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High-temperature ferromagnetism of $sp$ electrons in narrow impurity bands: Application to CaB$_6$

D. M. Edwards·M. I. Katsnelson
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Abstract

Ferromagnetism with high Curie temperature $T_c$, well above room temperature, and very small saturation moment has been reported in various carbon and boron systems. It is argued that the magnetization must be very inhomogeneous with only a small fraction of the sample ferromagnetically ordered. It is shown that a possible source of high $T_c$ within the ferromagnetic regions is itinerant electrons occupying a narrow impurity band. Correlation effects do not reduce the effective interaction which enters the Stoner criterion in the same way as in a bulk band. It is also shown how, in the impurity band case, spin wave excitations may not be effective in lowering $T_c$ below its value given by Stoner theory. These ideas are applied to CaB$_6$ and a thorough review of the experimental situation in this material is given. It is suggested that the intrinsic magnetism of the B$_2$ and O$_2$ dimers might be exploited in suitable structures containing these elements.

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D. M. Edwards, M. I. Katsnelson. 2006-05-21. High-temperature ferromagnetism of $sp$ electrons in narrow impurity bands: Application to CaB$_6$. https://doi.org/10.1088/0953-8984%2F18%2F31%2F016

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