Antiferromagnetic resonance in Mn2P2S6

The antiferromagnetic resonance (AFMR) spectra along the principal magnetic axes x, y, z of the compound Mn2P2S6 have been investigated in detail in a wide range of frequencies (8–142GHz) and magnetic fields (up to 75kOe) at T=4.2K. It is shown that this compound is a biaxial magnetic substance. At H=0, there are two gaps in the spin-wave spectrum: (101.46±0.1) and (115.52±0.1)GHz. The AFMR data were used to determine the effective magnetic-anisotropy fields: Ha1=0.619kOe and Ha2=0.803kOe. An anomalous interaction of the AFMR branches in Mn2P2S6 has been detected, along with the appearance of coupled spin–spin oscillations of the same symmetry. An additional absorption in the AFMR spectrum is a local mode associated with breakdown of translational order in a low-dimension magnet. It is shown for the first time that the appearance of additional absorption peaks depends on the sample-cooling rate. It is proven that the observed peaks are associated with the internal modes of the domain boundaries.