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[Abstract] In this work we focus in setting the limits of the tolerance factor and the size of the A-cations that stabilize the perovskite structure in hybrid dicyanamide compounds [A][Mn(dca)3]. For this purpose, we propose an alternative, simple approach to calculate a more realistic effective ionic radius for the large and anisotropic A-cations often present in these type of compounds. We test the proposed procedure by analysing the crystal structures of [A][Mn(dca)3] dicyanamide hybrids reported in the literature and recalculating the tolerance factors of such compounds, as well as by preparing five new [A][Mn(dca)3] members, discussing also the influence of the A-cation shape in the stability limits of the perovskite structure. Interestingly, such methodology is not only useful to develop new compounds of the emerging family of (multi)functional multi(stimuli)-responsive dicyanamide materials but can also be applied to other hybrid organic-inorganic perovskites and related materials. As for financial support, the authors thank Ministerio de Economía y Competitividad MINECO and EU-FEDER (projects MAT2017-86453-R and PDC2021-121076-I00), and Xunta de Galicia for the collaboration agreement “Development of research strategic actions Universidade da Coruña I ​+ ​D ​+ ​i 2021–2022: CICA-Disrupting Projects 2021SEM-A3 (NanoCool). J.G.-B. and J.M.B.-G. acknowledge Xunta de Galicia for Predoctoral and Postdoctoral Fellowships, respectively. I.D.-F thanks Ministerio de Universidades for a FPU Predoctoral Fellowship. A. G.-F. and U.B.C thank the Carl Tryggers foundation and the Göran Gustafsson foundation for financial support

In Solid-State Chemistry, a well-known route to obtain new compounds and modulate their properties is the formation of solid solutions, a strategy widely exploited in the case of classical inorganic perovskites but relatively unexplored among emergent hybrid organic–inorganic perovskites (HOIPs). In this work, to the best of our knowledge, we present the first dicyanamide-perovskite solid solution of [TPrA][Co0.5Ni0.5(dca)3] and study its thermal, dielectric and optical properties, comparing them with those of the parent undoped compounds [TPrA][Co(dca)3] and [TPrA][Ni(dca)3]. In addition, we show that the prepared doped compound can be used as a precursor that, by calcination, allows CNTs with embedded magnetic Ni:Co alloy nanoparticles to be obtained through a fast and much simpler synthetic route than other complex CVD or arc-discharge methods used to obtain this type of material.

Spin-phonon coupling in rare-earth based manganites with double perovskite structure plays a crucial role in the magnetoelectric properties of these ferromagnetic materials. Particularly, on Y2CoMnO6 (YCMO), it is assumed that spin-phonon coupling is related to the induced ferroelectric polarization. This confers to YCMO a multiferroic characteristic. In this work, we probed the spin-phonon coupling in YCMO by temperature-dependent Raman spectroscopy measurements in ceramic samples obtained by the nitrate decomposition method. Raman scattering revealed some anomalies that could be attributed to a weak spin-phonon coupling, an unconventional behavior for rare-earth based manganites with double perovskite structure, in which the coupling does not fit with the quadratic magnetization.

We investigate the magnetic ordering and the magnetization dynamics (from kHz to THz time scales) of the double perovskite Lu2MnCoO6 using elastic neutron diffraction, muon spin relaxation, and micro-Hall magnetization measurements. This compound is known to be a type II multiferroic with the interesting feature that a ferromagneticlike magnetization hysteresis loop couples to an equally hysteretic electric polarization in the bulk of the material despite a zero-field magnetic ordering of the type ↑↑↓↓ along Co-Mn spin chains. Here we explore the unusual dynamics of this compound and find extremely strong fluctuations, consistent with the axial next-nearest-neighbor Ising (ANNNI) model for frustrated spin chains. We identify three temperature scales in Lu2MnCoO6 corresponding to the onset of highly fluctuating long-range order below TN = 50 ± 3 K identified from neutron scattering, the onset of magnetic and electric hysteresis, with change in kHz magnetic and electric dynamics below a 30 K temperature scale, and partial freezing of ∼MHz spin fluctuations in the muon spin relaxation data below 12 ± 3 K. Our results provide a framework for understanding the multiferroic behavior of this compound and its hysteresis and dynamics.

Here we present an in-depth study of the magnetic properties of a family of metal–organic perovskites ABX3, [CH3NH3][M(HCOO)3] in which A = CH3NH3+ is the methylammonium cation, B = M is a divalent metal cation (Mn2+, Co2+, Ni2+ or Cu2+), and X is the formate anion (HCOO−). The magnetic properties have been measured on powdered samples and along the different orientations of mm-sized single crystals. They display spin-canted weak ferromagnetism with Néel temperatures of 8.0 K (Mn2+), 15.7 K (Co2+) and 34 K (Ni2+), which are inversely proportional to the ionic radii of the metal cations. The Cu2+ member displays low-dimensional magnetism as a result of orbital ordering of the Cu2+ d orbitals originating from a Jahn–Teller distortion. Pulsed-field magnetization experiments (fields of up to 60 T at temperatures down to 0.6 K) show that Mn2+, Co2+ and Ni2+ formates display cation-characteristic spin flop transitions. A saturation magnetization value of 5 μB (at 12.5 T) was observed for Mn2+, meanwhile the Co2+ formate shows an orientation dependent quasi saturation (5.1 μB at 21 T along [101] vs. 5.8 μB at 26 T along [010]). The different isotropic/anisotropic behaviour can be explained by the orbital contribution to the magnetic response The Spanish authors are grateful for financial support from Ministerio de Economía y Competitividad (MINECO) (Spain) and EU under the project ENE2014-56237-C4-4-R, and Xunta de Galicia under the project GRC2014/042. L. C. G.-A. acknowledges UDC for a predoctoral fellowship and Fundación Barrié for the research stay grant at LANL. Work at LANL, A. P. H. and B. P.-D.'s visit to LANL were funded by the Laboratory Directed Research and Development program at LANL. The NHMFL pulsed-field facility is funded by the U.S. National Science Foundation through Cooperative Grant No. DMR-1157490, the State of Florida, and the U.S. Department of Energy SI

