Eur. Phys. J. B 71, 321-329 (2009)
https://doi.org/10.1140/epjb/e2009-00203-7

Magnetoelectric Cr₂O₃ and relativity theory

¹ Institute for Theoretical Physics, University of Cologne, 50923 Köln, Germany
² Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
³ Department of Theoretical Physics, Moscow State University, 117234 Moscow, Russia
⁴ Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, Sciences II, 1211 Geneva 4, Switzerland

Received: 6 March 2009
Published online: 19 June 2009

Abstract

Relativity theory is useful for understanding the phenomenology of the magnetoelectric effect of the antiferromagnet chromium sesquioxide Cr₂O₃ in two respects: (i) one gets a clear idea about the physical dimensions of the electromagnetic quantities involved, in particular about the dimensions of the magnetoelectric moduli that we suggest to tabulate in future as dimensionless relative quantities; (ii) one can recognize and extract a temperature dependent, 4-dimensional pseudoscalar from the data of magnetoelectric experiments with Cr₂O₃. This pseudoscalar piece of Cr₂O₃ is odd under time reflections and parity transformations and is structurally related (“isomorphic”) to the gyrator of electric network theory, the axion of particle physics, and the perfect electromagnetic conductor of electrical engineering.