Spinel ferrite powder with a nominal composition Ni0.4Zn0.6Fe2O4 was prepared by a hydrothermal method, following by sintering at 700 °C and 900 °C, respectively. The structural and magnetic properties of specimens are studied. It is found that the large particles in specimens are the agglomerates of many small nanoscale crystallites. A strengthening of chemical polarization of the internal chemical bonds is found in the powder specimen after sintering. The saturation magnetization increases from 50.1 emu/g for as-synthesized powder to 63.1 emu/g for specimen sintered at 900 °C mainly due to the weakening of spin canting, while the coercivity exhibits a slight decreasing variation with the increase of sintering temperature.

A facile hydrothermal strategy is proposed to synthesize flower-like β-Co(OH)2 hierarchical microspherical superstructures with a diameter of 0.5-1.5 μm, which are self-assembled by β-Co(OH)2 nanosheets with the average thickness ranging between 20 and 40 nm. The magnetocaloric effect associated with magnetic phase transitions in Co(OH)2 superstructures has been investigated. A sign change in the magnetocaloric effect is induced by a magnetic field, which is related to a filed-induced transition from the antiferromagnetic to the ferromagnetic state below the Néel temperature. The large reversible magnetic-entropy change -ΔSm (13.4 J/kg K at 15 K for a field change of 5 T) indicates that flower-like Co(OH)2 superstructures is a potential candidate for application in magnetic refrigeration in the low-temperature range.