VP8-06 Time dependence of signal-to-noise ratio for recording media designed for microwave-assisted magnetic recording
Creators: Terumitsu Tanaka
Shuto Onaka
Shusuke Kashiwagi
Xiaorui Ya and Yasushi Kanai
Publisher: name: IEEE
Year: 2025

Microwave-assisted magnetic recording (MAMR) [1] has attracted as one of the promising next-generation ultra-high-density recording technologies of hard disk drives. Layer anisotropy structured media, such as notched type structures have been proposed [2] for improving MAMR writability. Magnetization switching of notched structured media follows incoherent process, so the nudged elastic band calculations are necessary to evaluate magnetization thermal stability of the magnetizations of the magnetic grains. This study employed 12-nm-thick 4-layered-stacked-media (4-2-2-4 nm) designed for MAMR. Averaged medium Hk and Ms were 26 kOe and 800 emu/cc, respectively. Average grain size <D> was 5 nm. The corresponding KuV/kBT@ 300K was 58. 16 dB of SNR without wide writing was obtained for MAMR simulations with the 30-nm-track-wide SPT head and 22 GHz [3] of microwave field generated by 30×30×10 nm3 of a spin torque oscillator. Figure 1 and 2 indicate time dependence of SNRs in terms of standard deviations of the grain size, σ(D). Here, ideal recorded bit patterns were artificially defined to evaluate magnetization thermal stability and the thermal stability indexes △E/kBT@300K were estimated using the nudged elastic band calculations. Time dependences of magnetization switching probability for magnetic grains were estimated using the Arrhenius-Néel law and the resultant SNRs were plotted as a function of storage time. In the case of σ(D)/<D> = 0.15, SNRs just after recording tend to be slightly higher than those for σ(D)/<D> = 0.10, but SNRs decrease faster for all the linear density signals. On the other hand, high SNRs retained relatively long period of time for high linear density signals for σ(D)/<D> = 0.10, and the SNRs abruptly decrease at the specific time. The reductions of the SNR at 5 years are significant, which imply that magnetizations of the grains need to be thermally much stable.References: [1] J.-G. Zhu, X. Zhu, Y. Tang, IEEE Trans. Magn. 44 (2008) 125-131. [2] X. Bai, J. Zhu, IEEE Magn. Lett. 7 (2016) 4507904. [3] Y. Kanai, R. Itagaki, S.J. Greaves, H. Muraoka, IEEE Trans. Magn. 55 (2019) 300061
Microwave-assisted magnetic recording (MAMR) [1] has attracted as one of the promising next-generation ultra-high-density recording technologies of hard disk drives. Layer anisotropy structured media, such as notched type structures have been proposed [2] for improving MAMR writability. Magnetization switching of notched structured media follows incoherent process, so the nudged elastic band calculations are necessary to evaluate magnetization thermal stability of the magnetizations of the magnetic grains. This study employed 12-nm-thick 4-layered-stacked-media (4-2-2-4 nm) designed for MAMR. Averaged medium Hk and Ms were 26 kOe and 800 emu/cc, respectively. Average grain size <D> was 5 nm. The corresponding KuV/kBT@ 300K was 58. 16 dB of SNR without wide writing was obtained for MAMR simulations with the 30-nm-track-wide SPT head and 22 GHz [3] of microwave field generated by 30×30×10 nm3 of a spin torque oscillator. Figure 1 and 2 indicate time dependence of SNRs in terms of standard deviations of the grain size, σ(D). Here, ideal recorded bit patterns were artificially defined to evaluate magnetization thermal stability and the thermal stability indexes △E/kBT@300K were estimated using the nudged elastic band calculations. Time dependences of magnetization switching probability for magnetic grains were estimated using the Arrhenius-Néel law and the resultant SNRs were plotted as a function of storage time. In the case of σ(D)/<D> = 0.15, SNRs just after recording tend to be slightly higher than those for σ(D)/<D> = 0.10, but SNRs decrease faster for all the linear density signals. On the other hand, high SNRs retained relatively long period of time for high linear density signals for σ(D)/<D> = 0.10, and the SNRs abruptly decrease at the specific time. The reductions of the SNR at 5 years are significant, which imply that magnetizations of the grains need to be thermally much stable.References: [1] J.-G. Zhu, X. Zhu, Y. Tang, IEEE Trans. Magn. 44 (2008) 125-131. [2] X. Bai, J. Zhu, IEEE Magn. Lett. 7 (2016) 4507904. [3] Y. Kanai, R. Itagaki, S.J. Greaves, H. Muraoka, IEEE Trans. Magn. 55 (2019) 300061