Recently, the use of externally applied magnetic fields has garnered significant attention as a promising strategy to enhance oxygen evolution reaction (OER) electrocatalytic performance. OER exhibits spin-dependent kinetics, producing triplet O₂ from singlet reactants (OH^-, H₂O). Notably, magnetization can reduce this kinetic barrier by aligning the spin ordering of ferromagnetic (FM) electrocatalysts. Unfortunately, some of the most active OER catalysts, namely, transition metal oxyhydroxides, are paramagnetic (PM). This can be circumvented by utilizing a spin pinning effect in FM/PM core/shell materials, which has already been successfully demonstrated in a bulk CoFe₂O (CFO)/CoFeOxHy system. In this work, the previous research is built upon by examining a similar system at the nanoscale. By utilizing star-like diblock copolymer nanoreactors, several sets of superparamagnetic CFO NPs of varying sizes are crafted. The resulting NPs then undergo a controlled surface reconstruction via sulfur doping followed by cyclic voltammetry in 1 M KOH, thus enabling a systematic study on the effects of NP size and core-to-shell ratio on the magnetic field-rendered OER enhancement.