Showing papers on "Charge ordering published in 2010"
TL;DR: Although their stability range decreases with n, the low-symmetry phases in metallic BaTiO(3-delta) are still retained up to an estimated concentration of n* approximately 1.9 x 10(21) cm(-3).
Abstract: The ferroelectric BaTiO(3) is a band-gap insulator. Itinerant electrons can be introduced in this material by doping, for example, with oxygen vacancies. Above a critical electron concentration of n(c) approximately 1 x 10(20) cm(-3), BaTiO(3-delta) becomes metallic. This immediately raises a question: Does metallic BaTiO(3-delta) still retain ferroelectricity? One may expect itinerant electrons to destroy ferroelectricity as they screen the long-range Coulomb interactions. We followed the phase transitions in BaTiO(3-delta) as a function of n far into metallic phase. Although their stability range decreases with n, the low-symmetry phases in metallic BaTiO(3-delta) are still retained up to an estimated concentration of n* approximately 1.9 x 10(21) cm(-3). Moreover, it appears that the itinerant electrons partially stabilize the ferroelectric phases in metallic BaTiO(3-delta) by screening strong crystal field perturbations caused by oxygen vacancies.
146 citations
TL;DR: The role of finite size effects in ultrathin polar films on a nonpolar substrate leading to another intriguing feature-the thickness-dependent insulator-to-metal transition in thin LaAlO(3) films on an SrTiO( 3)(001) substrate, driven by the impending polar catastrophe.
Abstract: Oxide interfaces have attracted considerable attention in recent years due to the emerging novel behavior which does not exist in the corresponding bulk parent compounds. This opens possibilities for future applications in oxide-based electronics and spintronics devices. Among the different materials combinations, heterostructures containing the two simple band insulators LaAlO3 and SrTiO3 have advanced to a model system exhibiting unanticipated properties ranging from conductivity, to magnetism, even to superconductivity. Electronic structure calculations have contributed significantly towards understanding these phenomena and we review here the progress achieved in the past few years, also showing some future directions and perspectives. A central issue in understanding the novel behavior in these oxide heterostructures is to discover the way (or ways) that these heterostructures deal with the polar discontinuity at the interface. Despite analogies to polar semiconductor interfaces, transition metal oxides offer much richer possibilities to compensate the valence mismatch, including, for example, an electronic reconstruction. Moreover, electronic correlations can lead to additional complex behavior like charge disproportionation and order, magnetism and orbital order. We discuss in some detail the role of finite size effects in ultrathin polar films on a nonpolar substrate leading to another intriguing feature—the thickness-dependent insulator-to-metal transition in thin LaAlO3 films on a SrTiO3(001) substrate, driven by the impending polar catastrophe. The strong and uniform lattice polarization that emerges as a response to the potential build-up enables the system to remain insulating up to a few layers. However, beyond a critical thickness there is a crossover from an ionic relaxation to an electronic reconstruction. At this point two bands of electron and hole character, separated both in real and in reciprocal space, have been shifted sufficiently by the internal field in LaAlO3 to impose the closing of the bandgap. We discuss briefly further parameters that allow one to manipulate this behavior, e.g. via vacancies, adsorbates or an oxide capping layer. (Some figures in this article are in colour only in the electronic version)
118 citations
111 citations
TL;DR: In this paper, a cubic phase and a trigonal phase with charge ordering state were identified at higher and lower temperatures, respectively, and the temperature dependence of the resistance indicates that the phase transition is a first-order transition.
