Professor Oleg Shpyrko
DEPARTMENT OF PHYSICS
UC San Diego

Domain Wall Dynamics in Antiferromagnetic Chromium

Motion of domain walls in ferromagnets underlies much of the modern science and technology and has been investigated for nearly a century. However, direct observations of domain wall dynamics in antiferromagnets, which are notoriously difficult to probe due to their lack of net magnetic moment, have remained far more elusive. I will present measurements of domain wall fluctuations in the simplest antiferromagnet, elemental chromium, performed using recently developed coherent x-ray scattering techniques [1]. Domain walls in Chromium separate regions with orthogonal orientations of incommensurate spin- (charge-) density wave, a long-range sinusoidal modulation of spin (charge) density. Temporal evolution of the coherent x-ray speckle, an interference pattern that effectively serves as the fingerprint of a randomly disordered domain configuration, reveals a remarkable feature that the domain wall fluctuations persist even at the lowest temperatures of these measurements. Antiferromagnetic domains fluctuations in chromium are part of a more general class of systems involving slow dynamics of elastic media in presence of quenched disorder: from motion of defects in crystalline solids, relaxation in glasses and soft matter undergoing jamming transitions to avalanches and earthquakes. Discussion of these results will be placed in a broader context of novel experimental approaches to studies of disordered, heterogeneous or non-equilibrium materials.

[1] O. G. Shpyrko et al., Nature 447, 68 (2007)