Optical properties and electronic structure of multiferroic hexagonal orthoferrites RFeO_3 (R= Ho, Er, Lu)

摘要

We report on optical studies of the thin films of multiferroic hexagonal (P.G. 6mm) rare-earth orthoferrites RFeO_3 (R = Ho, Er, Lu) grown epitaxially on a (111)-surface of ZrO_2(Y_2O_3) substrate. The optical absorption study in the range of 0.6-5.6 Ev shows that the films are transparent below 1.9 Ev; above this energy four broad intense absorption bands are distinguished. The absorption spectra are analyzed taking into account the unusual fivefold coordination of the Fe~(3+) ion. Temperature dependence of the optical absorption at 4.9 Ev shows anomaly at 124K, which we attribute to magnetic ordering of iron sublattices.