Antiferromagnetic resonance in Mn2P2S6

The AFMR spectra along the principal axes x, y, z of Mn2P2S6 were studied in detail in wide frequency (8-142 GHz) and magnetic field (up to 75 kOe) ranges at T = 4.2 K. It is shown that the compound belongs to biaxial magnets. At H = 0 there are two gaps in the spin wave spectrum, (101.46 ± 0.1) and (115.52 ± 0.1) GHz. The values of magnetic anisotropy effective fields Ha1 = 0.619 kOe, Ha2 = 0.803 kOe were obtained using the AFMR data. An anomalous interaction of AFMR branches in Mn2P2S6 and the appearance of coupled spin-spin oscillation of the same symmetry were detected. An additional absorption in the AFMR spectrum was observed, namely, a local mode connected with the violation of translational order in the low-dimensional magnet. It is first shown that the appearance of additional adsorption peaks depends on sample cooling rate. It is proved that the observed peaks are associated with internal modes of domain boundaries.