Spin-transfer Torque-induced Magnetization In Spin Valve

Spin transfer torque (STT) effect has attracted considerable attention since the prediction in1996that a spin polarized current flowing through a ferromagnetic device can exert a torque on the local magnetization. In a spin valve, STT can introduce magnetization switch or excite steady-state magnetization oscillations in the free layer, thereby possess potential applications in high-density MRAM, Race-Track Memory and microwave generation commonly referred as spin transfer oscillator. In this paper, based on micromagnetic simulations, two parts of work focused on spin transfer torque had been investigated. The content is as follows.Firstly, we designed and investigated the spin torque oscillation biosensor via micromagnetic simulations. Using the good linear response to magnetic field, spin torque oscillation can detect the stray field of magnetic beads via frequency shift, thereby detecting molecules labeled with magnetic beads and providing method for molecules recognition and biomedicine diagnostic. Simulations demonstrated that spin torque oscillator can detect40-nm-diameter magnetic beads with a frequency shift of0.26GHz. The frequency shift dependence on the size, position and number of magnetic particles were also investigated: it increases with increasing the size of magnetic particle or when magnetic particle moves from the sensor edge to the centre, and decreases monotonically as vertical distance increases; it is also linear with the number of40-nm-diameter particles.Secondly, we simulated the spin-transfer torque induced magnetization switch assisted by static magnetic field in a spin valve using OOMMF software. Via theory analyses, critical current density of magnetization reversal is strongly lowered in the presence of magnetic field in the plane of a spin valve. Simulations demonstrated that critical current density can reduce from1x10-7A/cm2to0.5x10-7A/cm2assisted by magnetic field of1Oe, thereby providing theory foundation for application in MRAM. In addition, the speed of magnetization switching become rapid and the switching time can be reduced from6to2ns due to an effect of magnetic field.