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

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) 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 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.

Charge density wave formation accompanying ferromagnetic ordering in quasi-one-dimensional BaIrO3

“…The Ir moment is much lower than expected for the low spin S 1=2; 2 T 2g state of Ir 4ϩ (5d 5 ) which has degenerate d xz and d yz orbitals and an excited half filled d xy orbital, but both T C and the moment value are in substantial agreement with the results of Lindsay et al [4] for polycrystalline material. Similar low Ir moments are found for ferromagnetic Sr 2 IrO 4 T C 250 K; m eff 0:04m B =Ir as well as for CaIrO 3 and Ca 2 IrO 4 [7,12].…”

“…The non-hysteretic large main feature of non-linearity of the I-V characteristics may be due to an electrothermal effect which can occur in systems with dr T =dT Ͻ 0 if the heat sinking to ambient temperature is insufficient to remove joule heating. (Recently, Young et al [12] found T C Ϸ 600 K and Ϸ0.001m B /x in Ca 1Ϫx La x B 6 for x Ϸ 0:005: Whether a similar dilute electronic gas mechanism accounts for the iridate anomalies remains an open question.) However, the sharp, hysteretic feature in Fig.…”

Singular or non-Fermi liquids

“…Recently, it has been found that CaB 6 or SrB 6 with low densities of trivalent Eu or quadrivalent Ce ions substituting for (Ca; Sr) are ferromagnets [295]. The most plausible explanation [303,34,36] is that this is a realization of the excitonic ferromagnetism predicted by Volkov et al [279].…”

“…A model band structure for a solid with more than one atom per unit cell. Actually in CaB 6 where excitonic singularities have been invoked to produce a ferromagnetic state [295] there are three equivalent points in the Brillouin zone where the conduction band minima and the valence band maxima occur.…”

Room-temperature ferromagnetism in Li-dopedp-type luminescent ZnO nanorods

“…Dilute ferromagnetism in oxide semiconductors generally has been reported with 3d dopants in ZnO particularly with Mn, Co, Ni, Fe, Cu, and V dopings. [1][2][3] Unexpected magnetization without transition metal has been reported in dielectric oxides such as HfO 2 , ZrO 2 , 4 and nonmagnetic oxides, e.g., ZnO, 5 hexaborides, 6 carbon-doped ZnO, 7 and in irradiated graphite. 8 The theory of Dietl et al 9 suggests that carrier-induced ferromagnetism in Mn-doped p-type material may be observed at higher temperature.…”