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Ceramic samples of Tb2FeCoO6 were synthesized by the solid-state reaction recipe. The crystallographic analysis revealed that the material crystallizes into a complex perovskite-type orthorhombic structure (space group P21/n, # 14) with octahedral distortions. The surface topography of the material was evaluated by means of scanning electron microscopy, observing densified submicrometric granular characteristics in the form of polyform sheets. Energy scattering spectra showed 98% agreement between the experimental composition and the stoichiometry of the Tb2FeCoO6 formula. The DC magnetization curves as a function of temperature exhibit irreversible behavior at low temperatures related to the distortionary character of the Fe–O6 and Co–O6 octahedra in the structure. Magnetization hysteresis curves as a function of the applied field at temperatures from 5 K up to 300 K reveal a ferromagnetic type ordering in the material. The I–V characteristic suggests a semiconductor electrical response with a varistor-type tendency and strong dependence of the polycrystalline nature of the samples. Calculations of band structure and density of electronic states predict the semiconductor characteristic for this double perovskite, with Eg = 2.48 eV and the ferromagnetic behavior is attributed to extended super-exchange spin interaction in the Fe–O–Co ions. The ferromagnetic semiconductor nature of the Tb2FeCoO6 material foresees potential applications in the novel spintronics industry.

In search of unconventional ferromagnetic mechanisms in perovskite-like materials, the synthesis process, crystal structure, surface morphology, composition, and optical and magnetic behaviors of the narrowly studied rare-earth antimoniate Ba2SbSmO6, as well as its electronic structure calculated using the density functional theory, are reported in the present. Samples were synthesized by means of the solid-state reaction method. The structural analysis of the obtained compound was performed by Rietveld refinement of the experimental X-ray diffraction experimental data, which revealed its crystallization in a cubic complex perovskite, belonging to the space group Fm $$\stackrel{-}{3}$$ m (#225) with lattice parameter a = 8.5085(5) A. Surface morphological studies revealed the polycrystalline character of the material, with inhomogeneous granular microstructure and nanometric average size. The measured composition is close to that expected from the stoichiometry of the material. Temperature-dependent magnetic susceptibility measurements exhibited magnetic anisotropy effects and magnetization hysteresis curves showed weak ferromagnetic response for the examined temperature values. The electronic structure was calculated by means linearized augmented plane waves (FP-LAPW) in the framework of the density functional theory (DFT). Curves of density of states as a function of the wave number revealed the insulator behavior of the Ba2SbSmO6 material. The weak ferromagnetism exhibited by this perovskite-like compound is attributed to the occurrence of spin-orbit interaction effects of the 4f-Sm3+ electrons hybridized with 2p–O2− orbitals.

With the aim to produce a material with magnetic and semiconductor properties, a lanthanide bismuth-ferrite type material is proposed in this work. Polycrystalline samples of Dy2Bi2Fe4O12 were produced following the standard solid-state reaction method. Structural characterization through the X-ray diffraction technique evidences that the synthesized ceramic crystallizes in a perovskite-like orthorhombic structure, belonging to the Pnma (#62) space group. Scanning electron microscopy images revealed the granular nature of the samples with mean grain sizes of nanometric order. X-ray energy dispersion spectra allowed establishing that in the samples there are no elements different from those expected in the stoichiometric proportions suggested by the chemical formula of the compound. Studies of electrical behavior were carried out using I–V curves and electrical permittivity as a function of frequency and temperature, which show the diode varistor feature of this material with a marked Maxwell–Wagner-type trend. The semiconductor band gap was determined from the analysis of diffuse reflectance spectra that reveal Eg = 1.88 eV. Temperature-dependent magnetization curves for applied fields of 1.0, 5.0 and 10 kOe showed the behavior expected for ferromagnetic type materials, with strong evidence of magnetic frustration causing irreversibility in curves obtained from Zero Field Cooling and Field Cooled measurement procedures. The magnetization hysteresis curves at temperatures of 50, 200 and 300 K exhibit a ferromagnetic response with evidence of superparamagnetic effects due to the significant presence of nano-sized ferromagnetic grains. Based on the obtained results, it can be affirmed that the material behaves like a soft ferrimagnetic semiconductor with low coercive field (between 500 Oe and 700 Oe) and remnant magnetization (between 2.15 × 10−4 emu/g and 3.25 × 10−4 emu/g) that would have eventual technological implications in the spintronic industry.

