FC was observed below the Neel temperatures for Ca2-xNdxMnO4, which shows the onset of a ferromagnetic moment below these temperatures. This moment is caused by the Dzyaloshinskii–Moriya interaction. [ABSTRACT FROM AUTHOR]

Evolution of the competing multiphase magnetic and charge orders in terms of the variance σ2 in the A-site cationic mismatch and Pr content (x) and their consequences on the magnetotransport in La0.60-xPrxCa0.40MnO3 (x = 0.30, 0.35, 0.40, 0.45) are reported. The coexistence of vivid electronic orders like ferromagnetism, antiferromagnetism, and charge order is confirmed by the hysteresis is seen in the field cooled cooling (FCC) and field cooled warming (FCW) magnetizations measured at H = 500 Oe. A sharp drop in Zero field cooled (ZFC) magnetization at T < 40 K and thermally reversibility of FCC and FCW magnetizations in the same temperature range confirms the occurrence of the glass-like state. The magnetic field induced insulator–metal transitions (IMT) are seen at all compositions. The robustness of the insulator state increases with an increase in the Pr content, which enhances the antiferromagnetic/charger order fractions. This is demonstrated by the thermally hysteretic insulator–metal transition appears at H = 20 kOe and 60 kOe at Pr concentrations of 0.30 and 0.45. At x ≥ 0.30, the IMT temperature gradually increases while the thermal hysteresis decreases as the field is increased. The thermal hysteresis almost disappears at x = 0.45. The localization length corresponding to the small polaron transport is larger in the PM regime than in AFM, and in the former, it increases with the disorder, and in the latter increases with increasing disorder. This is attributed to the ordered–disordered nature of the AFM and PM. [ABSTRACT FROM AUTHOR]

Observations of superconductivity and charge density waves (CDW) in graphene have been elusive thus far due to weak electron-phonon coupling (EPC) interactions. Here, we report a unique observation of anomalous transport and multiple charge ordering phases at high temperatures (T1∼213K,T2∼325K) in a 0D-2D van der Waals (vdW) heterostructure comprising of single layer graphene (SLG) and functionalized (amine) graphene quantum dots (GQD). The presence of functionalized GQD contributed to charge transfer with shifting of the Dirac point ∼ 0.05 eV above the Fermi level ( ab initio    simulations) and carrier densityn∼-0.3×1012 cm-2confirming p-doping in SLG and two-fold increase in EPC interaction was achieved. Moreover, we elucidate the interplay between electron-electron and electron-phonon interactions to substantiate high temperature EPC driven charge ordering in the heterostructure through analyses of magnetotransport and weak anti-localization (WAL) framework. Our results provide impetus to investigate strongly correlated phenomena such as CDW and superconducting phase transitions in novel graphene based heterostructures., (Creative Commons Attribution license.)

We investigated the structural and magnetic properties of 20 nm-sized nanoparticles of the half-doped manganite Ho0.5Ca0.5MnO3 prepared by sol-gel approach. Neutron powder diffraction patterns show Pbnm orthorhombic symmetry for 10 K < T < 290 K, with lattice parameters a, b, and c in the relationship c/√2 < a < b, indicating a cooperative Jahn–Teller effect, i.e., orbital ordering OO, from below room temperature. In contrast with the bulk samples, in the interval 250 < T < 300 K, the fingerprint of charge ordering (CO) does not manifest itself in the temperature dependence of lattice parameters. However, there are signs of CO in the temperature dependence of magnetization. Accordingly, below 100 K superlattice magnetic Bragg reflections arise, which are consistent with an antiferromagnetic phase strictly related to the bulk Mn ordering of a charge exchange-type (CE-type), but characterized by an increased fraction of ferromagnetic couplings between manganese species themselves. Our results show that in this narrow band half-doped manganite, size reduction only modifies the balance between the Anderson superexchange and Zener double exchange interactions, without destabilizing an overall very robust antiferromagnetic state.

