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Os materiais multiferróicos constituem um grupo de sistemas multifuncionais com propriedades de enorme aplicabilidade na tecnologia spintrônica. No presente manuscrito, são apresentadas as características fundamentais desse grupo de materiais interessantes, exemplificando-as por meio de um composto de hexaferrita do tipo M (BaTi2Mn2Fe8O19), cuja síntese foi realizada pela técnica de reação em estado sólido. Os resultados mostram uma estrutura hexagonal que consiste em várias subcélulas caracterizadas pela presença de poliedros, cujos centros são ocupados por cátions de Fe, Mn e Ti coordenados com ânions de oxigênio para formar estruturas octaédricas, tetraédricas e bipiramidais. O caráter multiferróico foi conferido por medições de magnetização e polarização elétrica em função de campos magnéticos e elétricos, respectivamente. Esse material exemplifica a metodologia a ser seguida no projeto de novos materiais multiferróicos.

chemical attributes. The specific domain within technology referred to as spintronics, encompasses the realm of spin transport electronics. Spintronics delves into the electron spin, its inherent magnetic moment and fundamental charge, and the manipulation of these intrinsic characteristics to develop solid-state devices. In metallic systems, spintronics encloses phenomena like spin-charge coupling, which includes ferro- and ferrimagnetic materials, giant and colossal magnetoresistive materials, and metallic spins. Among the most versatile materials in the evidence of exotic properties, one of the most representative families is the so-called perovskites, widely studied in recent years including their properties in solar cell technology. Here, we present some crystallographic, compositional, morphological, optical, and magnetic attributes of the Ca2TiFeO6 double perovskite material, synthesized by the standard solid-state reaction method from high-purity precursor oxides. Rietveld refinement of experimental X-ray diffraction data revealed that this material crystallizes in a monoclinic perovskite-type structure with alternating ordering of Ti-Fe cations along the three crystallographic axes. The strongly granular surface character of the Ca2TiFeO6 materials was observed in the images from a scanning electron microscope; the electron X-ray energy dispersive spectra revealed a close match of sample composition to that expected from their chemical formula. The diffuse reflectance spectrum showed the semiconductor feature of the material with a 1.02 eV bandgap. The magnetic characterization in the 50 K < T < 335 K regime and the applied fields up to 1 kOe showed the ferromagnetic response of the material over the entire temperature range measured. These properties are promising in the spintronics industry for devices where the same material serves to process, record, read, and erase information as in the spin transistors.

In this work a study of the synthesis process, crystal structure and magnetic behavior of gadolinium manganite with Fe substitutions in Mn positions of GdMn1-xFexO3 (x=0, 0.1, 0.2) is reported. The samples were synthetized by the conventional solid-state reaction method. Structural characterization of final compounds was analyzed by Rietveld refinement, which revealed its crystallization in an orthorhombic symmetry belonging to the Pbnm (No. 62) space group. Results reveal that a and c cell parameters and the unit cell volume increase, while the lattice parameter b and the cell volume decrease with Fe substitution. The main effect in the structure is related to oxygen positions, i.e. in the octahedral distortions and rotations. DC susceptibility measurements, in the temperature regime between 4 K and 300 K on the application of an external field of 200 Oe, show a paramagnetic feature at high temperatures for all x studied values, with magnetic transitions associated to a magnetic ordered state at low temperatures (21.8 K < T < 25.2 K). Meanwhile, a ferrimagnetic transition is detected for x=0.1 close to T=30.7 K. In order to explain the appearance of ferrimagnetism for this configuration, a model is suggested where an imbalance in the magnetic structure of GdMnO3 (type-A antiferromagnetic) generated due to the introducing a Fe3+ ion in each pair consecutive unit cells is proposed. The effective magnetic moment obtained agrees to the reported value for the material with x=0.0, confirming the ferrimagnetic behavior for this concentration of Fe3+ in the structure.

