Present paper describes variation of structure and magnetic properties in diamagnetically doped barium hexaferrites. Al3+ and In3+ diamagnetic ions were chosen for investigation of the correlation ...between the chemical composition, crystal structure, magnetic properties and microwave characteristics in BaFe12−xDIxO19 solid solutions. The changes of structure and electronic properties were investigated using neutron powder diffraction and Mossbauer spectroscopy. These data were used for discussion of the electromagnetic properties changes. It was demonstrated possibility of electromagnetic properties control in the samples. It was shown that all samples demonstrate correlation between electromagnetic properties and the level of chemical substitution. The transmission spectra of all the samples demonstrated a deep minimum in the frequency range 20–65 GHz which was associated with the natural ferromagnetic resonance (NFMR). Calculated data for electromagnetic absorption correlates well with experimental transmission spectra. External magnetic field leads to shift of the NFMR peak due to increase of magnetic anisotropy. It was concluded that the intrasublattice interactions were responsible for tailoring the magneto crystalline anisotropy and resonance parameters.
Thin Ni-Fe films were produced via electrodeposition onto silicon substrate using direct current and pulse (with different pulse durations) regimes. The correlation between technological regimes and ...chemical composition and microstructure for Ni-Fe nanogranular films was discussed. Analysis of the microstructure evolution revealed the changing mechanism of the films growth from the Volmer-Weber (describes island film growth) to the Stranski-Krastanov (layer by layer at the growth beginning) with the shortening of the pulse duration less than 10 μs. This anomalous behavior was explained by an increase of the binding energy between the initial atoms and the substrate surface. The results showed that using electrodeposition regimes, which ensure growth with the average crystal size less than the critical value (10 nm), provides less roughness, defectiveness and greater film uniformity in thickness, and, therefore, stable properties.
•Ni-Fe films have been formed via electrodeposition with direct and pulse current.•Correlation between regimes, chemical composition and microstructure was demonstrated.•Unexpected changing of the film growth mechanism was observed.•Explanation was found in critical grain size and binding energies competition.
•Multiferroic (NZF)-(100-x) wt.% BaTiO3 (BT) (x = 25, 50, 75) composites have been prepared;•Structural and electrical characterization has been done;•Correlation between composition, microstructure ...and electrical properties has been observed.
Multiferroics composite materials have been widely used in several applications, such as ceramic supercapacitors and multifunctional and active devices, owing to their high permittivity with ferroelectric and magnetic performance even at room temperature. The chosen preparation technique can be one of the most effective ways for obtaining multiferroic composite with different properties for the same composite. Here, multiferroic composite materials, (x) wt.% Ni0.5Zn0.5Fe2O4 (NZF)-(100-x) wt.% BaTiO3 (BT) (x = 25, 50, 75) were prepared by the co-precipitation synthesis route. The prepared multiferroic samples were characterized with various techniques like X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDXS), and vibrating sample magnetometer (VSM). The magnetic and AC electrical properties like conductivity, dielectric constant, dissipation factor (dielectric loss), and impedance spectroscopy analysis were studied in detail with different frequencies and temperatures. In our case, preparing nanosized NZF on or between microscale BT could enhance the electrical properties by decreasing the porosity (P) percentage, which reaches a low value for the sample x = 50 wt%, and increasing the conductivity. A relatively high dielectric constant (ε‘) at low frequencies and high temperatures was obtained, which is one of the main contributions in modern applications like a ceramic supercapacitor. Also, the studied samples show low dielectric loss (tanδ) values suggesting that it could be a contender for use in high-frequency microwave devices and tunable frequency filters.
The problem of increasing reliability of semiconductor devices under extreme ionizing radiation (electrons, protons, gamma radiation etc.) is relevant. Uses of WCu composite materials with high ...density and reduced mass-dimension characteristics offer a very attractive alternative to lead protection due to more environmentally friendly composite. W85Cu15 and W75Cu25 composites were obtained by solid-phase synthesis. XRD data showed that the main lines of the WCu spectrum correspond to the body-centered cubic phase of tungsten-copper alloy and the face-centered cubic phase of copper. The W85Cu15 and W75Cu25 composites consist two main phases: W0,6Cu0,4 phase and Cu phase. This may be due to the alloy presence on the outer part of the tungsten grains, which was formed as a result of thermal annealing and copper diffusion during composite synthesis. The most intense peak (110) is maintained when the tungsten concentration changes. The peaks shift towards large angles with a tungsten concentration decreasing in the composite is observed. The intensity of copper peaks increases and a new low-intensity peak appears (220) with the copper concentration increasing in the composite. The shielding properties of the W85Cu15 composite with n- and p-MOS transistors under 1.6÷1.8 MeV electron radiation have been studied. It has been established that maximum shielding efficiency for p-MOS transistors (Ka = 143÷155) have shields with 1.2÷1.5 mm thickness. Shields provide the total absorbed dose reduction up to 6 times for outer space protons (energies from 0.04 to 500 MeV for the 60° orbital inclination and a circular orbit with a height of 300 km).
