Enhanced relative cooling power of Ni1-xZnxFe2O4 (0.0 ≤ x ≤ 0.7) ferrites

We report on a detail study of the structural, magnetic and magnetocaloric properties of Zn-doped nickel-zinc ferrites with different Zn concentrations. Polycrystalline Ni1-xZnxFe2O4 (0.0 <= x <= 0.7) ferrite samples were prepared using the conventional solid-state reaction method. The X-ray diffraction results indicate that the ferrite samples have a cubic spinel type structure without any impurity phase. Temperature-dependent magnetization measurements and Arrott analysis reveal second-order ferromagnetic transition in all samples, with the Curie temperature decreasing progressively with increasing Zn concentration, from similar to 845 K for x = 0.0 to 302 K for x = 0.7. An increase in magnetization at low temperature was observed for Zn doping up to x = 0.5. A maximum in magnetic entropy change, vertical bar Delta S-M(max)vertical bar (similar to 1.39 J kg(-1) K-1 at 2.5 T), was observed in the Ni0.7Zn0.3Fe2O4 sample. The width of magnetic entropy curve was found to increase with the Zn concentration. Also, the vertical bar Delta S-M(max)vertical bar and relative cooling power were found to increase with increasing applied magnetic field, which indicates much greater cooling power is expected with a larger magnetic field. This investigation suggests that Ni1-xZnxFe2O4 (0.0 <= x <= 0.7) ferrite samples are possible candidates for magnetic refrigeration across a wide range of working temperatures. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.