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The microwave properties of epoxy composites filled with 30 wt.% of BaFe12–xGaxO19 (0.1 ≤ x ≤ 1.2) and with 1 wt.% of multi-walled carbon nanotubes (CNTs) were investigated in the frequency range 36–55 GHz. A sufficient increase in the microwave shielding efficiency was found for ternary 1 wt.%CNT/30 wt.% BaFe12–xGaxO19/epoxy composites compared with binary 1% CNT/epoxy and 30 wt.% BaFe12–xGaxO19/epoxy due to the complementary contributions of dielectric and magnetic losses. Thus, the addition of only 1 wt.% of CNTs along with 30 wt.% of barium hexaferrite into epoxy resin increased the frequency range where electromagnetic radiation is intensely attenuated. A correlation between the cation Ga3+ concentration in the BaFe12–xGaxO19 filler and amplitude–frequency characteristics of the natural ferromagnetic resonance (NFMR) in 1 wt.%CNT/30 wt.% BaFe12–xGaxO19/epoxy composites was determined. Higher values of the resonance frequency fres (51.8–52.4 GHz) and weaker dependence of fres on the Ga3+ concentration were observed compared with pressed polycrystalline BaFe12–xGaxO19 (fres = 49.6–50.4 GHz). An increase in the NFMR amplitude on the applied magnetic field for both random and aligned 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composites was found. The frequency of NFMR was approximately constant in the range of the applied magnetic field, H = 0–5 kOe, for the random 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composite, and it slightly increased for the aligned 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composite.

The structure, magnetic properties and ferromagnetic resonance curves of cobalt ferrite particles synthesized by chemical coprecipitation technique have been studied. The possibility of resonant heating of powder in a magnetic anisotropy field of particles is shown, which can find application in medicine for magnetic hyperthermia.

Herein report, we aim to study the structural, dielectric, and magnetic properties for multifunctional perovskite materials LaCo 0.2 Mn 0.8 O 3 and La 2 CoMnO 6 nanoparticles, which were synthesized by a modified sol–gel route. Citric acid was processed as the chelating agent; gelation slurry formed by irradiation process which exposed to a total gamma radiation dose of 25 kGy at a dose rate of ~1.2 Gy/h to obtain more stability and high purity multifunctional perovskite materials. XRD notarizes the genesis of one pure phase orthorhombic perovskite structure. A full agreement between the particle sizes was investigated by HRTEM and the XRD data was observed. Raman spectra result assigned to the antisymmetric stretching mode and symmetric stretching mode of the (Co/Mn) O 6 octahedra, which related to lattice distortions. The as-prepared perovskite materials exhibit ferromagnetic nature with different values of magnetization. Electron Spin Resonance (ESR) measurements are also carried out in the LCMO multifunctional nanoparticle systems, which suggests the occurrence of Jahn–Teller glass analogous to the spin-glass behavior. The complex impedance displayed high impacts on the electrical properties. The high value of dielectric constant for LCMO prepared nanoparticle systems may be used in electric tunable devices. Highlights Novel modified sol-gel route by gamma radiation used to synthesis more stability and high purity multifunctional perovskite materials (LaCo 0.2 Mn 0.8 O 3 , and La 2 CoMnO 6 ). These multifunctional materials have orthorhombic structure lattices. LCMO multifunctional nanoparticle systems have a spin-glass behavior. The high value of dielectric constant for LCMO nanoparticle multifunctional materials is promising in electric tunable devices.

