Electronic structure and tunnel magnetoresistance of FeMgOFe

1
Electronic structure and tunnel
magneto-resistance of Fe/MgO/Fe M. Bouhassoune,
A. Ernst, J. Henk, and P. Bruno, MPI Halle,
Weinberg 2, 06120 Halle, Germany M. Däne, D.
Ködderitzsch, W. Hergert, and I. Mertig,
University Halle-Wittenberg, Halle (Saale),
Germany Z. Szotek and W. M. Temmerman, Daresbury
Laboratory, Warrington, WA4 4AD, UK
Computational aspects
Motivation
Landauer Büttiker Approach

• self-consistent semi-relativistic screened KKR
  code (to provide self-consistent potentials and
  calculations of electronic structure )
• full-relativistic layer-KKR code omni2k for
  semi-infinite systems (for conductance
  calculations within Landauer-Büttiker formalism)

Conductance
Magnetic tunnel junction properties depend on
with

• relative orientation of the magnetizations in
  the leads
• electronic properties of the leads and spacer
  (specially the band gap of the spacer)
• thickness of the semiconducting spacer
• geometry of the interface between the leads and
  the semiconducting spacer

S is the reduced scattering matrix of the
spacer
Conductance calculations for Fe/MgO/Fe sandwiches
Electronic structure of MgO and Fe bulk
parallel alignment of leads
Possible application in electronics
Fe magnetic moment 2.25 µB
Magnetic Random Access Memory (MRAM)
MgO energy gap 4.2 eV
Energy gap is too small !
with oxygen at the Fe /MgO interface
without oxygen at the Fe /MgO interface
anti-parallel alignment of leads
General failure of LDA
Fe/MgO/Fe(001) sandwiches Geometry
MgO bulk fcc (NaCl structure), a4.05 Å
Fe bulk bcc , a2.81 Å
Electronic structure of Fe/MgO/Fe
Contrary to Butler et al. (Phys. Rev. B 63, p.
054416) magnetic moment of Fe in the second
layer is essentially reduced strong hybridization
effects due to relaxations (16) and deposition
of oxygen
O
Fe
Mg
2D lattice (001 direction)
TMR ratio
Charge transfer profiles
a2.87 Å
Conductance
G(P) parallel alignment of leads
a2.81 Å
G(AP) anti-parallel alignment of leads
Experiment x-ray diffraction
with oxygen at the Fe /MgO interface
Outlook
Magnetic profiles
without oxygen at the Fe /MgO interface

• Further studies of the electronic structure and
  tunneling in Fe/MgO/Fe with relaxations (also
  full-potential calculations)
• Alloying interface CPA
• Study of correlations in Fe/FeO/MgO/FeO/Fe with
  the SIC method

H. L. Meyerheim et al. Phys. Rev. Lett., V 87, p.
076102, 2001