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W. mF MPI Halle. The Unsolved Origin Of:. - Loop shift (UNIDIRECTIONAL anisotropy) - - Loop widening (UNIAXIAL anisotropy) - If a ferromagnet is coupled to an antiferromagnet. Giant Magneto Resistance: (GMR)-read head for hard disks. Co MCD. - PowerPoint PPT Presentation
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CoNiOx Interface
Interfacial Moments In Co/NiOOrigins Of Antiferromagnetic/Ferromagnetic Coupling
Hendrik Ohldag, Tom Regan, Andreas Scholl, Frithjof Nolting, Elke Arenholz, Franz Ulrich Hillebrecht and Joachim Stöhr
MPI Halle
Co And NiO
H. Ohldag, A. Scholl et al., Phys. Rev. Lett. 86(13), pp 2878 (2001).
F.U. Hillebrecht, H. Ohldag et al., Phys. Rev. Lett. 86(15), pp 3419 (2001).
H. Ohldag, N.B. Weber et al., Synch. Rad. News 13(6), pp. 25 (2001).
T.J. Regan, H. Ohldag et al., Phys. Rev. B, in print (2001).
Or on the web: http://www-als.lbl.gov/als/als_news/news_archive/vol.178_060601.html
X-ray absorption shows chemically active interfacePEEM reveals its polarization.
Co DEPOSITION CREATES AND POLARIZES CoNiOX INTERFACE
776 778 780
0.00
0.05
0.10 Co CoO Co/NiO Model
Ele
ctro
n Y
ield
(ar
b. u
nits
.)
Photon Energy (eV)
868 870 872 874
0.00
0.01
0.02
L3-edge
L2-edge
BA
Co
Ni Ni NiO Co/NiO Model
Line shape in x-ray absorption used to identify metal-oxide
transition:
M MxOy
“Real System”
Co/NiO Co/CoNiOx/NiO
5m
Co MCD
NiO MCD
NiO
Co
NiO
CoCoNiO
The Solution:
Chemical and magnetic characterization of all layers and their interface.
The Unsolved Origin Of:
-1500 -1000 -500 0 500 1000 1500
-1.0
-0.5
0.0
0.5
1.0
Mag
netiz
atio
n(a.
u.)
Applied Field (Oe)
FM 1
FM 2AFM
- Loop shift (UNIDIRECTIONAL anisotropy) - - Loop widening(UNIAXIAL anisotropy) -
If a ferromagnet iscoupled to anantiferromagnet
Giant Magneto Resistance:
(GMR)-read head for hard disks
PEEM to image AFM and FM domains in Co/ NiO(001)
AFM REORIENTATION UPON Co DEPOSITION
PARALLEL COUPLING
UNIAXIAL ANISOTROPY
PEEM to image AFM domains only at NiO(001) surface.
SURFACE WALLS ARE NOT MIRROR PLANES LIKE BULK
WALLS
References
The Method:
A Photoemission Electron Microscope (PEEM) magnifies the local electron yield onto a screen.
Spatial resolution ~ 50-100nm
790 795 800
1.5
2.0
2.5
3.0 Co L2
Ele
ctr
on
Yie
ld (
a.u
.)
Photon Energy (eV)
e-e-
876 879 882
100
200
300 NiO L2
Ele
ctr
on
Yie
ld (
a.u
.)
Photon Energy (eV)
e-e-
Absorption of monochromatic tuneable x-rays elemental and chemical contrast
Absorption of circular polarized x-rays (circular dichroism) spin orientation / ferromagnetic (FM) contrast
Absorption of linear polarized x-rays (linear dichroism) spin anisotropy / antiferromagnetic (AFM) contrast
500 600 700 800 900
3
6
Ele
ctr
on
Yie
ld (
a.u
.)
Photon Energy (eV)
e-
Ni Fe
e-
e-
FeO
Fe
e-
0
20
40
60
704 706 708 710P hoton Energy (eV)
Ele
ctr
on
Yie
ld (
a.u
.)
Fe
Fe+O x
e
30o
no FeFe3+
Fe2+
XAS and dichroism link between interface polarization and magnetic properties
“FREE” CoNiOx SPINS CAUSE UNIAXIAL ANISOTROPY (EXCHANGE COUPLING)
“PINNED” CoNiOx SPINS MAY CAUSE UNIDIRECTIONAL ANISOTROPY (EXCHANGE BIAS)
0 10 20 30 400.0
0.3
0.7
1.0
1.3
Inte
rfa
ce
th
ickn
ess (
nm
)
Annealing time at 600K (mins)
0
400
800
1200
Co
erc
ivity
(Oe
)
Free Interfacial moments:
- Exchange coupling
- Uniaxial anisotropy
- Coercivity increase
Pinned Interfacial moments:
- Exchange bias
- Unidirectional anisotropy
- Loop shift
-2000 -1000 0 1000 2000
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
Hysteresis of Uncompensated Interfacial Ni spins in 3nm Co/NiO
NiO
XM
CD
Asy
mm
etry
[%]
Applied Field (Oe)