This work presents a new methodology for fabrication of membrane-assisted elongated YIG nanostructures through the sol-gel method using low-cost materials, and the estimation of the average size of the geometries formed within the pores through ferromagnetic resonance measurements. A precursor solution was deposited on the internal surface of porous aluminum oxide membrane, using an assembly consisting of a vacuum system coupled to an apparatus, which assists in the entry of the used precursor solution, breaking the barriers related to the existing surface tension, with subsequent heat treatment to form the single phase of yttrium iron garnet (YIG). The data collected by X-ray diffraction and Raman spectroscopy indicated this result. The study of the contact angle of the precursor solution and the alumina template indicated great compatibility, an angle of 35.4°. SEM analysis showed that elongated structures were deposited inside the pore’s walls, with different lengths up to 3 micrometers and the EDS analysis showed the presence of the main elements of the YIG phase. The Kittel’s equation and FMR spectral data were used to estimate the mean size of the elongated nanostructures. We found six different size categories with 1856, 1768, 1661, 1588, 1570, 1498 nm . The methodology proved to be efficient for the characterization of elongated YIG nanostructures, becoming a perspective of future applications. Graphical Abstract Highlights Setup for the infiltration of the alumina membrane with the YIG precursor was proposed. Elongated YIG structures were obtained with diverse potential applications. The FMR was used to estimate the mean size of elongated YIG structures.

Sodium alginate, as one of natural polymer existing in marine plants, can function as precursor of carbon-based microwave-absorbing materials with the advantages of low cost, easy degradation, and non-toxicity. However, its resultant carbon-based materials suffer from the poor impedance matching and low lossy capacity due to no magnetism and small amount of interface. In this work, CoNi alloy nanoparticles were uniformly located on the surface of carbon nanofibers (CNFs) derived from the sodium alginate fabricated by the electrospinning and solvothermal method to construct the CNFs/CoNi nanocomposites. The results show that CNFs/CoNi nanocomposites have the good absorbing performance, where the minimum RL of − 56.96 dB at a very thin thickness of 1.63 mm and an effective absorption bandwidth of 5.3 GHz (12.7–18 GHz) at a very thin thickness of 1.7 mm are obtained, respectively. The excellent wave-absorbing performance is mainly attributed to the appropriate impedance matching and high attenuation factor. The multilevel interfacial polarization from the interfaces between CoNi nanoparticles and carbon nanofiber makes the main contribution to the wave-absorbing performance at the whole test frequency range, while the natural ferromagnetic resonance of CoNi composition dominates the low frequency range and eddy current loss plays a major role at higher frequency range. This work develops a simple method for designing high-performance microwave-absorbing nanocomposites by using the marine raw materials of sodium alginate.

W-type barium–nickel ferrite (BaNi 2 Fe 16 O 27 ) is a highly promising material for electromagnetic wave (EMW) absorption because of its magnetic loss capability for EMW, low cost, large-scale production potential, high-temperature resistance, and excellent chemical stability. However, the poor dielectric loss of magnetic ferrites hampers their utilization, hindering enhancement in their EMW-absorption performance. Developing efficient strategies that improve the EMW-absorption performance of ferrite is highly desired but remains challenging. Here, an efficient strategy substituting Ba 2+ with rare earth La 3+ in W-type ferrite was proposed for the preparation of novel La-substituted ferrites (Ba 1− x La x Ni 2 Fe 15.4 O 27 ). The influences of La 3+ substitution on ferrites’ EMW-absorption performance and the dissipative mechanism toward EMW were systematically explored and discussed. La 3+ efficiently induced lattice defects, enhanced defect-induced polarization, and slightly reduced the ferrites’ bandgap, enhancing the dielectric properties of the ferrites. La 3+ also enhanced the ferromagnetic resonance loss and strengthened magnetic properties. These effects considerably improved the EMW-absorption performance of Ba 1− x La x Ni 2 Fe 15.4 O 27 compared with pure W-type ferrites. When x = 0.2, the best EMW-absorption performance was achieved with a minimum reflection loss of −55.6 dB and effective absorption bandwidth (EAB) of 3.44 GHz.

