中文摘要：

利用Landau-Lifshitz-Gilbert-Slonczewski方程，在理论上研究了由磁矩垂直于膜面的自由层和磁矩平行于膜面的极化层组成的自旋转矩振荡器的振荡特性。数值结果表明面内的形状各向异性能，可以使自旋转矩振荡器在无磁场情形下产生自激振荡。此特性可以用能量平衡方程解释，即面内形状各向异性能可以导致系统中自旋转矩提供的能量与阻尼过程所消耗的能量之间的平衡。特别是，面内的形状各向异性能越大，自旋转矩振荡器的可操控电流范围越大，并且产生微波信号的频率越大，但其阈值电流几乎不变。

英文摘要：

The spin-torque oscillator, which can generate an AC voltage oscillation with the same frequency, have attracted considerable attention due to its potential applications in the frequency-tunable transmitters and receivers for wireless communication and the recording heads of high-density hard disk drives. However, from the energy-balance equation’s point of view, in the absence of in-plane shape anisotropy of spin torque oscillator, the energy supplied by the spin torque is always larger than the energy dissipation due to the Gilbert damping, thus, a finite magnetic field applied perpendicular to the plane is required for a steady-state precession. This feature has limited its potential applications. In this paper, the influence of the intrinsic in-plane shape anisotropy on the magnetization dynamics of spin torque oscillator consisting of an in-plane polarizer and an out-of-plane free layer is studied numerically in terms of the Landau-Lifshitz-Gilbert-Slonczewski equation. It is demonstrated that the additional in-plane shape anisotropy plays a significant role in the energy balance between the energy accumulation due to the spin torque and the energy dissipation due to Gilbert damping, which can stabilize a steady-state precession. Therefore, a stable self-oscillation in the absence of the applied magnetic field can be excited by introducing additional in-plane shape anisotropy. In particular, a relatively large current region with zero-field self-oscillation, in which the corresponding microwave frequency is increased while the threshold current still maintains an almost constant value, can be obtained by introducing a relatively large intrinsic in-plane shape anisotropy. Our results suggest that a tunable spin transfer oscillator without an applied magnetic field can be realized by adjusting the intrinsic in-plane shape anisotropy, and it may be a promising configuration in the future wireless communications.