## 4 Conclusions  
In this paper we have demonstrated that small nanoparticles (5.88-6.67 nm) of CoFe\({}_{2}\)O\({}_{4}\) ferrite can be successfully used in superparamagnetic hyperthermia for alternative cancer therapy, under the following optimal conditions for practical implementation:  
1. Obtaining the heating temperature of the nanoparticles at 43 \({}^{\circ}\)C for the amplitudes of the magnetic field of 5-60 kA/m, the frequencies of the magnetic field of 83-1000 kHz, and the diameters of the nanoparticles in the range 5.88-6.67 nm (Sections 3.4 and 3.5);
2. Optimal heating of the nanoparticles, by 18 \({}^{\circ}\)C above room temperature (25 \({}^{\circ}\)C), in a short period of time: 0.35-44.19 s, depending on the volume packing fractions;
3. The use of the linear approximation up to large magnetic fields, of \(\sim\)60-70 kA/m, for the maximum specific loss power, which greatly simplifies the practical implementation of magnetic hyperthermia in the case of CoFe\({}_{2}\)O\({}_{4}\) nanoparticles.
4. Possible intracellular therapy due to the use of very small nanoparticles (5.88-6.67 nm) of CoFe\({}_{2}\)O\({}_{4}\) that lead to obtaining the optimal maximum specific loss power (P\({}_{\text{sMo}}\)), a therapy that is much more effective in destroying tumor cells.  
All optimal values of the amplitude (H) and frequency (f) of the magnetic field, the optimal nanoparticle diameter (D\({}_{\text{o}}\)) and the optimal heating times (\(\Delta\)t\({}_{\text{o}}\)) are given in Table 3 (values marked in green), and the graphic in Figure 8. The corresponding optimal times are found in Tables 4 and 5, as well as Figures 9 and 10.  
These all results, under the appropriate biocompatible of CoFe\({}_{2}\)O\({}_{4}\) nanoparticles with the biological tissue into which they are to be inserted, may make CoFe\({}_{2}\)O\({}_{4}\) nanoparticles more effective than magnetite (Fe\({}_{3}\)O\({}_{4}\)) in cancer therapy by superparamagnetic hyperthermia.  
Also, the possible use of magnetic fields in a very wide range of values for its amplitude and frequency (5-60 kA/m and 83-1000 kHz) in the case of superparamagnetic hyperthermia with CoFe\({}_{2}\)O\({}_{4}\) ferrite nanoparticles is another major practical advantage. This will lead to eliminating the restrictive conditions in relation to the magnetic field used so far in the case of magnetite (10-25 kA/m and 200-500 kHz [53]).  
In addition, for greater accuracy in the practical application of magnetic hyperthermia, it is recommended to determine experimentally a priori the effective magnetic anisotropy and the spontaneous/saturation magnetization of nanoparticles to be used, give the possible surface effects in nanoparticles which could contribute to the modification of these parameters.  
All these will allow in practice to adjust on a case-by-case basis, the values used for magnetic field parameters and nanoparticle sizes to obtain the maximum effect in superparamagnetic hyperthermia for each particular tissue for maximum efficacy in destroying tumor cells.  
**Funding:** This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI--UEFISCDI, project number PN-III-P2-2.1-PED-2019-3067 (contract no. 263 PED/2020), within PNCDI III.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** This is not applicable.  
**Conflicts of Interest:** The author declares no conflict of interest.