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In this study, the effect of porosity on the structural and functional (dielectric, ferroelectric, nonlinear, and piezoelectric) properties in Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics was investigated. Various levels of microporosity in the range of 3% to 31 vol.% have been produced using poly(methyl methacrylate) microspheres as sacrificial templates. The structural investigation indicates a phase coexistence, as expected for this composition at room temperature. The maximum permittivity decreases with increasing porosity, from around 7000 (ceramic with 3 vol.% porosity) down to 3500 (ceramic with 31 vol.% porosity), and the Curie temperature shifts from 47 to 67°C when increasing porosity, related to the possible porosity‐induced structural and internal stress modifications. An enhanced piezoelectric response was found in the Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramic with intermediate porosity around 18 vol.%, with the highest value of piezoelectric response of 470 pC/N and a figure of merit of 7.3 pm2/N. The optimum piezoelectric properties at the intermediate porosity level are related to the microstructural changes (pore shape and connectivity) and possible field‐induced structural modifications. The piezoelectric energy harvesting measurement results have shown the possibility of using Pb‐free porous ferroelectric materials in devices for energy harvesting applications. [ABSTRACT FROM AUTHOR]

The induced thermal stress in a heating process is an important parameter to be known and controlled in the magnetization process of core-shell nanowires. This paper analyses the stress produced by a laser heating source placed at one end of a core-shell type structure. The thermal field was computed with the non-Fourier heat transport equation using a finite element method (FEM) implemented in Comsol Multiphysics. The internal stresses are essentially due to thermal gradients and different expansion characteristics of core and shell materials. The stress values were computed using the thermo elastic formalism and are depending on the laser beam parameters (spot size, power etc.) and system characteristics (dimensions, thermal characteristics). Stresses in the GPa range were estimated and consequently we find that the magnetic state of the system can be influenced significantly. A shell material as the glass which is a good thermal insulator induces in the magnetic core, the smaller stresses and consequently the smaller magnetoelastic energy. These results lead to a better understanding of the switching process in the magnetic materials.

The aim of this study was to synthesize a CoFe2O4@HaP nanocomposite (HaP-Hydroxyapatite) through the coprecipitation method in aqueous solution, with the purpose of using it in adsorption processes for the removal of Congo Red dye from aqueous solutions. Fourier Transform Infrared Spectroscopy (FT-IR) was used to characterize the synthesized material, identifying absorption bands specific to the functional groups of cobalt ferrite (Fe-O and Co-O at 603 and 472 cm−1) and hydroxyapatite PO43− at 1035, 962, 603 and 565 cm−1. Powder X-ray diffraction confirmed the cubic spinel structure of cobalt ferrite (S.G Fd-3m) and the hexagonal structure of hydroxyapatite (S.G P63/m). The nanocomposite's crystallite size was calculated to be 57.88 nm. Nitrogen adsorption/desorption isotherms and BET specific surface area measurements were used to monitor textural parameters, revealing an increase in specific BET surface area when cobalt ferrite nanoparticles (15 m2/g) were introduced into the hydroxyapatite heterostructure (34 m2/g). Magnetic properties were investigated by interpreting hysteresis curves in the ±10 kOe range, with the nanocomposite showing a saturation magnetization of 34.83 emu/g and a coercivity value of 0.03 kOe. The adsorption capacity of the CoFe2O4@HaP nanocomposite is up to 15.25 mg/g and the pseudo-second-order kinetic model (Type 1) fits the data with a high correlation coefficient of 0.9984, indicating that the chemical adsorption determines the rate-determining step of the process. The obtained nanocomposite is confirmed by the analyses, and the absorption measurements demonstrate that it can be utilized to degrade Congo Red dye. [ABSTRACT FROM AUTHOR]

The first-order reversal curve (FORC) diagram method is one of the most successful characterization techniques used to characterize complex hysteretic phenomena not only in magnetism but also in other areas of science like in ferroelectricity, geology, archeology, in spin-transition materials, etc. Because the definition of the FORC diagram involves a second-order derivative, the main problem in their numerical calculation is that the derivative of a function for which only discrete noise-contaminated data values are available magnifies the noise that is inevitably present in measurements. In this paper, we present the doFORC tool for calculating FORC diagrams of noise scattered data. It can provide both a smooth approximation of the measured magnetization and all its partial derivatives. Even if doFORC is mainly dedicated to FORC diagrams' computation, it can process a general set of arbitrarily distributed two-dimensional points. doFORC is a free, portable application working on various operating systems, with an easy to use graphical interface, with four regression methods implemented to obtain a smooth approximation of the data which may then be differentiated to obtain approximations for derivatives. In order to perform the diagnostics and goodness of fit, doFORC computes residuals to characterize the difference between the observed and predicted values, generalized cross-validation to measure the predictive performance, two information criteria to quantify the information that is lost by using an approximate model, and three degrees of freedom to compare different amounts of smoothing being performed by different smoothing methods. Based on these, doFORC can perform automatic smoothing parameter selection. [ABSTRACT FROM AUTHOR]

Systems of magnetic nanowires are considered strong candidates in many technological applications as microwave filters, sensors or for data storage. The main parameter that controls the response of magnetic nanowires assemblies is the aspect ratio of the nanowires. In this paper we modify the aspect ratio by keeping constant the length of nanowires and modifying the nanowires' diameter. Ni nanowires with diameters of 40, 60, 80 nm and constant lengths of 1000 nm and 500 nm were grown with a standard electrodeposition technique in Anodized Aluminum Oxide (AAO) membranes. The samples were studied using vibrating sample magnetometer and X-band ferromagnetic resonance experiments at room temperature. As the nanowire diameter increases, the coercive field increases and also two different types of dependence of resonance field versus aspect ratio were observed. The results are explained taking into account the effects of the magnetostatic interactions and shape anisotropy. Index Terms--FMR, magnetostatic interactions, nanowires.

