Stability Analysis Of Magnetization And Magnetic Rogue Wave In Ferromagnet Driven By Current

Recently,nonlinear wave excited by spin wave background has been one of the research hotspots of nonlinear physical system.Moreover,it is generally believed that the excitation of nonlinear waves on the spin wave background depends on the modulation instability of the system,which can be used to understand the dynamics of nonlinear waves such as the excitation of rogue waves and breathers.In magnetism,the all-magnonic spin-transfer torque can cause nonlinear magnetic excitation states,but the characteristics of nonlinear excitation mechanism and stability analysis in magnetism have not been well explored.In this paper,the following two studies are carried out on the magnetization in ferromagnet:Firstly,we studied the stability of spin wave states in isotropic ferromagnet by linear stability analysis.The exact Akhmediev breathers,Kuznetsov-Ma solitons and rogue waves can be structured by the Darboux transformation.Through applying a small perturbation,we have obtained the modulation stability region and modulation instability region,and give the instability phase diagram of Akhmediev breathers,Kuznetsov-Ma solitons and rogue waves.The region of instability corresponds to the range of all-magnonic spin-transfer torque.We also find how to control the effect of all-magnonic spin-transfer torque,and it is of great significance to nonlinear controllable excitation.In particular,Kuznetsov-Ma solitons and rogue waves comes from instability excitation with resonance disturbance.Secondly,we investigate the stability of the ground state of the uniaxial anisotropic system with Dzyaloshinskii-Moriya interaction under the action of polarization current.Without considering the damping effect,the stability condition of the ground state of magnetization is that the non-adiabatic term is zero.The Dzyaloshinskii-Moriya interaction can lead to the asymmetric propagation of the spin wave.Considering the damping effect,we obtained the critical current value of the ground state stability,indicating that the minimum critical current exists when the spin wave can be stably excited.The roles of Dzyaloshinskii-Moriya interaction affecting the ground states are completely different for different spin directions.In conclusion,we investigate the instability of magnetization dynamics by linear stability analysis in isotropic and uniaxial anisotropic ferromagnet.The excitation of allmagnonic spin-transfer torque is quantitatively located on the instability gain spectrum plane.It is of great significance to nonlinear controllable excitation.