Polycrystalline samples of Sm2Bi2Fe4O12 were produced by the standard solid state reaction method. The structural characterization revealed that the material crystallizes in an orthorhombic structure (Pnma # 62 space group). Scanning electron microscopic images showed granular and densified characteristics on the surface and inside the samples, with two well-differentiated grain sizes: micrometric and submicrometric. From energy-dispersive X-ray spectra, it was established that the samples contained the expected elements in stoichiometric proportions suggested by the chemical formula of the compound. I–V curves and measurements of electrical permittivity as a function of temperature showed semiconductor-type behaviors, strongly dependent on the polycrystalline character of the material and a Maxwell–Wagner-type dielectric tendency. The optical spectral analysis corroborated the semiconductor behavior with the optical bandgap Eg = 2.62 eV. Temperature-dependent magnetization results have the expected form for ferromagnetic-type materials, with evidence of disorder that gives rise to magnetic irreversibility between the zero-field cooling and field cooling measurement procedures. Magnetization curves as a function of the applied field showed a hysterical response, even at room temperature, revealing the occurrence of ferromagnetic ordering in the material. The ab initio calculations of the electron density of states reveal the appearance of a mean semiconductor band gap whose value is in agreement with that measured experimentally. The effective magnetic moment is attributed to the majority contributions of the 3d-Fe orbitals. At low temperatures, the behaviors of the specific heat at constant volume and pressure are similar, with a tendency of the former towards the Dulong–Petit limit. Strong changes in all the thermophysical properties studied are evident due to the effects of pressure and temperature on the wave behavior of the crystal lattice. At higher temperatures, a strong variation in the Debye temperature induces divergence in thermophysical parameters for different applied pressures. The physical parameters related to the coexistence of the semiconductor and ferromagnetic properties in the material suggest possible technological implications in the spintronics industry.

The Z-type Sr3Co2Fe24O41 hexaferrite constitutes a family of relatively new materials, which offers potential technological applications in the spintronics industry due to its magnetoelectric properties at room temperature. In this work, synthesis of the Sr3Co2Fe24O41 material following both citrate and Pechini methods is reported. X-ray diffraction patterns evidence that the obtained samples crystallize in hexagonal structures, belonging to the P63/mmc (#194) space group. Micrographs of scanning electron microscopy reveal the hexagonal characteristic of grains in the homogeneous and strongly densified surface. Measurements of magnetization as a function of applied fields show the ferromagnetic hysteretic behavior of material. Low-temperature curves of susceptibility (50 K T > TC). A drastic change in the thermogravimetric curve at T = 683 K is attributed to the loss of magnetic force caused by the transition between ferromagnetic and paramagnetic states.

The monophasic polycrystalline ceramic perovskite-based Eu2Bi2Fe4O12 was synthesized by the solid-state reaction method. X-ray diffraction measurements in the Bragg–Brentano geometry and Rietveld analysis reveal that this material crystallizes in an orthorhombic structure with Pnma (#62) space group. Average grain size of 450 nm is calculated of a log-normal distribution and obtained by means scanning electron microscopy images. Results from magnetization, pyroelectric and complex impedance measurements as a function of temperature (50 K up to 300 K) show the occurrence of dielectric and magnetic relaxation process starting simultaneously at 112.8 K. The tendency of real and imaginary curves of the dielectric permittivity at temperatures close to room temperature has also shown strong ac conductivity contributions attributed to porosity effects. The magnetization hysteresis loop at room temperature confirms that this new perovskite-based material has a ferromagnetic response. Signature of superparamagnetism effects is also observed as a consequence of the nanometric grain size. Thermostimulated current measurements as a function of temperature reveal the occurrence of ferroelectric polarization for the temperature regime below T = 112.8 K. Diffuse reflectance experiments permitted to establish the semiconductor nature of this material at room temperature with an energy gap of 2.65 eV.

