One of the applications of magnetic ferrofluids in biomedicine is magnetic therapy for the treatment of cancerous masses. In this way, sales are injected into the cancerous mass and, by being placed in an alternating magnetic field, causes the cells to warm up to 45 ° C and eventually destroy them. Cobalt ferrite is a very strong magnetic material with high saturation magnetism and high temperature (T C =520) and also has a very high chemical stability. The properties of cobalt ferrite have been developed as a suitable option for use in drug and pharmaceutical systems. For magnetic phenomena, it is necessary to have high-power dissipation (SLP) magnetic nanoparticles, and in the synthesis of cobalt-substituted magnetite nanoparticles, the power dissipation also varies by increasing the concentration of cobalt ions. The reaction parameters including temperature, reducing agent and pH of the solution also play an important role in the size of the nanoparticles, colloidal stability, magnetic properties, and the amount of power dissipation. In this research, we try to increase the power dissipation power of magnetite nanoparticles and cobalt-substituted magnetite (CoxFe3-xO4) by changing the concentrations of cobalt ions (x = 0, 0.3, 0.6, 1.0), and for Having nanoparticles with a uniform distribution in a nanometer size has been used for hydrothermal reduction with citric acid with different concentrations for the synthesis of nanoparticles. The nanoparticles produced by X-ray diffraction (XRD), scanning electron microscopy (TEM, SEM), FTIR and VSM have been characterized. In order to increase the biocompatibility of these nanoparticles, polymeric coatings were used and, using FTIR, electron microscopy (TEM), thermal gravimeter analysis (TGA) tests to ensure the presence of coating coverage was taken. Keywords Magnetic sales, Fractionation, Specific power dissipation, Carbonate substituted magnetite, Hydrothermal reduction