Polymer fe-rh / pvdf multicaloric composite

A technological protocol has been developed and a polymer magnetoelectric Fe-Rh / PVDF composite consisting of magnetocaloric particles of Fe₅₀ Rh₅₀ embedded in a polymer piezoelectric matrix of polyvinyldenfluoride has been manufactured by solvent casting method. The particles of Fe₅₀ Rh₅₀ used for the composite fabrication were obtained from an ingot of the same composition by mechanical filing. The average size of the Fe₅₀ Rh₅₀ particles fabricated by the mechanical treatment was about 50 μm. X-ray diffraction analysis demonstrates the presence of an electroactive β-phase of polyvinyldenfluoride and an ordered B2 phase corresponding to a crystal structure with a base-centered crystal lattice of Fe₅₀ Rh₅₀, which can exhibit magnetoelectric and multicaloric effects. It was shown that the temperature of the transition from the antiferromagnetic to the ferromagnetic state for Fe₅₀ Rh₅₀ microparticles is shifted towards higher temperatures of about 500 К as a result of the mechanical action in the process of obtaining Fe-Rh particles, and in the region of about 670 K, a transition from the ferromagnetic state to the paramagnetic one was observed. It has been demonstrated that annealing of the Fe₅₀ Rh₅₀ particles at a temperature of 1000°C for 20 minutes is able to recover the magnetic properties close to the bulk sample with a same composition. It should be noted that the annealing in this protocol does not completely eliminate the content of the disordered phase corresponding to the crystal structure with a face-centered cubic lattice, to the ordered structure with base-centered lattice that is seen from the data of magnetic and X-ray diffraction measurements. For the Fe-Rh / PVDF composite, a wide magnetic phase transition of at about 387 K (AFM-FM) in the heating mode and at approximately 364 K (FM-AFM) in the cooling mode was observed, which coincides with the results of magnetic measurements obtained for the heat-treated Fe₅₀ Rh₅₀ particles. The proposed method can be used for the design of new composite magnetoelectric composites with caloric effects.