The influence of metal ion to hydroxide ion ($\rm{Me^{2+} /OH^{−}}$) ratio on the synthesis of $\rm{Mn_{0.5}Zn_{0.5}Fe_{2}O_{4}}$ (MZ5) ferrite nanoparticles is reported. The aim of this low-temperature co-precipitation technique is to produce MZ5 nanoparticles with different sizes in single domain range. The variation in $\rm{Me^{2+} /OH^{−}}$ ratio affects the growth and shape of the particles. The mechanism of nucleation and growth of the particles is discussed. EDX and XPS measurements show the change in stoichiometry of the composition when $\rm{Me^{2+} /OH^{−}}$ ratio changes. When the ratio is 0.52, Zn ion was found to be absent and the structure resembles $\rm{Mn_{x}Fe_{3−x}O_{4}}$. The defect in the composition changes magnetic properties such as saturation magnetisation and Curie temperature of the samples. 119 nm crystalline size with highest magnetisation ($\rm{80 Am^{2}/kg}$) is obtained which shows quite good response to induction heating (specific absorption rate (SAR) = 78 W/g). Moreover, SAR and intrinsic loss power (ILP) are higher for MZ5 ferrite than that are reported earlier. This shows the potential of magnetic induction heating in the treatment of cancer.