Density functional theory conjugated with non-equilibrium Green's function-based first principle approach is used to determine the ferromagnetic-doping effect in the current-voltage characteristics for the heterojunction biomolecular analytical structure. The quantum-mechanical transport phenomenon and multiple switching activities associated with sequential negative differential resistance properties have been observed for this adenine-thymine chain. The authors investigate the quantum-transport properties of conventional doping effect for ferromagnetic atoms in this bimolecular chain. The results show an electronic enhancement effect in quantum-ballistic conductivity for this chain along with sequential switching property. Among these ferromagnetic metals, Nickel shows significant transmission spectrum, sharp and prominent highest occupied molecular orbital (MO) and lowest un-occupied MO peak along with maximum quantum-ballistic current at room temperature. It is observed from the device density of states that large numbers of conducting channels are available for Nickel doping. This ensures high quantum-transmission current flow within the central molecular region for these ferromagnetic dopants. Compared to Iron and Cobalt, the current has been enhanced up to 4.05 times for Nickel dopant. High doping concentration (13.3%) has been introduced for this ab-initio model. It has found that the number of total switching process is increased during ferromagnetic doping mainly for Cobalt and Nickel dopants.