Croissance et propriétés magnétiques de réseaux planaires auto-organisés de nanofils de Fer B. Borca, O.Fruchart, M. Hasegawa, C. Meyer Laboratoire Louis Néel (CNRS-UJF-INPG) Grenoble Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006
INTRODUCTION Context Self-organization at surfaces : 2D regular arrays of similar nanostructures Stripes and wires Dots Co/Pt(997) Co/Au(111) 350 x 350 nm A. Dallmeyer et al., PRB 61(8), R5153 (2000) P. Gambardella et al., Nature 416, 301 (2002) P. Gambardella et al., Science 300, 1130 (2003) D.D. Chambliss et al., PRL 66, 1721 (1991) B.Voigtlander et al., PRB 44, 10354 (1991) J. P. Bucher et coll.; S. Rousset et coll.; O. Fruchart et coll. What for? ªCheaper and beyond lithography ªFundamental research: weak distributions > reliable analysis ªApplications? lack of versatility (tunability; use no vicinal nor reconstructed surface) Laboratoire Louis N éel, Grenoble Néel, Grenoble,, France France.. Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.2 http://lab lab-neel.grenoble.cnrs.fr/ ext/ /slides/ http:// neel.grenoble.cnrs.fr/ ext slides/
INTRODUCTION Self-organization without reconstructions or steps Stripes and wires Ag Demonstrated path: ion etching Dots GaSb(001) 200nm T. Aste and U. Valbusa, New J. Phys. 7, 122 (2005) F. Facsko et al., Science 285, 1551 (1999) Magnetic wires Etched magnetic films (with or without mask) Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.3
INTRODUCTION Self-organization without reconstructions or steps Fe(110) homoepitaxy Hills and grooves by kinetically-limited growth on bcc(110) LEED W(110) homoepitaxy STM Simulation M. Albrecht et al., Surf. Sci. 294, 1 (1993) U. Köhler et al., Surf. Sci. 454-456, 676 (2000) Any use for magnetic wires? Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.4
GROWTH UHV-PLD chambers Pulsed Laser Deposition (DLP) in UHV Nd:YAG pulsed laser cc(110)/al 2 O 3 (11-20) Target cc=, W, Nb, etc. Analysis Wedges RHEED (Reflection High-Energy Electron Diffraction) STM (Scanning Tunneling Microscopy) AES (Auger Electron Spectroscopy) Mask Substrate Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.5
GROWTH Trenches: (1/2) Buffer layers for trenches Deposition of bcc refractory metals along (110) RT deposition Annealed 800 C RT-150 C deposition [1-10] [001] 50nm 200nm 50nm Al 2 O 3 Al 2 O 3 Al 2 O 3 Uniaxial array of trenches (epitaxial) Long-range orientational order Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.6
GROWTH Trenches: (2/2) RHEED, RT, annealed [1-10], RT STM 200nm [001] 50nm [-110] [001] (110) 8nm [001] [1-10] (110) Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.7
GROWTH Trenches: atomic structure Atomic structure of the facets Facets of type {210} (110) θ=18.43 [001] [1-10] (00-1) (110) [1-10] Figures for Lateral period ~5 nm Depth of trenches: 0.6-1 nm Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.8
GROWTH Trenches: W (1/2) Process for W STM W deposited at 150 C RHEED W W Al 2 O 3 [-110] (110) [001] 20nm Lateral period ~5.5 nm Order is improved with W Satellite streaks > Lateral period ~5.5 nm 9 Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.9
GROWTH Trenches: W (2/2) RHEED W deposited under decreasing temperature: 550 C 150 C STM >>> RHEED video 20 Angle of facets ( ) 15 10 5 0 0 5 10 15 20 25 30 Thickness (Å) Well-defined facets {210} is the limiting facet [contrary to statement of Köhler et al. On small trenches, {310} (2000)] 20nm Period ~ 10-12 nm Depth ~ 2-3 nm Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.10
GROWTH Fe (1/2) Fe/W(110) with small period (5nm) at 150 C Fe - 1.5 ML 5 1.7ML Fe 150nm x 150nm Cross-section (nm) 4 3 2 1 1.5ML Fe 1.2ML Fe 1ML Fe 0.8ML Fe 0.5ML Fe W Fe 1 ML Fe - 2.4 ML 0 0 5 10 15 20 25 30 Distance (across wires) Layer-by-layer growth Forms a smooth surface Fe - 1.8 ML [001] Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.11
GROWTH Fe (2/2) Some details about continuous films Residual corrugation across the trenches Zoology of misfit dislocations Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.12
Magnetism /Fe/W Structure 2.5ML Fe/W(110) with large period (12nm) at 150 C Capping for SQUID measurements Magnetism Fe W Fe stripes at the bottom of the trenches M/M S ment (A.m 2 x 10-9 ) 4 3 2 1 1.0 H//[001] 0.5 0.0-0.5-1.0-400 -200 0 200 400 B (mt) ZFC Applied field 10 mt FC 0 0 50 100 150 200 250 300 Temperature (K) 4K 25K 50K 100K Easy axis along in-plane [001] Mean blocking temperature 100K Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.13
Magnetism /Fe//W /Fe/W Fe W Fe W /Fe//W M/M S ment (A.m 2 x 10-9 ) 1.0 H//[001] 0.5 0.0-0.5-1.0 4 3 2 1-400 -200 0 200 400 ZFC Applied field 10 mt FC 4K 25K 50K 100K B (mt) 0 0 50 100 150 200 250 300 Temperature (K) M/M S ment (A.m 2 x 10-9 ) 1 H//[001] 0-1 8 6 4 2-400 -200 0 200 400 ZFC Applied field 10 mt FC 10K 25K 50K 100K H (mt) 0 0 50 100 150 200 250 300 Temperature (K) Fe/ surface anisotropy along [001] > Anisotropy increased Mean blocking temperature 175K Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.14
Current focus Engineer further magnetic anisotropy By what means? Magnetic material Capping material Etc. What for? Fabrication of multilayers (Widespread for semiconductor QDs) Q.Xie et al., PRL 75(13), 2542 (1995) Blocking temperature above 300K Get perpendicular anisotropy >>> RHEED vie (Step: W) What for? Unusual (not demonstrated?) for metals What becomes of strain, dislocations etc? Influence on magnetic anisotropy? Futuristic: trend of magnetic recording towards 3D (Cf S.S.P. Parkin, R. Cowburn) Olivier Fruchart JMC10 Toulouse Aug. 31st, 2006 p.15