Ferromagnetism and superstructure in Ca_1-xLa_xB_6
Abstract
A fundamentally new low temperature state was recently discovered in Ca_1-xLa_xB6 in the pioneering paper by Young et al.[D. P. Young et al. Nature 397, 412 (1999)]; it was found that at low La doping a ferromagnetic state with a small magnetic moment (< 0.07 μ_B) sets in at a large Curie temperature (Tc ~ 900K), which is comparable to the Fermi energy for doped carriers. Conventional theories (such as Stoner theory of ferromagnetism) provide no explanation of what is observed. We critically investigate the model of a doped excitonic insulator, which recently has been proposed as a candidate explanation of the peculiar ferromagnetic state in Ca_1-xLa_xB_6. We demonstrate that the ground state of this model is intrinsically unstable towards the appearance of a superstructure. In addition, the model leads to a phase separation of doped carriers into electron-enriched and neutral domains, which, however, may be prevented by Coulomb forces. We discuss other possible mechanisms of weak ferromagnetism in this material. This work was supported by the National High Magnetic Field Laboratory through NSF cooperative agreement No. DMR-9527035 and the State of Florida.
- Publication:
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APS March Meeting Abstracts
- Pub Date:
- March 2000
- Bibcode:
- 2000APS..MARV20001B