Journal of the Korean Magnetics Society (한국자기학회지)

The Korean Magnetics Society (한국자기학회)
권호 표지
DOI QR코드

DOI QR Code

First Principle Studies on Magnetism and Electronic Structure of Perovskite Structured CoFeX3 (X = O, F, S, Cl)

페로브스카이트 구조를 가지는 CoFeX3(X = O, F, S, Cl) 합금의 자성과 전자구조에 대한 제일원리계산

  • Received : 2016.11.30
  • Accepted : 2016.12.20
  • Published : 2016.12.31
Download PDF
⟨ Previous Next ⟩

Abstract

For an industrial spin-transfer torque (STT) MRAM, low switching current and high thermal stability are required, simultaneously. For this point of view, it is essential to find magnetic materials which satisfy high spin polarization and strong perpendicular magnetocrystalline anisotropy (MCA). In this paper, we investigate electronic structures and MCA energies of perovskite $CoFeX_3$ (X = O, F, S, Cl). For X = F and Cl, spin polarization at the Fermi level are 97 % and 96 %, respectively, which are close to a half metal. Furthermore, Co-terminated 5-monolayer (ML) $CoFeX_3$ (X = O, F, S, Cl) films show perpendicular MCA. In particular, the MCA energy of the Co-terminated $CoFeCl_3$ is about 1.0 meV/cell which is three times larger than that of a 5-ML CoFe film. Therefore, we expect to realize a magnetic material with high spin polarization and strong perpendicular MCA energy by utilizing group 6 and 7 elements in the periodic table, and to contribute to commercializing of the STT-MRAM.

스핀전달토크(Spin-Transfer Torque: STT) MRAM의 상용화를 위해서는 낮은 반전전류와 높은 열적 안정성을 동시에 만족해야 하고, 이를 위해서는 큰 스핀 분극, 강한 수직자기이방성 에너지을 가지는 물질이 요구된다. 본 연구에서는 STT-MRAM에 적합한 물질로 알려진 B2 CoFe 면심에 X(O, F, S, Cl) 원자가 위치한 $CoFeX_3$ 합금의 전자구조와 자기결정이방성(Magnetocrystalline anisotropy: MCA) 에너지를 계산하였다. X 원자가 F나 Cl일 때는 페르미 준위에서의 스핀 분극율이 각각 97 %, 96 %로, 반쪽 금속에 근접한 전자구조를 가짐을 확인할 수 있었다. 뿐만 아니라 표면이 Co 원자로 끝나는 5층 박막은 모든 X에 대해 수직 자기이방성를 가졌으며, 특히 $CoFeCl_3$의 자기이방성 에너지는 약 1.0 meV/cell로 상당히 컸다. 따라서 6, 7 족 원소를 잘 활용하면 높은 스핀 분극율과 강한 수직 자기이방성를 동시에 가지는 물질을 제조할 수 있게 되어 STT-MRAM의 상용화에 기여를 할 수 있을 것으로 기대한다.

