We investigate the effects of Fe and Co co-doping on the magnetic and electronic properties of ZrO2 ceramics prepared by a sol-gel method, and study their dependence on the annealing temperature. Dilute Fe and Co co-doping into ZrO2 exhibits ferromagnetic behavior at room temperature for annealing temperatures above 900 °C, accompanying the phase transition from tetragonal to monoclinic structure in ZrO2. The electronic structures are studied by x-ray absorption spectroscopy and Mössbauer spectroscopy, which suggest that the Fe3+ and Co2+/Co3+ mixing states are dominant in Fe and Co co-doped ZrO2

We have investigated Fe and Ni codoping effect into SnO2. Room-temperature diluted ferromagnetic semiconductors with the enhancement of magnetization can be prepared in case of codoping. The saturation magnetization can be controlled by means of the Fe and Ni codoping ratios. The electronic structures were investigated by x-ray absorption spectroscopy (XAS) and Mössbauer spectrometry. Fe3+ states were revealed by the isomer shift values. XAS revealed Ni2+ states, which suggests that the double-exchange-like ferromagnetic interaction between the diluted magnetic ions mediated by oxygen vacancies becomes a possible origin of room-temperature ferromagnetism.

1-5% Fe and 1% Co co-doped SnO 2 samples were synthesized by sol-gel method. Their magnetization increased with increasing crystal size of rutile SnO 2 . Their Mössbauer spectra contain a broad sextet, magnetic relaxation components, and paramagnetic doublet peaks for less than 3% Fe doping. The sextet of α-Fe 2 O 3 was observed instead of magnetic relaxation peaks for Fe doping of above 4%. The broad sextet and relaxation components may be related to the magnetic properties of Fe and Co co-doped SnO 2 .

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Dilutely Fe-Mn co-doped SnO 2 was synthesized by a sol-gel method. The co-doping effect enhances the magnetization in comparison with the case of single-ion doping. We found that saturation magnetization values are correlated with the crystalline sizes. Mö ssbauer spectrometry revealed the magnetic sextet and relaxation peaks, which suggest that Fe ions contribute to the magnetic ordering and superparamagnetic properties. X-ray absorption spectroscopy revealed that Mn 3þ states mixed with Mn 2þ states are dominant in Fe-Mn co-doped SnO 2 .