Surface imaging of flux-closure domains in thick micron-size - PowerPoint PPT Presentation

Surface imaging of flux-closure domains in thick micron-size self-assembled dots: a combined LEEM/XMCD-PEEM study O.Fruchart Laboratoire Louis Néel (CNRS-UJF-INPG) Grenoble Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. http:/ / lab http:/ / lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Jan. 17th, 2007 Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.2 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ /

Scientific context: nanomagnetism Nanomagnetism: many new effects over the past 20 years …thanks to improvements in: Transport : GMR, CMR, TMR etc. Fabrication : films, lithography etc. Switching : precessional, spin torque, F/AF Characterization : structure, magnetism Materials : semiconductors, molecules, multiferroic Micromagnetic simulations Cf talk by F. Petroff C. R. Physique 6 ( 2 0 0 5 ) : Spintronics Boosted or new applications Memories : hard disks, MO disks, MRAMs Sensors : sensitivity, down-scaling, read heads Magnetic logic : prospective (reprogrammable) Why still bother with static / quasi-static magnetization configurations? * Prerequisite for integrating concepts into devices * Some properties modified at the nanoscale: exchange, length scales, anisotropy etc. Magnetism in reduced dim ensions, O. Fruchart, A. Thiaville, C. R. Physique 6 , 9 2 1 ( 2 0 0 5 ) Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.3 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Magnetization states: from macrospins to bulk Increasing size Macrospins Single domains Closure domains (flat) E. Bonet-Orozco et al, K. J. Kirk et al., M. Schneider et al., APL 7 7 , 2 9 0 9 ( 2 0 0 0 ) PRL 8 3 , 4 1 8 8 ( 1 9 9 9 ) APL 7 1 , 5 3 9 ( 1 9 9 7 ) Cf talk by C. H. Back Issues for fundamental physics Very few reports: * Nanomagnetism for 3D flux-closure magnetization? M. Hehn et al., Science 2 7 2 , 1 7 8 2 ( 1 9 9 6 ) R. Hertel et al., PRB 6 0 , 7 3 6 6 ( 1 9 9 9 ) * From nanostructures to bulk W . Rave et al., JMMM 1 9 0 , 3 3 2 ( 1 9 9 8 ) J. K. Ha et al., PRB 6 7 , 2 2 4 4 3 2 ( 2 0 0 3 ) Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.4 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Motivations for studying 3D magnetization configurations � Micromagnetic state and hysteresis of domain walls (not domains) � Confine domain walls in nanostructures: • Single walls > low complexity • Walls are pinned > can be manipulated • Constraints can be put on the wall � Use self-assembled nanostructures for higher quality Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.5 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe/Mo(110) dots: growth and structure Pulsed Laser Deposition (DLP) in UHV Atomically flat facets Nd:YAG pulsed laser RHEED beam cc(110) / Al 2 O 3 (11-20) Target cc=Mo, W, Nb, etc. t n e d i c n I Sample n o i t c e l f e R Shape in real space Fe/ Mo(110) @ 450°C (101) ( 1 1 0 ) (110) [ 0 0 1 ] (100) (011) (101) [ 1 -1 0 ] AFM, 10x10 µ m P.-O. Jubert et al. , JMMM 2 2 6 , 1 8 4 2 ( 2 0 0 1 ) P.-O. Jubert et al. , PRB6 4 , 1 1 5 4 1 9 ( 2 0 0 2 ) Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.6 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Wulff-Kaischev theorem Wulff’s theorem Wulff Kaishev’s theorem Free standing crystal Supported crystal (growth on surfaces) γ i γ i h i h i h int h j γ j No facet with high surface energy Truncated crystal With strain : P. Müller and R. Kern, Simulations or more complex models (e.g. small dots) Surf. Sci. 4 5 7 , 2 2 9 ( 2 0 0 0 ) Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.7 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe/Mo(110) dots: magnetism Hysteresis loops Magnetization states Rem anent states after saturation along [ 0 0 1 ] [1-10] (110) [1-10] (110) [001] [001] 500 nm Magn. Force. Micr. 1.0 Collabo. Y. Samson (CEA-Grenoble) // [001] Magnetization 0.5 // [1-10] // [110] 0.0 -0.5 300K DIAMOND LANDAU -1.0 Finite-differences m ethod ( JC Toussaint) -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 P.-O. Jubert et al. , Phys. Rev. B6 4 , 1 1 5 4 1 9 ( 2 0 0 2 ) Applied field µ 0 H (T) P.-O.Jubert et al. , Europhys. Lett. 6 3 , 1 3 5 ( 2 0 0 3 ) Question: Why two magnetic states can occur? (Landau state has lower energy) Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.8 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ /

Reminder: the Van den Berg construction (model) Hypothesis mc = e 0 Infinitely soft material ( K =0) 2D geometry (neglect thickness) Z = e 0 Zero external magnetic field Size >> all magnetic length scales (wall width) ex ⎯→ ⎯ e 0 Solution d = e 0 = Looking for a solution with : (no volume charges) -div M 0 « Flux closure » = M . n 0 (no surface charges) y x ∂ ∂ M M = + y x div M ∂ ∂ x y H. A. M. Van den Berg, J. Magn. Magn. Mater. 4 4 , 2 0 7 ( 1 9 8 4 ) Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.9 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Van den Berg construction: example for self-assembled dots Landau Diamond Models based on sandpiles Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.10 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe/Mo(110) dots: micro-SQUID Measurement of single dots Micromagnetic calculations AFM, 2 µ m x 2 µ m ϕ = + 50° ϕ = + 40° H ext H ext 57 mT -5.8 mT Coll: W . W ernsdorfer, LLN-Grenoble O. Fruchart et al. , PRB 7 0 ( R) , 1 7 2 4 0 9 ( 2 0 0 4 ) D. Mailly, LPN-Paris Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.11 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe/Mo(110) dots – Issues to be clarified Unclear MFM patterns Bloch points predicted by simulations � Need to image surface magnetization with high resolution for better insight. Laboratoire Louis N Louis Né éel, Grenoble el, Grenoble, France , France. . Laboratoire Laboratoire Louis Néel, Grenoble, France. Olivier Fruchart – Magnetism Workshop, SOLEIL –Jan.2006 – p.12 http:/ / lab lab- - neel.grenoble.cnrs.fr neel.grenoble.cnrs.fr/ / them es them es/ couches/ / couches/ ext ext / / http:/ / http:/ / lab-neel.grenoble.cnrs.fr/ them es/ couches/ ext/