Perovskite-like materials which include magnetic elements have relevance due to the technological perspectives in the spintronics industry. In this work, the magnetic, structural and electronic properties of the Ba2CoMoO6 double perovskite are investigated. Calculations are carried out through the Full-Potential Linear Augmented Plane Wave method within the framework of the Density Functional Theory with exchange and correlation effects in the Generalized Gradient and Local Density approximations, including spin polarization. From the minimization of energy as a function of volume using the Murnaghan’s state equation the equilibrium lattice parameter and cohesive properties of this compound were obtained. The study of the electronic structure was based in the analysis of the electronic density of states, and the band structure, showing that this compound evidences a conductive character for a spin channel and insulation for the other, and presents an integer value for the effective magnetic moment (3.0 μB), which allows it to be classified as a half-metallic material. The effects of pressure and temperature on thermophysical properties such as specific heat, Debye temperature, coefficient of thermal expansion and the Grüneisen parameter were calculated and analyzed from the state equation of the system. The obtained results reveal that, in the low temperature regime, the specific heat at constant volume and pressure presents an analogous behavior to each other, with a tendency to the limit of Dulong-Petit typical of the structures of cubic perovskite type, showing a value of 246.3 J/mol.K at constant volume and slightly higher values at constant pressure. The dependence of the coefficient of thermal expansion, the temperature of Debye and the Grüneisen parameter with the increase in temperature is discussed in relation to other perovskite-like materials.

Perovskite-like materials, which include magnetic elements, have relevance because their technological perspectives of applications in the spintronics industry. In this work, the magnetic, structural, electronic and thermodynamic properties of the Ba2TiMnO6 of the perovskite-like manganite are investigated. Calculations are carried out through the Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations, including spin polarization. From the minimization of energy as a function of volume using the Murnaghan’s state equation the equilibrium lattice parameter and cohesive properties of this compound were obtained. The study of the electronic structure was based in the analysis of the electronic density of states (DOS), and the band structure, showing that this compound evidences an effective magneticmoment of 3.0 μB. The pressure and temperature dependence of specific heat, entropy, thermal expansion coefficient, Debye temperature and Grüneisen parameter were calculated by DFT from the state equation using the quasi-harmonic model of Debye. A specific heat behavior CV≈CP was found at temperatures below T = 400 K, with Dulong-Petit limit values, which are quite higher than those, reported for simple perovskites.

This study reports the effect of the concentration of magnetite powders (Fe3O4) on the electrical and magnetic properties of a resin-based composite of thermoset polyester. The samples were prepared by the casting method at different concentrations: 60-40, 70-30, 80-20, 90-10 and 100-0 (% in weight), where the primary phase was resin and the secondary, Fe3O4 powders. The crystalline structure was studied using X-ray diffraction and surface characterization was carried out applying the scanning electron microscopy technique. The electrical response was measured by electric polarization curves as a function of the electric field; and the volumetric electrical resistivity, by an electrometer. The magnetic response was determined by magnetization curves as a function of temperature and intensity of the applied magnetic field. The structural analysis indicates that crystallinity increases as higher concentrations of Fe3O4 are added to the samples. The electrical characterization of the material reveals that the volumetric resistivity decreases as the content of magnetite increases. These reactions indicate an insulation-conductor transition with increasing dielectric constant values. The magnetic characterization presents a linear increase of the saturation of magnetization and magnetic moment as a function of the amount of magnetite added to the polymer matrix, whereas the coercivity shows behaviors of soft magnetic materials for T ˃ Tv and for T < Tv, where Tv represents the temperature of Verwey.

In this paper the synthesis of the LaBiFe2O6 material by the modified Pechini method is reported. Structural, morphologic, magnetic and optic experimental studies were performed. Rietveld refinement of x-ray diffraction patterns revealed that LaBiFe2O6 crystallizes in an orthorhombic perovskite structure (space group Pnma, # 62). Scanning electron microscopy images showed the nanometric feature of grains. X-ray dispersive spectroscopy permitted to infer the obtaining of the LaBiFe2O6 expected stoichiometry. Results of magnetic susceptibility as a function of temperature and field magnetization evidenced mixed ferromagnetism and superparamagnetism behavior at T=300 K. Mössbauer spectroscopy supported the superparamagnetic and ferromagnetic responses as a result of the nanogranular morphology and anisotropy effects. Spectrum of diffuse reflectance suggest that this material behaves as a semiconductor with energy gap Eg=2.13 eV.

