Theory Of Ferromagnetic Resonance In Magnetic Trilayers With A Tilted Spin Polarizer

Recently, spintronics has become a hot research field in condensed matter physics due to its abundant physical connotation and widely device application prospect. Since giant magnetoresistive(GMR) and tunneling magnetoresistive(TMR) effect are put forward, they have been widely applied in read-write heads, magnetic storage devices, magnetic detectors and microwave excitation etc. Especially, as the result of theoretical predictions in 1996 and later experimental verification of spin-transfer torque, it breaks the traditional method driven by the magnetic field to change or switch the magnetization direction of thin film materials. This new physical mechanism initially realizes the magnetization reversal or excites spin wave by using the spin-polarized current. In this thesis, we mainly investigate the ferromagnetic resonance in magnetic trilayers with a tilted spin polarizer theoretically.First of all, we simply introduce the interaction energy and Landau-Lifshitz-Gilbert (LLG) magnetic dynamics equation. Then, under consideration of anisotropic energy and demagnetization energy, we spread the LLG equation including the spin torque term by the linearization method and obtain the current-and frequency-swept resonant spectra. At the same time, we analysis the dependences of the equilibrium position, resonant location and resonant linewidth on the current and the direction of the pinned magnetization. The influence of the dc current and the pinned magnetization on the power density is also discussed. The research shows that we can acquire the most energy pumping from the current to the free layer by optimizing the current density and the direction of the pinned magnetization in some regions. This is useful for improving the efficiency of current-driven microwave oscillation and current-induced magnetization reversal. Finally, we consider the static magnetic field and present a theoretical investigation of ferromagnetic resonance excited by rf magnetic field in magnetic trilayers with tilted anisotropy by the similar method. We find that the resonant magnetic field, the resonant linewidth, the precessional frequency, and the axis of the magnetization in the free layer are all changed by the spin-polarized current in the present of tilted pinned magnetization. Except for the direction and magnitude of spin polarized current, turning the direction of pinned magnetization provides a new choice of adjusting the pumping and dissipation of energy in the magnetic system.