Staffa Island, Scotland SPIE - Spintronics – San Diego 28 Aug – 1 Sep 2016
O. Fruchart 1. Institut NÉEL, Univ. Grenoble Alpes / CNRS, France 2. SPINTEC, Univ. Grenoble Alpes / CNRS / CEA-INAC, France www.spintec.fr email: olivier.fruchart@cea.fr Slides: http://fruchart.eu/slides SPIE - Spintronics – San Diego 28 Aug – 1 Sep 2016
Proposal for a 3D race-track memory What has been done? Dreams? Challenges? S. S. P. Parkin, Science 320, 190 (2008) Scientific American, June, 76 (2009) + patents (IBM) 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
Steady progress of HDD, however: incremental, keeping the design 1956 Today Staggering areal density Increasing fundamental and technological bottlenecks Any 2D-based technology is bound to face an end 2000 2014 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
Competing technologies go 3D 24-layer 3D NAND Flash 1Gb/mm2 → 600Gb/in2... Magnetic mass storage may only remain for niche applications K. T. Park et al., IEEE J. Sol. State Circuits 50 (1), 204 (2015) 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
ACHIEVEMENTS AROUND DW DEVICES Logic (field-driven) Memory (current-driven) L. Thomas et al., IEEE International Electron D. A. Allwood et al., Science 309, 1688 (2005) Devices meeting (2011) 2D demonstrators. Competitive? 3D appealing. Probably a dream with very severe bottlenecks 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
Motivation 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
Synthesis strategy Our focus: identify bottlenecks Synthesis: deep and structured pores Anodization of aluminum -> template Domain wall types in cylinders H. Masuda, Science 268, 1466-1468 (1995) S. Da-Col et al., PRB (R) 89, 180405, (2014) Electroplating -> Magnetic wires Move domain walls Simple metals and alloys : Co, Ni, Fe 20 Ni 80 , Co 20 Ni 80 S. Da-Col et al., APL109, 062406 (2016) Tackle dipolar interactions S. Da Col et al., APL 98, 112501 (2011) 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
DOMAIN WALLS EXPECTED IN CYLINDERS 2 2 𝐸 ≳ 7𝛦 d 𝐸 ≲ 7𝛦 d Transverse wall Bloch-point wall H. Forster et al., J. Appl. Phys. 91, 6914 (2002) Sometimes improperly A. Thiaville, Y Nakatani / B. Hillebrands, A. Thiaville (ed.), called vortex wall Spin dynamics in confined magnetic structures III, 101, 161-206 (2006) What is a Bloch point? A magnetization texture with local cancellation of the magnetization vector R. Feldkeller, Z. Angew. Physik 19, 530 (1965) W. Döring, J. Appl. Phys. 39, 1006 (1968) 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
EXPECTED PRECESSIONAL DYNAMICS LLG equation ‘Once - only’ Walker event H H Dynamically locked Dynamically unstable A. Thiaville et al., in Spin dynamics in confined magnetic structures III, p.161-206 (2006) ‘Once - only’ circulation Walker Right-hand rule vs direction of motion Same physics predicted (later) for tubes 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
TOPOLOGY OF TRANSVERSE-VORTEX WALLS Wires with square cross-section Side 44nm Side 30nm Transverse walls have both transverse and vortex features 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
TOPOLOGY OF DOMAIN WALLS Two topologies for domain walls Transverse and vortex walls share the same topology Transverse Vortex Also identical to Bloch and Néel walls for perp magnetization Néel Bloch Walker field = changes of texture within the same family Bloch-point walls have a Transverse-Vortex (TVW) different topology Bloch-point (BPW) 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
EXTENDED PHASE DIAGRAM OF WALLS IN 1D Analytics and simulation Covers from flat strip to square/disk wires Bloch-point walls should exist for a wide range of non-circular wire Review chapter : S. Jamet et al., in Magnetic Nano- and Microwires: Design, synthesis, properties and applications, M. Vázquez Ed., Woodhead (2015) (arXiv:1412.0679) 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