The effect of an external constant magnetic field on the dielectric properties and magnetodielectric (MD) coupling in La0.4Eu0.1Ca0.5MnO3 polycrystalline manganite at room temperature (RT) has been investigated. This sample exhibits negative colossal MD values under low applied magnetic fields (− 30% and − 45% under applied fields of 0.6 T and 1.2 T, respectively). The colossal MD values as well as the relatively low dielectric loss values suggest that the La0.4Eu0.1Ca0.5MnO3 sample can be a suitable␣candidate for technological applications at RT, like magnetic field sensing and gyrators. [ABSTRACT FROM AUTHOR]

The temperature dependences of the resistivity ρ(T) of ceramic La 1 − x Sr x Mn 1 − y Fe y O 3 samples at x = 0.5, and y = 0, 0.02 and 0.10 are investigated in the temperature range of 5-300 K in magnetic field B up to 1 T. It was found that dependences ρ(T) with x = 0.5; y = 0.02, and 0.10 obey the Shklovskii–Efros-like variable-range hopping conductivity law ρ (T) = ρ 0 (T) exp [ (T 0 / T) 1 / 2 ]. This behavior is governed by generation of a soft Coulomb gap Δ ≈ 0.3 eV in the density of localized states, as well as a rigid gap δ v ≈ 0.20 and 0.17 eV at y = 0.02 and y = 0.10, respectively. The obtained values of the rigid gap at y = 0.02 indicate the presence of charge ordering. It was shown that a decrease in the width of the rigid gap when y is increased, is accompanied by both a growing disorder attributed to the presence of Fe and a decrease in lattice distortions caused by charge ordering at y = 0.02. It is shown that the pre-exponential factor of resistivity follows the law ρ 0 (T) ∝ T m , where m changes from 9/2 at y = 0.02 to 5/2 at y = 0.10. This confirms that doping with Fe enhances microscopic disorder by introducing an additional fluctuating short-range potential. The calculated values of the carrier localization radius α ≈ 5.1 and 2.7 Å at y = 0.02 and y = 0.10, respectively, satisfy the condition for the formation of small polarons. [ABSTRACT FROM AUTHOR]

We have studied the contribution induced by a low magnetic field (0.6T and 1.2T) on the frequency dependent permittivity, impedance and conductivity recorded at room temperature for La 0.4 Gd 0.1 Ca 0.5 MnO 3 polycrystalline compound. Strong magnetodielectric (MD) coupling has been detected at room temperature. Colossal value of negative MD (more than 50%) has been observed under 1.2T field. The MD response is found to be stable in the studied frequency range (up to 2 MHz) suggesting the possibility of using this compound for technological applications at room temperature. The significant MD coupling has been correlated with the presence of charge ordering transition near room temperature. [ABSTRACT FROM AUTHOR]

Functional oxides whose physicochemical properties may be reversibly changed at standard conditions are potential candidates for the use in next‐generation nanoelectronic devices. To date, vanadium dioxide (VO2) is the only known simple transition‐metal oxide that demonstrates a near‐room‐temperature metal–insulator transition that may be used in such appliances. In this work, we synthesized and investigated the crystals of a novel mixed‐valent iron oxide with an unconventional Fe5O6 stoichiometry. Near 275 K, Fe5O6 undergoes a Verwey‐type charge‐ordering transition that is concurrent with a dimerization in the iron chains and a following formation of new Fe−Fe chemical bonds. This unique feature highlights Fe5O6 as a promising candidate for the use in innovative applications. We established that the minimal Fe−Fe distance in the octahedral chains is a key parameter that determines the type and temperature of charge ordering. This model provides new insights into charge‐ordering phenomena in transition‐metal oxides in general. [ABSTRACT FROM AUTHOR]