We are reporting on the dielectric properties of NaCu3(Ti3Nb)O12 and Na(Cu2.5Ti0.5)Ti4O12 which are related to the perovskite CaCu3Ti4O12 compound. The NaCu3(Ti3Nb)O12 perovskite, that is doped with Nb cations at the Ti B-site, shows high values of dielectric constant. Using impedance spectroscopy (IS), we have observed that this compound is electrically inhomogeneous, showing a semiconductive bulk and insulating grain boundaries. The presence of a semiconductive bulk seems to indicate that a charge delocalization process is taking place through the Cu A′-site. In the case of the Na(Cu2.5Ti0.5)Ti4O12 perovskite, the dielectric response comes from the bulk material and the IS results show an intrinsic homogeneous material. In this compound, the large doping of Ti cations at the Cu A′-site prevents a charge delocalization process and the material becomes insulating. These results highlight the importance of the A′-sites in the charge delocalization process. In addition, Na(Cu2.5Ti0.5)Ti4O12 provides evidence of a soft-mode behavior that could be responsible for the relatively high intrinsic dielectric constant of CaCu3Ti4O12 and related compounds. © 2009 Elsevier B.V. All rights reserved.

This is the accepted manuscript of the following article: Sánchez-Andújar, M., Yáñez-Vilar, S., Biskup, N., Castro-García, S., Mira, J., Rivas, J., & Señarís-Rodríguez, M. (2009). Magnetoelectric behavior in the complex CaMn7O12 perovskite. Journal Of Magnetism And Magnetic Materials, 321(11), 1739-1742. doi: 10.1016/j.jmmm.2009.02.018 We report a magnetoelectric effect in the double perovskite CaMn7O12, that shows a complex magnetic behavior below 90 K with two magnetic phases coexisting (one ferrimagnetic and the other modulated). A second magnetic transition, associated with changes in the magnetic modulation and magnetic ordering coherence lengths of the two magnetic phases occurs at 50 K (TN2). A detailed structural characterization of this compound, that we have carried out by means of high-resolution X-ray powder diffraction, reveals an anisotropic thermal expansion of its lattice parameters at 50 K (TN2). In addition, our study of the complex permittivity of this sample as a function of temperature, frequency and magnetic field shows very interesting results below 90 K and specially below 50 K: the dielectric constant ε′r that was decreasing continuously on cooling experiences an upturn, and even more, on application of a magnetic field it shows a moderate magnetoelectric response. We attribute such dielectric behavior to the formation of electric dipoles by magnetostriction in this charge and spin ordered system, that are sensible to the presence of an external magnetic field The authors are grateful from financial support for MEC (Spain) under project FEDER MAT 2007-66696 and Xunta de Galicia under project PGIDIT06PXB103298PR. S. Yáñez-Vilar want to thank to MEC of Spain for her FPI fellowship and M. Sánchez-Andújar acknowledges to Xunta de Galicia for support under program Parga Pondal SI

We report the magneto-transport properties of the layered mixed oxides Nd1−xSr1+xCoO4 (0 ≤ x ≤ 0.3) compounds. These materials are found to evolve towards an anomalous “cluster-glass” like behavior as x increases. The onset of the ferromagnetic order in the bidimensional phase is seen to occur in the x = 0.30 sample at Tc(2D) ≈ 125 K, followed by a blocking process around TB (2D) ≈ 55 K. In addition, present in the magnetic response of these materials is the paramagnetic contribution coming from the Nd3+ ions μ eff-N d 3+ = 3.62 μ B together with the signal coming from a minority perovskite phase, that is nevertheless not detected by powder X-ray diffraction. From the electrical point of view these materials are semiconducting and their resistivitiy decreases upon doping. In addition, at low temperatures T

In this work we introduce the use of a combined Rietveld refinement and Maximum Entropy Method (MEM), as a helpful new tool to gain insight into the charge ordering pattern present in CO-transition metal compounds. In particular we show the study made on two CO oxyborates A2OBO3 (A = Mn and Fe): (a) the Mn-oxyborate, that exhibits a strong charge lattice coupling, and whose charge ordering pattern had been previously satisfactory established from BVS analysis of single crystal X-ray diffraction data and that we have used as a test to confirm the validity of the new method; (b) the weakly charge-lattice coupled Fe-oxyborate, a compound not suitable for the BVS approach and for which nevertheless this method gives evidence for a new charge ordering pattern.

The La0.85Sr0.15CoO3 compound has been synthesized under different annealing temperatures. It has been observed that the transport properties and magnetoresistance of this compound depend on such temperatures. This response is discussed in the framework of a model of electronic phase segregation.

