Enhancement of magnetocaloric effect around room temperature in Zn0.7Ni0.3-xCuxFe2O4 (0 ≤ x ≤ 0.2) spinel ferrites

In this work, a profound study has been conducted on magnetocaloric effect in Zn0.7Ni0.3-xCuxFe2O4 (with x = 0, 0.1 and 0.2) spinel ferrites synthesized by the sol-gel method. The Rietveld analysis of the powder X-ray diffraction shows that the samples crystallize in the cubic system with Fd3¯m space group. Structural analysis shows that the lattice constant and the unit cell volume increase with increasing Cu content. Magnetization measurements versus temperature in a magnetic applied field of 0.05 T show that our samples exhibit a paramagnetic (PM)-ferromagnetic (FM) transition with decreasing temperature. The partial substitution of Ni by Cu leads to a monotonic decrease in the Curie temperature (TC) of the samples from 327 K for x = 0-282 K for x = 0.2. Additionally, Arrott plots and Landau theory were also studied to assess magnetic phase ordering in these materials, such investigations indicate that the phase transition from the PM to FM states is of second order. The magnetic entropy change |ΔSMmax| takes values of 0.67, 0.64 and 0.62 J/kgK for x = 0, 0.1 and x = 0.2, respectively at 2 T. The relative cooling power (RCP) amounts 111, 117 and 124 J/kg at 2T for x = 0, 0.1 and x = 0.2, respectively. Because of the relatively easy possibility of tuning the TC and the interesting values of relative cooling power, these samples can be considered as suitable candidates for magnetic refrigeration at around room temperature.