Functional oxides whose physicochemical properties may be reversibly changed at standard conditions are potential candidates for the use in next‐generation nanoelectronic devices. To date, vanadium dioxide (VO2) is the only known simple transition‐metal oxide that demonstrates a near‐room‐temperature metal–insulator transition that may be used in such appliances. In this work, we synthesized and investigated the crystals of a novel mixed‐valent iron oxide with an unconventional Fe5O6 stoichiometry. Near 275 K, Fe5O6 undergoes a Verwey‐type charge‐ordering transition that is concurrent with a dimerization in the iron chains and a following formation of new Fe−Fe chemical bonds. This unique feature highlights Fe5O6 as a promising candidate for the use in innovative applications. We established that the minimal Fe−Fe distance in the octahedral chains is a key parameter that determines the type and temperature of charge ordering. This model provides new insights into charge‐ordering phenomena in transition‐metal oxides in general. [ABSTRACT FROM AUTHOR]

Tetrahedrite, Cu12Sb4S13, is an abundant mineral with excellent thermoelectric properties owing to its low thermal conductivity. The electronic and structural origin of the intriguing physical properties of tetrahedrite, including its metal‐to‐semiconductor transition (MST), remains largely unknown. This work presents the first determination of the low‐temperature structure of tetrahedrite that accounts for its unique properties. Contrary to prior conjectures, the results show that the trigonal–planar copper cations remain in planar coordination below the MST. The atomic displacement parameters of the trigonal–planar copper cations, which have been linked to low thermal conductivity, increase by 200% above the MST. The phase transition is a consequence of the orbital degeneracy of the highest occupied 3d cluster orbitals of the copper clusters found in the cubic phase. This study reveals that a Jahn–Teller electronic instability leads to the formation of "molecular‐like" Cu57+ clusters and suppresses copper rattling vibrations due to the strengthening of direct copper–copper interactions. First principles calculations demonstrate that the structural phase transition opens a small band gap in the electronic density of states and eliminates the unstable phonon modes. These results provide insights on the interplay between phonon transport, electronic properties, and crystal structure in mixed‐valence compounds. [ABSTRACT FROM AUTHOR]

Isomorphic symmetry reductions are a special class of klassengleiche symmetry reductions where the subgroup has the same space group type. The present contribution highlights five different isomorphic transitions of index 5 (i5), all from I 4/m to I 4/m. These superstructure formations allow (i) atom ordering in MoNi4, (ii) vacancy ordering in Nb4N5, KxFe2−ySe2 and Nd10Au3As8O10 and (iii) charge ordering in CsInCl3 (≡Cs2InIInIIICl6). The group-subgroup schemes in the Bärnighausen formalism are discussed along with the crystal chemical consequences. [ABSTRACT FROM AUTHOR]

In this work, we report the attractive magnetic properties of La1-xCaxMnO3 manganites with x = 0.2 (LCMO-2) and x = 0.5 (LCMO-5). X-ray diffraction (XRD) measurements show that the prepared samples are single phase and they crystallize in the orthorhombic structure with Pnma space group. Scanning electron microscope (SEM) measurements reveal that the particles of samples are homogeneous and possess the diameter of several microns. Magnetization versus temperature measurements show paramagnetic (PM) to ferromagnetic (FM) transition at TC ≈ 200 K for LCMO-2 and at TC ≈ 250 K for LCMO-5. Below TC, FM nature is observed in LCMO-2. However, LCMO-5 displays the complex magnetic phase transition. Below TC, LCMO-5 shows a FM to charge-ordered antiferromagnetic (COAFM) transition at CO temperature TCO and a novel, unexpected FM phase transition at characteristic temperature T* (near 35 K). The FM and COAFM phases coexist in LCMO-5, and the competition of FM and AFM phases lead to the unexpected FM transition at T*. Furthermore, the inverse of susceptibility versus temperature measurements confirm the similar results. Magnetic hysteresis loop measurements suggest the typical FM feature of LCMO-2. However, LCMO-5 exhibits the hysteresis loops with butterfly-type structure at 100 and 150 K, suggesting the presence of COAFM phase. These attractive magnetic properties are explained by the existence of COAFM phase and the competition between FM and COAFM phases. [ABSTRACT FROM AUTHOR]

