  A detailed understanding of ultrathin film surface properties is crucial for
the proper interpretation of spectroscopic, catalytic and spin-transport data.
We present x-ray magnetic circular dichroism (XMCD) and x-ray resonant magnetic
reflectivity (XRMR) measurements on ultrathin $\mathrm{Fe_3O_4}$ films to
obtain magnetic depth profiles for the three resonant energies corresponding to
the different cation species $\mathrm{Fe^{2+}_{oct}}$, $\mathrm{Fe^{3+}_{tet}}$
and $\mathrm{Fe^{3+}_{oct}}$ located on octahedral and tetrahedral sites of the
inverse spinel structure of $\mathrm{Fe_3O_4}$. By analyzing the XMCD spectrum
of $\mathrm{Fe_3O_4}$ using multiplet calculations, the resonance energy of
each cation species can be isolated. Performing XRMR on these three resonant
energies yields magnetic depth profiles that correspond each to one specific
cation species. The depth profiles of both kinds of $\mathrm{Fe^{3+}}$ cations
reveal a $\mathrm{3.9 \pm 1~\r{A}}$-thick surface layer of enhanced
magnetization, which is likely due to an excess of these ions at the expense of
the $\mathrm{Fe^{2+}_{oct}}$ species in the surface region. The magnetically
enhanced $\mathrm{Fe^{3+}_{tet}}$ layer is additionally shifted about
$\mathrm{3\pm 1.5~\r{A}}$ farther from the surface than the
$\mathrm{Fe^{3+}_{oct}}$ layer.
