Atomic- and Nanoscale Magnetism (NanoScience and Technology)

This book provides a comprehensive overview of the fascinating recent developments in atomic- and nanoscale magnetism, including the physics of individual magnetic adatoms and single spins, the synthesis of molecular magnets for spintronic applications, and the magnetic properties of small clusters as well as non-collinear spin textures, such as spin spirals and magnetic skyrmions in ultrathin films and nanostructures. Starting from the level of atomic-scale magnetic interactions, the book addresses the emergence of many-body states in quantum magnetism and complex spin states resulting from the competition of such interactions, both experimentally and theoretically. It also introduces novel microscopic and spectroscopic techniques to reveal the exciting physics of magnetic adatom arrays and nanostructures at ultimate spatial and temporal resolution and demonstrates their applications using various insightful examples. The book is intended for researchers and graduate students interested in recent developments of one of the most fascinating fields of condensed matter physics. Preface 6 Contents 8 Contributors 15 Part I From Single Spins to Complex Spin Textures 20 1 Magnetic Spectroscopy of Individual Atoms, Chains and Nanostructures 21 1.1 Introduction 21 1.2 Single Atom Magnetometry 22 1.2.1 SPSTS on Individual Atoms 22 1.2.2 Single-Atom Magnetization Curves 25 1.2.3 Magnetic Field Dependent Inelastic STS 27 1.3 Measurement of the RKKY Interaction 29 1.3.1 RKKY Interaction Between a Magnetic Layer and an Atom 29 1.3.2 RKKY Interaction Between two Atoms 29 1.3.3 Dzyaloshinskii–Moriya Contribution to the RKKY Interaction 32 1.4 Dilute Magnetic Chains and Arrays 35 1.5 Logic Gates and Magnetic Memories 37 1.6 Conclusions 40 References 41 2 Scanning Tunneling Spectroscopies of Magnetic Atoms, Clusters, and Molecules 43 2.1 Tuning the Kondo Effect on the Single-Atom Scale 44 2.1.1 Co Atoms on a Quantum Well System 44 2.1.2 Kondo Effect in CoCun Clusters 47 2.1.3 Two-Site Kondo Effect in Atomic Chains 49 2.1.4 Spectroscopy of the Kondo Resonance at Contact 52 2.2 Magnetic Molecules 57 2.3 Graphene on Ir(111) 60 2.4 Ballistic Anisotropic Magnetoresistance of Single Atom Contacts 61 2.5 Shot Noise Spectroscopy on Single Magnetic Atoms on Au(111) 64 References 68 3 Electronic Structure and Magnetism of Correlated Nanosystems 72 3.1 Electron Correlations in Magnetic Nanosystems 72 3.2 Realistic Impurity Models for Correlated Electron Systems 74 3.3 Multiorbital Quantum Impurity Solvers 75 3.4 Transition Metal Impurities on Metallic Substrates 77 3.5 Hund's Impurities on Substrates 78 References 85 4 Local Physical Properties of Magnetic Molecules 88 4.1 High-Resolution Atomic Force Microscopy 88 4.2 Utilizing the Smoluchowski Effect to Probe Surface Charges and Dipole Moments of Molecules with Metallic Tips 91 4.3 Magnetic Exchange Force Microscopy and Spectroscopy 95 4.4 Adsorption Geometry of Co-Salen 98 4.5 Evidence for a Magnetic Coupling Between Co-Salen and NiO(001) 101 References 103 5 Magnetic Properties of One-Dimensional Stacked Metal Complexes 105 5.1 Introduction 105 5.2 Towards Molecular Spintronics 106 5.3 Paramagnetic 3d-Transition-Metal Complexes with Terdentate Pyridine-Diimine Ligands 111 5.3.1 Synthesis of Novel