Ferroelectromagnet Pb Research Articles

Sol‐gel method to obtain the ferroelectromagnetic ceramics (Pb(Fe0.5Nb0.5)O3) for micromechatronic applications

Lead iron niobate, Pb(Fe0.5Nb0.5)O3 belong to a family of materials with a perovskite structure with the general formula A(B′B″)O3, where in positions A–Pb ions substitute themselves, and in octahedral positions B′ and B″ ions of iron Fe and niobium Nb in a random way. The Pb(Fe0.5Nb0.5)O3 material is characterized by two ordered antiferromagnetic and ferroelectric sub‐systems. A technological process of the ferroelectromagnetic Pb(Fe0.5Nb0.5)O3 ceramics have a significant influence on a crystalline structure and a ceramics microstructure.In the present paper, we study a sol‐gel technology of the production of the Pb(Fe0.5Nb0.5)O3 ceramics. The obtained specimens were subjected to micro‐structural examinations and tests of mechanical and dielectric properties. Temperature dependences of mechanical loss Q–1(T) and Young's modulus E(T) were conducted by an automatic relaxator of acoustic frequencies of a RAK‐3 type and dielectric test were made on a capacity bridge of a QuadTech 1920 Precision LCR Meter type.

Influence of admixtures on the properties of biferroic Pb(Fe0.5Nb0.5)O3 ceramic

AbstractThe ferroelectromagnetic Pb(Fe0.5Nb0.5)O3 (PFN) ceramic was synthesized by a powder calcining method. The aim of this work was to decrease the electric conduction of the biferroic PFN ceramic as a result of admixing it with metal oxides or carbonates. Investigation results concerning the influence of admixtures of manganese, chromium and lanthanum oxides and potassium and strontium carbonates on direct current electric conduction and dielectric parameters of the PFN ceramic are presented. Crystallographic and morphological studies were carried out using X‐ray diffraction and scanning microscopy techniques. The specimens obtained were subjected to dielectric, electric direct current conductivity, hysteresis loop and electromechanical tests. By adding small amounts of admixtures it was possible to decrease (admixtures of manganese or chromium) or increase (admixtures of lanthanum, strontium or potassium) the area of the phase transition of the PFN ceramic. It was found that admixtures of manganese and potassium decreased the electric conduction of the PFN ceramic. PFN admixed with elements of small ions, manganese and chromium, is characterized by a better set of dielectric parameters and lower dielectric losses compared to the PFN ceramic without admixtures.

Electron paramagnetic resonance study of the ferroelectromagnet Pb(Fe 1/2Nb 1/2)O 3 through ferro-paraelectric transition

An electron paramagnetic resonance (EPR) study of ferroelectromagnet Pb(Fe 1/2Nb 1/2)O 3 (PFN) powders is presented. The EPR spectra show a single broad line in the 300–500 K temperature range, attributable to Fe 3+ ions. The onset of the ferro-paraelectric transition was determined from the temperature dependence of three main parameters deduced from the EPR spectra: g-factor, peak-to-peak linewidth and integrated intensity. These parameters indicate a behavior in agreement with a diffuse phase transition.

Microwave power absorption as a function of temperature and magnetic field in the ferroelectromagnet [formula omitted

We report on the effects of temperature and DC magnetic field on microwave power absorption measurements at 8.8–9.8 GHz, in powder samples of the ferroelectromagnet Pb ( Fe 1 / 2 Nb 1 / 2 ) O 3 (PFN). Two techniques recently implemented are used: magnetically modulated microwave absorption spectroscopy (MAMMAS) and low-field microwave absorption spectroscopy (LFMAS), the measurements were performed in the 77–520 K temperature range. The MAMMAS technique allows the detection of the para-antiferromagnetic and ferro-paraelectric transitions at T N 1 ∼ 144.1 K and T min ∼ 398.1 K , respectively. The profiles obtained by plotting the slope vs. temperature of the LFMAS line, while cooling or heating, are similar to those detected by the MAMMAS technique, giving evidence that both types of measurement are due to the same processes of absorption, by paramagnetic dipoles at all temperatures. We conclude that both measurements are a manifestation of the same response to electromagnetic absorption, in which the same physical processes take place.

