## 1 Introduction  
Perovskites with the general formula Re1-xAxMnO3 (Re--Nd, A--alkali metals) are materials with unique physical properties. These properties include colossal magnetoresistance (CMR), phase transitions, as well as unusual magnetic and electrical phenomena. The effect of colossal magnetoresistance is characterized by a sharp change in the material's electrical resistance under an external magnetic field. This effect is associated with transitions between different electronic states in manganites, induced by interactions among electrons, spins, and the crystal lattice. The perovskite structure promotes these phenomena due to the complex interactions between Mn\({}^{3+}\) and Mn\({}^{4+}\) ions and their spin states, as well as the ratio between rare-earth and alkali ions. By varying the composition and content of rare-earth and alkali elements, the physical properties of these materials can be controlled, making them promising for applications in spintronics, sensors, and other electronic devices [1; 2; 3; 4]. The study [5] describes the synthesis and investigation of Nd\({}_{2}\)NiMnO\({}_{6}\), a representative of the double perovskite family, known for its complex structural and magnetic properties. Sample preparation via the solid-state reaction method allows for the control of the phase composition and stoichiometry, which is crucial for studying its physical properties. A combination of X-ray and neutron diffraction provides detailed insights into the crystal structure, while X-ray photoelectron spectroscopy (XPS) delivers information on the valence state and chemical environment of the atoms. XPS results reveal the presence of mixed valence states of the transition metal ions in the samples, leading to intricate interactions between Ni and Mn. This, in turn, can influence the material's magnetic properties, such as the Curie temperature and magnetic anisotropy. Furthermore, the mixed valence states may contribute to electron transfer, which is essential for understanding the conductivity and magnetoresistance of Nd\({}_{2}\)NiMnO\({}_{6}\). The synthesis of the double perovskite La\({}_{1.95}\)Ca\({}_{0.05}\)BMnO\({}_{6}\) (where B = Ni and Co) via the sol-gel method yielded samples with a monoclinic crystal structure, confirmed through X-ray diffraction and Rietveld analysis. The lattice parameters, unit cell volume, and crystallite size increase with the ionic radius of the B-site ion, potentially influencing magnetic properties and phase transition behavior. The observed phase transitions from the paramagnetic (PM) to ferromagnetic (FM) state at 275 K and 201 K for La\({}_{1.95}\)Ca\({}_{0.05}\)NiMnO\({}_{6}\) and La\({}_{1.95}\)Ca\({}_{0.05}\)CoMnO\({}_{6}\), respectively, indicate the significant impact of the type of transition metal on the material's magnetic ordering [6]. The compound La\({}_{0.67}\)Ca\({}_{0.33}\)Mn\({}_{1-x}\)NixO\({}_{3}\) (\(0\leq\) x \(0.3\)) was synthesized via a solid-state reaction at low temperatures, followed by annealing in air. The resulting materials were analyzed using thermogravimetry and differential scanning calorimetry, X-ray powder diffraction, and scanning electron microscopy [7]. The study [8] conducted an in-depth investigation of the impact of monovalent doping on the magnetocaloric properties of manganites Nd\({}_{0.6}\)Sr\({}_{0.4-x}\)M\({}_{x}\)MnO\({}_{3}\) (x = 0.0, 0.1; M = K, Na), synthesized via the sol-gel method. The charge differences among Sr, K, and Na influence the Mn\({}^{4+}\)/Mn\({}^{3+}\) ratio, causing significant fluctuations in Nd\({}_{0.6}\)Sr\({}_{0.4}\)MnO\({}_{3}\) manganite. Various approaches were used to obtain critical parameters, which were shown to align with values predicted by the tricritical mean field. A second-order phase transition from ferromagnetic to paramagnetic was observed at the Curie temperature. The study highlights that substances doped with monovalent ions show promise for magnetic refrigeration near room temperature.