The synthesis process of the polycrystalline ceramic compound Nd2SrMn2TiO9 by means of the solid-state reaction procedure is reported. The crystalline structure was analyzed through X-ray diffraction experiments in the Bragg–Brentano recipe. The Rietveld refinement of the diffraction pattern by using the GSAS code shows that this material crystallizes in an orthorhombic structure, space group Pnma (#62), with lattice parameters a = 5.4764(6) Ǻ, b = 7.7468(6) Ǻ, and 5.4810(6) Ǻ. The surface morphology was studied by scanning electron microscopy images, which evidence the formation and compacting of grain with mean size 352.63 nm. Semiquantitative compositional analysis performed by means of Energy Dispersive X-ray Spectroscopy shows the stoichiometric composition of the samples. Measurements of magnetization as a function of temperature reveal that this compound has a ferromagnetic behavior. The analysis with the Curie equation permitted to establish an effective magnetic moment μeff = 4.33 μB, which is 95.7% in agreement with the theoretical value expected from the Hund's rules. Measurements of DC resistivity as a function of temperature show a conductor behavior below the Curie temperature and insulator above. Evidences of a nonlinear response as a function of frequency with high values of relative dielectric constant reveal the occurrence of giant dielectric constant with ϵr = 6480 for ν = 100 Hz.

1 recurso en línea (páginas 51-61)., We report structural analysis, surface morphology, magnetic ordering, dielectric response, optical feature and the electronic structure of the Dy2BiFeO6 novel complex perovskite. The samples were produced by the standard solid-state reaction recipe. Crystallographic analysis was performed by Rietveld refinement of experimental X-ray diffraction patterns. Results show that this material crystallizes in a perovskite with orthorhombic structure, which corresponds to the Pnma (#62) space group. From the Curie-Weiss fitting on the curve of susceptibility as a function of temperature we establish that the ordering corresponds to a paramagnetic-antiferromagnetic transition, with a Weiss temperature θ=-18,5 K, which is compatible with the behavior of the inverse of susceptibility as a function of temperature, and a Néel temperatura TN=50,8 K. The Curie constant allowed for us to obtain an effective magnetic moment of 15,7 μB. The result of magnetization as a function of the applied field, measured at T=50 K, shows a magnetic hysteresis behavior that corroborate the magnetic ordering present for this temperature value. Measurements of the dielectric constant as a function of applied frequencies at room temperature give as a result a high relative dielectric constant (ε=780). The reflectance curve as a function of the wavelength reveals the typical behavior of a double perovskite-like material and permits to obtain the energy gap 2,74 eV, which is characteristic of a semiconductor material., En este trabajo reportamos el análisis estructural, morfología superficial, ordenamiento magnético, respuesta dieléctrica y característica óptica de la nueva perovskita compleja Dy2BiFeO6. 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 ortorrómbica correspondiente al grupo espacial Pnma (#62). Por medio del ajuste de Curie-Weiss a la respuesta de la susceptibilidad magnética en función de la temperatura se estableció que el ordenamiento magnético se relaciona con una transición paramagnético-antiferromagnético con una temperatura de Weiss θ=-18,5 K, la cual es acorde con el comportamiento del inverso de la susceptibilidad en función de la temperatura, y una temperatura de Néel TN=50,8 K. La constante de Curie permitió determinar un momento magnético efectivo de 15,7 μB. Medidas de magnetización en función del campo aplicado a T=50 K, muestran un débil comportamiento histerético, que corrobora el ordenamiento magnético presente a esa temperatura. Mediciones de la constante dieléctrica en función de la frecuencia aplicada a temperatura ambiente dan como resultado una alta constante dieléctrica relativa a bajas frecuencias (ε=780). La curva de reflectancia en función de la longitud de onda revela el comportamiento típico de un material de tipo perovskita doble y permite la obtención de la brecha de energía de 2,74 eV característico de un material semiconductor., Bibliografía: páginas 60-61.

Se reporta el efecto de la concentración de polvos de magnetita (Fe3O4) sobre las propiedades eléctricas y magnéticas de un material compuesto a base de resina de poliéster termoestable. Las muestras se elaboraron mediante el método de colado manual en concentraciones de: 60-40, 70-30, 80-20, 90-10 y 100-0 (% en peso), donde la fase mayoritaria es la resina y la minoritaria los óxidos de Fe3O4. La estructura cristalina se estudió usando la técnica de difracción de rayos X y la caracterización superficial tuvo lugar a través de la técnica de microscopía electrónica de barrido. Se midió la respuesta eléctrica por medio de curvas de polarización eléctrica en función del campo eléctrico y de resistividad eléctrica volumétrica a través de un electrómetro. La respuesta magnética se determinó mediante curvas de magnetización en función de la intensidad de campo magnético aplicado y en función de la temperatura. El análisis estructural indica que el porcentaje de cristalinidad aumenta a medida que se adiciona la concentración de Fe3O4 a las muestras. La caracterización eléctrica del material evidencia que la resistividad volumétrica disminuye con el incremento de magnetita, mostrando una transición aislante-conductor, con valores de la constante dieléctrica cada vez mayores. La caracterización magnética evidencia un aumento lineal de la magnetización de saturación y del momento magnético en función de la cantidad de magnetita adicionada a la matriz polimérica, mientras que la coercitividad evidencia comportamientos de materiales magnéticos blandos tanto en T˃TV como en T

