GaMnAsPatterning |
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Présentation
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Main investigator: A. Lemaître
Permanent staff: L. Largeau and O. Mauguin
PhD student: T. Niazi
Post-doc: J. Curiale
Magnetic anisotropy in
GaMnAs
The major contribution to the
magnetic anisotropy in GaMnAs is the
biaxial expitaxial strain induced by the lattice mismatch between the
magnetic layer and the substrate. For a review see T. Dietl et al.
Phys. Rev. B 63, 195205 (2001). On GaAs substrate, GaMnAs layers are
under a slight compressive strain resulting in, in most cases, a strong
in-plane easy axis (for high TC layers). The strain state of
the magnetic layer, and therefore the easy axis orientation, can be
modified by changing the lattice parameter of either the substrate or
the magnetic layer itself.
The first approach, developed at the very beginning of the GaMnAs story
by growing the GaMnAs layer on a metamorphic GaInAs substrate (Ohno's
group and others, including us).
However, even though we achieved very high film quality, the
metamorphic growth is inherently associated to the formation of
threading dislocations. These defects act as blocking centers for DW
propagation.
Epitaxial growth of
GaMn(As,P)
To circumvent this problem we have developed a new alloy, GaMnAsP on
GaAs substrate, to tune the lattice mismatch at will, hence the
magnetic anisotropy. Growth was performed under the same conditions as
for GaMnAs,
namely a low growth temperature and a quasi III-V stiochiometry.Fig 1
shows as the incorporation of P in
substitution to As ions modifies the strain state of the magnetic
layer.
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Fig. 1: Strained lattice mismatch of 50 nm thick
GaMn(As,P) layers as a function of the P2 to As2
Beam Equivalent
Pressure ratio. The strain state changes from compressive to tensile
upon increasing Phosphorus concentration.
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Magnetic properties
The magnetic properties were investigated by SQUID
magnetometry, ferromagnetic resonance and magneto-transport (in collaboration with INSP and UMPhy). For low P
concentrations (up to 10 %) GaMnAsP layers show very good properties,
comparable to P-free GaMnAs, with low resistivity, TC
above
100 K and high magnetization. Fig. 2 shows the strong modification of
the magnetization curves vs magnetic field as phosphorous is inserted
into the matrix. The magnetic field was applied perpendicularly to the
sample plane. Without phosphorous no hysterisis cycle is visible, the
out-of-plane axis is a hard axis. A large magnetic field is needed to
rotate the magnetization out of the plane. With phorphorous (9%), a
clear hysterisis loop is visible, the out-of-plane axis is now an easy
axis. Hence P incorporation induces a strong modification of the
magnetic anisotropy.
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Fig. 2: Magnetization curves vs magnetic field applied perpendicular to the plane for two 50 nm thick layers.
Left: GaMnAs. Right: GaMnAsP0.09. The hysteresis loop indicates an easy axis perpendicular to the plane.
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Magnetic domain self-organization
Thanks to the reduced number of defects in GaMnAsP compared to GaMnAs
grown on a relaxed InGaAs substrate, magnetic domain self-organization
has been evidenced by INSP. Fig. 3 shows two Kerr images obtained at
LPS and INSP for both systems after an AC demagnetization. In the case of GaMnAsP, the domain
organization is governed by the competition between the domain wall
energy and the magnetic energy. In the metamorphic approach, the
self-organization is limited by numerous defects, mostly threading
dislocation impeding the domain wall motion.
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Fig. 3: Magnetic
domain organization after an AC demagnetization. Left: GaMnAs grown on
a relaxed InGaAs substrate (LPS). Right: GaMnAs on GaAs substrate
(INSP). The pattern on the right is typical of a self-organisation
process, indicating a very high quality layer, presenting only few
defects to domain wall motion.
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Collaborations
- J. von Bardeleben, C.
Gourdon, L. Thevenard, C. Testelin,
E. Peronne at INSP
- J.-M. George and H. Jaffrès
at UMPhy
- V. Jeudy, A. Thiaville and
J. Ferré at LPS
- N. Vernier at IEF
References
- Effect of picosecond strain
pulses on thin layers of the
ferromagnetic semiconductor (Ga,Mn)(As,P), L. Thevenard, E. Peronne, C.
Gourdon, C. Testelin, M. Cubukcu, E. Charron, S. Vincent, A. Lemaître,
and B. Perrin, Phys. Rev. B 82, 104422 (2010)
- Exchange constant and
domain wall width in (Ga,Mn)(As,P)
films with self-organization of magnetic domains, S. Haghgoo, M.
Cubukcu, H. J. von Bardeleben, L. Thevenard, A. Lemaître, and C.
Gourdon, Phys. Rev. B 82, 041301 (2010)
- Temperature induced
in-plane/out-of-plane magnetization
transition in ferromagnetic GaMnAsP/ (100) GaAs thin films, M. Cubukcu,
H. J. von Bardeleben, J. L. Cantin, and A. Lemaître, Appl. Phys. Lett.
96, 102502 (2010)
- Adjustable anisotropy in
ferromagnetic (Ga,Mn) (As,P)
layered alloys, M. Cubukcu, H. J. von Bardeleben, Kh. Khazen, J. L.
Cantin, O. Mauguin, L. Largeau, and A. Lemaître, Phys. Rev B 81, 041202
(2010)
- Strain control of the
magnetic anisotropy in (Ga,Mn) (As,P)
ferromagnetic semiconductor layers, A. Lemaître, A. Miard, L. Travers,
O. Mauguin, L. Largeau, C. Gourdon, V. Jeudy, M. Tran, and J.-M.
George, Appl. Phys. Lett. 93, 021123 (2008)
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