Subthreshold absorption in low-dimensional uniaxial antiferromagnets

Two-magnon subthreshold absorption (TSA) in uniaxial quasi-two-dimensional and quasi-one-dimensional antiferromagnets is investigated theoretically. As in ferromagnets, this absorption reflects the characteristics of the magnon density of states that are due to the low dimensionality of the magnetic structure. For orientations of the external magnetic field H with respect to the anisotropy axis of the crystal H∥ z, H ┴ z and various polarizations of the radio-frequency field hω ∥ H, hω ┴ H there are four types of TSA corresponding to excitation of two magnons from the same or different branches of the spectrum. A comparison of the integral intensities of antiferromagnetic resonance and TSA in such crystals shows that they can be of the same order of magnitude.

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