Role of commensurability of spin order for optical magnetoelectric effect with electromagnons in multiferroic YMn2O5

摘要

The optical magnetoelectric effect, which produces the nonreciprocal directional dichroism, on the electromagnon resonances is investigated for multiferroic phases of YMn2O5 by terahertz spectroscopy. For the electromagnon driven by the exchange striction, the crucial role of the commensurability of spin order in the magnetoelectric coupling is manifested by the suppression of the directional dichroism in the incommensurate spin phase. Furthermore, the gapped electromagnon via the spin-current mechanism is identified in terms of the directional dichroism, irrespective of commensurability/incommensurability in the cycloidal spin order.