Relativistic analysis of magnetoelectric crystals: Extracting a new 4-dimensional P odd and T odd pseudoscalar from Cr2O3 data

Earlier, the linear magnetoelectric effect of chromium sesquioxide Cr₂O₃ has been determined experimentally as a function of temperature. One measures the electric field-induced magnetization on Cr₂O₃ crystals or the magnetic field-induced polarization. From the magnetoelectric moduli of Cr₂O₃ we extract a 4-dimensional relativistic invariant pseudoscalar . It is temperature dependent and of the order of ∼¹⁰⁻⁴Y₀, with Y₀ as vacuum admittance. We show that the new pseudoscalar is odd under parity transformation and odd under time inversion. Moreover, is for Cr₂O₃ what Tellegen's gyrator is for two port theory, the axion field for axion electrodynamics, and the PEMC (perfect electromagnetic conductor) for electrical engineering.