Investigation of Impact of the Annealing on Magnetothermal Properties of Zn0.2Mn0.8Fe2O4 Nanoparticles

Magnetic and magnetothermal properties of annealed Zn0.2Mn0.8Fe2O4 nanoparticles with diameter value, ranging from 9 to 35 nm, have been investigated and compared with earlier investigated unannealed Zn0.2Mn0.8Fe2O4 magnetic nanoparticles (MNPs). A single-phase spinel structure was observed in both types of MNPs. It has been demonstrated that for the large annealed Zn0.2Mn0.8Fe2O4 nanoparticles (24.7, 31.4, 35.1 nm) the value of specific absorption rate (SAR) is proportional to the amplitude of the magnetic field as similar to H-4. However, for earlier investigated unannealed Zn0.2Mn0.8Fe2O4 MNPs, superquadratic dependence SAR similar to H-5 have been found starting from 13 nm. Significant change of dependence of the character of SAR(d) may be explained by low values of hysteresis area of small annealed MNPs and, thus, dominant role of Neel relaxation in these annealed Zn0.2Mn0.8Fe2O4 nanoparticles.