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Information × Registration Number 0225U004997, (0125U001466) , R & D reports Title Nanoscale multiferroics with improved magnetocaloric properties. popup.stage_title Вдосконалення експериментальних методик досліджень нанорозмірних мультифероїків, характеризація зразків та проведення тестових вимірювань. Head Bodnaruk Andrii V., Кандидат фізико-математичних наук Registration Date 23-12-2025 Organization Institute of Physics of National Academy of Sciences of Ukraine popup.description1 The aim of the work is to establish the size-composition-structure-properties relationships and to obtain new nanoscale multiferroics based on rare earth manganites, perovskites and/or orthoferrites with improved magnetocaloric properties. popup.description2 This work presents a comprehensive picture of defect- and size-controlled magnetic and polar phenomena in heterogeneous nanostructured systems, ranging from oxygen-deficient perovskite-like ferrites to oxide nanoparticles of HfₓZr₁₋ₓO₂₋ᵧ, polymer–ceramic composites based on P(VDF-TrFE)–BaTiO₃, and densely packed arrays of ferroelectric nanowires. It is shown that single-phase CaFeO₂ nanoparticles synthesized by the sol–gel method exhibit a pronounced temperature evolution of the saturation magnetization and coercive field, with a transition from ferromagnetic to superparamagnetic behavior upon cooling below room temperature. Calorimetric measurements of aqueous suspensions subjected to alternating magnetic fields of different amplitudes confirm controllable heating losses and their relevance to magnetic hyperthermia. For ultrasmall (5–10 nm) HfₓZr₁₋ₓO₂₋ᵧ nanoparticles obtained by solid-state organonitrate synthesis, a combination of Raman spectroscopy, elemental analysis, and X-ray diffraction reveals the dominance of the orthorhombic phase in the absence of detectable magnetic impurities. In P(VDF-TrFE) composite films containing BaTiO₃ nanoparticles (average size ≈ 24 nm), a nontrivial temperature–frequency behavior of the dielectric permittivity is observed. Near the “freezing” temperature of the polymer matrix (≈ −50 °C), a crossover from weakly to strongly nonlinear behavior emerges, followed by a diffuse step-like change in the 0–40 °C range and, depending on the BaTiO₃ volume fraction (20–70%), either a pronounced maximum or a quasi-plateau. The frequency dispersion increases sharply in the vicinity of these extrema, while the photoresponse under infrared modulation is predominantly photoelectric rather than pyroelectric in origin. A phenomenological model accounting for screening and mutual dipole–dipole interactions explains the observed effects and predicts the emergence of a negative-capacitance state at high nanoparticle concentrations. Product Description popup.authors Bodnaruk Andrii V. Vladyslav Zamorskyi Denys O. Stetsenko Oleksii V. Bereznykov popup.nrat_date 2025-12-23 Close