  The interrelation between Ferreira's Hopf solitons of a conformal nonlinear
$\sigma$ model and the electromagnetic knots found by Ra$\tilde{\rm{n}}$ada et
al. is investigated. It is shown that the electromagnetic knots yield exact
solutions of the conformal nonlinear $\sigma$ model different from those
obtained by Ferreira. Conversely, It is discussed that Ferreira's solutions
realize magnetic knots. The energy associated with these two kinds of knots are
compared. The structure of the electric charge distribution and the electric
current density associated with the magnetic knots is investigated.