In this work we have measured the complex dielectric permittivity of a polycrystalline material using samples of different thickness (frequency range 20–1 MHz). The results reveal that the CaMn 7 O 12 material is electrically heterogeneous as it consists of regions of different conductivities. In this kind of electrically heterogeneous materials the variation of the dielectric permittivity as a function of temperature can be fitted to a Maxwell–Wagner model. In the case of the CaMn 7 O 12 sample this model fits only partially the experimental data and we need to include three regions of different conductivities to explain the obtained dielectric response.

We present the first example of magnetic ordering-induced multiferroic behavior in a metal-organic framework magnet. This compound is [CH3NH3][Co(HCOO)3] with a perovskite-like structure. The A-site [CH3NH3](+) cation strongly distorts the framework, allowing anisotropic magnetic and electric behavior and coupling between them to occur. This material is a spin canted antiferromagnet below 15.9 K with a weak ferromagnetic component attributable to Dzyaloshinskii-Moriya (DM) interactions and experiences a discontinuous hysteretic magnetic-field-induced switching along [010] and a more continuous hysteresis along [101]. Coupling between the magnetic and electric order is resolved when the field is applied along this [101]: a spin rearrangement occurs at a critical magnetic field in the ac plane that induces a change in the electric polarization along [101] and [10-1]. The electric polarization exhibits an unusual memory effect, as it remembers the direction of the previous two magnetic-field pulses applied. The data are consistent with an inverse-DM mechanism for multiferroic behavior.

A multistimuli response to temperature and pressure is found in the hybrid inorganic–organic perovskite-like [TPrA][Mn(dca)3] compound, which is related to a first-order structural phase transition near room temperature, Tt ≈ 330 K. This phase transition involves a transformation from room temperature polymorph I, with the noncentrosymmetric space group P4̅21c, to the high temperature polymorph II, with the centrosymmetric space group I4/mcm, and it implies ionic displacements, order–disorder phenomena, and a large and anisotropic thermal expansion (specially along the c-axis). As a consequence, [TPrA][Mn(dca)3] exhibits a dielectric anomaly, associated with the change from a cooperative to a noncooperative electric behavior (antiferroelectric (AFE)–paraelectric (PE) transition). The former implies an AFE distribution of electric dipoles in polymorph I, related to the described off-shift of the apolar TPrA cations and the order–disorder of the polar dca ligands mechanisms, that are different from those reported, up to now, for others perovskite-type hybrid compounds. Such cooperative electric order, below Tt ≈ 330 K, coexisting with long-range antiferromagnetic ordering below T = 2.1 K render the [TPrA][Mn(dca)3] a new type-I multiferroic material. In addition, the obtained experimental results reveal that this compound is also a multistimuli-responsive material, with a very large sensitivity toward temperature and applied external pressure, δTt/δP ≈ 24 K kbar–1, even for small values of pressure (P < 2 kbar). Therefore, this material opens up a potential interest for future technological applications, such as temperature/pressure sensing., The authors are grateful for the financial support from Ministerio de Economia y Competitividad MINECO (MINECO) ENE2014-56237-C4-4-R and Xunta de Galicia under the project GRC2014/042. J. M. B.-G. also wants to thank Barrié Foundation for a predoctoral fellowship and S. Y.-V. to the Xunta de Galicia for a postdoctoral grant (Plan I2C).

We report the magnetic and transport properties of the cobalt layered mixed-oxides La1−xSr1+xCoO4 ( 0 ⩽ x ⩽ 0.40 ) . An evolution towards an anomalous “cluster-glass”-like behavior as x increases has been found. The onset of the ferromagnetic order in the layered phases occurs at around 150 K followed by a blocking process around 125 K. Also, present in the magnetic response of these materials is the signal coming from small intergrowths of a perovskite phase, also detected by TEM, although invisible for powder-X-ray diffraction. From the electrical point of view these materials are semiconducting and their resistivity decreases upon doping. Most interestingly, at low temperature these layered compounds show rather large magnetoresistance (MR). The highest effect is found in the sample with x = 0.20 that shows a magnetoresistance MR max = − 24 % at T = 15 K under a field H max = 50 kOe .

In this work, we study the dielectric properties of the layered perovskites La 3/2 Sr 1/2 NiO 4 and La 5/3 Sr 1/3 NiO 4 in the frequency range 20 Hz-1 MHz and in the temperature range 110-350 K. For this study, we have synthesized single phase polycrystalline samples by a conventional solid-state reaction. These nickelates show very high values of the dielectric constant at room temperature (e' r ∼ 10 5 ), that make them very attractive for potential applications, provided that their rather high losses can be minimized. The obtained results reveal that even if their dielectric behavior is strongly enhanced by extrinsic polarization effects, there is also a very interesting correlation between their dielectric response and their electronic state.

We present in this paper a detailed investigation of the dielectric properties of the mixed oxide CaMn7O12 that shows a charge-ordering transition at TCO = 440 K. Surprisingly, this compound presents a high dielectric constant at room temperature. Data taken at several frequencies and temperatures point to relaxor dielectric behaviour, that can be attributed to the electronic inhomogeneities present in the material. Extrinsic Maxwell–Wagner effects make a significant contribution to this dielectric response, as revealed by the studies made on samples of different particle size and using different types of contact. The intrinsic dielectric constant of this material is e �(intrinsic) ∼ 30 at room temperature, a value that is relatively high for this type of compound and that we relate to the presence of the electronic process of charge ordering in this material.

