Evolution of photospheric properties for model r0e2 powered by a magnetar and model r0e2n without a magnetar (the sustained source of power comes from radioactive decay alone in model r0e2n). Bottom panel: ionization of oxygen at the photosphere (i.e., [∑_iiN(Oⁱ⁺)/N(O)]_ph) where N(Oⁱ⁺) is the oxygen number density when i-times ionized and N(O) is the total oxygen number density. Oxygen is chosen since it is the main constituent of the ejecta and because it is associated with the emblematic spectroscopic signatures of SLSNe Ic. Only the electron-scattering opacity is used to locate the photosphere. Compared to its unmagnetized counterpart, model r0e2 shows photospheric properties that are hotter and more ionized over the period 3 − 200 d.