Magnetic properties

Ferromagnetism in the hexaborides


The cubic hexaborides of the rare-earth elements have a wide variety of physical properties, despite their simple crystallographic structures. For example, the ‘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 a ferromagnet with a small magnetic moment but with a high Curie temperature can be obtained by doping an excitonic insulator (one containing a condensate of a spin-triplet state of electron–hole pairs). We propose that this mechanism is responsible for the ferromagnetism of doped hexaborides.

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Figure 1: Structure of energy spectrum in a semimetal (left) and in an excitonic insulator (right).
Figure 2: Phase diagram of the excitonic state in Ca1−xLaxB6.


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Correspondence to T. M. Rice.

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Zhitomirsky, M., Rice, T. & Anisimov, V. Ferromagnetism in the hexaborides. Nature 402, 251–253 (1999).

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