We report the dielectric response of Ca2?xPrxMnO4 (x = 0 and 0.25). Specifically, their intrinsic dielectric constants are calculated by impedance spectroscopy from the values of the obtained bulk capacitances. For Ca2MnO4, that does not show charge-order, the measured intrinsic dielectric constant is 14. The Pr doping induces charge-order in the system, and also a noteworthy increase in , that reaches a value of ~220 for x = 0.25, unusual in these kind of oxides. This result provides a new link between both phenomena.

The dielectric properties of mixed-oxide CaMn7O12 are reported. This compound exhibits a high dielectric constant at room temperature (er >1 0 4 ), for frequencies up to 10 4 Hz, values that make it very attractive for potential applications provided that its rather high losses can be minimized. Complex plane analysis of the obtained data reveal an important extrinsic contribution to these high er values; and also that the

We have prepared Ca2−xPrxMnO4 ( x = 0 , 0.25 , 0.33 and 0.50) compounds by the so-called “liquid-mix” method. X-ray powder diffraction indicated that these compounds are single-phase materials and resistivity measurements showed that the Pr-doped samples experience charge-ordering (CO) transitions at 275 K ( x = 0.25 ), 330 K ( x = 0.33 ) and 315 K ( x = 0.50 ). The intrinsic dielectric constants calculated by impedance spectroscopy (IS) from the values of the obtained bulk capacitances were remarkably high: 217, 37 and 80 for the x = 0.25 , 0.33 and 0.50 samples, respectively. In addition, extrinsic factors play an important role on their dielectric response, especially at T > 150 K , giving rise to very high dielectric constants at room temperature ( ɛ r ′ ∼ 10 6 ). Also, and for comparison, we have studied the dielectric response of Ca2MnO4 (non charge-ordered compound), finding much smaller dielectric constant values and an intrinsic contribution ɛ r ′ (bulk)=14, remarkably lower than in the case of Pr-doped compounds. These results could be a new evidence of the link between the charge ordered state and the increase of the dielectric constant.

In this work, the behaviour of the real and imaginary components of the dielectric permittivity of layered perovskite La 1 5 Sr 0 . 5 CoO 4 have been studied, in the frequency range 20 Hz-1 MHz and in the temperature range 115-350 K. Polycrystalline samples were prepared by the ceramic method. The powder diffraction results showed the pattern of the desired phase together with a small quantities of La 2 O 3 impurities. A comparative study of the electrical and magnetic properties of this charge-ordered compound (T C O ∼750 K) has revealed a basically semiconductor behaviour with a complex bidimensional antiferromagnetism which can be explained on the basis of a thermally activated evolution of the spin state of the Co 3 + ions. A detailed investigation of the dielectric properties of this system has allowed us to identify two superimposed relaxation processes: the first one in the low frequency range (f

By using the nitrate decomposition method in the presence of KNO3, we have been able to enlarge the compositional range of the solid solution of the layered compounds with K2NiF4 structure Ln1−x Sr1+xCoO4 (Ln: La, Nd, Gd) to 0 x 0.40 in the case of Ln = La, to 0 x 0.30 for Ln = Nd and to 0 x 0.20 for Ln = Gd. In this paper we present the results of their structural characterization by means of powder X-ray diffraction and Rietveld analysis as a function of composition (x) and the rare earth (Ln), information that has been complemented by the results obtained from electron diffraction and transmission electron microscopy.  2003 Elsevier SAS. All rights reserved.

We report the synthesis of the Ruddlesden–Popper material Sr 3 Fe 1.5 Co 0.5 O 6.67 (a compound usually obtained under high-pressure conditions) by a simpler normal pressure liquid-mix method and its structural characterization by means of X-ray powder diffraction. In this material—which is semiconducting and shows a glassy magnetic behavior—the combination of the reduced dimensionality of the structure compared to 3D perovskites, the small grain size obtained by our synthesis method and the selected stoichiometry, results in a record magnetoresistance in these kind of compounds, −47% at T =5 K and H =50 kOe, that is explained on the basis of intragranular and intergranular effects.

We introduce the magnetotransport properties of Gd 1-x Sr x CoO 3 (0 < x ≤ 0.30) materials. These compounds are semiconducting and show a magnetic transition at T c 160 K associated with the onset of magnetic order of cobalt ions within superparamagnetic clusters, which have a freezing point T B < T c . Very remarkably, the more resistive samples showed rather large magnetoresistance at the lowest available temperature: MR max (x = 0.10) -16% at T = 4.2 K under H max = 40 kOe. We relate these results to the inhomogeneous electronic structure of these cobaltates and to the presence of the paramagnetic Gd 3+ sublattice, which at low temperatures influences the cobalt ions of the superparamagnetic clusters, provoking an increase in the size of the hole-rich regions and in the hopping probability of the charge carriers, and gives rise to the negative magnetoresistance observed.

We have prepared polycrystalline, single-phase Nd1−xSrxCoO3 materials (0≤x≤0.40) using the nitrate decomposition method and we have studied how their structural, magnetic and transport properties change upon Sr2+ doping. In this context we find that these series of compounds crystallize in GdFeO3-type perovskite structures whose cell volume increases as x gets higher. From the magnetic point of view, this doping makes the materials evolve towards a ferromagnetic behavior as x increases, so that for x>0.20 the samples are already ferromagnetic below a Tc∼225 K. Also, their electrical conductivity progressively increases with x. Nevertheless the materials remain semiconducting for x≤0.30 and only the sample with x=0.40 displays a M–I transition as a function of temperature (TMI∼160 K).

