Spin-transfer torque induced reversal in magnetic domains

Abstract

Using the complex stereographic variable representation for the macrospin, from a study of the nonlinear dynamics underlying the generalized Landau-Lifshitz(LL) equation with Gilbert damping, we show that the spin-transfer torque is effectively equivalent to an applied magnetic field. We study the macrospin switching on a Stoner particle due to spin-transfer torque on application of a spin polarized current. We find that the switching due to spin-transfer torque is a more effective alternative to switching by an applied external field in the presence of damping. We demonstrate numerically that a spin-polarized current in the form of a short pulse can be effectively employed to achieve the desired macro-spin switching.

Nonlinear dynamics of spin transfer nano-oscillators

“…(11) or (14) using variable step size Runge-Kutta method. In figure 1 we have shown the switching dynamics of the magnetization in the free layer [15]. It can be observed that the direction of magnetization gets reversed at the point m = (1, 0, 0).…”

“…This spin-polarized current exerts a torque on the free layer, which is termed as spin transfer torque (STT), and this exerts a rich variety of dynamics in the free layer. The expression for this torque has been given by Slonczewski and the redefined LLG equation with the STT is read as [7,15] …”

“…Switching of magnetization of a ferromagnetic thin film used typically in magnetic memory devices is generally achieved by varying the applied external magnetic field [15,16]. Alternatively, switching can be achieved and the switching time can be enhanced by using the STT.…”

“…However, the above nanoscale level microwave source lacks efficiency on two counts: (1) low output power (∼ nW), (2) high signal-to-noise ratio. Both the issues can be handled by phase locking a large array of oscillators [13][14][15][16][17][18][19][20][21]. Phase locking and synchronizing several STNOs is a typical nonlinear problem to enhance the power and to reduce the signal-to-noise ratio of the oscillators.…”

Spin-Transfer-Torque Driven Magneto-Logic Gates Using Nano Spin-Valve Pillars

“…The switching time due to the spin-current is roughly 0.2 ns, while that due to the magnetic field is slower, at nearly 0.7 ns, accompanied by a ringing effect. This delay and ringing effect are well understood to be due to the fact that, even with α = 0, a spin-transfer-torque leads to both precession and dissipation whereas a magnetic field alone can only cause a precession of magnetization vector about the applied field [23]. Field induced switching is thus exclusively due to the damping factor, leading to a longer switching time, consequently.…”