Signature of weak ferromagnetism by electron paramagnetic resonance in the ferroelectromagnet Pb(Fe 1/2Nb 1/2)O 3

An electron paramagnetic resonance (EPR) study on the ferroelectromagnet Pb(Fe 1/2Nb 1/2)O 3 (PFN) powder is presented. The EPR spectra show one single broad line in the 300–90 K temperature range. The onset of the para-antiferromagnetic (AF) transition has been determined from the temperature dependence for three main parameters deduced from the EPR spectra: the g-factor, the peak-to-peak linewidth (Δ H pp) and the integrated intensity ( I EPR). Below 147 K, a weak ferromagnetic signal (WFS) is observed. This WFS is attributed to canting of Fe +3 ion sublattices in the AF matrix, and can be associated with the magnetoelectric effect in this material.

Frequency-temperature response of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained by different precursors. III. Dielectric relaxation near the transition temperature

Dielectric relaxation processes occurring near the ferroelectric-paraelectric phase transition of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained by different precursors are discussed using microstructural and equivalent circuit modeling and the impedance spectroscopy technique. The frequency-temperature response was obtained from room temperature to 300°C and from 20Hzto1Mz. In correspondence with a previous structural, morphological, and temperature response study, appropriate microstructural, and equivalent circuit models were established. The frequency response study was carried out by means of the simultaneous analysis of the complex dielectric constant ε̃ and admittance Ỹ functions and the dielectric loss, tanδ. A strong absorption near the transition temperature region at a frequency around 1MHz is discussed and is attributed with relaxation processes associated with domain reorientation, domain wall (DW) motion, and the dipolar behavior of ferroelectric materials. Such processes were found to take place inside the grain, and their low characteristic frequencies are explained by clamping effects of the DW due to the thermally activated diffusion of oxygen vacancies. At frequencies before relaxation, the high polarization values are due to small polaron mechanisms associated with the presence of Fe2+. The relaxation processes are very much conditioned by the grain and domain sizes, the degree of deformation of the lattice and the crystallites, as well as the potential barriers in the grain boundaries. Values of the activation energy corresponding to the different relaxation processes were determined from fitting of experimental data, identifying thus the involved mechanisms, and an excellent agreement with those obtained from the temperature response [Raymond et al., J. Appl. Phys. 97, 084107 (2005)] was found. The relaxation processes studied here are an evidence of domain structure.

Additional transition induced by magnetoelectric interaction in ferroelectromagnet Pb(Fe 1/2Nb 1/2)O 3

Abstract Besides the two phase transitions known in ferroelectromagnets, an additional transition was observed experimentally in Pb(Fe 1/2Nb 1/2)O 3 and the possible mechanism was explored. The magnetic moment shows that anomalous increases when the temperature goes down away from the Néel temperature of 20–30 K. The existence of the hysteresis verifies the weak ferromagnetic property. This additional phase transition is considered to originate from the magnetoelectric coupling between the ferroelectric and antiferromagnetic orders in this compound. From the Mössbauer parameter analysis, it is confirmed that the hybridization of the O 2p, Fe 3d and Nb 4d electron states makes the realization of magnetoelectric coupling possible.

Frequency-temperature response of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained by different precursors. Part I. Structural and thermo-electrical characterization

With the purpose of fabricating ceramics where ferroelectric and magnetic order coexist, ceramics of Pb(Fe1∕2Nb1∕2)O3 have been prepared using the traditional ceramic method following three different routes. The first is a direct via starting from oxide reagents and the other two use different kinds of FeNbO4 precursors with either monoclinic or orthorhombic structures. Crystallographic and surface morphological studies were carried out by the powder x-ray diffraction and scanning microscopy techniques. The presence of Fe2+, detrimental to the ferroelectric and magnetic performance, was evaluated by x-ray photoelectron spectroscopy. The samples showed no structural differences, uniformly distributed grains, a ferro-paraelectric transition temperature at 110°C and a normal diffuse phase transition (nonrelaxor behavior). Differences in the degree of diffuseness, densities and grain size were observed depending on the kind of precursor. Measurements of dc and ac electrical resistivity, dielectric constant and dielectric loss were made as functions of temperature from room temperature to 250°C, at different frequency values (between 20Hz and 1MHz). Four conduction mechanisms were identified: hopping charge corresponding to low temperatures, small polarons and oxygen vacancies conduction at intermediate temperatures, and intrinsic ionic conduction at high temperatures. The best set of values of dielectric loss and dielectric constant, from the ferroelectricity point of view, were obtained when the precursor with orthorhombic structure was employed.

