Raman scattering studies of the magnetic ordering in hexagonal HoMno₃ thin films

We present the results of the temperature dependence of the Raman spectra of hexagonal HoMnO3 thin films in the 13-300 K temperature range. The films were grown on Pt(111)//Al₂O₃ (0001) substrates using the laser ablation method. In the HoMnO₃ thin films, we initially observed several broad Raman peaks at~510, 760, 955, 1120, and 1410 cm^-1. These broad Raman peaks display an anomalous behavior near the magnetic transition temperature, and the intensity difference of the Raman spectra at different temperatures shows several pairs of negative and positive peaks as the temperature is lowered below the Néel temperature. Our analyses indicate that all the broad peaks are correlated with magnetic ordering, and we have assigned the origin of all the broad peaks. Purely on the basis of the Raman analysis, we have deduced the Néel temperature and the spin exchange integrals of HoMnO₃ thin films. We also investigated the effects of the growth condition on the strongest broad peak at~760 cm^-1,which is related with pure magnetic ordering. This result indicates that the oxygen defect in the HoMnO3 sample has negligible effect on magnetic ordering.