Recent progress in Synchrotron based soft Xray microscopy

Recent progress in Synchrotron based soft X-ray microscopy for thin films and Nanostructures studies 2µm R. Belkhou. Synchrotron SOLEIL, Gif sur yvette. France

Technological Needs Magnetic Recording Devices Magneto-optical Hard Disk Tb. Fe. Co Interligne 100 nm Artificials devices - Non magnétic, - Ferromagnetic, - Antiferro…… P. Fischer et al, CXRO/LBLNL High storage capacity media: >10 Gbits. cm -2 Size of individual Information Unit: bit = Single Magnetic Domain < 30 nm 2 R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Challenges in magnetism Spatial Resolution Time Resolution Complex Materials, Nanostructures… Dynamic Processes Need for very Specific Experimental Setups R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Development of specific tools Fabrication of complex nanostructures Requires Development of new experimental setups sensitive to: ØElemental ØChemistry ØStructure, Electronic…. Over Broad spatial resolution scales: Ølaterally Ø transverse Coupled to Local Analysis of ØElectronic properties, structure. . ØMagnetism, catalyzis. . R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Sof X-ray Microscopy with Synchrotron radiation 2 Microscopies: Photon-Electron and Photon-Photon STXM X-PEEM Monochromator Spatial filter Fresnel zoneplate lens Sample Detector Computer Raster scan Spatial Resolution: <25 nm Energy Resolution: < 150 me. V Spectral range: 5 e. V – > 10 ke. V üSurfaces and interfaces ü Probing depth< 10 nm ü Local Spectroscopy ü Fast acquisition Parallel imaging ü UHV or controlled environment ü In ou Ex-situ samples ü Time resolved mode(<100 ps) R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 ü“Bulk” soft and hard condensed matter ü Probing depth< 500 nm ü No UHV requirement ü Sequential imaging (raster scanning) ü Controlled sample environment High magnetic field, Cryogenic, wet cell, living cells …. .

Applications v Magnetic Domain Imaging: Ø Circular and linear Dichroism. Ø Magnetic coupling Ferro/Ferro, Ferro/Antiferro Ø Nanostructures Ø Domain and domain wall dynamic…. . v Surface and interfaces: Ø Growth mode. Ø Elemental, compositional, topological inhomogeneities Ø Diffusion, inter-diffusion, alloying Ø Phase transition Ø Band offset……. Ø Small samples (toxic, radioactive…. ) y x 2 mm n En Photo ergy v Surface Chemistry Ø Reaction Mechanism Ø Chemical waves Ø Catalytic reaction Ø Chemical Domains Imaging…. R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 C=O carbonate 0. 8 mm C=C Carbonate in organic matrix

X-ray Microscopy: Methods Absorption Photoemission § Element specific § Co-localization § Quantification ALS-1998 R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 ESRF-1998

X-PEEM : Magnetic Contrast Magnetic Circular Dichroism : XMCD Fe L 2, 3 Edges hv Mixed Contrast magnetic, topologic. . . Mn L 2, 3 Edges Mn. As Thin t=5 min Film The valance band acts as a spin detector. R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

X-PEEM : Antiferromagnetic Contrast Magnetic Linear Dichroism: XMLD Energy XMLD Sensitive to charge anisotropy 2µm Ni. O L 2 Fine Structure XMLD Max: Pol. Vect. // AFM axis Unic tool for studying AFM thin films and nanostructures R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 ALS J. Stohr et al Phys. Rev. Lett 83(1999) 1862.

Nanospectroscopy: Local Spectroscopy d Orbitales vaccancies Co/Ni/Cu(100) Orbital Moment hn Spin reorientation depends on the energy of the magnetic anisotropy: 370 nmx 370 nm Ni> 8 -10 ML M Perp Co M Para Co 1. 33 -2. 6 MC Ni 10 -14 MC Cu(100) R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 Spin Moment

