1. Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755, USA
   
2. Present address: Department of Material Science and Engineering, University of Illinois, Urbana-Champaign, Illinois 61801, USA.

Correspondence to: Yeong-Ah Soh¹ Correspondence and requests for materials should be addressed to Y.-A.S. (Email: yeong-ah.soh@dartmouth.edu).

The role of magnetic domains (and the walls between domains) in determining the electrical properties of ferromagnetic materials¹ has been investigated in great detail for many years, not least because control over domains offers a means of manipulating electron spin to control charge transport in 'spintronic' devices². In contrast, much less attention has been paid to the effects of domains and domain walls on the electrical properties of antiferromagnets: antiferromagnetic domains show no net external magnetic moment, and so are difficult to manipulate or probe. Here we describe electrical measurements on chromium—a simple metal and quintessential spin density wave antiferromagnet³—that show behaviour directly related to spin density wave formation and the presence of antiferromagnetic domains. Two types of thermal hysteresis are seen in both longitudinal and Hall resistivity: the first can be explained by the quantization of spin density waves due to the finite film thickness (confirmed by X-ray diffraction measurements) and the second by domain-wall scattering of electrons^{4, 5}. We also observe the striking influence of the electrical lead configuration (a mesoscopic effect) on the resistivity of macroscopic samples in the spin density wave state. Our results are potentially of practical importance, in that they reveal tunable electrical effects of film thickness and domain walls that are as large as the highest seen for ferromagnets^6,