This work is devoted to the study of the magnetic properties and Electron Paramagnetic Resonance (EPR) spectroscopy of TiO₂:Fe nanoparticles doped with Al in different structural states. The sol-gel methods have been used to obtain the particles in both crystalline (average size from 3 to 20 nm) and X-ray amorphous states. The electron paramagnetic resonance spectra of crystalline samples TiO₂:Fe doped with aluminum besides a resonance line with g-factor ~2 exhibit a small signal with a g-factor of 4.3 from Fe³⁺ ions with rhombohedral distortions. The fraction of Fe³⁺ with rhombohedral distortions increases with increasing aluminum content. For the amorphous state at Al doping, the resonance with a g-factor of 4.3 is completely dominant in the electron paramagnetic resonance spectrum. The density functional theory calculation shows that aluminum prefers to be localized near iron ions, distorting the nearest Fe³⁺ environment. The complex integral electron paramagnetic resonance spectrum of all samples was fitted with sufficient accuracy by three separate resonance lines with different widths and intensities. The temperature behavior of the electron paramagnetic resonance spectrum can be described by the coexistence of paramagnetic centers (isolated Fe³⁺ ions including dipole-dipole interactions) and iron clusters with negative exchange interactions.

Li₃V₂(PO₄)₃ cathodes for Li-ion batteries (LIBs) were synthesized using a hydrothermal method with the subsequent annealing in an argon atmosphere to achieve optimal properties. The X-ray diffraction analysis confirmed the material’s single-phase nature, while the scanning electron microscopy revealed a granular structure, indicating a uniform particle size distribution, beneficial for electrochemical performance. Magnetometry and electron spin resonance studies were conducted to investigate the magnetic properties, confirming the presence of the relatively low concentration and highly uniform distribution of tetravalent vanadium ions (V⁴⁺), which indicated low lithium deficiency values in the original structure and a high degree of magnetic homogeneity in the sample, an essential factor for consistent electrochemical behavior. For this pure phase Li₃V₂(PO₄)₃ sample, devoid of any impurities such as carbon or salts, extensive electrochemical property testing was performed. These tests resulted in the experimental discovery of a remarkably high lithium diffusion coefficient D = 1.07 × 10⁻¹⁰ cm²/s, indicating excellent ionic conductivity, and demonstrated impressive stability of the material with sustained performance over 1000 charge–discharge cycles. Additionally, relithiated Li₃V₂(PO₄)₃ (after multiple electrochemical cycling) samples were investigated using scanning electron microscopy, magnetometry and electron spin resonance methods to determine the extent of degradation. The combination of high lithium diffusion coefficients, a low degradation rate and remarkable cycling stability positions this Li₃V₂(PO₄)₃ material as a promising candidate for advanced energy storage applications.

The temperature dependence of the ESR linewidth in La_{1 − x} Ca _x MnO₃ single crystals with various dopant concentrations (x = 0.18, 0.2, 0.22, 0.25, and 0.3) has been studied. An abrupt decrease in the ESR linewidth has been observed in the samples with a dopant concentration of x = 0.18 and 0.2 near the respective temperatures T _OO′ ≈ 260 and 240 K of the orthorhombic to pseudocubic structural phase transition. The abrupt decrease in the ESR linewidth by approximately 180 Oe has been also observed in the whole temperature range when the concentration is increased from x = 0.2 to x = 0.22. The formula for the fourth moment of the ESR line has been derived including both crystal fields and isotropic exchange interactions and taking into account the difference between the exchange coupling of a spin to its nearest in-plane and out-of-plane neighbors. The formula has been used to estimate the parameter D of the crystalline field on Mn³⁺ ions.

Here, we present the investigation of the magnetic properties of Li₃V₂(PO₄)₃/Li₃PO₄ composites, which can be potentially used as a cathode material in lithium-ion batteries. Li₃V₂(PO₄)₃/Li₃PO₄ was synthesized by the thermal hydrolysis method and has a granular mesoporous structure. Magnetic properties of the composite were investigated using magnetometry and electron spin resonance methods. Based on magnetization measurements, the simultaneous existence of the paramagnetic phase with antiferromagnetic interactions between spins of V³⁺ ions and magnetically correlated regions was suggested. Most probably, magnetically correlated regions were formed due to anti-site defects and the presence of V⁴⁺ ions that was directly confirmed by electron spin resonance measurements.

Li₃V₂(PO₄)₃/Li₃PO₄ (LVPO/LPO) composites as cathodes for Li-ion batteries were synthesized by the hydrothermal method and subsequently annealed in an Ar atmosphere. The effect of Li₃PO₄ content on the crystal structure, morphology and the related magnetic and electrochemical properties of Li₃V₂(PO₄)₃/Li₃PO₄ composites, containing 7.5 wt% and 14 wt% of Li₃PO₄ (LVPO/LPO-7.5 and LVPO/LPO-14) was investigated. The microstructure and morphology of the obtained composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM); magnetic and electrochemical properties investigations were performed using the electron spin resonance and galvanostatic methods, respectively. It was shown that Li₃V₂(PO₄)₃/Li₃PO₄ composites exhibit a high discharge capacity, good cycle performance (105 and 120 mAh g⁻¹ for the 200th cycle at 1C for LVPO/LPO-7.5 and LVPO/LPO-14, respectively), and insignificant changes in the surface morphology after 200 lithiation/delithiation cycles. Our results demonstrate that the increase in Li₃PO₄ content led to a decrease in the Li stoichiometry and magnetic inhomogeneity in Li₃V₂(PO₄)₃ phase; thus, the improvement in the electrochemical performance of LVPO/LPO composites due to incorporation of Li₃PO₄ can be attributed to their chemical and magnetic inhomogeneity.

Mercury chalcogenide (Hg_0.865Mn_0.135Te) monocrystal was grown by crystallization from a two-phase mixture with replenishment of the melt from a tellurium solution and has n-type conductivity. The ESR spectra of a single crystal were studied before and after X-irradiation. Only one intense anisotropic ESR line was observed at 4.2 K before X-irradiation. The anisotropy parameters were established from the angular dependence of the resonance field of ESR line. After X-irradiation, three ESR lines were registered in the spectrum. First and second lines with a large g-factor and an unusual temperature dependencies were associated with charge carriers localized on defects with strong the exchange interaction with the manganese ion spins. The third ESR narrowed line was identified as signal from Mn²⁺ ions. Estimated anisotropic exchange parameters from angular dependencies of magnetic resonance field depend on temperature. The temperature dependencies of ESR linewidths are well described by the Korringa law and spin-lattice relaxation contributions. The discontinuities in temperature dependencies of resonance field and linewidth at 18 and 65 K were observed.