Controlling the Curie temperature (TC) in the range from 42-46 °C in magnetic hyperthermia (MH) therapy is an essential research topic because overheating can cause irreversible damage to healthy tissue. When TC is in the above temperature range, the magnetic nanoparticles reach a paramagnetic state, effectively turning off the MH treatment. In this work, we synthesized Zn-Co nanoparticles of representative composition Zn0.54Co0.46CrxFe2-xO4, where the Fe3+ cations are carefully replaced by Cr3+ ions, which allow a precise tuning of TC and hence the self-regulation of MH. The X-ray diffraction analysis of the prepared nanoparticles confirms the formation of a single-phase cubic spinel structure. The average crystallite of the nanoparticles increases with Cr3+ doping, while the TC and saturation magnetization decrease considerably from 78 °C (x = 1) to 27 °C (x = 0.6) and 46.6 emu/g (x = 1) to 15.3 emu/g (x = 0.6), respectively. Besides MH potential of the investigated samples as revealed from specific absorption rate (SAR) assays and the maximum temperature reach (Tmax), vary from 7 W/g and 37.3 °C, for x = 0.6, to 38 W/g and 62.9 °C, for x = 0.1, we found that the composition Zn0.54Co0.46Cr0.4Fe1.6O4 is more promising with SAR of 22 W/g and Tmax = 42.3 °C, which is precisely lies in the safe temperature range to automatically activate the self-regulation during the magnetic hyperthermia treatment. The results reveal an excellent combination between size distribution and Cr3+ content in Zn-Co-based ferrite, which has a great potential for self-regulated magnetic hyperthermia applications.

Self-regulated magnetic hyperthermia is a promising alternative for cancer treatment based on tumor annihilation by heating using appropriate Curie temperature ($T_{C}$) as an internal temperature controller. We successfully prepared strontium-doped lanthanum manganite nanoparticles (LSMO-$x$) using the sol-gel method. The $T_{C}$ can be adjusted by modifying both the composition and diameter of the particles, that is, varying the Sr content (0.2 $\leq$ x $\leq$ 0.3) and the annealing temperature (600, 700, and 800 °C). Structural, morphological, chemical, and magnetic properties were investigated. The samples exhibit the structure of perovskites with average particle sizes ranging from 17 nm to 27 nm, depending on the annealing temperature. This diameter range ensures that all samples investigated are have negligible remanence at room temperature. Magnetization studies show that $T_{C}$ increases as Sr content and particle size increase, indicating that the $T_{C}$ is governed by both. Thus $T_{C}$ can be adjusted by combining these two parameters for self-regulated magnetic hyperthermia. Magnetic hyperthermia measurements showed that samples with larger particle sizes ($\geq$ 19 nm) were more efficient in promoting heat, that is, presenting a higher specific absorption rate (SAR), probably due to the adequate balance between the Néel and Brownian relaxations behavior. We figure out that the SAR value is essential for this specific finality, but it should also consider the maximum temperature reached during the hyperthermia essays. Finally, we build up a nanoparticle diameter vs. Sr concentration phase diagram, where the SAR values are displayed, which allows for predicting the best sample for the self-regulated hyperthermia

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