A comprehensive investigation of the general properties of the Sr2DyRuO6 complex perovskite was undertaken. Crystal structure characterization performed by X-ray diffraction measurements and Rietveld analysis allowed establishing that the material crystallizes in a distorted monoclinic perovskite-like structure belonging to the P21/n (#14) space group, with alternating distribution of Dy3 + (2c: 0, 0.5, 0) and Ru5 + (2d: 0.5, 0, 0). Because of the mismatch in the ionic radii, the DyO6 and RuO6 octahedra are forced to tilt around the cubic directions so as to optimize the Sr–O inter-atomic bond lengths. Morphological characterization carried out by scanning electron microscopy indicated a particle size D = 37.17 nm and an activation energy Q = 109.8 kJ/mol. Semi-quantitative compositional study, performed through energy-dispersive X-ray experiments, corroborated that the pure phase of the Sr2DyRuO6 was correctly obtained. Magnetic properties determined from the fit of the Curie–Weiss law to the curves of magnetic susceptibility as a function of temperature showed that Sr2DyRuO6 exhibits an antiferromagnetic-like behavior at low temperatures as a consequence of a magnetic transition at T = 38 K. Data collected with respect to the field dependence of the magnetization showed the existence of a weak ferromagnetic moment relationship with antiferromagnetic-like behavior. Density functional theory allowed establishing the optimum electronic structure for Sr2DyRuO6, and the study of the density of states showed that Dy3 + and Ru5 + are responsible for the magnetic character of the compound, with the prediction that at T = 0 K it behaves as a half-metallic material. The spin magnetic moment of the cell is close to 16 μB, and the integer number of Bohr magneton is a signature of half-metallic character. Evolution of crystal structure at high temperature revealed that Sr2DyRuO6 does not undergo any structural phase transitions, since the Bragg reflections [hkl] do not undergo changes, and the structure is preserved.