Frequency-temperature response of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained by different precursors. Part II. Impedance spectroscopy characterization

The dielectric behavior of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained using the traditional ceramic method employing three different precursors was investigated by impedance spectroscopy in the temperature range of 200–300°C. This study was carried out by means of the simultaneous analysis of the complex impedance Z̃, electric modulus M̃, and admittance Ỹ functions from the measurements in the frequency range of 20Hz–1MHz. In correspondence to a previous structural, morphological, and temperature response study, appropriate microstructural and equivalent circuit models were established. Based on the brick layer model, three series of interconnected electrically distinct regions are considered: a conductive grain boundary layer, a capacitive grain boundary surface layer, and a resistive-ferroelectric bulk layer. Two conduction mechanisms were identified: a dielectric relaxation process due to localized conduction associated with the presence of oxygen vacancies and the nonlocalized conduction corresponding to long range conductivity associated with extrinsic mechanisms due, fundamentally, to Fe2+ presence. Both mechanisms were discerned to occur inside the grains and where the contributions of the grain boundary are neglected. Three conductivity components were deconvoluted: a longe range dc conductivity at the low frequency region, a capacitive behavior at higher frequencies, and a universal power law behavior in an intermediate-frequency region. Values of the activation energy corresponding to relaxation processes and dc conductivity were determined and excellent correlation with those obtained from the temperature response was found. A comparative analysis between the behaviors of each sample is presented.

Characteristics of the magnetosensitive non-resonant power absorption of microwave by magnetic materials

By means of the modification of an electron paramagnetic resonance (EPR) spectrometer, two experimental techniques have been implemented to measure the magnetosensitive non-resonant absorption of microwaves (MANRAM): magnetically modulated microwave absorption spectroscopy (MAMMAS) and low field non-resonant microwave absorption spectroscopy (LFNORMAS). These techniques are proposed to be used in the characterization of magnetic materials at microwave frequencies. They are very sensitive, hence require very little amount of material for test in the form of crystals, glasses, powders, liquids; these wireless techniques are non-destructive. Magnetically modulated microwave absorption spectroscopy is carried out cooling or heating a sample under study in presence of a modulated magnetic field. The temperature of the material is taken and a graph of it versus the modulated absorption of microwaves is constructed. Low field non-resonant microwave absorption spectroscopy measures the magnetosensitive-modulated absorption of microwaves, by the material, with respect to cycled sweepings of an applied dc magnetic field. We present results for the ceramic superconductor YBa 2Cu 3O 7− x (YBCO), the antiferromagnetic (AF) MnO oxide and ferroelectromagnetic Pb(Fe 1/2Nb 1/2)O 3 (PFN). The absorption spectra are shown highlighting their main characteristics.

Ferroelectric and dielectric properties of ferroelectromagnet Pb(Fe1/2Nb1/2)O3 ceramics and thin films

The ferroelectric and dielectric properties of ferroelectromagnet Pb(Fe1/2Nb1/2)O3 (PFN) ceramics and thin films prepared by pulsed laser deposition (PLD) have been investigated systematically. PFN ceramics experienced a para-ferroelectric transition and a para-antiferromagnetic transition at 380 K and 145 K, respectively. At room temperature, it has an electrical remnant polarization of 11.5 μC/cm2 and a coercive field of 4.04 kV/cm. The dielectric behaviors show characteristics of diffusive phase transition at a wide temperature range around 380 K. Anomalies in the dielectric constant and loss tangent have been observed near the Neel temperature of 145 K, indicating a coupling between the ferroelectric and antiferromagnetic orders in PFN ceramics. At room temperature, the PFN films exhibited a remnant electric polarization of 7.4 μC/cm2, a coercive field of 10.5 kV/cm, and a dielectric constant of 486 at frequency of 10 kHz, indicating their potential applications in memory devices.