High-resolution transmission electron microscopy observations and magnetic ac susceptibility measurements have been carried out to study the changes in the magnetic properties of La1-xSrxCoO3 samples (x≤0.3) processed at different annealing temperatures, ranging from 1273 to 1573 K. Although neutron diffraction excludes the coexistence of distinct phases with different chemical composition, room temperature micrographs taken along the [0,-1,1] rhombohedral zone-axis show bright fringes of different widths, extending over regions with sizes ranging from 8 to 40 nm. These regions are detected in all the samples, whatever the Sr content or the annealing temperature Ta. However, their number depends strongly on the processing conditions and becomes smaller and smaller as Ta increases. The periodicity of the bright fringes cannot be accounted for, either by variations in the sample thickness or by crystallographic defects, but it can be simulated if the presence of aperiodically alternate Sr-rich and La-rich (0,1,1) planes is assumed. On the other hand, the susceptibility measurements show that the amount of ferromagnetic phase present in each specimen depends on its thermal history. This suggests that the segregation of a second electronic phase takes place, the nucleation of which is influenced by the spatial homogeneity of the dopant distribution.

We prepared in this work La1−xBaxCoO3−δ (0 0.15, Tc≈200 K) in the temperature range 77 K≤T≤300 K. We find that while for x 0.20 they show metallic behavior for T>100 K, with a transition to semiconducting behavior being observed for T ≤ 100 K. For x=0.20, small changes in the oxygen stoichiometry of the samples - due to slight variations in the thermal treatments - greatly affect the transport properties of the materials that can show either two metal-insulator transitions as the temperature increases or a semiconducting behavior. Very interestingly all these ferromagnetic samples are very sensitive to the polarity of the applied electrical current, and display peculiar “diodic” behaviors. All these observations are explained on the basis of an inhomogeneous electronic structure in the Ba-doped cobalt perovskites.

Neutron diffraction and small-angle scattering on La1 − xSrxCoO3 (0 < x ≤ 0.30) show that for x = 0.3 the system is near a two-phase percolation threshold and undergoes a transition from itinerant to polaronic conduction at the Curie temperature TC. The stabilization of superparamagnetic clusters on warming through TC is revealed by an anomalous thermal expansion of the volume and a deviation of the paramagnetic susceptibility from the Curie-Weiss law. The development of a temperature-dependent small-angle-scattering signal confirms that regions of short-range ferromagnetic order are present above TC.

The crystallographic structure and the magnetic order of the distorted perovskite ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{3}$ $(0.10l~xl~0.30)$ has been studied by neutron diffraction, high-resolution electron microscopy, and magnetic-susceptibility measurements. The results give direct evidence for an inhomogeneous distribution of the ${\mathrm{Sr}}^{2+}$ ions and the segregation of the material into hole-rich ferromagnetic regions and a hole-poor semiconducting matrix at lower values of x. The holes introduced by Sr doping are attracted to the ${\mathrm{Sr}}^{2+}$ ions where they stabilize to lowest temperatures an intermediate-spin state at neighboring trivalent cobalt. The antibonding e electrons so stabilized increase the mean unit-cell volume and are delocalized over the cobalt atoms of the cluster where they couple the localized ${t}^{5}$ configurations ferromagnetically. Long-range ferromagnetic order between clusters is realized even for Sr doping as low as $x=0.10.$ The transition to a spin glass state is observed only for Sr concentrations smaller than 0.10. The volume of a hole-rich cluster grows in a magnetic field, and the origin of the large negative magnetoresistance observed near ${T}_{C}$ for $0.15l~xl~0.25$ appears to be due to a growth of the clusters to a percolation threshold. For $x=0.30,$ the ${\ensuremath{\sigma}}^{*}$ band of the intermediate-spin state below ${T}_{C}$ is at the threshold of a transition from itinerant to polaronic conduction and, above ${T}_{C},$ the system transforms smoothly to a cluster state.

The critical exponents of the second-order ferromagnetic-paramagnetic phase transition of (Formula presented) (Formula presented) compounds are obtained. The results (Formula presented) (Formula presented) and (Formula presented) are qualitatively different than those reported in the literature for parent manganites, and are taken as the indication of the absence of long-range interactions below the Curie point. Electronic phase segregation in hole-rich ferromagnetic and hole-poor (Formula presented)-like regions is supposed to explain the observations. The hole-poor regions would dilute the magnetic lattice and prevent the occurrence of long-range order. Also, a spin transition of the (Formula presented) ions at (Formula presented) or the hole-poor regions (acting equivalently to missed spin clusters in amorphous ferromagnets) could be the reason for the high β value in the framework of a Heisenberg model. © 1999 The American Physical Society.

HREM, EDX and EELS techniques have been used to study the transformations that occur in the high-temperature superconductors YBa 2 Cu 3 O 7 − δ (commonly referred to as ‘123’) and YBa 2 Cu 4 O 8 (‘124’) in their reaction with the lithiating agent n-BuLi. This study confirms that the original ‘123’ and ‘124’ materials transform into a heterogeneous product that mainly consists of higher members of the Y 2 Ba 4 Cu 6 + n O 14 + n homologous series of compounds. The amount of lithium present in these new phases is quantified through systematic EELS experiments. Study of the energy-loss near-edge structures (ELNES) of the Li-K edge shows that Li is present in the main phases of the lithiated YBaCuO materials under two different forms: (i) in an ionic state (ii) in a more metallic-like state. These results allow to rationalize both the high lithium ionic conductivity displayed by these materials and the influence of lithium on the superconducting properties of these cuprates.

