Investigation of Impact of the Annealing on Magnetothermal Properties of Zn_0.2Mn_0.8Fe₂O₄ Nanoparticles

Magnetic and magnetothermal properties of annealed Zn _0.2 Mn _0.8 Fe ₂ O ₄ nanoparticles with diameter value, ranging from 9 to 35 nm, have been investigated and compared with earlier investigated unannealed Zn _0.2 Mn _0.8 Fe ₂ O ₄ magnetic nanoparticles (MNPs). A single-phase spinel structure was observed in both types of MNPs. It has been demonstrated that for the large annealed Zn _0.2 Mn _0.8 Fe ₂ O ₄ 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 ∼ H ⁴ . However, for earlier investigated unannealed Zn _0.2 Mn _0.8 Fe ₂ O ₄ MNPs, superquadratic dependence SAR ∼ 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 Néel relaxation in these annealed Zn _0.2 Mn _0.8 Fe ₂ O ₄ nanoparticles.