The manifestation of spin-phonon coupling in CaMnO3

Abstract

Recently predicted presence of spin-phonon coupling in the CaMnO3 is experimentally confirmed in infrared (IR), Raman and time-domain THz spectra. Most of phonon frequencies seen below 350 cm−1 exhibit significant shifts on cooling below antiferromagnetic phase transition at TN ≅ 120 K. Moreover, several new modes activate in the IR and Raman spectra on cooling below TN. Sum of phonon contributions to static permittivity exhibits small but reliable anomaly at TN. On the other hand, the spin-phonon coupling is not manifested in temperature dependence of radio-frequency permittivity, because intrinsic permittivity is screened by extrinsic contribution from conductivity, which enhances the permittivity to giant values.