We report a theoretical discussion of the impact the composition on the maximum energy product ((BH)max) of core@shell FePt@CoFe2 and FePt@Fe nanocylinders. We have found that the best composition is determined by the competing trends imposed by a strong ferromagnetic core@shell interface exchange energy, and the core@shell dipolar interaction energy. The dipolar interaction has a negative impact on the nanocylinder (BH)max value, for shell thickness above a shell material dependent threshold value. We have also found that Fe is the best shell material owing to its much larger exchange stiffness.