We report experimental and theoretical results of crystal structure, morphology, magnetic and electric features, and electronic structure for the Sr2DyNbO6 ceramic compound. Samples were produced by the solid-state reaction recipe. X-ray diffraction experiments show that the material crystallizes in a monoclinic structure, P21/n space group. SEM images exhibit a granular submicrometric surface. Temperature curves of magnetic susceptibility reveal a paramagnetic response. Curie law fitting permitted to obtain a magnetic moment 10.28 μB. Polarization as a function of electric fields shows a hysteretic feature with 264.28 relative dielectric constant at 300 K. DFT calculations of electronic structure suggest the semiconductor character of this material, energy gap 3.21 eV for the spin-up polarization and 0.26 eV for spin-down. The calculated effective magnetic moment was 10.0 μB, which is strongly in accordance with the measured value. The theoretical cell parameters obtained from the Murnaghan state-equation are 98.5% in agreement with the experimental result.

The Sr2HoNbO6 complex perovskite has been synthesized by solid-state reaction. X-ray diffraction pattern reveals that Sr2HoNbO6 material crystallizes in a cubic structure, Fm3̅m space group, lattice constant a=8.018 Å, which has a lattice mismatch ~3% with YBa2Cu3O7-δ. The chemical stability of Sr2HoNbO6 with YBa2Cu3O7-δ superconducting has been studied by x-ray diffraction and measurements of magnetization as a function of temperature on Sr2HoNbO6-YBa2Cu3O7-δ composites. X-ray diffraction patterns of the composite shown that all the X-ray diffraction peaks could be indexed for either Sr2HoNbO6 or YBa2Cu3O7-δ with no extra peak detectable. This result implies that these compounds remain as two different separate phases in the composite with no chemical interaction. Magnetic response shows that superconducting transition temperature of pure YBa2Cu3O7-δ and Sr2HoNbO6-YBa2Cu3O7-δ composites is 93,5 K. These favorable characteristics of Sr2HoNbO6 show that it can be used as a potential substrate material for growth of YBa2Cu3O7-δ superconducting films.

En este trabajo reportamos la síntesis, la caracterización estructural, el comportamiento ferroeléctrico y las propiedades electrónicas de la perovskita compleja Ba2ZrTiO6. Las muestras fueron sintetizadas mediante el método estándar de reacción de estado sólido. La estructura cristalina se estudió a través de experimentos de difracción de rayos X y análisis de tipo Rietveld. Los resultados revelan que el material cristaliza en una estructura romboédrica, perteneciente al grupo espacial R-3 (#148), con un parámetro de red a= 5,8038(7) Å. La respuesta ferroeléctrica del material se estableció a partir de curvas de polarización en función del campo eléctrico aplicado. Nuestros resultados muestran que la perovskita Ba2ZrTiO6 evidencia un comportamiento histerético ferroeléctrico a temperatura ambiente. Los estudios de la estructura electrónica muestran que esta cerámica se comporta como un material no metálico con brecha de energía 2,32 eV. Los parámetros estructurales obtenidos a partir de la minimización de energía, a través de la ecuación de estado Murnaghan, son 99.5% acordes con los datos experimentales.

We reported a study of the structural and magnetic properties of BaZrO3 (BZO) as possible substrate material for the production of YBa2Cu3O7-δ (YBCO) superconducting films. Rietveld analyses of the X-ray diffraction pattern show that BZO crystalizes as a cubic perovskite, space group Pm3m (#221). Chemical stability and crystallographic coupling between BZO and YBCO were examined by characterizing YBCO/BZO (10, 30 and 50 YBCO vol%) polycrystalline composites. Morphological and compositional analyses of composites were performed through scanning electron microscopy and energy dispersive X-ray experiments, respectively. Response of magnetization measurements revealed that the proximity of BZO does not affect the superconducting transition temperature (Tc=90,2 K) of YBCO material. Our results evidenced that the BZO is an excellent candidate to be substrate for the fabrication of YBCO superconducting thin films.

