Ferromagnetism in the hexaborides

摘要: The cubic hexaborides of the rare-earth elements have a wide variety physical properties, despite their simple crystallographic structures. For example, ‘doped’ hexaboride Ca1−xLaxB6 is ferromagnetic1, even though it has no partially filled d- or f-orbitals, which are usually required for magnetism. Here we show that ferromagnet with small magnetic moment but high Curie temperature can be obtained by doping an excitonic insulator (one containing condensate spin-triplet state electron–hole pairs). We propose this mechanism responsible ferromagnetism doped hexaborides.