Direct measurement of antiferromagnetic domain fluctuations

Antiferromagnetism tamed? Ferromagnets are everywhere, but ferromagnetism itself is a rare property. The more subtle cousins, antiferromagnets, are more common, but have been recognized for less than 100 years and have only become technologically relevant in the past 20 years. One reason for this is the unavailability of the analogues of ferromagnetic domains — the bar magnets that a larger ferromagnet divides into. Using a new technique, X-ray photon correlation spectroscopy, it is now possible to examine the nanometre-scale superstructure of spin- and charge-density in the antiferromagnet chromium, and the results could lead to magnetic engineering techniques that bring antiferromagnets into wider use. The new technique shows that the antiferromagnetic domain walls are in fact never at rest, but are constantly advancing and retreating over micrometre distances. And though domain wall motion is thermally activated at temperatures above 100K, it is not so at lower temperatures, and on cooling below 40K the motion saturates at a finite value consistent with quantum fluctuations.