Hostname: page-component-586b7cd67f-2brh9 Total loading time: 0 Render date: 2024-11-25T15:29:23.774Z Has data issue: false hasContentIssue false
  • English
  • Français

Magnetism and Spin Tunneling in Nanostructures

Published online by Cambridge University Press:  10 February 2011

Alexander Bratkovsky
Alexander Bratkovsky*
Affiliation:
Hewlett-Packard Laboratories, 3500 Deer Creek Road, Palo Alto, CA 94304–1392, [email protected]
Get access

Abstract

In the present paper different tunneling mechanisms in conventional and half-metallic ferromagnetic tunnel junctions are analyzed within the same general method. Theoretically calculated direct tunneling in iron group systems leads to about a 30% change in resistance, which is close but lower than experimentally observed values. It is shown that the larger observed values of the TMR might be a result of tunneling involving surface polarized states. We find that tunneling via resonant defect states in the barrier radically decreases the TMR (down to 4% with Fe-based electrodes), and a resonant tunnel diode structure would give a TMR of about 8%. With regards to inelastic tunneling, magnons and phonons exhibit opposite effects: one-magnon emission generally results in spin mixing and, consequently, reduces the TMR, whereas phonons are shown to enhance the TMR. The inclusion of both magnons and phonons reasonably explains an unusual bias dependence of the TMR.

The model presented here is applied qualitatively to half-metallics with 100% spin polarization, where one-magnon processes are suppressed and the change in resistance in the absence of spin-mixing on impurities may be arbitrarily large. Even in the case of imperfect magnetic configurations, the resistance change can be a few 1000 percent. Examples of half-metallic systems are CrO2/TiO2 and CrO2/RuO2, and an account of their peculiar band structures is presented. The implications and relation of these systems to CMR materials, which are nearly half-metallic, are discussed.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 491: Symposium R – Tight Binding Approach to Computational Materials Science , 1997 , 117
Copyright
Copyright © Materials Research Society 1998

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1. Julliere, M., Phys. Lett. 54A, 225 (1975).Google Scholar
2. Maekawa, S. and Gäfvert, U., IEEE Trans. Magn. 18, 707 (1982).Google Scholar
3. Meservey, R. and Tedrow, R.M., Phys. Reports 238, 173 (1994).Google Scholar
4. Moodera, J.S. et al, Phys. Rev. Lett. 74, 3273 (1995); J. Appl. Phys. 79, 4724 (1996).Google Scholar
5. Miyazaki, T. and Tezuka, N., J. Magn. Magn. Mater. 139, L231 (1995).Google Scholar
6. Steams, M.B., J. Magn. Magn. Mater. 5, 167 (1977); Phys. Rev. B 8, 4383 (1973).Google Scholar
7. Slonczewski, J.C., Phys. Rev. B 39, 6995 (1989).Google Scholar
8. Bratkovsky, A.M., Phys. Rev. B 56, 2344 (1997); JETP Lett. 65, 452 (1997).Google Scholar
9. Bardeen, J., Phys. Rev. Lett., 6, 57 (1961).Google Scholar
10. Mahan, G.D., Many-Particle Physics, 2nd ed., Plenum, New York, 1990, Ch. 9;Google Scholar
Duke, C.B., Tunneling in Solids, Academic Press, New York, 1969, Ch. 7.Google Scholar
11. Bratkovsky, A.M. (to be published).Google Scholar
12. Nickel, J., Anthony, T., and Brug, J., private communication.Google Scholar
13. Shu, Q.Q. and Ma, W.G., Appl. Phys. Lett. 61, 2542 (1992) give even smaller m2 = 0.2 for Al-Al2O3-metal junctions.Google Scholar
14. Irkhin, V.Y. and Katsnelson, M.I., Sov. Phys. - Uspekhi 164, 705 (1994).Google Scholar
15. Larkin, A.I. and Matveev, K.A., Zh. Eksp. Teor. Fiz. 93, 1030 (1987);Google Scholar
Lifschitz, I.M. and Kirpichenkov, V. Ya., Zh. Eksp. Teor. Fiz. 77, 989 (1979).Google Scholar
16. Jansen, R. and Moodera, J.S. (1997), to be published.Google Scholar
17. Poliak, M. and Hauser, J.J., Phys. Rev. Lett. 31, 1304 (1973);Google Scholar
Tartakovskii, A.V. et al, Sov. Phys. Semicond. 21, 370 (1987);Google Scholar
Levin, E.I. et al, Sov. Phys. Semicond. 22, 401 (1988);Google Scholar
Pendry, J.B., J. Phys. C 20, 733 (1987).Google Scholar
18. Glazman, L.I. and Matveev, K.A., Sov. Phys. JETP 67, 1276 (1988).Google Scholar
19. Xu, Y., Ephron, D., and Beasley, M., Phys. Rev. B 52, 2843 (1995).Google Scholar
20. Smirnov, A.V. and Bratkovsky, A.M., Phys. Rev. B 54, R17371 (1996);Google Scholar
Smirnov, A.V. and Bratkovsky, A.M., Phys. Rev. B 55, 14434 (1997).Google Scholar
21. Chaiken, A., Michel, R.P., and Wall, M.A., Phys. Rev. B 53, 5518 (1996).Google Scholar
22. Duke, C.B., Silverstein, S.D., and Bennett, A.J., Phys. Rev. Lett. 19, 315 (1967).Google Scholar
23. Moodera, J., private communication.Google Scholar
24. In a recent attempt to explain the I – V curves of ferromagnetic junctions Zhang, S., Levy, P.M., Marley, A.C., and Parkin, S.S.P. [Phys. Rev. Lett. 79, 3744 (1997)] have apparently neglected a strong bias dependence of the direct tunneling and did not consider the effect of phonons.Google Scholar
25. Appelbaum, J., Phys. Rev. Lett. 17, 91 (1966).Google Scholar
26. Monsma, D.J. et al, Phys. Rev. Lett. 74, 5260 (1995).Google Scholar
27. Tanaka, C.T. and Moodera, J.S., J. Appl. Phys. 79, 6265 (1996).Google Scholar
28. Okimoto, Y. et al, Phys. Rev. B 55, 4206 (1997); Phys. Rev. Lett. 75, 109 (1995).Google Scholar
29. Pickett, W.E. and Singh, D.J., Phys. Rev. B 53, 1146 (1996);Google Scholar
Singh, D.J., Phys. Rev. B 5, 313 (1997).Google Scholar
30. Allodi, G. et al. Phys. Rev. B 56, 6036 (1997);Google Scholar
Nagaev, E.L., JETP Lett. 6, 484 (1967); Phys. Rev. B 54, 16608 (1996);Google Scholar
Nagaev, E.L., JETP Lett. 56, 14583 (1997).Google Scholar
31. Gubkin, M.K. et al. Phys. Sol. State 35, 728 (1993);Google Scholar
Hwang, H.Y. et al., Phys. Rev. Lett. 77, 2041 (1996);Google Scholar
Sun, J.Z. et al., Appl. Phys. Lett. 69, 3266 (1996);Google Scholar
Kimura, T. et al., Science 274, 1698 (1996).Google Scholar
32. Hwang, H.Y. and Cheong, S.W., Nature 389, 942 (1997).Google Scholar