•It has been shown that WCu composites consist three main phases (W,W0,6Cu0, 4 and Cu).•Isostructural W/W0,6Cu0,4 phases ratio critical determines shielding properties.•It has been demonstrated the optimal WCu thickness for best electron protection.•Shields based on W85Cu15 provide a reduction of the proton up to 6 times.
Abstract
A new method for the specific surface energy investigation based on a combination of the force spectroscopy and the method of nanofriction study using atomic force microscopy was proposed. ...It was shown that air humidity does not affect the results of investigation by the proposed method as opposed to the previously used methods. Therefore, the method has high accuracy and repeatability in air without use of climate chambers and liquid cells. The proposed method has a high local resolution and is suitable for investigation of the specific surface energy of individual nanograins or fixed nanoparticles. The achievements described in the paper demonstrate one of the method capabilities, which is to control the growth mechanism of thin magnetic films. The conditions for the transition of the growth mechanism of thin Ni
80
Fe
20
films from island to layer-by-layer obtained via electrolyte deposition have been determined using the proposed method and the purpose made probes with Ni coating.
This paper described to the ceramics (inorganic) two-component composites with controllable magnetic and electrical properties. Ceramic composite samples were produced via solid state reaction method ...(standard ceramic technique) from initial magnetic (BaFe11.9Al0.1O19 or BF) and ferroelectric (BaTiO3 or BT) phases. BT and BF initial compounds were mixed in stoichiometric ratios (BF)1-x - (BT)x (x = 0, 0.25, 0.5, 0.75 and 1) and sintered. Initial compounds BaFe11.9Al0.1O19 (x = 0) and BaTiO3 (x = 1) were also produced via standard ceramic technique. The constituent materials were chosen considering their perspective ferrimagnetic and ferroelectric properties, respectively for BF and BT. Moreover, Ba-hexaferrites are reported to exhibit ferroelectricity at room temperature as well, and the combination of two ferroelectric phases is of interest. Systematic investigations of the structural, magnetic and electrical properties versus chemical composition (x) were performed. As structural properties we have defined the features of crystal structure (a and c lattice parameters, volume of unit cell) and peculiarities of microstructure (density, porosity, average grain size). The ferrimagnetic phase transition temperature is almost independent of the content of BT, which is determined by the exchange interactions Fe3+-O2--Fe3+in the magnetic phase. However, the coercivity of composite samples is lower which is due to the contribution of the microstructure dependent shape-anisotropy to the total magnetic anisotropy energy. The permittivity vs. temperature behavior confirmed the existence of two ferroelectric phase transitions corresponding to structural phase transitions in BT (at about 400 K) and BF (at about 700 K). It was observed that the electrical properties of composite samples, including the temperatures of the phase transitions, critically depended on concentration x which affects the composite microstructure. This behavior was discussed in terms of microstructure analysis (grain size, porosity and density).
