The temperature dependence of magnetic properties for cobalt ferrite nanoparticles by the hydrothermal method

Cobalt ferrite nanoparticles were synthesized via the hydrothermal route with the addition of trisodium citrate dihydrate (Na3CA⋅2H2O). The characterizations including x-ray diffraction (XRD) and transmission electron microscope showed that the products of this hydrothermal reaction are composed of cobalt ferrite nanocrystallite and a small amount of FeOOH, and the average crystallite size of the nanoparticles is 7.6±0.3 nm by XRD. The magnetic measurements revealed the temperature-dependent magnetic properties: The superparamagnetism occurs above 380 K due to the overcoming of energy barrier for the flip of spins, which arises from the magnetocrystalline anisotropy energy and the interparticle interactions due to the aggregation of the nanoparticles; a frozen spin-glasslike state was observed below 20 K, which is accompanied with the decrease in coercivity and high-field paramagnetic susceptibility, as well as the enhancement of saturated magnetization and the effective magnetic anisotropy constant.