Quantitative measurements: Sum rules Effective spin moment Orbital moment Transition Para-perpend DE (d. Ni , d. Co)= 0 üThe magnetic anisotropy depend on the thickness. üCorrelation between m. L and the Magnetocristalline anisotropy. üReduction of the domains size approaching the transition region R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Dynamical Processes & Time Resolved: Low Dynamic (>1 ms): - Growth, Phase transition… 2µm Magnetic Exchange coupling Fe/Mn. As(0001) @ the a/b Mn. As Phase transition R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Fast Dynamic Use of single buch mode of SR e- 100 ps 2. 8 ms Synchronization between the magnetic pulses (Pump) and the Photon bunches (Probe) Inter-Coil: Champ max 0. 2 T @ 357 k. Hz R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 ESRF J. Vogel et al

Time resolved Magnetic Imaging Landau vortex precession: Pump Probe XPEEM Laser Pulse X-ray pulse R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 S. -B. Choe, et al. Science 304, 420 (2004).

Time resolved Magnetic Imaging Landau vortex precession: Pump Probe XPEEM Laser Pulse X-ray Pulse Resolution 50 ps Two phases: linear Acceleration, then precession R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 S. -B. Choe, et al. Science 304, 420 (2004).

Combining all the contrast modes Linear Polarization: Antiferro Domains Circular Polarization: FM Domains Exchange bias anisotropy: Co/La. Fe. O 3 Unic tool for studying The AFM/FM Coupling R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 F. Nolting et al Nature 405 (2000) 767.

FM/AFM Coupling & Exchange Bias FM Mapping Of the Exchange Anisotropy AFM Distribution Of the Exchange Field Local Hysteresis Cycle The Exchange Bias is due to the statistical add-on of spin moments pinned at the interface. R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 A. Scholl et al. , APL (2004)

Magnetic Microstructures Computers, Storage and magnetic recording: Ferromagnetic bit states C state Vortex state Onion state 1 0 B || I bit plane R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 B ||

Magnetic Microstructures assymetric see aee sev aev svv avv svav avov sv av s s Micromagnetic simulations R. Hertel, unpublished R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Magnetic Microstructures Measurements at the L 2, 3 Co Edge 1: 1 600× 600 R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 avv 2: 1 1200× 600 3: 1 1200× 400 S. Cherifi et al. , JAP 98 (2005) 043901

Domains Distribution Co 20 nm Simulations Aspect ratio 3: 1 X-PEEM Measurements 400 200 400 600 R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Magnetic Tunnel junction & Finite size effect Si//Pt/Co(4 nm)/Al 2 O 3(2 nm)/Ni. Fe(4 nm)/Ru(2 nm) Thin films Magnetic component Along the X axis Co Ni (x) • Magnetic coupling due to the dipolar field Py - + Co + - 5 µm Size Reduction R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 D. Lacour et al, APL (2008)

MTJ & Finite size effect Magnetic component along the X axis (x) (y) Co Ni ü Width<1µm, Co Stray Field is enough to reverse the magnetization in the Py. üStatistical distribution of the DW in the Py üStrong size effect. 1 x 3µm 0. 3 x 0. 9µm R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 0. 5 x 1. 5µm

Nature and origin of the DW in the MTJ Ni 0° (x) (y) 1 µm Simulation Magnetic component along the Y axis Formation of two 360° DW with two opposite Chirality R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Origin of the DW: Micromagnetic Simulation C S Single Domain 360° DW The « curling » direction of the magnetization on both edges determines The formation of the DW and its chirality. R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Magnetic Frustration In ‘Spin Ice’ Systems Kagomé Network Square Network Wang et al, Nature 439 (2006) 303 Favorables Pairs ‘ 3 In’ ‘ 2 In, 1 out’ Forbiden Paires ‘ 1 In, 2 Out’ ‘Spin Ice’ rule: Two In/ Two Out Nanostructures allow alternative methode to study the frustration: R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 ‘ 3 Out’

‘Spin Ice’: Kagomé Network Honeycomb Network 100 x 400 nm 80 x 320 nm Py/MTJ 60 x 240 nm LEEM 500 nm Fe XPEEM ØCompetition/ Synergy: Ø Exchange coupling Ø Dipolar Interaction Ø Stray Field…. Ø Short/long range order R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Magnetic Frustration In ‘Spin Ice’ Systems ‘’ 3 Out’’ ‘ 3 In’’ R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 Collab. F. Montaigne LPM - Nancy

