uniaxial magnetic anisotropy tuned by nanoscale ripple formation: ion-sculpting of co/cu(001) thin...
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Uniaxial magnetic anisotropy tuned by nanoscale ripple formation: ion-sculpting of
Co/Cu(001) thin films
• R. Moroni• Unità INFM di Genova
• Dipartimento di Fisica• via Dodecaneso, 33
• 16146 Genova• Italy
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ion sputtering 2 μA of Ar+ at 1 keV
70o incidence angle to [1-10]
Tsputter=180 K
Co deposition normal incidence
Rdep ~ 3·10-3 MLE/s
Tdep = 300 K
sample preparation 1 keV Ar+ sputtering annealing at 800 K
Cu(001)[110] [1-10]
[001]20o
CoAr+
STM (nanostructure morphology)
longitudinal MOKE (in-plane magnetic anisotropy)
Tmeas=140 K
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Ripples on single-crystal surfaces
Cu(001)
low-temperaturegrazing-incidence
ion sputtering
Cu(001)
h
ion beam
S. Rusponi et al.,Appl. Phys. Lett. 75, 3318 (1999)
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Ripples on films
Cu(001)Co film
t
h
Cu(001)hf
Cu(001)
low ion dose < c
higher ion dose > c
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In-plane uniaxial magnetic anisotropy
12 MLE Co/Cu(001)
12 MLE of Ar+ at 1 keV
saturation magnetization(1422 emu/cm3)
uniaxial anisotropy constant(erg/cm3)
shift field(Oe)
R. P. Cowburn et al.,Phys. Rev. Lett. 79, 4018 (1997)
a
[110][1-10]
c
[110]
[1-10]
20nm
20nm
b
d
H // [110]
H // [1-10]
Ke
rr sign
al (a
rb. u
n.)
Hc
H // [110]
H // [1-10]
Hs
Hs1
Hs2
Ke
rr sign
al (a
rb. u
n.)
-500 -250 0 250 500H (Oe)
a
[110][1-10]
c
[110]
[1-10]
20nm
20nm
b
d
H // [110]
H // [1-10]
Ke
rr sign
al (a
rb. u
n.)
Hc
H // [110]
H // [1-10]
Hs
Hs1
Hs2
Ke
rr sign
al (a
rb. u
n.)
-500 -250 0 250 500H (Oe)
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(c)
(d) (e)
(b)[110]
[1-10]
Ker
r in
ten
sity
(a
rb.
un
.)
-400 -200 0 200 400H (Oe)
12 ML Co/Cu(001)
60 s
120 s
180 s
240 s
360 s
480 s
600 s
(a)
Magnetic anisotropy vs. ion dose
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Magnetic anisotropy vs.
ion dose
400
300
200
100
0
Hs
(Oe
)
1612840
Ion dose (MLE)
100
50
0
Cu
920 /Co
716 (%)
I II
h=4w
CoCu
Co wires
Cu
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Ripple morphology vs.
ion dose
initial roughness
power-law behavior
U. Valbusa et al.,J.Phys.:Condens.Matter 14, 8153 (2002)
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Néel pair-bonding model
[110]
[1-10]
Anisotropy energyper atom
at step siteEth
atom = 70 μeV
D. S. Chuang et al.,Phys. Rev. B. 49, 15084 (1994)
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Shape anisotropy
micromagnetic calculations
http://math.nist.gov/oommf/
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Néel and magnetostatic contributions
400
300
200
100
0
Hs
(Oe)
151050
Ion dose (MLE)
I II
Néel contribution
magnetostatic contribution
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Surface-type anisotropy
200
150
100
50
Hs (
Oe)
1210864Co coverage (MLE)
Ion dose 1MLE
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Magnetic anisotropy vs.
annealing temperature200
150
100
50
0
Hs (
Oe)
400350300250200150
T (K)
12 MLE Co/Cu(001)Ion dose 7.7 MLE
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Ker
r in
ten
sity
(ar
b.
un
.)
-500-250 0 250 500H (Oe)
1 ML
2 ML
4 ML
6 ML
(a)
(b) (c)
(d) (e)
Co deposition on nanostructured Cu(001)
substrate
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Perspectives
• Investigation of different systems:– different film/substrate mismatch (role of
magnetoelastic contributions)– different film structure (interplay between Néel and
magnetostatic contributions)
• Nanostructuration of polycrystalline films• Film deposition on nanostructured
polycrystalline substrates