BaFe12-xTixO19 barium hexaferrites up to x = 2.00 were synthesized by the usual ceramic technology. Crystal structure refinement was realized by Rietveld method of powder XRD at room temperature. The ...unit cell parameters change non-monotonically with titanium concentration. The minimum volume of ~698.75 Å3 was determined for the x = 1.00. The mechanism of nonequivalent crystallographic positions occupation with titanium cations is established. SEM investigation was shown that the obtained samples are ceramics with a tightly compacted polycrystals (>95%) and average crystallite size of ~5 μm. The Mössbauer investigation confirms such localization of Ti4+ cations. The field dependence of magnetization at 5 K and 300 K was measured and the main magnetic parameters were determined using the law of approach to saturation. These values decrease almost monotonically with increase in titanium concentration and temperature. The minimum values of these quantities of ~23.4 emu/g, ~1.9 emu/g, 1.2*106 Erg/g and ~105 Oe were fixed for the x = 2.00 at 300 K. With an increase in the doping concentration, both the magnitude of the electrical ac-resistivity and the temperature of transition to the activation type of conductivity increase non-monotonically. At x = 0.50, the lowest electrical resistivity of ρ ~5.1*103 Ohm*cm is observed at room temperature with the electrical transition temperature is Tel ~406.5 K. With an increase in frequency the ac-resistivity decreases, as the value of the band gap. The real part of the permittivity increases constantly with increasing temperature and decreases with increasing frequency for all the compositions. The temperature peak of the tg(d) loss tangent with the doping concentration changes nonmonotonically in magnitude and position. An interpretation of the magnetic and electric states of the substituted BaFe12-xTixO19 barium hexaferrite is given taking into account the mechanism of occupation nonequivalent crystallographic positions with titanium cations.
•Structure vs. temperature for BaFe12−xInxO19 hexaferrites was investigated.•Atomic coordinates and lattice parameters were Rietveld refined.•Exchange interactions vs. structure were ...investigated.•Magnetic moments at different position and total moment per iron ion were defined.•Comparison with BaFe12−xAlxO19 hexaferrites was performed.
Indium doped barium hexaferrites were synthesized by usual ceramic technology. They were investigated by the high resolution neutron powder diffraction and vibration sample magnetometry in temperatures up to 730 K. Analysis of NPD data was performed by FullProf in classical approximation. Structure parameters as well as bond lengths and bond angles were determined versus the substitution level and the temperature. Main attention was paid to the distribution of indium cations between different crystallographic positions and temperature change of bond lengths and bond angles. Effect of these two structure parameters on Fe3+(i) – O− – Fe3+(j) (i, j = 1, 2, 3, 4, 5) indirect superexchange interactions with the substitution level and temperature was established. A dominant effect of a positive intrasublattice Fe3+(i) – O2− – Fe3+(i) (i = 1, 2, 3, 4, 5) indirect superexchange interactions on a magnetic ordering was detected.
Multilayer CoFeP/Cu spin-valve nanowires with period of four {FMs/Cu/FMh/Cu}n and five {FMs/Cu/FMs/FMh/Cu}n layers were synthesized by the electrodeposition in the pores of polycarbonate membranes ...from single electrolyte where FMs are magnetically soft and FMh are magnetically hard layers. The results of magnetic measurements showed that the field dependence of the magnetoresistance of nanowires obtained in the work are typical for multilayer structures with a giant magnetoresistance, the maximum of which reaches ∼9%. Multilayered nanowires based on the giant magnetoresistive effect are interesting objects from fundamental point of view as model objects for explanation of the nature of magnetic ordering in strongly coupled bias magnetic multilayers. These materials are promising for practical applications as sensitive elements in magnetic field sensors, biomedical applications and functional spintronic materials.
•First time multilayer CoFeP/Cu nanowires were synthesized from combined electrolyte.•Nanowires were characterized by the sharp soft/hard layers interfaces.•Maximal value of the GMR at room temperature was ∼9%.•Anisotropic magnetoresistance contribution due to spin-orbit interaction was estimated.
Hard/soft nanocomposites (NCs) of SrNi0.02Zr0.02Fe11.96O19 (SrNiZr)/MFe2O4 (M = Mn, Co, Cu, and Zn) were prepared using a one-pot sol-gel auto-combustion technique. All produced samples showed smooth ...M − H curves and single peaks on the dM/dH against H curves. This indicates that complete exchange-coupled effects between phases were achieved. Furthermore, the squareness ratio SQR=(Mr/Ms) was obtained and found to be higher than 0.5 at 300 K. This refers to the occurrence of excellent exchange coupling behavior among the soft and hard ferrites, and their structures consist of a single magnetic domain. The electrodynamic parameters were investigated in the 2–18 GHz frequency band using a coaxial line. The dependences of the real and imaginary parts of μ and ε as a function of frequency were determined from the measured S-parameters. A strong correlation between the chemical composition of the soft magnetic phase and the electrodynamic parameters of the composite was observed. This was analyzed in terms of the atomic weight and configuration of the electronic shells of the A-cation in the soft phase. The electromagnetic absorption (EMA) of the investigated composites was estimated from the reflection losses calculated from μ and ε. The maximal EMA value was observed.
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