Self -organized growt h on t he Au(111) surf ace Olivier Fruchart 02/03/2002 Olivier Fruchart - Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart - Laboratoire Louis Néel, Grenoble, France. Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
TABLE OF CONTENTS The Au(111) reconst ruct ion, convent ional self -organizat ion: growt h and magnet ism Grazing I ncidence Small Angle Xray Scat t ering : ‘dif f ract ion’ on dot s ar r ays Ver t ical self -organizat ion : growt h and magnet ism Acknowledgment s Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.2 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.2 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Au(111) > A t emplat e f or self -or ganizat ion 350 x 350 nm FACTS : Co, Ni, Fe, Cu, Rh growth on Au(111) gives rise to self-organized arrays of dots ORIGIN ? (0.20AL Co @300K) nm 2Co 0.4 0.3 0.2 0.1 0 nm 0 5 10 15 20 Fe, Ni : 1 AL-high dots D.D. Chambliss et al., PRL 66, 1721 (1991) B.Voigtlander et al., PRB 44, 10354 (1991) Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.3 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.3 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Basic s x √ 3 r econst r uct ion Au(111) > Planar view of Au(111) HCP HCP FCC FCC M O O Z 50 x 28 nm Second layer atoms Cross-sectional view Site B Corrugation hcp : ABA fcc : ABC Atoms of the topmost layer C C A A B B B B B B B B B Site A A A A A A A A A A C C C C C C C C C Site C B B B B B B B B B Bridge position A A A A A A A A A (smaller diameter for clarity only) Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.4 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.4 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Au(111) > secondary ‘ chevr on’ r econst r uct ion 250 x 250nm Corrugation ~ 0.2 Å Unit cell size : ~ 7.5 x 25nm � Isotropic surface relaxation J. V. Barth et al., Phys. Rev. B 4 2 ( 1 5 ) , 9 3 0 7 ( 1 9 9 0 ) A.R. Sandy et al., Phys. Rev. B 4 3 ( 6 ) , 4 6 6 7 ( 1 9 9 1 ) Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.5 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.5 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Au(111) deposit s > nucleat ion st age Fe, Co, Ni (etc.) nucleation: atomic place exchange mechnism with Au atoms 0.25ML Ni@ 300K : 1ML-high dots 0.002ML Ni@300K J.A.Meyer et al., Surf.Sci. 3 6 5 , L647 (1996) 0.005ML Co@300K Leading parameter : deposit has a higher surface energy. (and Au atoms stress near chevrons) V. Repain et al., Mater. Sci. Eng., B96, 178 (2002) Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.6 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.6 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Co/ Au(111) magnet ism > t he super par amagnet ic limit issue Spontaneous magnetization is perpendicular to the plane [similar to Co/ Au(111) films] Co/Au(111) Anisotropy barrier ~KV ~25kT DOWN UP Blocking temperature Tb ~ 20K H.Dürr et al., PRB5 9 , R7 0 1 ( 1 9 9 9 ) K. Koide et al., PRL8 7 , 2 5 7 2 0 1 ( 2 0 0 1 ) Ph. Ohresser, F. Scheurer et al., private comm. H.Takeshita et al., JMMM1 6 5 , 3 8 ( 1 9 9 7 ) see also: S. Padovani et al., Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.7 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.7 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Co/ Au(111) magnet ism > spin and or bit al moment s Spin and orbital moments at films interfaces : • Spin moment : � slightly increased because of band narrowing (up to 30%) • Orbital moment : quenched in bulk 3d (~0). Symmetry breaking at the interface � Non-zero orbital moment (up to some 0.1 µ B /atome) Probe : XMCD (X-ray Magnetic Circular Dichroism) and sum rules. Expected in dots : further symmetry breaking at the dots edges: enhanced effects ? (similarity with atomic steps) Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.8 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.8 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Co/ Au(111) magnet ism > spin and or bit al moment s H.Dürr et al., PRB5 9 , R7 0 1 ( 1 9 9 9 ) K. Koide et al., PRL8 7 , 2 5 7 2 0 1 ( 2 0 0 1 ) 1/ N 1/ 2 fit Bulk Conclusion : extra orbital 2 µ B /edge atome Problems : Conclusion : no extra orbital moment for • dots coalescence above 1300 atoms: edge atoms (dot=‘small thin film’). non-valid fit… Problems : • Estimation of dot size by Langevin • function (Brillouin ½ better suited) dot size is still large. Need smaller systems ! Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.9 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.9 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Fe/ Au(111) magnet ism > spin and or bit al moment s P. Ohresser et al., PRB6 4 , 1 0 4 4 2 9 ( 2 0 0 1 ) Conclusions : • Spin moment not modified at edges (spin more influenced by deformation) • Edge orbital moment ~ 0.5 µ B , similar to steps on vicinal Fe. • Orbital moment anisotropy: not constant during growth. Strain-dependent interface anisotropy ? High-spin fcc Problem = not even solved in thin films… Low-spin fcc Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.10 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.10 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Orbit al moment > Co/ Pt (997) Co/ Pt( 9 9 7 ) Co/ Pt( 1 1 1 ) A. Dallmeyer et al. , Phys.Rev.B 61(8), R5153 (2000) Conclusions • Bulk: m L = 0.14 µ B / at. P. Gambardella et al., Science 300, 1130 (2003) • Surface: m L = 0.31 µ B / at. Conclusions • • Bi-atomic wire: m L = 0.37 µ B / at. From bulk to atoms: considerable increase of orbital m om ent • Mono-atomic wire: m L = 0.68 µ B / at. • 2 atom s closer to w ire than 1 atom • bi-atom: m L = 0.78 µ B / at. • bi- atom ic w ire closer to surface than w ire • atom: m L = 1.13 µ B / at. P. Gambardella et al., Nature 416, 301 (2002) Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.11 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.11 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Magnet ic anisot ropy > From sur f aces t o at oms From surface to w ires ( 1 D) Self-organized Co/ Pt(997) a Monatomic b 1 monolayer C Bulk L 3 chains + + - - + a.u. − L 2 0 − − + + - + −2 a.u. −4 2. Magnetic anisotropy [ 3.5 From surfaces to atoms] −6 C z Co atoms −8 Pt terrace x −10 y 770 780 790 800 810 770 780 790 800 810 770 780 790 800 810 Photon energy (eV) Photon energy (eV) Photon energy (eV) ∫ ∫ µ ≈ + L L L 3 2 Conclusion: • Increase of orbital moment ∫ ∫ µ eff ≈ − + 2 L 4 L (necessary condition for s 3 2 anisotropy) • Anisotropy of orbital moment? P. Gambardella et al., Nature 416, 301 (2002) Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.12 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.12 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Magnet ic anisot ropy > From sur f aces t o at oms z z From surface to w ires ( 1 D) x Method y • XMCD > Orbital moment 0.4 0.2 • Fit magnetization curves > Anisotropy functional 0.3 M (a.u.) 0 ° + 43° 0.2 0.1 - 5 7 ° MAE 9 0 ° • Bulk Co: 40 µ eV/ atom 0.1 0.0 0.0 • Co ML: 140 µ eV/ atom -9 0 -6 0 -30 30 60 90 -9 0 -6 0 -30 30 60 90 (deg) (deg) • Co bi-wire: 0.34meV/ atom • Co wire: 2meV/ atom T = 45 K T = 10 K 0 ° Conclusions: M (a.u.) • Easy axis of magnetization 9 0 ° perpendicular to the wires, but not the the mean film surface, + 43° −57° nor to Pt(111) • See anisotropy of orbital moment on the saturation XMCD. -6 -4 -2 0 2 4 6 -6 -4 -2 0 2 4 6 B (T) B (T) Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.13 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.13 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Magnet ic anisot ropy > From sur f aces t o at oms 8 atom s 4 atom s From surface to atom s ( 0 D) Co/ Pt( 1 1 1 ) 10K 10K 1 atom STM, 8 .5 nm , 5 .5 K P. Gambardella et al., Science 300, 1130 (2003) 5.5K Cf quest ion by Dominique GI VORD Qualitatively: • Easy axis of magnetization perpendicular to Pt(111) • See anisotropy of orbital moment on the saturation XMCD. Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.14 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.14 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
Magnet ic anisot ropy > From sur f aces t o at oms From surface to atom s ( 0 D) Co/ Pt( 1 1 1 ) MAE • Bulk Co: 40 µ eV/ atom • Co ML: 140 µ eV/ atom • Co bi-wire: 0.34meV/ atom • Co wire: 2meV/ atom • Co bi-atom: 3.4meV/ atom • Co atom: 9.2meV/ atom Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.15 ] Olivier Fruchart - LLN-CNRS. [ 02/03/2002 / p.15 ] Slides on- line: http:/ / la b- neel.grenoble.cnrs.fr / them es/ couches/ e x t/
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