Interparticle interaction effects on the magnetocaloric properties of γ-Fe₂O₃ nanoparticles dispersed in polyvinyl alcohol

We report on the effects of interactions on the magnetocaloric properties of γ-Fe₂O₃ nanoparticles with an average fixed size of 4.7 nm. The influence of particles interaction was investigated by changing their surrounding through the dispersion of γ-Fe₂O₃ nanoparticles in polyvinyl alcohol with different concentrations: powder, IN (isolated particle near) and IF (isolated particle far). T_B decreases from 124 to 21 K with increasing volume fraction of γ-Fe₂O₃ nanoparticles in polyvinyl alcohol from powder to IF sample, due to decrease in the magnetic interparticle interactions (dipolar interaction). The temperature dependence of the magnetic entropy change (− ΔS_M) was determined using isothermal magnetization. The caret shape of (− ΔS_M) curves shows that the magnetic transition near T_B for all samples was a second-order phase transition. Under a magnetic field change of 10 kOe, the (− ΔS_M) and relative cooling power (RCP) decrease from 1.11 to 0.65 J/kg K and 64–23 J/kg when passing from powder to IF samples, respectively. The decrease in the magnetocaloric performance with decreasing the magnetic interparticle interactions was attributed to the decrease of magnetization.