This is the accepted manuscript of the following article: Pato-Doldán, B., Gómez-Aguirre, L., Bermúdez-García, J., Sánchez-Andújar, M., Fondado, A., & Mira, J. et al. (2013). Coexistence of magnetic and electrical order in the new perovskite-like (C3N2H5)[Mn(HCOO)3] formate. RSC Advances, 3(44), 22404. doi: 10.1039/c3ra43165g In this work we further the structural characterization of the recently discovered (C3N2H5)[Mn(HCOO)3] metal–organic framework with perovskite-like structure, and we present its magnetic and dielectric properties up to 350 K. At low temperature, the C3N2H5+ imidazolium cations, that sit oblique within the cavities of the [Mn(HCOO)3]− framework structure, show a cooperative order resulting in an antiparallel arrangement of their electrical dipole moments. Very interestingly, it is only above 220 K that thermal energy seems to be able to break this antiferroelectric order, resulting in a linear increase of its dielectric constant with temperature. In addition, this Mn(II) compound is antiferromagnetic below TN = 9 K, with a slightly non-collinear arrangement of its magnetic moments, yielding to a weak ferromagnetism. Therefore, this is a new multiferroic material which exhibits coexistence of magnetic and electric ordering The authors are grateful for financial support from Ministerio de Economía y Competitividad MINECO (Spain) under project FEDER MAT2010-21342-C02-01 and from Xunta de Galicia under project PGIDIT10PXB103272PR. B.P.-D. also wants to thank MICINN for a FPI fellowship SI

Magnetic and transport measurements on the system La{sub 1-x}Sr{sub x} CoO{sub 3-{delta}}(0 < x {le} 0.50, {delta} = 0 for 0 {le} x < 0.30, and {delta} (x) {le} 0.06 for 0.30 {le} x {le} 0.50) have led to a phase diagram for this system. Upon Sr doping, the material segregates into hole-rich, metallic ferromagnetic regions and a hole-poor matrix similar to LaCoO{sub 3}. The Co ions of the ferromagnetic phase are in intermediate-spin configurations; the hole-poor matrix experiences a thermally induced low-spin to high-spin transition. For low Sr doping (x < 0.20), the hole-rich regions are isolated from one another and show superparamagnetic behavior below T{sub c}{approx}240 K; longrange magnetic order via frustrated intercluster interactions occurs below a superparamagnetic freezing temperature T{sub g} that increases with x. At x = 0.20, the coupling between the intermediate-spin, metallic ferromagnetic clusters within an interpenetrating matrix reaches a magnetic percolation threshold that orders the clusters ferromagnetically below T{sub c}{approx} 250 K. However, the electrical conduction in the ferromagnetic regions is modulated by the matrix, which has a spin state that varies with temperature. This causes a reentrant semiconductive behavior in the samples with 0.20 {le} x {le} 0.25. Metallic ferromagnetic behavior ismore » found for 0.30 {le} x {le} 0.50 even though the presence of an interpenetrating hole-poor matrix persists to x = 0.50. A ferromagnetic fraction less than unity leads to peculiar magnetic properties that have been attributed in the literature to a magnetic {open_quotes}cluster glass.{close_quotes}« less

We present Lu${}_{2}$MnCoO${}_{6}$, a multiferroic member of the double perovskites that we have investigated using x-ray and neutron diffraction, specific heat, magnetization, electric polarization, and dielectric constant measurements. This material possesses a net electric polarization strongly coupled to a net magnetization below 35 K, despite the antiferromagnetic ordering of the $S=3/2$ Mn${}^{4+}$ and Co${}^{2+}$ spins in an $\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$ configuration along the $c$ direction. We discuss the magnetic order in terms of a condensation of domain boundaries between $\ensuremath{\uparrow}\ensuremath{\uparrow}$ and $\ensuremath{\downarrow}\ensuremath{\downarrow}$ ferromagnetic domains, with each domain boundary producing an electric polarization due to spatial inversion symmetry breaking. In an applied magnetic field the domain boundaries slide, controlling the size of the magnetization, electric polarization, and magnetoelectric coupling.

[Abstract] We have prepared polycrystalline single-phase ACo2+xRu4−xO11 (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10−5 Ωm and their Seebeck coefficients are positive and range from 1 μV K−1 (T = 100 K) to 20 μV K−1 (T = 450 K). The maximum power factor at room temperature is displayed by BaCo2Ru4O11 (P.F.: 0.20 μW K−2 cm−1), value that is comparable to that shown by compounds such as SrRuO3 and Sr6Co5O15. Ministerio de Ciencia e Innovación; Project FEDER MAT 2007-66696