En este trabajo reportamos el análisis estructural, ordenamiento magnético, carácter ferroeléctrico y estructura electrónica de la perovskite compleja Sr2TiMnO6. Las muestras fueron producidas mediante reacción de estado sólido. El análisis cristalográfico fue realizado a través de refinamiento Rietveld de los patrones experimentales de rayos x. Los resultados muestran que este material cristaliza en una perovskita tetragonal correspondiente al grupo espacial I4/mmm. Hemos obtenido un acuerdo del 99% entre las propiedades estructurales predichas por la teoría del funcional de la densidad y el ordenamiento estructural determinado mediante refinamiento Rietveld. A través de medidas de susceptibilidad en función de la temperatura encontramos ordenamiento magnético para una temperatura crítica de 44.8 K. Por medio del ajuste con la teoría molecular de ferrimagnetismo establecimos que el ordenamiento magnético se relaciona con una transición paramagnético-ferrimagnético, la cual se corrobora por el comportamiento del inverso de la susceptibilidad en función de la temperatura. La constante de Curie permitió determinar un momento magnético efectivo de 3.5 mB. Medidas de magnetización en función del campo aplicado a T = 40 K, muestra un comportamiento histerético. La curva de polarización en función del campo eléctrico evidencia una característica ferroeléctrica. Experimentalmente se demuestra que el material se comporta como un multiferróico. Cálculos Ab initio de la densidad de estados fueron realizados por medio de la teoría de funcional densidad y del método ondas planas aumentadas linealizadas para orientaciones de espín arriba y abajo. Los cálculos de intercambio y potencial de correlación fueron incluidos a través de la aproximación de densidad local LDA+U. Los resultados de la densidad de estados muestran la característica aislante de este material con un momento magnético efectivo de 3.3mB.

Las propiedades de las películas superconductores de alta temperatura crítica son dependientes de parámetros cristalográficos y de la estabilidad química entre sustrato y película. Por lo tanto, con el fin de producir una perovskita cúbica compleja policristalina de NdBa2SbO6, en forma de pastilla, por medio de la técnica de reacción de estado sólido. Este material no conductor fue mezclado con el policristal superconductor YBa2CuO(7-δ) en proporciones volumétricas. Se encontró un buen acoplamiento de los parámetros de red a través de la técnica experimental de difracción de rayos X. La influencia de los porcentajes de volumen del NdBa2SbO6 sobre las propiedades superconductoras del YBa2CuO(7-δ) fue estudiada a través de las medidas de magnetización dc. Los resultados obtenidos muestran que el material NdBa2SbO6 es un excelente candidato a sustrato para crecer películas superconductoras de YBa2CuO(7-δ).

We report here the synthesis process of the perovskite-like complex material Bi0.5R0.5FeO3 (R=Eu, Sm, Dy) using the ceramic method, as well as its structural, optical, magnetic, and electrical characterizations. Refined X-ray diffraction data revealed that this material crystallizes in an orthorhombic structure (space group Pnma number 62). The band gap value in the optical response shown in the diffuse reflectance spectroscopy curve was typical of semiconductor materials. The magnetization exhibited a very low coercive field hysteretic behavior, which is characteristic of weak ferromagnetism, for all temperatures examined below 300 K and the various magnetic fields applied. The real and complex electric permittivity curves showed the occurrence of dielectric relaxation processes at 113 K in agreement with reports of pyroelectric and thermo-stimulated currents as a function of temperature revealing the appearance of ferroelectric polarization below 113 K with possible magnetoelectric coupling. On the other hand, we made a theoretical study of the electronic structure with and without the inclusion of a Berry distortional phase and ab-initio calculations following the density functional theory formalism and the pseudopotential plane wave method. In this formalism, the exchange and correlation mechanisms are described by the generalized gradient approach (GGA + U) considering spin polarization. The Berry phase analysis suggested the occurrence of ferroelectricity at temperatures below 113 K consistent with the experimental analysis evidencing a biferroic behavior at low temperatures given that the distortional phase introduces hybridizations between the 3d-Fe and 2p-O states favoring the appearance of Dzyaloshinskii-Moriya interactions, which, in turn, facilitate the appearance of ferroelectricity coexisting with a weak ferromagnetism. The thermodynamic properties in the presence or absence of the Berry phase by means of the Debye quasiharmonic model revealed the appearance of a ferroelectric transition at 113 K, which corroborates their magnetoelectric nature at low temperatures. The ferromagnetic semiconducting character found at room temperature enhances this material for applications in spintronics technology.

