Magneto-electric anomalies in bamnf4

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Abstract
A theoretical evaluation of the second-order magnetoelectric tensor for BaMnF4 at 4.2 K based upon dielectric anomalies along the a-axis yields β xzz = 1.0 × 10−19 sA−1, compared with the direct measurement by Sciau et al. of 1.6 × 10−19 sA−1. This numerical agreement within ±50% and the temperature dependence of Δε(T), which varies as the square of the sublattice magnetization (in accord with the general theory of Bonfim and Gehring)—a mean-field S = 5/2 dependence—confirms the validity of the Landau-theory analysis used. A geometric argument is given to explain the pairwise cancellation of the linear magnetoelectric effect in the incommensurate phase.