Nonlinear absorption of radio waves in a noncollinear antiferromagnet

The nonlinear absorption of radio waves ($200$–$800$ MHz) in a noncollinear cubic antiferromagnet Mn$_3$Al$_2$Ge$_3$O$_{12}$ in an external magnetic field ${\mathbf H}\parallel[001]$ has been studied in the temperature range of $1.2$–$4.2$ K. We attribute the observed dissipation of the electromagnetic energy to the parametric excitation of inhomogeneous surface waves at the boundaries of antiferromagnetic domains.