2005 APS March Meeting
Monday–Friday, March 21–25, 2005;
Los Angeles, CA
Session X6: Frontiers in Computational Materials
8:00 AM–11:00 AM,
Friday, March 25, 2005
LACC
Room: 502A
Sponsoring
Unit:
DCOMP
Chair: Mei-Yin Chou, Georgia Tech
Abstract ID: BAPS.2005.MAR.X6.5
Abstract: X6.00005 : Predicition and Discovery of High Tunneling Magnetoresistance in Magnetic Tunnel Junctions with Crystalline Barriers*
10:24 AM–11:00 AM
Preview Abstract
Abstract
Author:
William Butler
(MINT Center, University of Alabama)
Tunneling magnetoresistance in excess of 200{\%} has recently
been observed
in magnetic tunnel junctions using bcc Fe or bcc CoFe electrodes
with
crystalline MgO tunnel barriers[1,2]. These results demonstrate that
tunneling magnetoresistance depends on more than the ``electrode
polarization''. This talk will describe the calculations that
predicted high
TMR in these and other systems[3,4,5]. These calculations helped
us to
understand certain principles that may lead to high TMR through
coherent
electron tunneling. They can be briefly summarized as follows:
(1) If the symmetry of a Bloch state can be preserved as
electrons cross the
interfaces between the electrode and the tunnel barrier, this be
used to
advantage for spin filtering.
(2) Evanescent states of different symmetries decay at different
rates in
the barrier.
(3) Interfacial bonding can be very important in determining the
probability
that an electron can traverse the interface.
(4) Electrons of disallowed symmetry cannot propagate in an
electrode.
Once these simple principles are understood, simple band codes
can be used
to screen and to develop heterostructures with the proper
symmetries to
obtain high TMR.
[1] S. S. P. Parkin, C. Kaiser, A. Panchula, P. M. Rice, B.
Hughes, M.
Samant AND S.-H. Yang, ``Giant tunnelling magnetoresistance at room
temperature with MgO (100) tunnel barriers,'' Nature Materials,
Advance
Online Publication
[2] S. Yuasa, T. Nagahama, A. Fukushima, Y. Suzuki, K. Ando, ``Giant
room-temperature magnetoresistance in single-crystal Fe/MgO/Fe
magnetic
tunnel junctions,'' Nature Materials, Advance Online Publication
[3] W. H. Butler, X.-G. Zhang, T. C. Schulthess, and J. M. MacLaren,
``Spin-dependent tunneling conductance of Fe $\vert $ MgO $\vert
$ Fe
sandwiches'' Phys. Rev. B \textbf{63}, 054416 (2001)
[4] J. Mathon, A. Umerski, ``Theory of tunneling
magnetoresistance of an
epitaxial Fe/MgO/Fe(001) junction,'' Phys. Rev. B \textbf{63},
220403(R)
(2001).
[5] X.-G. Zhang, and W. H. Butler, ``Large magnetoresistance in bcc
Co/MgO/Co and FeCo/MgO/FeCo tunnel junctions,'' Phys. Rev. B
\textbf{70},
172407 (2004)
*Coauthors: X.-G. Zhang, T.C. Schulthess, J. M. MacLaren, M. Chshiev, and S. Vutukuri; Supported by NSF MRSEC-DMR 0213985 and by DARPA/ONR
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2005.MAR.X6.5