Abstract: Polycrystalline PrCuMn6O12 sample has been successfully synthesized. It has been characterized by x-ray diffraction (XRD), magnetic and magnetotransport measurements at ambient pressure, and transport property measurements under pressures. From the refinements of XRD data, a cubic phase and a trigonal phase with charge ordering state were identified at higher and lower temperatures, respectively. The temperature dependence of the resistance indicates that the phase transition is a first-order transition. Both effective paramagnetic moments of the trigonal and cubic phases can be explained by orbital moment freezing theory. The transport property of the trigonal phase has been fitted with Mott's law for variable range hopping. Though the magnetoresistance value is not large, the pressure-induced resistance value change of PrCuMn6O12 is positive and achieves 264.8%. The cubic phase is suppressed under pressure and transformed to the trigonal phase at 15 kbar, indicating favor of the charge ordering state under pressure. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3294608]
80 citations
TL;DR: In this paper, the authors reviewed electronic ferroelectricity from a view point of frustration, where electronic degrees of freedom and electronic interactions are directly responsible for electric polarization and ferroelect transition.
Abstract: Beyond a conventional classification of ferroelectricity, there is a class of materials where electronic degrees of freedom and electronic interactions are directly responsible for electric polarization and ferroelectric transition. This is termed electronic ferroelectricity. In this article, we review electronic ferroelectricity from a view point of frustration. Experimental and theoretical examinations in spin driven ferroelectric materials, recently termed multiferroics, are introduced. Spin frustration caused by competing magnetic interactions is of prime importance for this type of ferroelectricity. Charge driven ferroelectricity where electronic charge order induces electric polarization is reviewed. In particular, exotic dielectric and magneto-dielectric properties in layered iron oxides are focused on. Through a number of recent experimental and theoretical researches, charge fluctuation due to frustrated geometry plays essential roles on electronic ferroelectricity in this compound.
78 citations
TL;DR: The magnetic and charge properties in the ground state of the Hubbard model are characterized as a function of doping, with antiferromagnetic order and essentially homogeneous charge correlation at intermediate interaction strengths.
Abstract: Determining the properties of the two-dimensional Hubbard model is an outstanding problem in physics. Applying recent advances in constrained path auxiliary-field quantum Monte Carlo techniques and simulating large rectangular supercells, we characterize the magnetic and charge properties in the ground state as a function of doping. At intermediate interaction strengths, an incommensurate spin density wave (SDW) state is found, with antiferromagnetic order and essentially homogeneous charge correlation. The wavelength of the collective mode decreases with doping, as does its magnitude. The SDW order vanishes beyond a critical doping. As the interaction is increased, the holes go from a wavelike (delocalized) to a particlelike (localized) state, and charge ordering develops which eventually evolves into stripelike states.
67 citations
TL;DR: In this paper, a series of single or two-phase samples in the LiFePO4−FePO 4 system with different overall lithium contents, and containing the two end-members and/or two metastable solid solution phases, Li0.6,7Li and 31P NMR experiments were conducted on a series, at different temperatures in order to search for vacancy/charge ordering and ion/electron mobility in the metastable phases.
Abstract: 6,7Li and 31P NMR experiments were conducted on a series of single- or two-phase samples in the LiFePO4−FePO4 system with different overall lithium contents, and containing the two end-members and/or two metastable solid solution phases, Li0.6FePO4 or Li0.34FePO4. These experiments were carried out at different temperatures in order to search for vacancy/charge ordering and ion/electron mobility in the metastable phases. Evidence for Li+−Fe2+ interactions was observed for both Li0.6FePO4 and Li0.34FePO4. The strength of this interaction leads to the formation of LiFePO4-like clusters in the latter, as shown by the room temperature data. Different motional processes are proposed to exist as the temperature is increased and various scenarios are discussed. While concerted lithium-electron hopping and/or correlations explains the data below 125 °C, evidence for some uncorrelated motion is found at higher temperatures, together with the onset of phase mixing.
51 citations
TL;DR: In this paper, the effects due to strong frustration have also been observed in some metallic correlated systems compounds containing rare-earth or transition metal magnetic atoms, which were theoretically predicted but not yet observed.
