Influence of the Second-Order Uniaxial Anisotropy on the Dynamical Proprieties of Magnetic Tunnel Junctions

The magnetization dynamics of a ferromagnet can be influenced by the second-order anisotropy contribution when the magnetocrystalline perpendicular anisotropy is of the same order of the out-of-plane demagnetizing field (compensation point). This condition can be fulfilled in magnetic tunnel junctions (MTJs) where the induced interfacial perpendicular anisotropy can be controlled by the thickness of the free layer. This paper describes, within a both micromagnetic and analytical/numerical framework, how switching and self-oscillation of the magnetization are affected by the second order magnetocrystalline anisotropy near the compensation point. We have derived analytical expressions for the switching critical current and the oscillation frequencies that are well reproduced by numerical simulations. Our results can support the design of MTJs for application either in storage and nanoscale signal generators.