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

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

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)

Ripples on films

Cu(001)Co film

t

h

Cu(001)hf

Cu(001)

low ion dose < c

higher ion dose > c

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)

(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

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

Ripple morphology vs.

ion dose

initial roughness

power-law behavior

U. Valbusa et al.,J.Phys.:Condens.Matter 14, 8153 (2002)

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)

Shape anisotropy

micromagnetic calculations

http://math.nist.gov/oommf/

Néel and magnetostatic contributions

400

300

200

100

0

Hs

(Oe)

151050

Ion dose (MLE)

I II

Néel contribution

magnetostatic contribution

Surface-type anisotropy

200

150

100

50

Hs (

Oe)

1210864Co coverage (MLE)

Ion dose 1MLE

Magnetic anisotropy vs.

annealing temperature200

150

100

50

0

Hs (

Oe)

400350300250200150

T (K)

12 MLE Co/Cu(001)Ion dose 7.7 MLE

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

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