This work describes the production and characterization of a composite material based on magnetite filled HDPE, which is commonly known for its magnetic properties. Composites of this kind are used in different applications such as microwave absorption, transducers and biomedical applications like drug delivery, organs tagging, etc. The samples were produced according to different volume ratios of magnetite and HDPE. The semiquantitative analysis conducted by XRD revealed the presence of hematite within the mineral magnetite used as a filler in the composites. The crystallinity degree was calculated through X-ray diffraction tests. The XRD results showed how there is an amorphous-crystalline transition due to the magnetite increasing content. The crystallinity percent (χc ) for samples filled with 40% of magnetite volume was 90% while the (χc ) for samples filled with 10% of magnetite volume was 80%. Which may be related to the increased magnetite particles into the plastic matrix for reinforcement contents up to 30% by volume, as evidenced in the images obtained through scanning electron microscopy (SEM). The samples were electrically characterized through volume resistivity measurements and electric polarization. The results showed that for ratios less than the 20% of magnetite there is no substantial reduction in the resistivity of the composite samples compared to the unfilled HDPE samples, but for magnetite ratios above 30% the composite samples showed a substantial reduction of six orders of magnitude in their volumetric resistivity. The electric polarization showed how the composite material undergoes a transition, going from an insulating material (for samples with 10% of magnetite volume) to a resistive material where the current and voltage are in phase (for samples with 30% and 40% of magnetite volume). The magnetization curves showed that the saturation magnetization (from 17,3 to 60,5 emu/g) and remanence (from 0,94 to 5 emu/g) increase in samples with high magnetite contents. The presence of the hematite phase in the samples could have affected the magnetization saturation and the remanence values in the hysteresis curves. Magnetization curves as a function of temperature showed the Verwey samples transition around the 120K and confirmed that the magnetization increases as the magnetite volume within the matrix increases. © 2017. Acad. Colomb. Cienc. Ex. Fis. Nat. Se describe la producción y caracterización de un material compuesto basado en matrices de polietileno de alta densidad (HDPE) reforzadas con magnetita pulverizada. Compuestos de este tipo son usados para diferentes aplicaciones como la fabricación de escudos de absorción electromagnética, transductores, entrega focalizada de medicamentos, marcación de órganos, etc. Las muestras fueron producidas de acuerdo a diferentes proporciones en volumen de magnetita y HDPE. Los análisis semicuantitativos llevados a cabo por medio de DRX dejan en evidencia la presencia de hematita al interior de la magnetita mineral usada como refuerzo del compuesto. El porcentaje de cristalinidad de los compuestos se calculó a través de difracción de rayos X. Los resultados de la difracción mostraron una transición amorfo-cristalino del compuesto, debida al creciente contenido de magnetita al interior de la matriz. El porcentaje de cristalinidad (χc) de las muestras reforzadas con un 40% en volumen de magnetita fue del 90% mientras que para las muestras reforzadas con el 10% en volumen la cristalinidad fue del 80%. Esto puede estar ligado a la mayor proliferación de partículas de magnetita al interior de la matriz plástica para contenidos de refuerzo superiores al 30% en volumen, tal y como se evidenció en las imágenes obtenidas a través de microscopía electrónica de barrido (SEM). Las muestras fueron eléctricamente caracterizadas a través de medidas de resistividad volumétrica y polarización eléctrica. Los resultados mostraron que para proporciones del refuerzo de magnetita iguales o inferiores al 20% no hay una reducción substancial en la resistividad de los compuestos comparada con la del polietileno sin reforzar. En cambio, para proporciones de magnetita iguales o superiores al 30% en volumen los compuestos muestran una reducción en la resistividad de hasta seis ordenes de magnitud. La polarización eléctrica deja en evidencia como el material compuesto presenta una transición al pasar de ser completamente aislante (10% en volumen de magnetita) a ser un material resistivo donde la corriente y el voltaje se encuentran en fase (muestras reforzadas con 30%-40% de volumen de magnetita). Las curvas de histéresis magnética en función del campo aplicado muestran un incremento constante en la magnetización de saturación (de 17,3 a 60,5 emu/g) y en la magnetización remanente (de 0.94 emu/g a 5 emu/g), al aumentarse el contenido de magnetita en las muestras. La presencia de hematita en las muestras pudo haber afectado los valores de la magnetización de saturación y de remanencia en las curvas de histéresis magnética. Las curvas de magnetización en función de la temperatura dejan en evidencia la transición de Verwey de la magnetita alrededor de los 120K, a la vez que confirman el aumento en la magnetización de las muestras conforme el contenido del refuerzo aumenta al interior de la matriz. © 2017. Acad. Colomb. Cienc. Ex. Fis. Nat.

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 the synthesis and characterization of the new Bi4LaSmFe2Ti3O18 ferroelectric ceramic. X-ray characterization reveals reflections for layered perovskite Aurivillius system. Rietveld analyses of the powder pattern shows that Bi4LaSmFe2Ti3O18 crystallizes in orthorhombic structure, which corresponds to the space group F2/mm (#42), with lattice parameters a=5.4240(16) Ǻ, b=5.4078(23) Ǻ and c=50.2440(12) Ǻ. Scanning electron microscopy (SEM) reveals the formation of dense material with plate-like morphology. Electric polarization curves were measured by means of a radiant ferroelectric tester, at room temperature in bulk samples and exhibit an intrinsic ferroelectric response, even at low applied fields. Measurements of the magnetization as a function of temperature after Zero field cooling and field cooling were carried out by using a MPMS Quantum Design SQUID magnetometer. We found an effective magnetic moment of 7.95 µB, which is 95.8% in agreement with the expected value calculated from Hund׳s rules. Magnetization curves as the function of applied fields reveal an incipient hysteretic behavior at room temperature.

Comprehensive research of the synthesis process by high temperature solid-state reaction method, the crystal structure characterization, and the magnetic properties of the Aurivillius type Bi-layered perovskite-like structure Bi4Gd2Ti3Fe2O18 was undertaken. Patterns of X-ray diffraction measurements and Rietveld analysis allow us to establish that this material crystallizes in a pseudo-orthorhombic structure which belongs to the I2cm (#46) space group. The crystal structure is characterized by Bi2O2 layers and complex perovskite-like structures, with quintuplets octahedra TiO6, and the Bi-cations occupying the A-site. The unit-cell parameters are given by a=5.5234(2) Å, b=5.5312(2) Å, and c=52.5642(2) Å, the angles are α = β = γ = 90.0°, and unit-cell volume V=1605.9(1) Å3. Magnetic properties found from the fit of Curie-Weiss law to the curves of magnetic susceptibility χ as a function of temperature show that the Bi-layered Aurivillius material Bi4Gd2Ti3Fe2O18 behaves as a paramagnetic material with evidence of ferromagnetic contributions, and allows for determining the Curie constant, given by C=0.014 emuK/mol, effective magnetic moment of PeffμB=7.78μB, and temperature independent susceptibility χo=0.0064 emu/mol. Field dependence of magnetization proves strongly paramagnetic behavior of the Bi-layered Bi4Gd2Ti3Fe2O18.

