Re-orientation of easy axis in $\varphi_0$ junction

Abstract

We study theoretically a dynamics of $\varphi_0$ junction with direct coupling between magnetic moment and Josephson current which shows features close to Kapitza pendulum. We have found that starting with oscillations along $z$-axis, the character of magnetization dynamics changes crucially and stable position of magnetic moment $\vec m$ is realized between $z-$ and $y$-axes depending on parameters of the system. Changes in critical current and spin-orbit interaction lead to the different stability regions for magnetization. An excellent agreement between analytical and numerical results is obtained for low values of the Josephson to magnetic energy ratio.