Abstract: While consequences of frustration of magnetic interactions are much studied in localized spin systems, less studies have been performed on frustrated metallic systems. In this review I show that several effects due to strong frustration have also been observed in some metallic correlated systems compounds containing rare-earth or transition metal magnetic atoms. There are also effects, specific to frustrated metallic systems, which were theoretically predicted but not yet observed. This paper will review some of these aspects, concerning either the magnetically ordered systems, as the existence of mixed magnetic structures, or the anomalous Hall effect in chiral magnetic structures, or in non ordered systems, as the heavy fermion behavior or the possibility of superconductivity. The last part is devoted to the metal–insulator transition in these systems.
50 citations
TL;DR: In this article, the relationship between ferrimagnetic and ferroelastic domain structures in monoclinic magnetite was revealed using electron microscopy, revealing a diversity of unexpected interaction phenomena between crystallographic twins and magnetic domain walls.
48 citations
TL;DR: In this paper, the authors present a careful study of a quarter filled extended Hubbard model, and discuss its relevance for the understanding of the phenomenology of low-density two dimensional electron gases.
Abstract: Strong correlations effects, which are often associated to the approach to a Mott insulating state, in some cases may be observed even far from half-filling. This typically happens whenever the inter-site Coulomb repulsion induces a tendency towards charge ordering, an effect that confines the electrons, and in turn favors local moment formation, i.e. Mott localization. A distinct intermediate regime then emerges as a precursor of such a Wigner-Mott transition, which is characterized by both charge and spin correlations, displaying large mass enhancements and strong renormalizations of other Fermi liquid parameters. Here we present a careful study of a quarter filled extended Hubbard model - a simple example where such physics can be studied in detail, and discuss its relevance for the understanding of the phenomenology of low-density two dimensional electron gases.
47 citations
TL;DR: In this article, the structure, magnetic and magnetocaloric properties of poly- and nanocrystalline La0.5Ca 0.5MnO3 manganites were studied in a broad temperature range.
TL;DR: In this paper, the authors reported the direct observation of 180° polar domains growing in the ferroelectric phase by means of optical second-harmonic generation interferometry, illustrating a strong tendency of single-domain growth in the organic conductor α-[bis(ethylenedithio)tetrathiafulvalene]2I3.
Abstract: The organic conductor α-[bis(ethylenedithio)tetrathiafulvalene]2I3 undergoes a ferroelectric transition due to the Wigner-crystal-like charge ordering. The present paper reports the direct observation of 180° polar domains growing in the ferroelectric phase by means of optical second-harmonic generation interferometry. Mapping observation of the nonlinear optical interference revealed the development of large polar domains, illustrating a strong tendency of single-domain growth in the ferroelectric compound. The domain structures were varied when the crystal was annealed above the transition temperature and recooled into the ferroelectric phase. The variation indicates the mobile nature of the domains in the ferroelectric organic conductor.
TL;DR: In this article, the authors reported a constant threshold resistivity for the insulating phase of a metal-to-glass transition, regardless of the initial resistivity, transition temperature, and strain state.
Abstract: We report a constant threshold resistivity observed for the insulating phase of ${\text{VO}}_{2}$ before it transfers into the metallic phase, regardless of the initial resistivity, transition temperature, and strain state. The value of the threshold resistivity is also comparable for different lattice structures of the insulating phase. Such a constant threshold resistivity suggests that a constant critical free-electron concentration is needed on the insulating side to trigger the insulator-to-metal transition, indicating the electronic nature of the mechanism of the transition.
TL;DR: Novel magnetization measurements, designed by a special high field measurement protocol, show that the dominant ground state magnetic phase is ferromagnetic-metallic (FM-M), which is an equilibrium phase, which coexists with the residual charge ordered anti-ferromagnetic phase (CO AFM) (an arrested phase) and exhibits the characteristic features of a 'magnetic glassy state' at low temperatures.