Motivation Expectations for domain walls 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
NUCLEATE DOMAIN WALLS BOTTLENECK: how to nucleation domain walls in cylindrical wires? Route 1: bends Route 2: diameter modulations FeNi AFM SEM AFM MFM MFM NB: similar to procedure with strips Increase of diameter induces an T. Taniyama, Phys. Rev. Lett. 82, 2780 (1999) energy barrier for domain walls S. Da-Col et al., Appl. Phys. Lett. 109, 062406 (2016) 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
Motivation Expectations for domain walls Nucleate walls 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
XMCD-PEEM TECHNIQUE X-Ray magnetic circular dichroism Photo-Emission Electron Microscopy Element selectivity Magnetic sensitivity Synchrotron-based Secondary electrons -> surface sensitive 25nm resolution in best case 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
IMAGE BOTH WIRES AND SHADOW Locate walls Image domain walls FeNi FeNi Beam along wire Beam across wire Non-trivial patterns Need for modeling 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
MODELING SHADOW XMCD-PEEM SHADOW XMCD-PEEM SIMULATION OF CONTRAST Example: Bloch-point wall S. Jamet et al., PRB92, 144428 (2015) 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
TWO WALL TOPOLOGIES OBSERVED Bloch-point walls Transverse walls Experiment Experiment Simulation Simulation WIRE SHADOW Breaking of symmetry Orthoradial curling Symmetry with respect to Also imaged with electron plane perpendicular to axis holography: N. Bizières et al., Nanolett. 13, 2053 (2013) S. Da-Col et al., Phys. Rev. B (R) 89, 180405, (2014) 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
Motivation Identify walls Expectations for domain walls Nucleate walls 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
MOVE DOMAIN WALLS FeNi Quasistatic motion Pinning fields Measured distribution SEM AFM MFM Electron holography – No clear correlation with structure M. Staňo et al., JMMM, submitted S. Da-Col et al., Optimization of Appl. Phys. Lett. 109, 062406 (2016) material / structure 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
DYNAMICS – SELECTION OF CIRCULATION CoNi Modulated diameter to keep domain walls in wire Focus on wire Focus on shadow Selection of circulation (to be confirmed) Final Initial Field pulse Field pulse 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
DYNAMICS – DOMAIN WALL TRANSFORMATION BPW CW BPW CW TW Initialized +20mT +20mT TW BPW CCW TW -20mT -20mT THE DARK SIDE BPW CCW TW -30mT BPW CW 2µm BPW CW +15mT +15mT BPW CCW Switch circulation Initialized +20mT -20mT No topological BPW CW BPW CW TW protection Work on material +30mT -15mT -15mT A. Wartelle, in preparation 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
Motivation Identify walls Expectations for Move walls domain walls Nucleate walls 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
Magnetization process Applies to remagnetization with wall motion Dominated by shape anisotropy for soft magnetic materials Nucleation - Propagation Ni, diameter 39nm Remagnetization loops Minor loops Magnetic induction (T) Shear largely dominated by Solutions are needed to avoid inter-wire dipolar interactions cross-talk -> Cross-talk 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
HARDWARE OPTION – REDUCE POROSITY Shear related to demagnetization factor Application to domain walls 𝐹 d = 1 2 3𝑞 − 1 cos 2 𝜄 2 𝜈 0 𝑁 s 2 2 Matrix 𝜌 𝑒 𝑞 = porosity: 𝐸 2 3 A. Encinas-Oropesa et al., PRB 63, 104415 (2001) Scalable to very low porosity Reduce porosity Interaction 𝑞 = 0.3% Apply atomic layer deposition to reduce inner diameter at constant pitch FORC measurements Coercivity Coll. Univ. Hamburg & Erlangen S. Da Col et al., APL 98, 112501 (2011) 1 st Sep. 2016 Olivier FRUCHART Challenges for a 3D race-rack memory SPIE 2016 Spintronics – San Diego
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