High-temperature weak ferromagnetism in a low-density free-electron gas.

Young, D P; Hall, D; Torelli, M E; Fisk, Z; Sarrao, J L; Thompson, J D; Ott, H-R; Oseroff, S B et al. · Nature · 1999

basic_science · Level V

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Abstract

The magnetic properties of the ground state of a low-density free-electron gas in three dimensions have been the subject of theoretical speculation and controversy for seven decades. Not only is this a difficult theoretical problem to solve, it is also a problem which has not hitherto been directly addressed experimentally. Here we report measurements on electron-doped calcium hexaboride (CaB<sub>6</sub>) which, we argue, show that-at a density of 7× 1019 electrons cm-3-the ground state is ferromagnetically polarized with a saturation moment of 0.07 µ<sub>B</sub> per electron. Surprisingly, the magnetic ordering temperature of this itinerant ferromagnet is 600 K, of the order of the Fermi temperature of the electron gas.