2018 年 28 巻 3 号 p. 206-216
Recent progress on perovskite-type oxides with unusually high-valence Fe4+ and Co4+ ions, especially for the latter system, is reviewed with showing magnetic phase diagrams. All the compounds are obtained by high-pressure oxygen annealing for the oxygen-deficient perovskites in the form of polycrystalline or single-crystalline samples prepared at ambient pressure. While cubic perovskite-type SrFeO3 has been found to show various types of novel helimagnetic phases, cubic perovskite-type SrCoO3 known as a room-temperature ferromagnet has been revealed to show helimagnetic ordering either by Ba substitution or Ca substitution for Sr. These systems provide rich magnetic phase diagrams and anomalous cross-correlation effects such as a giant inverse magnetovolume effect, which are inherent to the strong p-d hybridization generating itinerant oxygen ligand holes.
