The effect of lattice distortion and orbital mixing on the optical and magnetic properties of cubic RMnOsub 3 (R = La, Pr, Nd, Gd, Tb)

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We investigated the ab-plane absorption spectra of RMnO%₃ (R = La, Pr, Nd, Gd, and Tb) thin films. As the R-ion size decreases, we observed a drastic suppression of the 2 eV peak, i.e. the inter-site optical transition between spin- and orbital-aligned states across the Mott gap. We found that both lattice distortion and the corresponding orbital mixing of the ordered orbital state should play an important role in the 2 eV peak suppression. We also found that the 2 eV spectral weight is proportional to the A-type antiferromagnetic ordering temperature, which suggests that the magnetic interaction might be sensitively coupled to the orbital mixing.