The electronic, magnetic, optical and elastic properties of nanomaterials are governed partially by the crystallite size and crystal defects. Here, the crystalline size of hexagonal La_1−xSr_xMnO₃ (x = 0.3) nanoparticles was determined using various methods. Single-phase La_0.7Sr_0.3MnO₃ nanopowders were produced after 10 h of milling in a commercial high-energy SPEX 8000D shaker mill, and then they were heated at 700 °C and 800 °C to study the effect of calcined temperature on the crystallization of nanoparticles. The modified Scherrer, Williamson–Hall, size–strain, and Halder–Wagner methods were used to determine the crystallite sizes and the elastic properties, such as intrinsic strain, stress, and energy density, from the X-ray diffraction peak broadening analysis. The obtained results were then compared with one another. The difference in crystallite sizes calculated from the different methods was due to the different techniques.

It is well-known that Ag–Au bimetallic nanoplates have attracted significant research interest due to their unique plasmonic properties and surface-enhanced Raman scattering (SERS). In recent years, there have been many studies on the fabrication of bimetallic nanostructures. However, controlling the shape, size, and structure of bimetallic nanostructures still has many challenges. In this work, we present the results of the synthesis of silver nanoplates (Ag NPls), and Ag–Au bimetallic core/shell and alloy nanostructures, using seed-mediated growth under green LED excitation and a gold salt (HAuCl₄) as a precursor of gold. The results show that the optical properties and crystal structure strongly depend on the amount of added gold salt. Interestingly, when the amount of gold(x) in the sample was less than 0.6 μmol (x < 0.6 μmol), the structural nature of Ag–Au was core/shell, in contrast x > 0.6 μmol gave the alloy structure. The morphology of the obtained nanostructures was investigated using the field emission scanning electron microscopy (FESEM) technique. The UV–Vis extinction spectra of Ag–Au nanostructures showed localized surface plasmon resonance (LSPR) bands in the spectral range of 402–627 nm which changed from two peaks to one peak as the amount of gold increased. Ag–Au core/shell and alloy nanostructures were utilized as surface enhanced Raman scattering (SERS) substrates to detect methylene blue (MB) (10⁻⁷ M concentration). Our experimental observations indicated that the highest enhancement factor (EF) of about 1.2 × 10⁷ was obtained with Ag–Au alloy. Our detailed investigations revealed that the Ag–Au alloy exhibited significant EF compared to pure metal Ag and Ag–Au core/shell nanostructures. Moreover, the analysis of the data revealed a linear dependence between the logarithm of concentration (log C) and the logarithm of SERS signal intensity (log I) in the range of 10⁻⁷–10⁻⁴ M with a correlation coefficient (R²) of 0.994. This research helps us understand better the SERS mechanism and the application of Raman spectroscopy on a bimetallic surface.

Polycrystalline La0.7Sr0.3Mn1−xCoxO3 (x = 0.0–1.0) samples were synthesized by solid-state reaction. Structural and magnetization studies reveal the replacement of Co for Mn in La0.7Sr0.3Mn1−xCoxO3, and the decrease of the Curie temperature (TC) from 360 K (for x = 0) to 224 K (for x = 1). Positive slopes observed in the H/M versus M2 curves prove all the samples undergo a second-order magnetic phase transition. By analysis of the M(H) data at temperatures around TC using the Kouvel-Fisher method, we obtained the values of critical parameters (TC, β, γ, and δ). The results suggest an existence of short-range FM order in the sample x = 0 with β = 0.377. Meanwhile, for the case of Co-doped samples, their β values in the range of 0.403–0.457 indicate a coexistence of short and long-range FM order. This means that Co-doping favors establishing FM long-range order in La0.7Sr0.3Mn1−xCoxO3. From M(H) data, we have also determined the magnetic entropy change (ΔSm) for the samples. We have found that the ΔSm(T) curves for different applied fields are collapsed onto a universal curve by normalizing the ΔSm(T) curves to their respective maximum value ΔSmax (i.e., ΔSm(T)/ΔSmax) and rescaling the temperature axis above and below TC with θ=(T−TC)/(Tr−TC), where Tr is the reference temperature.

We have studied the magnetic and spin-glass (SG) properties of La_0.7Ca_0.3MnO₃ single-crystalline nanoparticles, which were prepared by the mechanical milling method with different milling times (t_m). Analyzing the susceptibility data in the paramagnetic region indicates both ferromagnetic (FM) and anti-FM interactions coexisting in nanoparticles. Additionally, there is a peak associated with the freezing temperature (T_f) appearing on the real part curve of the ac susceptibility, χ′(T). The T_f value increases with increasing frequency as expected for SG systems. The SG behavior was also checked by using the criterion parameter c = ΔT_f/T_fΔ(log₁₀f), and the power law τ = τ₀(T/T_g − 1)^−zν. The obtained values of c ≈ 5 × 10⁻², τ₀ ≈ 10⁻⁵ s and zν ≈ 2–3 are consistent with those expected for SG-like systems, suggesting an existence of a SG phase transition at T_g below T_f, which decreases with decreasing ⟨D⟩. Basing on ln(f) versus T_f data, and the Néel-Arrhenius model [ln(f) = ln(f₀) - E_a/k_BT] and Vogel–Fulcher law [ln(f) = ln(f₀) - E_a/k_B(T - T₀)], the Larmor frequency (f₀), activation energy (E_a) and effective temperature (T₀) for the samples with different ⟨D⟩ were determined. Obtained results indicate the existence a strong interaction between nanoparticles.

Multiferroic nanocomposites of xNiFe₂O₄/(1-x)BaTiO₃ (x = 0, 0.1, 0.2, 0.3, and 0.4) (denoted as NFO-BTO) with the particle size about of 70 nm were prepared by the high energy mechanical milling combined with the thermal annealing methods. The x-ray diffraction patterns show a presence of NiFe₂O₄ (NFO) and BaTiO₃ (BTO) phases. The values of the characteristic parameters of nanocomposites such as the coercive field (E _c), the residual polarization (P _r), the remanent magnetization (M _r), the saturation magnetization (M _s), and the coercive force (H _c) increase gradually with an increase in NFO concentration. For an applied electric field below 10 kV cm⁻¹, the values P _r and E _c are found to be 0.004–0.038 μC cm⁻² and 0.7–2.0 kV cm⁻¹, corresponding x = 0.1–0.4, respectively. Changes in electrical and magnetic properties of composites depend heavily on the NFO content, which will be studied specifically. Additionally, the ability to absorb microwave at room temperature of a representative sample with x = 0.3 mixed in acrylic paint (denoted as NFO-BTO-AP) in a frequency range of f = 12–18 GHz has also been investigated. It shows a large negative reflection loss (RL) with RL = −39.8 dB occurring at around 16.8 GHz corresponding to the absorptivity of over 99.9% for an absorbing layer with thickness of 5.5 mm. This suggests that NFO-BTO nanocomposites could be considered as a potential material in the field of absorbing and shielding electromagnetic waves.