Motivated by the fast-developing spin dynamics in ferromagnetic/piezoelectric structures, this study attempts to manipulate magnons (spin-wave excitations) by the converse magnetoelectric (ME) coupling. Herein, electric field ( E -field) tuning magnetism, especially the surface spin wave, is accomplished in Ni/0.7Pb(Mg 1/3 Nb 2/3 )O 3 -0.3PbTiO 3 (PMN-PT) multiferroic heterostructures. The Kerr signal (directly proportional to magnetization) changes of Ni film are observed when direct current (DC) or alternative current (AC) voltage is applied to PMN-PT substrate, where the signal can be modulated breezily even without extra magnetic field ( H -field) in AC-mode measurement. Deserved to be mentioned, a surface spin wave switch of “1” (i.e., “on”) and “0” (i.e., “off”) has been created at room temperature upon applying an E -field. In addition, the magnetic anisotropy of heterostructures has been investigated by E -field-induced ferromagnetic resonance (FMR) shift, and a large 490 Oe shift of FMR is determined at the angle of 45° between H -field and heterostructure plane.

The present study discusses the synthesis and characterization of Co-doped CeO 2 quantum dots obtained via the chemical precipitation technique. The crystalline nature, optical properties, nanostructure, and magnetic behavior of the prepared samples have been investigated using various experimental techniques. The face-centered cubic structure of the Co-doped CeO 2 quantum dots was demonstrated by the structural confirmation. The crystallite size was observed to decrease from 10.11 to 5.84 nm when the cobalt dopant concentration increased from 0 to 6%. Optical analysis revealed a significant blue shift in the UV absorption spectrum from 246 to 220 nm, resulting in a bandgap increase from 5.04 to 5.64 eV. The photoluminescence analysis indicates that the added Co dopant decreased the emission intensity. The peak shift from 512 to 532 cm −1 in Fourier transform infrared spectra confirmed the cobalt ion doping. The displacement of the Raman peak from 462 to 441 cm −1 further confirmed the space group Fm 3 ¯ m of CeO 2 . TEM images revealed that the CeO 2 samples without Co were spherical, but those with Co were nanorods. Energy-dispersive x-ray spectrum and x-ray photoelectron spectra confirmed the Co dopant. The vibrating sample magnetometer study confirmed the magnetic transition from weak to strong ferromagnetic transition due to Co dopant. Electron spin resonance spectra established the ferromagnetic character of undoped and Co-doped cerium oxide quantum dots.

Mg–Ti substituted strontium hexa-ferrites nanopowders (SrFe 12− x (MgTi) x /2 O 19 , x  = 0–3) were prepared by the sol–gel method. The morphology, structure and composition of the nanostructures were examined by field emission scanning electron microscopy (FESEM) and X-ray diffraction. The effect of Mg–Ti doping on the magnetic properties of the powders was investigated by vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) at ambient temperature. Experimental results showed that the materials exhibit hexagonal structures with tunable magnetic properties. The saturation magnetization and the coercive field ( H c ) decreased through the Mg and Ti substitution. FMR proved that by incorporation of Mg and Ti in strontium ferrite lattice, crystalline anisotropy, and microwave absorption can be tuned. SrFe 12− x (MgTi) x /2 O 19 ferrites are good candidate for applications at X-band microwave frequencies. A low field absorption signal was observed with the same phase as the FMR absorption in all doped ferrites.

Ferromagnetic SrFe12O19/ZnFe2O4 nanostructure composite particles were synthesized by the co-precipitation of chloride salts utilizing the sodium hydroxide solution. The resulting precursors were heat treated from 900 to 1200 °C for 4 h. The microwave absorption properties of the nanostructure composite particles were studied by ferromagnetic resonance, transmit-line theories, and reflection loss (RL) plots. Based upon the theoretical results, the microwave absorption properties can be improved by increasing the saturation magnetization and the thickness to the optimum size and decreasing the coercivity. By increasing the thickness to the optimum size and raising the heat treatment temperature (HT), the microwave absorption properties were increased (according to theoretical results). For example, the RL (at the resonance frequency) was increased from − 5 to − 15 dB by increasing the temperature from 900 to 1200 °C.