Probing the Defect-Induced Magnetocaloric Effect on Ferrite/Graphene Functional Nanocomposites and their Magnetic Hyperthermia

Recently, the development of an alternative magnetic refrigerant for the conventional fossil fuels attracts the researchers. We discussed the structural defect-induced magnetocaloric effect (MCE) in Ni0.3Zn0.7Fe2O4/graphene (NZF/G) nanocomposites for the first time. Single-phase spinel ferrite nanocomposites with an average size of 7–11.4 nm were achieved by using the microwave-assisted coprecipitation method. The effect of graphene loading on the structural and magnetism of NZF/G nanocomposites was elaborated. Raman analysis proved that the interface interaction between NZF and graphene yielded different densities of structural defects. In view of magnetism, superparamagnetic NZF nanoparticles showed a magnetic entropy change (−ΔS M max) of −0.678 J·kg–1 K–1 at 135 K, whereas the NZF/G nanocomposites exhibited superior −ΔS M max at cryogenic temperatures and the defect-induced MCE change was indeed similar to the I D/I G intensity ratio. The nanocomposites exhibited different magnetic orderings between 5 and 295 K, and it was varying for I D/I G, 1.83 > 1.68 > 1.57 as antiferromagnetic (AFM) > AFM/ferrimagnetic (FiM) > FiM, respectively. Till now, NZF/G nanocomposites showed an inverse MCE of 4.378 J·kg–1 K–1 at 35 K and a refrigerant capacity of 88 J·kg–1 for 40 kOe, which was greater than the ferrites reported so far. Finally, MCE and magnetic hyperthermia were correlated at ambient conditions. These results pave the way for ferrite/graphene nanocomposites for cooling applications.