This work describes the production and magnetic characterization of a compound base on epoxy resin and powdered rubber reinforced with magnetite (𝐹𝑒3𝑂4) poder. Also it is presented the análisis carried out on the components, which are according to the magnetic charging inside the polymeric matrix. the magnetic properties of the material they were made at different temperaturas in a magnetic range from -30000 to 30000 Oe the morphology of both the precursons like the compounds was determined by scanning electron microscopy and structural characterizatin was performed by X- ray diffraction (XRD). The diffraction pattern obtained in the XRD measurements allows us to observe that, with the addition of powdered magnetite in the plastic matrix, an amorphous-crystalline transition is created in the material. Through the images obtained by SEM, the presence of hematite in the precursor (𝐹𝑒3𝑂4) and irregular size in the samples is observed. The compounds behave like a soft magnetic material and present changes in the variation of the coercive force, both with the increase in temperature and with the percentage variation of magnetite volume in the polymer matrix. The manufactured material can be used in applications where the compound should be easily detectable.

In this work we report the synthesis and characterization of the high-temperature superconductor La0.5RE0.5BaCaCu3O7-δ (RE=Y, Gd, Dy, Ho, Yb). The samples were prepared by the solid-state reaction process, starting from precursory powders of RE2O3 of 99.9% of purity. The structural analysis was made by means of Rietveld refinement of powder X-ray Diffraction data. The results show that the system crystallizes in a structure tri-perovskita tetragonal, for all the RE. Resistivity measurements in function of the temperature evidence the beginning of the transition superconductor however above 70 K., the width of the transition and the value of temperature for which the resistance is rigorously null, they depending strongly of the ionic radius of the RE [ABSTRACT FROM AUTHOR]

Este trabajo tiene como propósito revisar el estado del arte en la síntesis y caracterización de materiales de matriz polimérica reforzados con compuestos a base de carbón o ferritas para su uso como materiales atenuadores de interferencia electromagnética (EMI). Recientemente, este tipo de materiales han sido objeto de investigación debido a sus potenciales aplicaciones tecnológicas, economía y de ser además ambientalmente amigables, puesto que polímeros o cauchos reciclados se pueden utilizar para su fabricación. Estos compuestos pueden ser empleados en la producción de blindajes electromagnéticos, transductores, entrega focalizada de medicamentos, marcación de órganos, hipertermia magnética, etc. Para la fabricación de este tipo de materiales compuestos se usan refuerzos particulados, fibras o láminas y como matrices polímeros termoplásticos o termoestables, cauchos sintéticos o naturales. El método de producción de los compuestos (mezcla fundida, métodos químicos, etc.) influye en las propiedades eléctricas, magnéticas y electromagnéticas del material obtenido, debido a la relación de aspecto de los refuerzos: compuestos con elevada relación de aspecto de sus refuerzos tendrán mejores propiedades magnéticas, eléctricas y desempeño frente a la interferencia electromagnética. El blindaje electromagnético de estos materiales se cuantifica a través de la efectividad del blindaje (SE) o en otros casos a través de la pérdida reflectiva (RL). Una efectividad de blindaje de 30 dB corresponde a 99,9% de atenuación de la radiación electromagnética incidente. En todos los trabajos se comprueba que las propiedades del compuesto dependen de la cantidad y del tipo de refuerzo adicionado a la matriz.

One very interesting characteristic of the type II superconductor materials is observed in the neighborhood of the transition between normal and superconductor states, which is related with the occurrence of new transport channels of superparticles still in the normal phase. This phenomenon is known as thermodynamic fluctuations and is conformed by some types of observable effects in the high temperature oxides. These are experimentally accessible by measurements of equilibrium and transport properties. Although it is relatively easy t o obtain information of the experimental evidence of this phenomenon, the understanding of the physical mechanisms involved is not frequently explicit in the literature. The aim of this article is to present the origin, the consequences and any experimental evidences of the effects of thermal fluctuations in the electric conductivity, on the magnetic fields application, in high critical temperature superconductors.