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, Genova Italy

ion sputtering 2 μA of Ar + at 1 keV 70 o incidence angle to [1-10] T sputter =180 K Co deposition normal incidence R dep ~ 3·10 -3 MLE/s T dep = 300 K sample preparation 1 keV Ar + sputtering annealing at 800 K Cu(001) [110] [1-10] [001] 20 o Co Ar + STM (nanostructure morphology) longitudinal MOKE (in-plane magnetic anisotropy) T meas =140 K

Ripples on single-crystal surfaces Cu(001) low-temperature grazing-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) hfhf 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/cm 3 ) uniaxial anisotropy constant (erg/cm 3 ) shift field (Oe) R. P. Cowburn et al., Phys. Rev. Lett. 79, 4018 (1997)

(c) (d) (e) (b) [110] [1-10] (a) Magnetic anisotropy vs. ion dose

h=4w Co Cu 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 energy per atom at step site E th atom = 70 μeV D. S. Chuang et al., Phys. Rev. B. 49, (1994)

Shape anisotropy micromagnetic calculations

Néel and magnetostatic contributions Néel contribution magnetostatic contribution

Surface-type anisotropy

Magnetic anisotropy vs. annealing temperature

(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