Abstract: We show from conventional magnetization measurements that the charge order (CO) is completely suppressed in 10 nm Pr(0.5)Ca(0.5)MnO(3)(PCMO 10) nanoparticles. Novel magnetization measurements, designed by a special high field measurement protocol, show that the dominant ground state magnetic phase is ferromagnetic-metallic (FM-M), which is an equilibrium phase, which coexists with the residual charge ordered anti-ferromagnetic phase (CO AFM) (an arrested phase) and exhibits the characteristic features of a 'magnetic glassy state' at low temperatures. It is observed that there is a drastic reduction in the field required to induce the AFM to FM transition (∼5-6 T) compared to their bulk counterpart (∼27 T); this phase transition is of first order in nature, broad, irreversible and the coexisting phases are tunable with the cooling field. Temperature-dependent magneto-transport data indicate the occurrence of a size-induced insulator-metal transition (T(M-I)) and anomalous resistive hysteresis (R-H) loops, pointing out the presence of a mixture of the FM-M phase and AFM-I phase.
TL;DR: It is argued that observations of a large magnetoresistance (MR), high resistivity, and a high saturation field are observed as compared with the case of probing a single Fe(3)O(4) domain are indicative of profound changes in the electronic transport across APBs.
Abstract: We have probed one antiferromagnetic (AF) antiphase boundary (APB) and a single Fe3O4 domain using nanogap contacts. Our experiments directly demonstrate that, in the case of probing one AF-APB, a large magnetoresistance (MR), high resistivity, and a high saturation field are observed as compared with the case of probing a single Fe3O4 domain. The shape of the temperature-dependent MR curves is also found to differ between the single domain and one of the AF-APB measurements, with a characteristic strong temperature dependence for the single domain and temperature independence for the one AF-APB case. We argue that these observations are indicative of profound changes in the electronic transport across APBs. The investigated APB defects increase the activation energy and disturb the long-range charge ordering of monodomain Fe3O4.
TL;DR: The Verwey transition in magnetite (Fe3O4) has been studied extensively with a wide assortment of experimental techniques to investigate the effects of impurities, oxygen stoichiometry, and crystal properties as discussed by the authors.
Abstract: The Verwey transition in magnetite (Fe3O4) has been studied extensively with a wide assortment of experimental techniques to investigate the effects of impurities, oxygen stoichiometry, and crystal...
TL;DR: In this article, a solid-state route reaction method was used to obtain polycrystalline samples of Fe 3− x Mn x O 4 (0.10 and 0.50) for the first order phase transition at the Verwey transition.
TL;DR: In this article, inelastic light scattering experiments on single-crystalline La2-xSrxCuO4 in the doping range 0.00 ≤ x = p ≤ 0.30 and Tl2Ba2CuO6+δ at p = 0.24.
Abstract: We present results of inelastic light scattering experiments on single-crystalline La2-xSrxCuO4 in the doping range 0.00 ≤ x = p ≤ 0.30 and Tl2Ba2CuO6+δ at p = 0.20 and p = 0.24. The main emphasis is placed on the response of electronic excitations in the antiferromagnetic phase, in the pseudogap range, in the superconducting state, and in the essentially normal metallic state at x ≥ 0.26, where no superconductivity could be observed. In most of the cases we compare B1g and B2g spectra which project out electronic properties close to (π, 0) and (π/2,π/2), respectively. In the channel of electron-hole excitations we find universal behavior in B2g symmetry as long as the material exhibits superconductivity at low temperature. In contrast, there is a strong doping dependence in B1g symmetry: (i) In the doping range 0.20 ≤ p ≤ 0.25 we observe rapid changes of shape and temperature dependence of the spectra. (ii) In La2-xSrxCuO4 new structures appear for x < 0.13 which are superposed on the electron-hole continuum. The temperature dependence as well as model calculations support an interpretation in terms of charge-ordering fluctuations. For x ≤ 0.05 the response from fluctuations disappears in B1g and appears in B2g symmetry in full agreement with the orientation change of stripes found by neutron scattering. While, with a grain of salt, the particle-hole continuum is universal for all cuprates the response from fluctuating charge order in the range 0.05 ≤ p < 0.16 is so far found only in La2-xSrxCuO4. We conclude that La2-xSrxCuO4 is close to static charge order and, for this reason, may have a suppressed Tc.