We report here a study on the electrical and magnetic properties of La1-xBaxCoO3 in the re-entrant semiconducting region (x = 0.20). We find that in this material: (i) the insulator-metal-insulator sequence is unstable and evolves toward a purely semiconducting behavior; the initial ρ versus T curve can be reinstated upon appropriate annealing treatments; (ii) there are relaxation effects that can be seen by changing the polarity of the electrodes; (iii) there is a negative magnetoresistance Δρ/ρ approx. 2-3%, for a field as low as 9 kOe, especially at the metal-insulating transition temperatures; and (iv) there are important fluctuations in the electrical resistivity. Taking into account these experimental observations, we can interpret this material as an inhomogeneous system where two thermodynamic phases, one semiconducting and the other metallic and ferromagnetic, coexist, although they are crystallographically indistinguishable. Fil: Sanchez, Rodolfo Daniel. Universidad de Santiago de Compostela. Facultad de Física; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Mira, J.. Universidad de Santiago de Compostela. Facultad de Física; España Fil: Rivas, J.. Universidad de Santiago de Compostela. Facultad de Física; España Fil: Breijo, M. P.. Departamento de Química Fundamental E Industrial; España Fil: Señarís Rodríguez, M. A.. Departamento de Química Fundamental E Industrial; España

Superconducting La 1.78 K 0.22 CuO 4− y has been studied by means of X-ray diffraction, scanning electron microprobe and transmission electron microscopy, in order to characterize the relative distribution of K within these samples. From microprobe and X-ray diffraction data, these materials appear to be homogeneous and show a tetragonal structure ( a≃ 3.77 A , c≃ 13.3 A ). Nevertheless, as shown below, X-ray microanalysis, electron diffraction and low resolution electron microscopy studies indicate that, on a local scale, the situation is more complex and different modulated structures based on a tetragonal La 2 CuO 4 subcell are present.

This is the accepted manuscript of the following article: Yáñez-Vilar, S., Sánchez-Andújar, M., Gómez-Aguirre, C., Mira, J., Señarís-Rodríguez, M., & Castro-García, S. (2009). A simple solvothermal synthesis of MFe2O4 (M=Mn, Co and Ni) nanoparticles. Journal Of Solid State Chemistry, 182(10), 2685-2690. doi: 10.1016/j.jssc.2009.07.028 Nanoparticles of MFe2O4 (M=Mn, Co and Ni), with diameters ranging from 5 to 10 nm, have been obtained through a solvothermal method. In this synthesis, an alcohol (benzyl alcohol or hexanol) is used as both a solvent and a ligand; it is not necessary, therefore, to add a surfactant, simplifying the preparation of the dispersed particles. We have studied the influence of the synthetic conditions (temperature, time of synthesis and nature of solvent) on the quality of the obtained ferrites and on their particle size. In this last aspect, we have to highlight that the solvent plays an important role on the particle size, obtaining the smallest diameters when hexanol was used as a solvent. In addition, the magnetic properties of the obtained compounds have been studied at room temperature (RT). These compounds show a superparamagnetic behaviour, as was expected for single domain nanoparticles, and good magnetization values. The maxima magnetization values of the MFe2O4 samples are quite high for such small nanoparticles; this is closely related to the high crystallinity of the particles obtained by the solvothermal method The authors are grateful for financial support from the MEC of Spain (Project CSD2006-00012 of Consolider-Ingenio 2010 Programme and FPI fellowship to S. Yáñez-Vilar), from the Xunta de Galicia (Project PGIDIT06PXIB103298PR, Rede Galega de Nanomedicina and Parga Pondal Programme) and from the EU (FEDER) SI

HREM has been used to study the process induced by the reaction of the HTSC YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} (commonly referred to as '123') with the lithiating agent n-BuLi. High resolution electron micrographs reveal that this reaction promotes, at room temperature, irreversible microstructural modifications into the '123' structure leading to a rather heterogeneous product. In this respect, both '247' (Y{sub 2}Ba{sub 4}Cu{sub 7}O{sub 15{minus}z}) and the '124' (YBa{sub 2}Cu{sub 4}O{sub 8}) structures appear as either extended defects within the '123' matrix or disordered intergrowths. A structural model is proposed to justify the high lithium conductivity displayed by these materials.

Following our work on lithium insertion into YBa 2 Cu 3 O 7− δ (commonly referred to as “123”) in which we observed the room-temperature formation of YBa 2 Cu 4 O 8 (“124”) [1,2], we have now found, by the same procedure using “124” as starting material, a novel phase with Y:Cu:Ba in the ratio 1:2:6 (“126”), intergrown in different proportions with YBa 2 Cu 4 O 8 and YBa 2 Cu 5 O 9 (“125”). Powder X-ray diffraction patterns and electron microscopy and diffraction suggest a unit cell of ≈ 3.80 × 3.86 × 33.4 A containing four [CuO 4 ] chain layers instead of the two observed in the original “124”.

Measurements of the temperature dependence of the magnetization (and parameters like coercivity and susceptibility) of La1-xSrxCoO3 (0.20 ≤ x ≤ 0.30) perovskites are presented. Particular attention is given to the interval of temperatures containing the ferro-paramagnetic phase transition. Curie temperature values lower than those reported previously and critical exponents are given. Additionally, the coercivity as well as the parameters of the law of approach to magnetic saturation are experimentally determined. Anomalies in Curie temperature, coercivity and law of approach to saturation are introduced confirming a non-conventional transition from ferromagnetic to paramagnetic states. © 1999 Elsevier Science B.V. All rights reserved.