Charge-order-driven ferroelectrics are an emerging class of functional materials, distinct from conventional ferroelectrics, where electron-dominated switching can occur at high frequency. Despite their promise, only a few systems exhibiting this behavior have been experimentally realized thus far, motivating the need for new materials. Here, we use density-functional theory to study the effect of artificial structuring on mixed-valence solid-solution La1/3Sr2/3FeO3 (LSFO), a system well studied experimentally. Our calculations show that A-site cation (111)-layered LSFO exhibits a ferroelectric charge-ordered phase in which inversion symmetry is broken by changing the registry of the charge order with respect to the superlattice layering. The phase is energetically degenerate with a ground-state centrosymmetric phase, and the computed switching polarization is 39 μC/cm², a significant value arising from electron transfer between FeO6 octahedra. Our calculations reveal that artificial structuring of LSFO and other mixed valence oxides with robust charge ordering in the solid solution phase can lead to charge-order-induced ferroelectricity. [ABSTRACT FROM AUTHOR]

Charge-order-driven ferroelectrics are an emerging class of functional materials, distinct from conventional ferroelectrics, where electron-dominated switching can occur at high frequency. Despite their promise, only a few systems exhibiting this behavior have been experimentally realized thus far, motivating the need for new materials. Here, we use density-functional theory to study the effect of artificial structuring on mixed-valence solid-solution La1/3Sr2/3FeO3 (LSFO), a system well studied experimentally. Our calculations show that A-site cation (111)-layered LSFO exhibits a ferroelectric charge-ordered phase in which inversion symmetry is broken by changing the registry of the charge order with respect to the superlattice layering. The phase is energetically degenerate with a ground-state centrosymmetric phase, and the computed switching polarization is 39 μC/cm², a significant value arising from electron transfer between FeO6 octahedra. Our calculations reveal that artificial structuring of LSFO and other mixed valence oxides with robust charge ordering in the solid solution phase can lead to charge-order-induced ferroelectricity. [ABSTRACT FROM AUTHOR]

• Provides a method to investigate the change in orbital order of strongly correlated solids. • Investigates the change of orbital orders in Fe3O4 across the Verwey transition. • Provides a mechanism for change of sign of AC magnetoresistance across the measurement range. • Gives a detailed relaxation time based analysis to understand the change of orbital orders which are difficult to detect in bulk solids using DC methods. Fe 3 O 4 is a fascinating material due to its charge localization physics, variable range hopping (VRH) and its potential implications in the field of spintronics. In this investigation, we explore the formation and interaction of charge-ordered clusters and change of orbital order in cold-pressed Fe 3 O 4 , employing a comprehensive magnetoimpedance analysis in the low-frequency, low magnetic field domain spanning the Verwey transition. The physical and magnetic inhomogeneities due to particle size distribution and capacitive interparticle contact, are found to induce a substantial dispersion in the impedance response. Exploiting the variation in relaxation time as a function of temperature and magnetic field, we meticulously monitor the reorientation of orbitals and the consolidation of charge-ordered clusters, a consequence of localization phenomena. The shielding and deshielding of charge-ordered clusters are interpreted through AC magnetoresistance, which exhibits a sign inversion from negative to positive, synchronous with the dissolution of the charge order. The AC magnetoresistance showed the interaction of clusters of 'charge -ion order' in the higher and lower frequency regimes. This study reveals the chage of orbital order at around 39 K and 150 K along with the one at 120 K due to change in relaxation time associated with the impedance responce mediated by magbetic inhomogenity. Notably, across the studied frequency range, the charge conduction mechanism remains consistent, as elucidated by a variable range hopping model. Our study demonstrates that Fe 3 O 4 nanoparticles exhibit a complex interplay of charge ordering and magnetic ordering, with implications for understanding the electrical properties of such materials. This research provides insight into the charge conduction processes and its coupling to change of orbital ordering in Fe 3 O 4 , a material of considerable interest for its promising electronic applications. [ABSTRACT FROM AUTHOR]