Ghostly magnetism comes from nowhere.

Magnetism starts small. A substance becomes magnetic from the alignment of particles, such as some atoms or electrons that behave as tiny bar magnets. The discovery of a magnetic material with virtually no sign of such micromagnets, known as magnetic moments, has physicists stumped.

"There are just no moments other than a few free electron spins in there," says Zachary Fisk of Florida State University in Tallahassee of a variant of calcium hexaboride that he and his colleagues are studying. "It doesn't make sense" to see magnetic effects from so few elements. The researchers were probing the material's electronic traits when they made the surprising discovery reported in the Feb. 4 NATURE.

The finding revives a 60-year-old debate about the magnetic influence of low densities of electrons. Nobel laureate Eugene Wigner and others suggested how dilute clouds of so-called conduction electrons, which roam freely in a metal, might become ordered and generate magnetism. Other theorists countered that the spins of conduction electrons are usually randomly oriented, with every up spin canceled by a down spin.

Since the early 1980s, however, computer calculations have indicated that some types of magnetically effective ordering of scarse electrons can occur. Fisk and his colleagues may now have come up with experimental evidence.

The magnetism of the calcium-boron compound, which also includes a little lanthanum, is about a thousandth that of iron, Fisk estimates. Not only was that magnetism surprising, but its persistence up to 327 [degrees] C has also stunned researchers.

Ordinarily, weak micromagnets fall out of alignment---canceling magnetism--at a much lower temperature than strong micromagnets. "Here that is absolutely not true," says Hans R. Ott of the Federal Institute of Technology in Zurich. The new compound's maximum magnetic temperature uncharacteristically approaches iron's, 770 [degrees] C.

No atoms in the compound have the requisite electronic configurations to generate magnetic moments, Ott says. "I can't tell you how, but the moments somehow form in this very-low-density [conduction] electron ensemble."