Employing temperature ($T$)-dependent soft x-ray magnetic circular dichroism (XMCD) and soft x-ray absorption spectroscopy (XAS) at the Co, Cr, and Fe $2p$ absorption edges, we have investigated the electronic structures of ${\mathrm{CoCr}}_{2-x}{\mathrm{Fe}}_x{\mathrm{O}}_4$ ($0\le x\le 0.2$) spinel ferrites, which were reported to reveal the negative magnetization phenomenon. We have found that Co ions are divalent and occupy the tetrahedral ($T_d$) sites, while both Fe and Cr ions are trivalent and occupy the octahedral ($O_h$) sites with a little mixture of $T_d$-site Fe ions. XMCD measurements demonstrate that the magnetic moments of Co ions are antiparallel to those of Fe/Cr ions and that all the Co, Cr, and Fe ions are in the high-spin (HS) states. With increasing $x$, the XMCD signals of all elements exhibit the sign changes for $x>\sim 0.15$, demonstrating the magnetization flip due to the change of the majority spins from the Co spins to the Fe/Cr spins for $x>\sim 0.15$. With increasing $T$, all the magnetic moments vanish above $T\sim 140\mathrm{K}$, except for $x$ = 0.15 that exhibits nonvanishing moments up to $T\sim 200\mathrm{K}$. This work provides direct evidence for the magnetization flip in ${\mathrm{CoCr}}_{2-x}{\mathrm{Fe}}_x{\mathrm{O}}_4$ at $x\ge 0.2$. The magnitudes of the spin ($m_{\mathrm{spin}}$) and the orbital ($m_{\mathrm{orb}}$) magnetic moments are determined from the sum-rule analysis of their low-$T$ XMCD spectra. Based on the systematic XMCD/XAS study, we have provided a model for the electronic and spin configurations of Co, Cr, and Fe ions in ${\mathrm{CoCr}}_{2-x}{\mathrm{Fe}}_x{\mathrm{O}}_4$ in the low-$T$ regime.

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• Electronic structure
• Magnetism
• Magnetic systems
• X-ray absorption spectroscopy
• X-ray magnetic circular dichroism