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.

This work reports the synthesis, structural characterization, ferroelectric and magnetic behavior of the La0.53Ca0.26 Ba0.21Mn0.77Ti0.21Zr0.02O3 (LCBMTZ) complex perovskite. The material is obtained by the solid state reaction method. Rietveld refinement of X-ray diffraction experiments shows that the material crystallizes in a tetragonal perovskite structure, space group P4mm (#99). Impedance spectroscopy measurements give evidence of ferroelectricity with high values of electric permittivity (e′=119.2) and electrical polarization curves confirm it. Measurements of magnetic hysteresis loops at 10 and 150 K reveal a ferromagnetic behavior. On the other hand, the comparison of the FC and ZFC magnetization and resistivity measurements shows different magnetic regimes associated with changes in the resistivity. The analysis of these curves suggests the existence of magnetoelectric coupling in temperature regimes below 228.09 K.

In this work, we report synthesis and characterization of the new La2SrCo2FeO9 triple perovskite material. The samples were produced by the solid-state reaction method. The analyses of the XRD patterns were made by Rietveld refinement through the GSAS code. The results reveal that the material crystallizes in an orthorhombic complex perovskite, space group Immm (#71) with lattice parameters a=5.4314(3) Ǻ, b=5.4583(3) Ǻ and c=7.7018(2) Ǻ. SEM micrographs evidence a strongly diffused granular morphology with mean grain size of 2 μm and the EDX spectra show that the chemical composition of samples are in good agreement with the nominal values of the stoichiometric formula. 57Fe Mossbauer spectroscopy recorded at 300 K reveals two sites in concordance with the X-ray diffraction measurements, and its valence state is +3, as determined from the isomer shift found. At 4.2 K magnetic ordering with canting of the Fe moments is found. Measurements of the magnetization as a function of temperature permitted us to determine the ferromagnetic characteristic of material with an effective magnetic moment of 9.7μ B.

In this work we report analysis of experimental data of the magnetization of La1.5−x Ba1.5+x−y Ca y Cu3O z superconducting system. The data are analyzed in terms of thermal fluctuations on the magnetization excess M(T) for different values of temperature in each of the samples. We describe a procedure for extracting the penetration depth in the ab plane (1537–1650 A) and the coherence length in the ab plane (21–23 A) parameters from the magnetization, as a function of the applied magnetic field. This procedure was performed for polycrystalline samples using the theory of Bulaevskii, Ledvij and Kogan, which analyzes the vortex fluctuation in superconducting materials within the Lawrence-Doniach framework. These data allowed one to determine the characteristic temperature value T ∗ (53–73 K) in the magnetization curves for several magnetic fields. We calculated the data of magnetization excess from the curves of the magnetization as a function of the logarithm of the applied field. We notice that the values for these superconducting parameters are in agreement with reports for high-temperature superconductors. The value obtained of the superconducting volumetric fraction is compared with the value obtained through the measure of the Meissner effect.

We report synthesis and characterization of new Sr 2 ZrMnO 6 manganite-like material. Samples were produced by the solid state reaction method with sinterization temperatures up to 1400 °C. X-ray diffraction experiments reveal that structure belongs to the perovskite system, space group Fm 3 ¯ m ( # 225 ) . Lattice parameter a = 7.86 A ˚ was obtained by means of Rietveld-type refinement, through the GSAS code. Magnetic properties were studied by using an MPMS Quantum Design SQUID. From measurements of magnetization as a function of temperature, we determine the occurrence of a paramagnetic–antiferromagnetic transition with Neel temperature 50 K. Curie–Weiss fitting permitted to obtain the magnetic characteristic parameters. At temperature regimes below the Neel temperature, strong evidences of frustration and an irreversibility temperature between zero field cooling (ZFC) and field cooling (FC) measurements were observed. Curves of magnetization as a function of applied field were performed at T = 4 K . Results show a hysteretic feature for Sr 2 ZrMnO 6 magnetic material. This response is attributed to formation of magnetic clusters as a consequence of cationic (magnetic and no magnetic) disorder along the double perovskite structure.

