>“The value and sign of the superexchange interaction depend strongly on the types of d orbitals (eg or t2g) involved, the number of electrons, and also the angle M1-O-M2. superexchange interactions can lead to elevated ordering temperature, up to nearly 900K in the ferrites. Whilst it is commonly negative,ferromagnetic insulators such as EuO (69K) or CrBr3 (37K) are known. This interaction is effective only over short distances, because it necessarily involves overlap between orbitals centered on neighboring ions.”
From MAGNETISM fundamentals by T. de Lacheisserie, D. Gignoux and M. Schlenker
> 诚然,双钙钛矿结构氧化物是一种现实的途径。Goodenough在60年代他的magnetism and chemical bond一书中已从理论上讲了这件事,也是现在很多人(包括我)在努力的一件事。需要指出的是,他在此书中就对材料制备技术感到灰心。亚稳态钙钛矿结构材料的制备科学技术这点这是我能有今天突破的关键所在。所以,我的看法是,即使实验慢半拍还是需要理论加快推进!
>>> Recently, I free me to survey those research on ferromagnetic insulator mentioned at our forum. The known materials are very scarce!!! Please refer to the following information. I am looking forward to hearing your comments. Thanks for your kindness.
>>>The recent research interest in the field of spin-based electronics (or spintronics)[1] has generated a demand for multifunctional materials that combine ferromagnetism with additional desirable properties, such as semiconducting transport or large magneto-optical response. This theme of the CDM focuses on the
particularly challenging task of combining ferromagnetism with insulating behavior. In addition to having potential spintronic applications, strong insulation is also a prerequisite for polarity, since conductors cannot support electric polarization. The task is challenging because ferromagnetic insulators are scarce; among simple oxides, they include the f-electron system EuO, [2] (TC =79 K) and the Jahn-Teller (orbital-ordered) systems YTiO3[3] (TC = 29 K), SeCuO3[4] (TC = 29 K) and BiMnO3[5] (TC = 105 K). None of these compounds can be used at room temperature, since their TCs are near 100 K or below.