Manufactured multilayer magnetism
Date: Tuesday, August 11, 2015 @ 19:49:34 EDT
From PhysicsToday: Having the right neighbor prompts copper and manganese to join the short list of magnetic elements. /Sung Chang/ 06 August 2015
Ferromagnets are often described as a collection of atomic dipole moments all pointing in the same direction. But itinerant magnets—like iron, nickel, and cobalt—whose magnetic properties originate in the conduction electrons require a more sophisticated explanation. Nearly 80 years ago, Edmund Stoner showed that the conduction electron band in those systems splits into two subbands—one each for spin-up and spin-down electrons—that are shifted in energy relative to each other. Further, the splitting can occur only if the dimensionless product of the electronic density of states and the strength of the magnetic exchange between electrons is greater than one.
The Stoner criterion, as it’s come to be known, explains why Fe, Ni, and
Co are the only elements that order magnetically at room temperature...
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