Spin-Torque-Oscillator Designs in Microwave-Assisted Magnetic Recording

With the requirement of increasing data areal density in hard disk drive applications, microwave assisted magnetic recording (MAMR) [1] has become one of the effective approaches that reduce recording bit size. By incorporating a spin torque oscillator (STO) device in the write gap (WG) between the main writer pole (MP) and the write shield (WS), one or more large magnetic moment layers, called field generation layers (FGL), are driven into large angle oscillations, by the spin-transfer-torque (STT) interactions with the adjacent spin injection layers (SIL), for a sufficiently large radiofrequency (rf) field output to the recording media. A dual oscillator design [2], shown in Fig. 1(a) was proposed recently with a pair of FGLs oscillating out of phase so that the detrimental component of the rf field [3] perpendicular to the air bearing surface (ABS) is mostly canceled, but the component in the direction along the written track is enhanced. Micromagnetic simulations of the magnetic device inside the WG were conducted incorporating STT interactions between the magnetic layers. Simulation and measurement results of different dual oscillator designs will be discussed in this talk.