Abstract
AFe1-xCoxO3-δ (A=Sr, Ca) with minimized oxygen deficiency was prepared using high pressure technique. An oxider KCIO4 was encapsulated with the sample powder. The Co-substitution makes Fe3d electrons of AFeO3 more delocalized and induces metallic conduction and ferromagnetism. Cubic SrFe1-xCoxO3 shows ferromagnetism above 300 K for 0.4≤x≤0.9. From the composition dependence of unit cell volume, a possibility of negative magnetovolume effect has been raised. In orthorhombic CaFe1-xCoxO3 (0≤x≤0.5) Fe3d electrons seem to be more localized as judged from the magnetic hyperfine field measured by Mossbauer spectroscopy, and Tc is lower and the magnetization is smaller in comparison with the Sr-analogue. These seem to indicate that the σ* band is narrow in the Ca-phase because the Fe-O-Fe band is bent to -150.
