Ultrafast spin dynamics and switching via the spin transfer torques in antiferromagnet with weak ferromagnet

The spin-torque driven dynamics of the antiferromagnet with canted moments was investigated analytically based on the Landau-Lifshitz-Gilbert-Slonczewski equation with the antiferromagnetic (\textbf{\textit{l}}) and ferromagnetic (\textbf{\textit{m}}) order parameters. Although Dzyaloshinskii-Moriya (DM) torque splits the degenerate resonant mode into Sigma-mode and Gamma-mode, the equation of motion was found to be described by 2-dimansional pendulum model of \textbf{\textit{l}} as like simple antiferromagnet. Because \textbf{\textit{l}} is coupled to \textbf{\textit{m}}, the close examination of m leads both to reveal \textbf{\textit{l}}'s dynamics and to estimate DM energy. For example, the second harmonic of resonant frequency, together with the resonant frequency softening phenomenon, is the evidence for the non-linear behavior of \textbf{\textit{l}}. The precessional ellipticity of m in Sigma-mode determines the DM energy through the following relation; $m_{\mbox{y}} /m_{\mbox{x}} \sim \hslash \omega_{\mbox{sigma}} /D$ where $\omega _{\mbox{sigma}} $ is resonant frequency in Sigma-mode. Finally, we discuss magnetization reversal efficiency by varying DM energy, anisotropy barrier and damping.