The new YBa 2 Cu 3-x( PO 4)x O 7-δ (x = 0; 0.03; 0.06; 0.09; 0.12) superconducting material was synthesized by the standard solid state reaction recipe. X-ray diffraction results show the effective substitution of copper for phosphate and also show no evidence of any impurity related with phosphate content. Resistivity, DC magnetization and heat capacity measurements reveal a superconducting transition for all samples with a maximum critical temperature up to 97 K, corresponding to the x = 0.03 sample. For higher doping values, the critical temperature decreases in an approximately linear response. In agreement with the charge transfer model, the critical temperature decreases with the carrier density. For x = 0.03, the critical temperature shows a rise up due to an approximation to the optimum density which separates over-doped and under-doped regimes. The maximum critical temperature achieved is one of the highest ever seen for the 123-type superconductors.

In this work, we report analysis of magnetization fluctuations for the CaLaBaCu 3 O 7− δ superconducting system. We describe a procedure for extracting the penetration depth λ ( T ) and the coherence length ξ parameters from the magnetization, as a function of the applied magnetic field. This procedure takes the vortex fluctuation into account. The data of the magnetization excess Δ M ( T ) are analyzed for different values of temperature in the interval from 65 to 73 K. For several magnetic fields we observed a crossover in the magnetization curves at the characteristic temperature value T * =72.2 K. We calculated the data of magnetization excess from the curves of magnetization as a function of the logarithm of the applied field. This procedure was performed for polycrystalline samples of CaLaBaCu 3 O 7− δ by using the proposition of Bulaevskii, Ledvij and Kogan. We notice that the values for these superconducting parameters are in agreement with reports for high-temperature superconductors.

We report structural and magnetic studies of Sr2FeMnO6 (SFMO) as possible substrate material for the production of YBa2Cu3O7–δ (YBCO) superconducting films. X-ray diffraction experiments show that SFMO belongs to the complex cubic perovskite family. Chemical stability and crystallographic coupling between SFMO and YBCO were examined by characterizing SFMO-YBCO (0 to 100 vol%) polycrystalline composites. Morphological and qualitative compositional analyses were performed through scanning electron microscopy and energy dispersive X-ray experiments. Magnetization measurements reveal that the proximity of SFMO does not affect the superconducting transition temperature (Tc = 89.2 K) of YBCO material. Our results evidenced that the SFMO is an excellent candidate to be substrate for the fabrication of YBCO superconducting thin films. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The irreversibility properties of high-Tc superconductors are of major importance for technological applications. For example, a high irreversibility magnetic field is a more desirable quality for a superconductor [1] . The irreversibility line in the H–T plane is constituted by experimental points, which divides the irreversible and reversible behavior of the magnetization. The irreversibility lines for series of La1.5+xBa1.5+x−yCayCu3Oz polycrystalline samples with different doping were investigated. The samples were synthesized using the usual solid estate reaction method. Rietveld-type refinement of x-ray diffraction patterns permitted to determine the crystallization of material in a tetragonal structure. Curves of magnetization ZFC–FC for the system La1.5+xBa1.5+x−yCayCu3Oz, were measured in magnetic fields of the 10–20,000 Oe, and allowed to obtain the values for the irreversibility and critical temperatures. The data of irreversibility temperature allowed demarcating the irreversibility line, Tirr(H). Two main lines are used for the interpretation of the irreversibility line: one of those which suppose that the vortexes are activated thermally and the other proposes that associated to Tirr a phase transition occurs. The irreversibility line is described by a power law. The obtained results allow concluding that in the system La1.5+xBa1.5+x−yCayCu3Oz a characteristic bend of the Almeida–Thouless (AT) tendency is dominant for low fields and a bend Gabay–Toulouse (GT) behavior for high magnetic fields. This feature of the irreversibility line has been reported as a characteristic of granular superconductors and it corroborates the topological effects of vortexes mentioned by several authors [1] , [2] .