Keywords

References

  1. S. A. Wolf, D. D. Awschalom, R. A. Buhrman, J. M. Daughton, S. von Molnar, M. L. Roukes, A. Y. Chtchelkanova, and D. M. Treger, Science 294, 1488, (2001). https://doi.org/10.1126/science.1065389
  2. A. V. Khvalkovskiy, D. Apalkov, S. Watts, R. Chepulskii, R. S. Beach, A. Ong, X. Tang, A. Driskill-Smith, W. H. Butler, P. B. Visscher, D. Lottis, E. Chen, V. Nikitin, and M. Krounbi, J. Phys. D: Appl. Phys. 46, 074001 (2013). https://doi.org/10.1088/0022-3727/46/7/074001
  3. I. Zutic, J. Fabian, and S. D. Sarma, Rev. Mod. Phys. 76, 323 (2004). https://doi.org/10.1103/RevModPhys.76.323
  4. A. Fert, Rev. Mod. Phys. 80, 1517 (2008). https://doi.org/10.1103/RevModPhys.80.1517
  5. C. Felser, G. H. Fecher, and B. Balke, Angew. Chem. Int. Edit. 46, 668 (2007). https://doi.org/10.1002/anie.200601815
  6. D. D. Awschalom, M. E. Flatte, and N. Samarth, Sci. Am. 286, 66 (2002). https://doi.org/10.1038/scientificamerican0602-66
  7. Y. M. Lee, J. Hayakawa, S. Ikeda, F. Matsukura, and H. Ohno, Appl. Phys. Lett. 90, 2507 (2007).
  8. S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, N. C. Emley, R. J. Schoelkopf, R. A. Buhrman, and D. C. Ralph, Nature 425, 380 (2003). https://doi.org/10.1038/nature01967
  9. N. N. Mojumder, C. Augustine, D. E. Nikonov, and K. Roy, J. Appl. Phys. 108, 104306 (2010). https://doi.org/10.1063/1.3503882
  10. J. E. Pask, L. H. Yang, C. Y. Fong, W. E. Pickett, and S. Dag, Phys. Rev. B 67, 224420 (2003). https://doi.org/10.1103/PhysRevB.67.224420
  11. C. Y. Fong, M. C. Qian, J. E. Pask, L. H. Yang, and S. Dag, Appl. Phys. Lett. 84, 239 (2004). https://doi.org/10.1063/1.1639934
  12. S. Jekal, O. Kwon, S. C. Hong, and J. I. Lee, J. Nanosci. Nanotech. 15, 2356 (2015). https://doi.org/10.1166/jnn.2015.10264
  13. X. Hu, Adv. Mater. 24, 294 (2012). https://doi.org/10.1002/adma.201102555
  14. S. Ikeda, K. Miura, H. Yamamoto, K. Mizunuma, H. D. Gan, M. Endo, S. Kanai, J. Hayakawa, F. Matsukura, and H. Ohno, Nat. Mater. 9, 721 (2010). https://doi.org/10.1038/nmat2804
  15. G. Kim, Y. Sakuraba, M. Oogane, Y. Ando, and T. Miyazaki, Appl. Phys. Lett. Appl. Phys. Lett. 92, 172502 (2008).
  16. K. Yakushiji, T. Saruya, H. Kubota, A. Fukushima, T. Nagahama, S. Yuasa, and K. Ando, Appl. Phys. Lett. 97, 232508 (2010). https://doi.org/10.1063/1.3524230
  17. S. Jekal, S. H. Rhim, O. Kwon, and S. C. Hong, J. Appl. Phys. 117, 17E105 (2015). https://doi.org/10.1063/1.4908141
  18. D. Sander, A. Enders, C. Schmidthals, J. Kirschner, H. L. Johnston, C. S. Arnold, and D. Venus, J. Appl. Phys. 81, 4702 (1997). https://doi.org/10.1063/1.365532
  19. W. Wang, H. Sukegawa, R. Shan, S. Mitani, and K. Inomata, Appl. Phys. Lett. 95, 182502 (2009). https://doi.org/10.1063/1.3258069
  20. S. Emori, U. Bauer, S. M. Ahn, E. Martinez, and G. S. Beach, Nat. Mater. 12, 611 (2013). https://doi.org/10.1038/nmat3675
  21. X. Jiang, R. Wang, R. M. Shelby, and S. S. P. Parkin, IBM J. Res. Dev. 50, 111 (2006). https://doi.org/10.1147/rd.501.0111
  22. G. Kresse and D. Joubert, Phys. Rev. B 59, 1758 (1999).
  23. J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996). https://doi.org/10.1103/PhysRevLett.77.3865
  24. P. E. Blochl, Phys. Rev. B 50, 17953 (1994). https://doi.org/10.1103/PhysRevB.50.17953
  25. H. J. Monkhorst and J. D. Pack, Phys. Rev. B 13, 5188 (1976). https://doi.org/10.1103/PhysRevB.13.5188
  26. E. G. Kim, S. Jekal, O. Kwon, and S. C. Hong, J. Kor. Magn. Soc. 24, 35 (2014). https://doi.org/10.4283/JKMS.2014.24.2.035
  27. D. S. Wang, R. Wu, and A. J. Freeman, Phys. Rev. B 47, 14932 (1993). https://doi.org/10.1103/PhysRevB.47.14932