Optical Investigation on the Effect of Vortex Domains on Electronic Transitions in HoMnO3 Single Crystals

We investigated on the effect of vortex domain on the electronic transitions of HoMnO3 using optical spectroscopy. We observed different characteristics for d-d and p-d electronic transitions, which are centered near 1.7 eV and 5 eV at room temperature, respectively. The band edge energy of the p-d transition with vortex domains appears to show a clear increase which is attributed to the reduced hybridization between O p and Mn d states, while characteristics of the d-d transition does have distinct difference between vortex and normal states. However, from temperature dependent measurement, on the contrary, we observed the peak position of the d-d transition varying significantly with temperature between 10K to 300K, while the edge energy of the p-d transition is almost invariable. Such huge shifts of the d-d transition peak energy with temperature is known due to the antiferromagnetic superexchange interaction between nearest-neighbor Mn ions separated by oxygens.