Mono-, Di- and Trinuclear Iron(II) Complexes 111 5.3.2 Electronic and Magnetic Properties 114 5.3.3 Molecules on Surfaces 118 5.4 One-Dimensional Stacked Metallocenes 119 5.4.1 Different Metal Centers 120 5.4.2 More Stacking 124 References 130 6 Designing and Understanding Building Blocks for Molecular Spintronics 133 6.1 Introduction 133 6.2 Local Pathways in Exchange Spin Coupling 136 6.2.1 Transferring a Green's Function Approach to Heisenberg Coupling Constants J from Solid State Physics to Quantum Chemistry 136 6.2.2 Decomposing J into Local Contributions 139 6.2.3 Application to Bismetallocenes: Through-Space Versus Through-Bond Pathways 141 6.3 Chemically Controlling Spin Coupling 143 6.3.1 Photoswitchable Spin Coupling: Dithienylethene-Linked Biscobaltocenes 143 6.3.2 Redox-Switchable Spin Coupling: Ferrocene as Bridging Ligand 144 6.3.3 Introducing Spins on the Bridge: A Systematic Study 146 6.4 From Spin Coupling to Conductance 147 6.5 Conclusion 150 References 150 7 Magnetic Properties of Small, Deposited 3d Transition Metal and Alloy Clusters 153 7.1 Introduction 153 7.2 Experiments 155 7.2.1 Cluster Sample Preparation 155 7.2.2 X-Ray Absorption and Magnetic X-Ray Spectroscopy 158 7.3 3d Metal Cluster 159 7.3.1 Chromium Clusters 160 7.3.2 Cobalt Clusters 165 7.4 Alloy Clusters 166 7.4.1 Co Alloy Clusters 167 7.4.2 FePt 167 7.5 Magnetism and Chemical Reactivity 169 7.5.1 CoO 170 7.5.2 CoPd Dimers 171 7.5.3 CoRh Oxidised Clusters 171 7.6 Summary 174 References 175 8 Non-collinear Magnetism Studied with Spin-Polarized Scanning Tunneling Microscopy 178 8.1 Introduction 178 8.2 Magnetic Interactions 179 8.3 Spin-Polarized Scanning Tunneling Microscopy 180 8.4 Spin Spirals with Unique Rotational Sense 182 8.4.1 A Manganese Monolayer on W(110) and W(001) 182 8.4.2 Fe and Co Chains on Ir(001): Magnetism in One Dimension 183 8.5 Nanoskyrmion Lattices in Fe on Ir(111) 186 8.6 Magnetic Skyrmions in Pd/Fe on Ir(111) 188 8.6.1 Pd/Fe/Ir(111): Magnetic Phases 188 8.6.2 Isolated Skyrmions: Material Parameters and Switching 189 8.6.3 Non-collinear Magnetoresistance 191 8.7 (SP-)STM of Higher Layers of Fe on Ir(111) 192 8.7.1 Influence of Strain Relief and Temperature 192 8.7.2 Influence of Magnetic and Electric Field 194 8.8 Conclusion 195 References 195 9 Theory of Magnetic Ordering at the Nanoscale 198 9.1 Stability of Magnetic Quasiparticles 198 9.2 Higher-Order Complex Magnetic Interactions 199 9.3 Two-Dimensional Quasiparticles: Interfacial Skyrmions 201 9.4 One-Dimensional Quasiparticles 207 9.5 Zero-Dimensional Magnetic Objects 210 References 214 10 Magnetism of Nanostructures on Metallic Substrates 216 10.1 Introduction 216 10.2 Indirect Magnetic Exchange 218 10.3 The Kondo-Versus-RKKY Quantum Box 220 10.4 Underscreening and Overscreening 223 10.5 Inverse Indirect Magnetic Exchange 225 10.6 Frustrated Quantum Magnetism 227 10.7 Conclusions 230 References 230 Part II Spin Dynamics and Transport in Nanostructures 233 11 Magnetization Dynamics on the Atomic Scale 234 11.1 Telegraphic Noise Experiments on Nanomagnets 236 11.2 Current-Induced Magnetization Switching 238 11.3 Spin Transfer-Torque Based Pump-Probe Experiments 243 11.4 The Oersted Field Induced by a Tunnel Current 246 11.5 Electric Field-Induced Magnetoelectric Coupling 247 11.6 Spin-Polarized Field Emission 249 11.7 