Numerical Simulation on Temporal Response of Spin-Torque Oscillator to Magnetic Pulses

Abstract

For the application of the spin-torque oscillator to a high-data-transfer-rate read head, it is indispensable that the oscillation frequency responds promptly to the magnetic field from recorded bits. In this paper, we numerically exemplify the phase response to a short magnetic pulse. The phase basically follows the magnetic pulse although it takes several nanoseconds to return to the steady state because of the frequency nonlinearity. We also demonstrate the differential detection of recorded bits at the data-transfer rate beyond 5 Gbit/s.

Oscillation characteristics of zero-field spin transfer oscillators with field-like torque

“…Thus, it can be used as the frequency-tunable transmitters and receivers for wireless communication purposes, 15 nanoscale dynamic magnetic field sensors 16 and recording heads of high-density hard disk drives. 17,18 However, the necessity of an applied magnetic field has severally limited the STOs' potential applications in microwave generation and other fields. Recently, various solutions in the zero magnetic field case have been suggested to produce the steady-state precession, namely, STO with a perpendicularly magnetized pinned layer, 19,20 magnetic vortex oscillators, 21,22 a tilted magnetization of the fixed layer respect to the film plane, 23 and a synthetic ferromagnetic free layer.…”

High-data-transfer-rate read heads composed of spin-torque oscillators

“…On the contrary, the precession frequency of the magnetization in STO is expected to change promptly irrespective of the relaxation rate in response to ± h s applied along H bias as shown in figure 1 (b), followed by a small change of the precession angle θ. The prompt frequency changes are also predicted by micromagnetic simulations [7]. An FM (frequency modulation) signal from the STO head is schematically shown in figure 2, in which the small change in amplitude caused by that of the angle θ is suppressed by a power limiter (PWL in figure 3).…”

Scaling effect of spin-torque nano-oscillators

“…For nanoscale magnetic recording sensing, a novel spintorque oscillator (STO)-based read head sensor has been proposed as a promising candidate. [1][2][3] When a spin-polarized current is injected into a magnetic layer, depending on the direction and intensity of the charge, the local magnetization is switched to the opposite direction or is driven into a permanent precession along the effective field. The precession frequency is tunable by the external magnetic field or applied current.…”

“…Compared to the conventional magnetoresistive (MR) read head, which is functioning based on the giant magnetoresistive (GMR) effect or tunneling magnetoresistance (TMR) effect, the STO read head has two key benefits, including the signal-tonoise ratio (SNR) 1 and data-transfer rate. 3 Calculations have shown that high SNRs can be obtained in devices smaller than 30 × 30 nm 2 by using a delay detection method. 1 For conventional MR sensors, the data-transfer rate is limited by the ferromagnetic energy relaxation rate, since the bias field is applied along the hard-axis of the free layer.…”

“…Numerical simulations have demonstrated that the data-transfer rate can be above 5 Gbit/s. 3 As the STO device is scaled down to smaller than 40 nm, the linewidth of the output signal increases because of large phase noise induced by thermal effects. Therefore, understanding the magnetization dynamics and the relation between the linewidth and device size is crucial.…”