Dreams for a 3D storage device Fundamentals: curved and 3D magnetism - PowerPoint PPT Presentation

O. Fruchart 1 1. SPINTEC, Univ. Grenoble Alpes / CNRS / CEA-INAC, France 2. Institut NÉEL, Univ. Grenoble Alpes / CNRS, France www.spintec.fr email: olivier.fruchart@cea.fr Slides: http://fruchart.eu/slides Intermag2018 – Singapore – 24 th April

Dreams for a 3D storage device Fundamentals: curved and 3D magnetism S. S. P. Parkin, Science 320, 190 (2008) + patents (IBM) R. Streubel, J.Phys.D: Appl.Phys. 49, 363001 (2016) Note: 3D devices make the decision! K. T. Park et al., IEEE J. Sol. State Circuits 50 (1), 204 (2015) A. Fernandez-Pacheco, Nat. Comm. 8, 15756 (2017) Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

DOMAIN WALLS IN CYLINDERS What is a Bloch point? Domain wall topology of domain walls in 1D Transverse Vortex Néel Bloch Magnetization texture with local vanishing of magnetization R. Feldkeller, Z. Angew. Physik 19, 530 (1965) W. Döring, Transverse-Vortex (TVW) Bloch-point (BPW) J. Appl. Phys. 39, 1006 (1968) H. Forster, JAP91, 6914 (2002); A. Thiaville, Spin dynamics in confined magnetic structures III, 101, (2006). Review : S. Jamet, in Magnetic Nano- and Microwires, M. Vázquez Ed., Woodhead (2015) (arXiv:1412.0679) Transverse and vortex walls for IP have same topology: subject to Walker field Bloch-point walls have a different topology Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

MOTIVATION FOR MODULATIONS Devices Physics: trap for domain wall Need for digital coding Basis for pump-probe experiment and resetting the initial state Pathways Modulation of diameter Modulation of composition Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

Standard processes Specific aspects Anodization of Electroplating Pulsed or multi-steps anodization aluminum -> template -> Magnetic wires S. Bochmann et al., submitted Simple metals and H. Masuda, Science 268, alloys : Co, Ni, 1466-1468 (1995) Fe 20 Ni 80 , Co 20 Ni 80 Work under way… Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

EXISTING BACKGROUND Simulations / Theory Experiments D. Allende, PRB80, 174402 (2009) K. Pitzschel, JAP109, 033907 (2011) [S] Seminal work. Thick wires, Global M(H) domain walls fill part of the wire Imaging D. Allende, PRB83, 174452 (2011) stray field at [T] Seminal work. Complex modulations analytics. No scaling law. No domain wall A. A. Ivanov, Phys. Sol. State 53, 2441 (2011) [T] Fluctuations of diameters, link with E. Berganza, Sci. Rep. 6, 29702 (2016) Kondorski model. Not single item First hint of wall motion. No trend extracted M. Franchin, PRB84, 094409 (2011) [S] Particular case. No general view D. Salazar-Aravena, JMMM346, 171 (2013) [S] Wires and tubes. Interesting, however no scaling law. Our goal here: Tractable analytics -> Scaling law for trends, although not perfect Simulations -> Confirm scaling law, and quantitative approach Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

Analytics: principle Principle Modeling the modulation Two arcs of circles Domain wall modelled as a sphere (reasonable for moderate diameter) � � � � � � Dipolar energy 3�/5 � � � � 3�/5 � � � � � � � /3 � � � � /3 � Exchange energy Zeeman energy � � � � �′ d�′ � � �′ d�′ 2� � � � �� � 2� � � � �� � J. Fernandez-Roldan, submitted ��/� ��/� Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

Analytics: results H Energy landscape Wall position and depinning Transverse wall z final 1 H≤0 Energy (a.u.) 0 H 1 min Pinned -1 H 2 >H crit Depinning field Unpinned -2 � � � -200 -100 0 100 200 � � � � 9� � 10� �� � ���� 1 + DW position(nm) 27 � � + � � � � 5 Textbook case of the Becker-Kondorski model: � � � � ����� � � � ����� � � � R. Becker, Phys. Z.S. 33, 905 (1932) E. Kondorski, Phys. Z. Sowjetunion 11, 597 (1937) Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

Analytics: results Critical field Critical current (local) J e - H app app � � � � � � � � � � 9� � 10� �� � �� � � � + � � � � � � 9�� � 10� �� � ���� = 1 + � ���� 1 + 27 � � + � � � � 5 1 + �� �� 27 � � + � � � � 5�� � 400  = 100 nm R 1 (nm) R 1 (nm) 5 5, 10, 15, 20 300 10 15  0 H crit (mT) � = 100�� 20 200 J crit (a.u.) 100 0 5 10 15 20 25 R 2 (nm) R 2 (nm) Almost linear with R 2 -R 1 Further (R 1 /R 2 ) 2 reduction against j 0 Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

Simulations: methods Tools � = 1 � = 1 For quasistatics (energy landscape) Modified LLG �� �� = � � � � × � + � � × � � � + � � �� � � �� �� � � � � �� � × �� � � � �� � �� � damping effective field driving force due to spin transfer torque Finite elements for smooth description of the wire http://feellgood.neel.cnrs.fr/ DW DW Typical experiment � � = 5 nm � � = 5 nm � � = 12.5 nm � � = 12.5 nm � = 100 nm � = 100 nm Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

Simulations versus model Principle of pinning Modulation length J. Fernandez-Roldan, � � = 5 nm � � = 5 nm submitted � � = 7.5 nm � � = 7.5 nm � = 100 nm � = 100 nm Modulation strength Analytics reasonably valid, except for short modulations � � � � ����� � � � ����� � � � Scaling law valid: Under way Finite-length modulation Current-induced depinning Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

NEEL / SPINTEC A. De Riz, B. Trapp, C. Thirion, JC. Toussaint, O. Fruchart, D. Gusakova ICMM-CSIC, Madrid J. Fernandez-Roldan This project has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n ° 309589 (M3d). Olivier FRUCHART 24 April 2018 Domain wall motion in cylindrical nanowires with modulated diameter Intermag 2018, Singapore

www.spintec.fr email: olivier.fruchart@cea.fr Slides: http://fruchart.eu/slides Intermag2018 – Singapore – 24 th April