Demagnetization: ‘low spin’ State. - Single initial state. - in-plane demagnetization - Random demagnetization - Decreasing AC Field R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Spin Ice: Dipolar Interaction. w 1: +M w 2: +0. 5*M Favorable Config. w 3: -0. 5*M w 4: -M w 5: -0. 5*M w 6: +0. 5*M Excluded Config. ‘’Pauli’’ w 7: M=0 w 8: M=0 R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Spin Ice: Dipolar Interaction. w 1: +M w 2: +0. 5*M Favorable Config. w 3: -0. 5*M w 4: -M w 5: -0. 5*M w 6: +0. 5*M Excluded Config ‘’Pauli’’ w 7: M=0 w 8: M=0 The network follow the ‘Spin Ice’ rule R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 N. Rougemaille et al. , PRL In press

Spin Ice: Dipolar Interaction. Distribution des états Distribution de l’aimantation Local magnetization per node: 0. 1467 M R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Spin Ice: Dipolar Interaction. Chirality 2 -4 -2 4 0 0 -2 -2 -4 -6 -4 0 2 4 0 -2 2 0 -2 -4 -6 4 6 0 -2 2 6 -4 0 4 2 4 -4 2 2 6 0 4 Ø Flux closures configuration are favorable Ø Micromagnetic simulation and Monte-Carlo Simulation Ø Long range interactions are important R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 -4 -4 2 0 0 2 2 -6 -6 2 0 4 0 2 0 0 -2 0 4 0 -6 4 4 -2 -2 0 4 -4 2 0 0 2 2 -4 -6 6 -4 0 0 -4 2 -4 4 -2 0 0 0 4 -2 -4 4 0 2 6 -2 0 2 -2 -4 4 -6 0 4 4 6 -2 -6 0 -4 0

Electronic confinement in Mg thin films Electronic Confinement m. XPS (dispersive plane mode): Local valance bande measurements (~1µm) 2. 6 e. V 10 mm 49 e. V (~3 mm 2) The Electron conduction is confined in the overlayers: • Few “quantum-well” sates are allowed • Modulation of the electron density near the R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 Fermi edge (EF)

Electronic confinement in Mg thin films Oxydation O 2 exposure ü O 2 ü Spontaneous Dissociation ü Sub-surface O 2 ML Mg oxidised ü Coalescence of Mg. O-like islands Iox/Itot R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 oxidation extent Goonewardene et al, Surf. Sci. 501, 102 (2002) Bungaro et al, PRL 79, 4433 (1997)

Electronic confinement and oxydation in Mg thin films Oxidation: LEEM/PEEM LEEM: morphology (atomic steps) XPEEM: chimestry (Oxyde component) The oxidation state depends on the thickness!! R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 L. Aballe et al, Phys. Rev. Lett. 93, 196103 (2004)

Local Spectroscopy µ-électronic µ-ARPES Band Structure R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 µ-XPD Photoelectrons Diffraction ELETTRA – Italy (2009)

Dynamical Processes: Chemical Waves Oxygen Waves Sub-surface Oxygen Waves Annihilation collision Two in one collision Two in two Novel class of chemical waves propagation: Bright wave correspond to the propagation of Oxygen via a conversion of surface oxygen to subsurface. R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010

Dynamical Process: Rh(110)/NO + H 2 (3 x 1)→(2 x 1) →c(2 x 4) →c(2 x 6) LEEM – field of view 20 mm R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010 micro-LEED Dispersive plane Schaak et al. ; Phys. Rev. Lett. 83, 1882 -1885 (1999) Schmidt et al; Chem. Phys. Lett. , 318, 549 -554 (2000)

Outlook • Powerful tool for studying surfaces, Interfaces et Nanostructures. • New upgrades (Aberration correctors) may allow to provide resolution compatible and complementary to the STM (<2 nm). • Development of in-situ preparation methods • High spectroscopic capabilities, fast imaging… • Open to users! R. Belkhou: Soft X-ray Microscopy – ICNMRE 2010 - SAFI Juillet 2010