Blue shifts of the optical transitions in MnO below TN

Abstract
The temperature dependence of the optical transitions (A, B and C bands) in MnO was measured between 27 and 295K, with particular attention to the region near TN approximately=118K. All three bands undergo blue shifts below TN, with the total shift Delta E approximately=1% between TN and 27K. Using the Penn model for dielectric constant, it is argued that the observation of square root Delta E being proportional to sigma (order parameter) for the A and B band is consistent with the dielectric anomaly reported recently in MnO below TN.