In this work we report the analysis of magnetization experimental data of the La 0.5 RE 0.5 BaCaCu 3 O 7 - δ ( RE = Y , Sm, Gd, Dy, Ho, Yb) superconducting system. The data are analyzed in terms of thermal fluctuations on the magnetization excess Δ M ( T ) for different values of temperature in each one of the samples. We describe a procedure for extracting the penetration depth λ ab ( ≈ 1571 A ˚ ) and the coherence length ξ ab ( ≈ 1.52 A ˚ ) parameters from the magnetization, as a function of the applied magnetic field. This procedure was performed for polycrystalline samples of La 0.5 RE 0.5 BaCaCu 3 O 7 - δ by using the theory of Bulaevskii, Ledvij and Kogan, which analyzes the vortex fluctuation in superconducting materials within the Lawrence–Doniach framework. These data allowed to determine the characteristic temperature value T * (73, 58, 48, 57, 56, 71 K, for RE = Y , Sm, Gd, Dy, Ho, Yb, respectively) in the magnetization curves for several magnetic fields. We calculated the data of magnetization excess from the curves of magnetization as a function of logarithm of applied field. We notice that the values for these superconducting parameters are in agreement with the reports for high temperature superconductors. The obtained value of superconducting volumetric fraction is compared with that obtained through the measure of the Meissner effect.

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.

Many multifunctional properties have been the focus of our interest in Perovskite research. Herein, we report synthesis and characterization of a new Sr2DyNbO6 Perovskite-like material. Samples were produced via standard solid-state reaction method. Rietveld refinement of X-ray diffraction experimental data through the GSAS code reveals that this material crystallizes in a monoclinic complex Perovskite (space group P21/n, #14) with lattice parameters a=5.730(3) A, b=5.905(1) A and c=8.221(0) A. Scanning electron microscopy images reveal that samples evidence a surface with strongly diffuse granular structure. From curves of magnetization as a function of temperature, we determined the paramagnetic behaviour of this complex Perovskite in the temperature regime between 50 and 320 K. Curie fitting allows obtaining an effective magnetic moment of 10.28 μB. Polarization curves as a function of the applied electric field show a hysteretic behavior of typical dielectric loss with relative dielectric constant of 264.28 at room temperature.

In this work, we report the synthesis and characterization of the new La2SrFe2CoO9 triple perovskite material. Samples were produced by the solid state reaction method from high purity precursor powders of La2O3, SrCO3, Co2O3 and Fe3O4. XRD pattern was analyzed by Rietveld refinement through the GSAS code, revealing that observed diffraction peaks are indexed, to the complex perovskite system, and showed that La2SrFe2CoO9 crystallizes in an orthorhombic structure, space group Immm (#71). The lattice parameters were a=5.4314(3) , b=5.4583(3) and c=7.7018(2) . SEM micrographs evidence a strongly diffused granular morphology with mean grain size of 1 μm and EDX spectra show that the chemical composition of samples are in good agreement with the nominal values of the stoichiometric formula. Measurements of magnetization as a function of temperature permitted to determine the ferromagnetic characteristic of material with an effective magnetic moment of 6.18 μB, which is in agreement with the value calculated from the Hund's rules.

In this paper, details of synthesis and structural, morphological, electrical, and magnetic characterization of the new La 0.37 Ca 0.17 Ba 0.43 Mn 0.52 Ti 0.44 Zr 0.04 O 3 multiferroic complex perovskite are reported. Mixtures with 50% mass of ferromagnetic lanthanum calcium manganite La 0.67 Ca 0.33 MnO 3 and ferroelectric barium-lanthanum zirconate titanate Ba 0.9 La 0.067 Ti 0.91 Zr 0.09 O 3 were prepared by the solid state reaction technique. Patterns of X-ray diffraction showed that the materials have reacted resulting in a new perovskite-like structure with tetragonal symmetry, space group P4mm(#99). The structure of the material was refined using the Rietveld method through the GSAS code. ZFC and FC magnetization curves show the occurrence of two phase transitions at 42.25 K and 203.9 K which have been associated with two different magnetic regimes. Hysteresis curves measured confirm that the relationship between the applied field and the magnetization does not evidence a linear behavior. These curves also show that in the low temperature regime the magnetic memory of the material is greater than in the high temperature region. AC impedance as a function of temperature measurements show the same two regions observed in the magnetization curves. The ferroelectric behavior with relative permittivity of 153.12 is observed by polarization curves performed at room temperature in the synthesized materials.

We report reversible magnetization data and the scaling for the magnetization obtained for magnetic fields ( H ) applied at various tilt angles θ of the dc magnetic field with respect to the c axis in a single crystal of Bi 2 Sr 2 CaCu 2 O 8 . Our data show the crossover of the magnetization below the superconducting onset temperature, which indicates a dominant vortex fluctuation.