This study is focused on the possibility to extend the use of the first-order reversal curve (FORC) diagram method to rate-dependent hysteresis observed experimentally on soft magnetic wires. The FORC system of an amorphous magnetic wire was measured with an inductometric experimental setup in which the field-rate was maintained constant. The FORC experiment was performed for four different field-rates. We have developed and implemented a model based on the hypothesis that the magnetization processes in the samples are mainly due to the movement of a domain wall between the central domains of the wire. The differential equation of the domain wall movement is able to give a remarkably accurate description of the experimental FORC diagrams for all the field rates used in the experiment. The experimental FORCs, the FORC susceptibility diagram, and the classical FORC diagram show, however, a number of details that the model is not able to describe. In each such case, one discusses the possible physical cause of the observed behavior. [ABSTRACT FROM AUTHOR]

The ferromagnetic resonance experiments (FMR) were used to examine the interactions between magnetic nanowire systems produced by electrodeposition within alumina template membranes. The experimental hysteresis loops and FMR spectra are interpreted using a statistical method that is based on the integration of the static and dynamical response in the Preisach plane. The theoretical FMR spectra obtained using the statistical Preisach type method for strong interactions fit well the experimental FMR spectra. Index Terms--Dynamic susceptibility, ferromagnetic resonance, magnet wire, magnetostatics.

Nanowire arrays are characterized using ferromagnetic resonance (FMR) experiments. The dipolar interactions between nanowires are studied by investigating the angular variation of the FMR resonant field. Two qualitatively different angular variations in the resonant field are experimentally observed and explained using the interaction field. The experimental data are explained using a theoretical model that considers the interaction field in nanowire networks as arising from magnetic charges at the wire's surface (wire's extremities and lateral cylindrical surface) and takes into account the finite wire length and porosity of the sample. Index Terms--Ferromagnetic resonance, magnetic nanowires.

A micromagnetic model based on magnetization vector dynamics described by the stochastic Landau-Lifshitz-Gilbert (SLLG) equation for the transverse susceptibility (TS) of particulate media is presented. The effect of the amplitude of excitatory ac field and the effect of thermal relaxation is taken into account. Index Terms--Magnetic particles, relaxation processes, stochastic processes, transverse susceptibility.

The study is focused on creating magnetic mesoporous materials through the insertion of a nickel ferrite into the structure of kaolintype clay. Sol-gel auto-combustion method was employed to synthesize the materials, using glycine and tartaric acid as chelating/combustion agents. This is the first study on the combined effect of different fuel agents and of clay-to-ferrite molar ratio on the structural, textural, magnetic and adsorptive properties of nanocomposites. The value of the average pore size, registered in a range of 6.01 and 12.9 nm, indicates the dependence on both molar ratio and fuel agent. The textural properties of the materials, corroborated with those obtained from XRD, SEM and TEM and VSM, suggest that magnetic nanocomposites can be successfully used as adsorbents in the removal of harmful organics. The obtained nanocomposites show excellent adsorption, with up to 98% BB41 dye removal, and a facile recuperation, due to their magnetic properties. The maximum adsorption capacity of dye, of 752.2 mg/g, was obtained for C3Ni_act350, in the presence of H2O2 in solution. More than that, the adsorption capacity of magnetic composites increased with increasing the NiFe2O4 content. [ABSTRACT FROM AUTHOR]

The ferroelectric-magnetic composite materials are very suitable for designing and producing microwave devices and components, due to their dielectric and magnetic properties. For microwave antennas, sensors, resonators, oscillators, filters, phase shifters, attenuators, and amplifiers, the output and input impedances, the resonance frequencies, the quality factor (the losses), and the attenuation or the amplification can be very easily adjusted by modifying the dielectric permittivity or/and the magnetic permeability. This is possible by a right choice of the ratio between the ferroelectric and magnetic phases in the composite material. Therefore, it is highly important to accurately determine these characteristics of the composite material in microwave range. [ABSTRACT FROM AUTHOR]

The effect of interparticle interactions on the processional switching process of coupled ellipsoidally shaped particles subject to pulsed magnetic fields is analyzed. The purpose of this analysis to highlight some of the effects of the dipolar interactions on the ability to efficiently store and control the switching in interacting magnetic elements subjected to pulsed magnetic fields.

Hyperthermia induced by the heating of magnetic particles (MPs) in alternating magnetic field receives a considerable attention in cancer therapy. An interesting development in the studies dedicated to magnetically based hyperthermia is the possibility to control the temperature using MPs with selective magnetic absorption properties. This paper analyzes the temperature field determined by the heating of MPs having low Curie temperature (a FeCrNbB particulate system) injected within a malignant tissue, subjected to an ac magnetic field. The temperature evolution within healthy and tumor tissues was analyzed by finite element method simulations in a thermo-fluid model. The cooling effect produced by blood flowing in blood vessels was considered. This effect is intensified at the increase of blood velocity. The FeCrNbB particles, having the Curie temperature close to the therapeutic range, transfer the heat more homogeneous in the tumor keeping the temperature within the therapeutic range in whole tumor volume. Having the possibility to automatically control the temperature within a tumor, these particle type opens new research horizons in the magnetic hyperthermia. [ABSTRACT FROM AUTHOR]

In order to counteract the growing number and sophisticated nature of cyber threats, having up-to-date information on vulnerabilities, attacks, threats, countermeasures and risks is crucial. Equally important are the data and information we hold and their importance to our organization. Information classification is a process in which organizations and states evaluate the data they hold and the level of protection they should provide. Organizations usually classify information in terms of confidentiality - that is, who is allowed access to view it. [ABSTRACT FROM AUTHOR]