U. Nagel, T. Katuwal, H. Engelkamp, D. Talbayev, Hee Taek Yi, S. -W. Cheong, T. Rõõm
We have studied the magnetic field dependence of far-infrared active magnetic modes in a single ferroelectric domain BiFeO$_3$ crystal at low temperature. The modes soften close to the critical field of 18.8T along the [001] (pseudocubic) axis, where the cycloidal structure changes to the homogeneous canted antiferromagnetic state and a new strong mode with linear field dependence appears that persists at least up to 31 T. This allows us to assign the low field modes to the excitations of the cycloid and the high field mode to the antiferromagnetic resonance. We found that the zero field spectra at low temperature are different before and after application of high magnetic field and this change persists at low temperature. We interpret this as a change from a state with three magnetic domains into a state with one domain with the lowest energy in high magnetic field.
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http://arxiv.org/abs/1302.2491
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