TL;DR: In this paper, the photo-induced melting of horizontal-stripe charge orders in quasi-two-dimensional organic conductors was investigated theoretically by numerically solving the time-dependent Schrodinger equation.
Abstract: Photoinduced melting of horizontal-stripe charge orders in quasi-two-dimensional organic conductors θ-(BEDT-TTF) 2 RbZn(SCN) 4 [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene] and α-(BEDT-TTF) 2 I 3 is investigated theoretically. By numerically solving the time-dependent Schrodinger equation, we study the photoinduced dynamics in extended Peierls–Hubbard models on anisotropic triangular lattices within the Hartree–Fock approximation. The melting of the charge order needs more energy for θ-(BEDT-TTF) 2 RbZn(SCN) 4 than for α-(BEDT-TTF) 2 I 3 , which is a consequence of the larger stabilization energy in θ-(BEDT-TTF) 2 RbZn(SCN) 4 . After local photoexcitation in the charge ordered states, the growth of a photoinduced domain shows anisotropy. In θ-(BEDT-TTF) 2 RbZn(SCN) 4 , the domain hardly expands to the direction perpendicular to the horizontal-stripes. This is because all the molecules on the hole-rich stripe are rotated in one direction and those on the hole-poor stripe in the other direction. They m...
TL;DR: Analyzing the electronic and magnetic properties within first principles electronic structure calculations, it is found that the doped electrons due to K induce a charge-ordered and insulating ground state and interestingly also introduce a ferromagnetic coupling between the Cr ions.
Abstract: Usually metallicity accompanies ferromagnetism. K2Cr8O16 is one of the less common examples of magnetic materials, exhibiting ferromagnetism in the insulating state. Analyzing the electronic and magnetic properties within first principles electronic structure calculations, we find that the doped electrons due to K induce a charge-ordered and insulating ground state and interestingly also introduce a ferromagnetic coupling between the Cr ions. The primary considerations driving the charge ordering are found to be electrostatic ones with the charge being localized on two Cr atoms that minimize the electrostatic energy. The structural distortion that accompanies the ordering gives rise to a rare example of a charge-order driven ferromagnetic insulator.
TL;DR: In this article, the authors investigated the structure and magnetic properties of the La 0.5−xBixCa0.5MnO3 (x = 0, 1/16, 1/8, 1 /4, 3/8 and 1/2) system and showed that the substitution of Bi3+ ion for La 3+ ion systematically enhances the charge ordering (CO) temperature.
TL;DR: In this article, the photoinduced time evolution of charge and spin correlation functions on the basis of exact many-electron wave functions coupled with classical phonons in extended Peierls-Hubbard models on anisotropic triangular lattices was theoretically studied.
Abstract: To elucidate the different photoinduced melting dynamics of charge orders observed in the quasi-two-dimensional organic conductors θ-(BEDT-TTF) 2 RbZn(SCN) 4 and α-(BEDT-TTF) 2 I 3 [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene], we theoretically study the photoinduced time evolution of charge and spin correlation functions on the basis of exact many-electron wave functions coupled with classical phonons in extended Peierls–Hubbard models on anisotropic triangular lattices. In both salts, the so-called horizontal-stripe charge order is stabilized by nearest-neighbor repulsive interactions and electron–lattice interactions. In θ-(BEDT-TTF) 2 RbZn(SCN) 4 (abbreviated as θ-RbZn), the stabilization energy due to lattice distortion is larger, so that a larger quantity of energy needs to be absorbed to melt charge and lattice orders. The photoinduced charge dynamics shows a complex behavior owing to a substantial number of nearly degenerate eigenstates involved. This is related to the high structural symmetr...
