Investigation of Electronic Structures of TCr2O4 (T = Fe, Co, Ni) Spinel Oxides by Employing Soft X ray Synchrotron Radiation Spectroscopy

The electronic structures of TCr2O4 (T = Fe, Co, Ni) spinel oxides have been investigated by employing synchrotron radiation-based soft X ray absorption spectroscopy (XAS). The measured 2p XAS spectra of transition-metal ions reveal that Cr ions are trivalent (Cr3+), and all the T (T = Fe, Co, Ni) ions are divalent (Fe2+, Co2+, Ni2+). It is also found that most of T (T = Fe, Co, Ni) ions occupy the A sites under the tetrahedral symmetry, while Cr ions occupy mainly the B sites under the octahedral symmetry. These findings show that the structures of TCr2O4 (T = Fe, Co, Ni) are very close to the normal spinel structures. Based on these findings, it is expected that Jahn-Teller (JT) effects are important in FeCr2O4 and NiCr2O4. In contrast, CoCr2O4 maintains the cubic structure without having the JT distortion since both Cr3+ and Co2+ ions are non-JT ions. This work suggests that the antiferromagnetic interaction between Cr3+ and T2+ ions plays an important role in determining the magnetic properties of TCr2O4 (T = Fe, Co, Ni).