Comprehensive design and achieved recording performance of MAMR with dual-FGL STO

We investigated the effect of the relative position between the microwave field distribution and the transition point for achieving higher recording resolution with microwave-assisted magnetic recording (MAMR). We employed a recording head having a spin-torque oscillator (STO) with a dual-field generation layer (dual-FGL), whose oscillation had been proved experimentally. Our numerical calculations found that its microwave field shifted from the FGLs center toward the trailing shield (TS) due to the interaction between FGLs and TS. We measured the recording performance on recording media with various coercivities and confirmed that media having the transition point near TS is optimal for our current MAMR head, as we expected from the matching description. We achieved an effective signal-to-noise ratio improvement compared to a conventional medium by 3.5 dB. We further discuss STO designs that suppress the interaction between TS to match with media having higher coercivity, which is preferable for higher recording density with smaller track pitches. Our results show that, with the optimization of the matching between STO and medium under the interaction with TS, MAMR can provide higher recording density in hard disk drives.