TL;DR: In this paper, the authors presented experimental evidences to verify the peculiar multiferroics predicted in the half-doped manganite La 0.5Ca0.5MnO3.
Abstract: We present experimental evidences to verify the peculiar multiferroics predicted in the half-doped manganite La0.5Ca0.5MnO3. The dielectric constant exhibits a frequency-independent peak just at the antiferromagnetic charge ordering transition temperature TCO, indicating a close correlation between the ferroelectriclike transition and charge ordering. In addition to a large magnetodielectric effect, the dynamic magnetoelectric coupling measurements provide solid evidences to an enhanced magnetoelectric coupling below TCO. Moreover, the magnetic field dependence of the coupling coefficient shows a close correlation with the magnetization hysteresis loop, which reveals that a large magnetoelectric coupling only persists in the charge ordering state.
TL;DR: In this paper, a lattice gas model of CO within mean-field theory and a model of interactions which stabilizes the spin ordering in the mixed valence compound was proposed.
Abstract: Landau theory and symmetry considerations lead us to propose an explanation for several seemingly paradoxical behaviors of charge ordering (CO) and spin ordering (SO) in the mixed valence compound ${\text{LuFe}}_{2}{\text{O}}_{4}$ Both SO and CO are highly frustrated We analyze a lattice gas model of CO within mean-field theory and determine the magnitude of several of the phenomenological interactions We show that the assumption of a continuous phase transitions at which CO or SO develops implies that both CO and SO are incommensurate To explain how ferroelectric fluctuations in the charge-disordered phase can be consistent with an antiferroelectric-ordered phase, we invoke an electron-phonon interaction in which a low-energy (20 meV) zone-center transverse phonon plays a key role The energies of all the zone center phonons are calculated from first principles We give a Landau analysis which explains SO and we discuss a model of interactions which stabilizes the SO state, if it is assumed commensurate However, we suggest a high-resolution experimental determination to see whether this phase is really commensurate, as believed up to now The applicability of representation analysis is discussed A tentative explanation for the sensitivity of the CO state to an applied magnetic field in field-cooled experiments is given
TL;DR: In this article, the effect of annealing on ferromagnetic charge ordering using charge density studies was investigated using powder XRD data sets of the samples annealed at various temperatures (500, 600, 700, 800 and 900 ǫ).
Abstract: Nano sized diluted magnetic semiconductor Co 2+ :ZnO (with composition Zn 0.99 Co 0.01 O) was prepared by sol–gel method and studied for the effect of annealing on ferromagnetic charge ordering using charge density studies. Powder XRD data sets of the samples annealed at various temperatures (500, 600, 700, 800 and 900 °C) have been investigated by the Rietveld refinement analysis and the charge density distribution using the maximum entropy method (MEM). The mid bond electron densities between the Zn(Co) and O atoms are analyzed to understand the origin of ferromagnetic behaviour between the temperature range 600–700 °C. Zn 0.99 Co 0.01 O is found to switch “on” the ferromagnetic behaviour range 600–700 °C and then to switch “off”. The charge ordering that results in ferromagnetic occurrence is dealt for the first time through charge density route.
TL;DR: In this article, a direct evidence of a lattice deformation at the CO of deuterated (TMTTF ) 2 PF 6 using powder neutron diffraction is presented.
Abstract: The molecular charge order (CO)–ferroelectric transition of the strongly correlated organic conductors ( TMTTF ) 2 X is investigated. We present here, a direct evidence of a lattice deformation at the CO of deuterated ( TMTTF ) 2 PF 6 using powder neutron diffraction. Our data show that the intensity of several Bragg reflections is affected by the CO. Their analysis leads to a simple description of the CO mechanism and evidences a sizeable coupling between lattice and charge degrees of freedom.
TL;DR: Rodriguez-Carvajal et al. as mentioned in this paper showed that the phase transition is induced by charge-ordering of Mn3+/Mn4+ accompanied by orbital-ordering due to Jahn-Teller distortion.
