Two-magnon absorption of electromagnetic waves in the exchange noncollinear antiferromagnet Nd2CuO4.

Abstract

The two-magnon absorption of electromagnetic waves in the noncollinear magnetic phase of the four-sublattice antiferromagnet ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4}$ has been considered. The crystal is shown to exhibit a distinguishing feature that the electric dipole moment associated with the pair of spins has an exchange nature. Consequently, the two-magnon absorption of the electromagnetic waves is electrodipole active in the exchange approximation. We have studied theoretically both the magnetic-dipole and electric-dipole channels of the two-magnon absorption and analyzed the frequency dependences of the coefficient of the absorption. The intensities of the absorption processes involving the exchange magnons are shown to be of the same order of magnitude as that involving the acoustic magnons only.