Tunnel magnetoresistance

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In physics, the tunnel magnetoresistance effect (TMR), occurs when two ferromagnets are separated by a thin (about 1 nm) insulator. Then the resistance of the tunneling current changes with the relative orientation of the two magnetic layers. The resistance is normally higher in the anti-parallel case.

It was discovered in 1975 by Michel Julliere, using iron as the ferromagnet and germanium as the insulator.

Room temperature TMR was discovered in 1995 first by Terunobu Miyazaki and independently by Moodera et al. following renewed interest in this field fueled by the discovery of the giant magnetoresistive effect. It is now the base for the magnetic random access memory (MRAM) and read sensors in hard disk drives. For more technical information see [Moodera and Mathon 1999].

In 2001 Butler et al and Mathon et al independently made the theoretical prediction that using iron as the ferromagnet and MgO as the insulator, the tunnel magnetoresistance can reach several thousand percent. In 2004, Parkin et al and Yuasa et al were able to make Fe/MgO/Fe junctions that reach over 200% TMR at room temperature. In 2007, MgO based TMR devices completely displaced GMR devices on the magnetic storage device market.

[edit] References

M. Julliere (1975). "Tunneling between ferromagnetic films". Phys. Lett. 54A: 225-226. sciencedirect

T. Miyazaki and N. Tezuka (1995). "Giant magnetic tunneling effect in Fe/Al₂O₃/Fe junction". J. Magn. Magn. Mater. 139: L231-L234. mit

J. S. Moodera et al. (1995). "Large Magnetoresistance at Room Temperature in Ferromagnetic Thin Film Tunnel Junctions". Phys. Rev. Lett. 74: 3273–3276. doi:10.1103/PhysRevLett.74.3273. aps

G. Binasch et al. (1989). "Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange". Phys. Rev. B 39: 4828–4830. doi:10.1103/PhysRevB.39.4828. aps

M. N. Baibich et al. (1988). "Giant Magnetoresistance of (001)Fe/(001)Cr Magnetic Superlattices". Phys. Rev. Lett. 61: 2472–2475. doi:10.1103/PhysRevLett.61.2472. aps

J. S. Moodera and George Mathon (1999). "Spin polarized tunneling in ferromagnetic junctions". Magn. Magn. Mater. 200: 248-273. doi:10.1016/S0304-8853(99)00515-6. sciencedirect

W. H. Butler, X.-G. Zhang, T. C. Schulthess, and J. M. MacLaren (2001). "Spin-dependent tunneling conductance of Fe/MgO/Fe sandwiches". Phys. Rev. B 63: 054416. doi:10.1103/PhysRevB.63.054416. aps

J. Mathon and A. Umerski (2001). "Theory of tunneling magnetoresistance of an epitaxial Fe/MgO/Fe (001) junction". Phys. Rev. B 63: 220403. doi:10.1103/PhysRevB.63.220403. aps

S Yuasa, T Nagahama, A Fukushima, Y Suzuki, and K Ando (2004). "Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions". Nat. Mat. 3: 868-871. nature