DOI•
01 Jan 2010
TL;DR: Mialitsin et al. as discussed by the authors investigated the effect of charge ordering, two-band superconductivity, and structural disorder on the spectral renormalization of layered superconductors.
Abstract: OF THE DISSERTATION Raman scattering from layered superconductors: Effects of charge ordering, two-band superconductivity, and structural disorder by Aleksej Mialitsin Dissertation Director: Prof. Girsh Blumberg Subject of this dissertation is the investigation with experimental means of how the Raman response of three structurally similar materials − MgB2, NbSe2, and CaC6 − is affected by superconductivity (all three), charge ordering (NbSe2), or crystalline order-to-disorder phase transitions (CaC6). Universal characteristics of spectral renormalization pertaining to the superconducting phase transition are observed in all three compounds. Yet, the crystalline and electronic structures are sufficiently distinct, such that specific for each compound characteristics are imposed on this superconductivity-induced renormalization. Consequently, the method of polarized Raman scattering has been used to establish a variety of physical concepts: ∙ Multi-band superconductivity in the layered superconductor MgB2 and its primary mediation by the strongly coupled 640 cm−1 E2g phonon. Additionally, it is shown how a Josephson-like coupling of two SC condensates in the reciprocal space is responsible for an exotic collective mode, the Leggett’s resonance.
TL;DR: It is noted that the non-monotonic variation of the supercooling limit is anomalous according to the classical concepts of the first-order phase transition, and H(up) values below ∼20 K are unsuitable to represent the super Cooling limit.
Abstract: Gadolinium strontium manganite single crystals of the composition Gd(0.5)Sr(0.5)MnO(3) were grown using the optical float zone method. We report here the magnetic and magnetotransport properties of these crystals. A large magnetoresistance ∼10(9)% was observed at 45 K under the application of a 110 kOe field. We have observed notable thermomagnetic anomalies such as open hysteresis loops across the broadened first-order transition between the charge order insulator and the ferromagnetic metallic phase while traversing the magnetic field-temperature (H-T) plane isothermally or isomagnetically. In order to discern the cause of these observed anomalies, the H-T phase diagram for Gd(0.5)Sr(0.5)MnO(3) is formulated using the magnetization-field (M-H), magnetization-temperature (M-T) and resistance-temperature (R-T) measurements. The temperature dependence of the critical field (i.e. H(up), the field required for transformation to the ferromagnetic metallic phase) is non-monotonic. We note that the non-monotonic variation of the supercooling limit is anomalous according to the classical concepts of the first-order phase transition. Accordingly, H(up) values below ∼20 K are unsuitable to represent the supercooling limit. It is possible that the nature of the metastable states responsible for the observed open hysteresis loops is different from that of the supercooled ones.
TL;DR: In this article, the microstructure and magnetic properties of polycrystalline La0.25Ca0.75MnO3 nanowires with diameter of about 60 nm prepared by a sol−gel template method were studied with use of X-ray diffraction, transmission electron microscopy, and superconducting quantum interference device magnetometry.
Abstract: The microstructure and magnetic properties of the polycrystalline La0.25Ca0.75MnO3 nanowires with diameter of about 60 nm prepared by a sol−gel template method were studied with use of X-ray diffraction, transmission electron microscopy, and superconducting quantum interference device magnetometry. Compared with the robust charge ordering (CO) state with CO transition temperature TCO ≈ 240 K in the bulk counterpart, the CO is suppressed with TCO ≈ 138 K and CO transition becomes wide, at the same time the ferromagnetic (FM) cluster glass state and the exchange bias effect are detected in La0.25Ca0.75MnO3 nanowires. This exotic behavior is attributed to the uncompensated surface spins which change the spin configuration of nanowires and enhance the eg charge density at the surface compared to bulk compound and thereby induce the FM cluster glass state as well as exchange bias effect, and weaken the CO.