[Abstract] The Pr0.79Na0.21MnO3 perovskite has been prepared in polycrystalline form by a ceramic method. We have carried out its structural characterization by synchrotron X-ray powder diffraction (SXRPD) at room temperature and at 150 K (T

We are reporting the dielectric response of La1.5Sr0.5NiO4, a system that presents a charge-ordered state above room temperature and a rearrangement of its charge-order pattern in the temperature region 160-200 K. A careful analysis of the role of the electric contacts used, sample thickness and grain size on the experimental data allows us to determine that this material exhibits high values of intrinsic dielectric constant. The variation of the dielectric constant with temperature shows a maximum in the region of the rearrangement of the charge-order pattern, which constitutes an evidence of the link between both phenomena., The original version, submitted on 31 July 2003, has been replaced, because the role of extrinsic effects is now taken into account in the calculation of the dielectric constant

We have prepared LiCo1−yAlyO2 and LiNi0.5−yAlyCo0.5O2 (0≤y≤0.3) powder samples by a low temperature sol–gel method using succinic acid as chelating agent. We have studied the details of their crystallographic and local structure by X-ray diffraction (XRD) and FTIR spectroscopy, respectively; we have analyzed their chemical composition by ICP and obtained information about the morphology of the polycrystalline particles by SEM. Also, we have studied the electrochemical performance of the as-prepared materials in the LiLiNi0.5−yAlyCo0.5O2 cells cycled in the potential range 2.5–4.2 V finding that the overall capacity of the oxides has been reduced due to the metal substitution. For example, at 4.2 V cut-off, the charge capacity of the LiLiNi0.35Al0.15Co0.5O2 cell is ca. 115 mA h/g. However, more stable charge–discharge cycling performances have been obtained as compared to those displayed by the native oxides. Finally, we have characterized the kinetics of Li-diffusion by the galvanostatic intermittent titration technique and, according to our results, Al substitution provides an increase in the chemical diffusion coefficients of Li ions in the LiNi0.5−yAlyCo0.5O2 matrix. Spanish and French Foreing Office; PAI Picasso 00717TC Spanish and French Foreing Office; HF 1999-0101

In this letter, we investigated the temperature-dependent Raman spectra of CaMn7O12 helimagnet from room temperature down to 10 K. The temperature dependence of the Raman mode parameters shows remarkable anomalies for both antiferromagnetic and incommensurate transitions that this compound undergoes at low temperatures. The anomalies observed at the magnetic ordering transition indicate a spin-phonon coupling at higher-temperature magnetic transition in this material, while a magnetostriction effect at the lower-temperature magnetic transition.

In this work we explore the overall structural behaviour of the [(CH 3)2NH2][Mn(HCOO)3] multiferroic compound across the temperature range where its ferroelectric transition takes place by means of calorimetry, thermal expansion measurements and variable temperature powder and single crystal X-ray diffraction. The results clearly prove the presence of a structural phase transition at Tt ~ 187 K (the temperature at which the dielectric transition occurs) that involves a symmetry change from R3c to Cc, twinning of the crystals, a discontinuous variation of the unit cell parameters and unit cell volume, and a sharp first-order-like anomaly in the thermal expansion. In addition, the calorimetric results show a 3-fold order-disorder transition. The calculated pressure dependence of the transition temperature is rather large (dTt/dP = 4.6 ± 0.1 K kbar-1) in that it should be feasible to shift it to room temperature under adequate thermodynamic conditions, for instance by application of an external pressure. © 2014 the Partner Organisations.

Thermoelectric, electrical resistivity and thermal conductivity studies reveal the remarkable influence of lead doping onto formation and improving properties of the Pb x Bi 2- x Sr 2 Ca 2 Cu 3 O y superconductors.

Measurements of thermoelectric power and electrical resistivity of granular Bi1.5Pb0.5Sr2Ca2Cu 3Oy are reported. Rounding of thermoelectric power near and above the critical temperature is analysed in terms of thermodynamic fluctuations of the superconducting order parameter.

In this work we report magnetically modulated microwave absorption experiments performed at 9.4 GHz from 110 up to 300 K on samples of Pr 1−x Ba x CoO 3−δ (0.10 which were prepared by the “Pechini” method.

We have studied the AC and DC magnetic properties of the lamellar compounds La 1− x Sr 1+ x CoO 4 (0⩽ x ⩽0.4). These materials are found to evolve towards an anomalous “cluster-glass”-like behaviour as x increases. The onset of the ferromagnetic order in the bidimensional phases is seen to occur at around 150 K, followed by a blocking process around 125 K. Also, present in the magnetic behaviour of these materials is the signal coming from small intergrowths of a perovskite phase, also detected by TEM, although invisible for powder-X-ray diffraction.

We have synthesized two divanadates M2V2O7 (M2+ = Co2+ and Cu2+), that are known to show different and complex magnetic arrangements at low temperatures and have studied their dielectric behavior. We have observed a change in the slope of the dielectric constant at the magnetic transition temperature, result which confirms the existence of magnetodielectric coupling in these two divanadates. The origin of the magnetodielectric coupling seems to be different in the Cu- and Co-compounds, although in both cases it is related to their frustrated magnetic arrangement. In Cu2V2O7, the dielectric anomaly arises from a spin canting due to the antisymmetric exchange which is allowed by structural symmetry. In the Co-divanadate, the structural symmetry does not allow antisymmetric exchange but the compound shows correlation between the behavior of the dielectric constant and inverse magnetization, which points to a dependence of its electrical polarization with the pair correlation function of neighboring magnetic spins.