Relativistic analysis of magnetoelectric crystals: extracting a new 4-dimensional P odd and T odd pseudoscalar from Cr_2 O_3 data

Understand

Earlier, the linear magnetoelectric effect of chromium sesquioxide Cr_2 O_3 has been determined experimentally as a function of temperature.

• One measures the electric field-induced magnetization on Cr_2 O_3 crystals or the magnetic field-induced polarization.
• From the magnetoelectric moduli of Cr_2 O_3 we extract a 4-dimensional relativistic invariant pseudoscalar \tilde\alpha.
• It is temperature dependent and of the order of ~ 10^{-4} Y_0, with Y_0 as vacuum admittance.