Magnetic properties and heating efficacy of magnesium doped magnetite nanoparticles obtained by co-precipitation method

•Ferrofluids based on MgxFe3−xO4 NPs were synthesized by a chemical co-precipitation.•NPs size decreases while their aggregation in ferrofluids increases with Mg content.•All samples show superparamagnetic behaviour at room temperature.•Saturation magnetization increase of ≈40% compared to undoped Fe3O4 was obtained.•SAR values of ferrofluides in AC fields displayed decrease with Mg increase.