1. 1) Western Digital: private communication.
2. 2) T. Kobayashi, Y. Nakatani, and Y. Fujiwara: J. Magn. Soc. Jpn., 44, 34 (2020).
3. 3) T. Kobayashi, Y. Nakatani, and Y. Fujiwara: J. Magn. Soc. Jpn., 44, 122 (2020).
4. 4) M. Mansuripur and M. F. Ruane: IEEE Trans. Magn., MAG-22, 33 (1986).
5. 5) J. -U. Thiele, K. R. Coffey, M. F. Toney, J. A. Hedstrom, and A. J. Kellock: J. Appl. Phys., 91, 6595 (2002).