Magnetization Dynamics of Quasiclassical Magnets 252 11.8 Magnetization Dynamics of Quantum Magnets 256 References 260 12 Magnetic Behavior of Single Nanostructures and Their Mutual Interactions in Small Ensembles 262 12.1 Introduction 262 12.2 Experimental Details 264 12.3 The Physics of Single Nanostructures and Small Ensembles of Nanostructures 268 12.4 Conclusions 276 References 277 13 Fluctuations and Dynamics of Magnetic Nanoparticles 279 13.1 Introduction 279 13.2 Dynamics of Spins Coupled to Conduction Electrons 280 13.3 Tight-Binding Spin Dynamics 281 13.4 Linear-Response Theory 283 13.5 Correlated Conduction Electrons 285 13.6 Critical Properties and Magnetization Reversal in Nanosystems 287 13.6.1 Crossover Temperatures of Finite Magnets 287 13.6.2 Switching of Nanoparticles in Systems with Long-Range Interactions 290 13.7 Control of Ferro- and Antiferromagnetic Domain Walls with Spin Currents 291 13.8 Conclusions 294 References 295 14 Picosecond Magnetization Dynamics of Nanostructures Imaged with Pump–Probe Techniques in the Visible and Soft X-Ray Spectral Range 297 14.1 Direct Observation of Spin-Wave Packets in Permalloy 299 14.2 Time-Resolved Imaging of Domain Pattern Destruction and Recovery 302 14.3 Conclusion 309 References 309 15 Magnetic Antivortices 311 15.1 Introduction 311 15.2 Magnetic Singularities – Antivortices 313 15.3 Antivortex Generation 315 15.4 Higher Winding Numbers 321 15.5 Thickness Dependence 322 15.6 Antivortices Influenced by Static and Dynamic External Magnetic Fields 323 15.7 Bias Field Dependence 326 15.8 Annihilation Process 329 15.9 Conclusion 333 References 334 16 Nonequilibrium Quantum Dynamics of Current-Driven Magnetic Domain Walls and Skyrmions 336 16.1 Introduction 336 16.2 Model and Equations of Motion 338 16.3 Ferromagnetic Chiral Domain Walls 341 16.4 Steep Domain Walls 344 16.5 Skyrmion Creation 347 16.6 Conclusions 352 References 352 17 Imaging the Interaction of Electrical Currents with Magnetization Distributions 354 17.1 Introduction 354 17.1.1 Spin-Transfer Torque 354 17.1.2 SEMPA as a Unique Tool for Magnetic Imaging 356 17.2 Determining the Nonadiabaticity Parameter from the Displacement of Magnetic Vortices 357 17.2.1 Proposal from Theory 358 17.2.2 Sample Preparation 358 17.2.3 Experimental Results 359 17.3 Applications of Vectorial Magnetic Imaging 360 17.4 Development of Time-Resolved SEMPA 362 17.4.1 Concept 363 17.4.2 Experimental Setup 364 17.4.3 Results and Analysis 365 17.5 Conclusion and Outlook 366 References 368 18 Electron Transport in Ferromagnetic Nanostructures 370 18.1 Introduction 370 18.2 Domain Walls 372 18.3 Domain-Wall Dynamics 375 18.4 Domain-Wall Mass 379 18.5 Fast Generation of Domain Walls with Defined Chirality in Nanowires 380 18.6 Time-resolved imaging of nonlinear magnetic domain-wall dynamics in ferromagnetic nanowires 385 18.7 Conclusion 391 References 392 Index 395 Front Matter ....Pages i-xix Front Matter ....Pages 1-1 Magnetic Spectroscopy of Individual Atoms, Chains and Nanostructures (Jens Wiebe, Alexander A. Khajetoorians, Roland Wiesendanger)....Pages 3-24 Scanning Tunneling Spectroscopies of Magnetic Atoms, Clusters, and Molecules (Jörg Kröger, Alexander Weismann, Richard Berndt, Simon Altenburg, Thomas Knaak, Manuel Gruber et al.)....Pages 25-53 Electronic Structure and Magnetism of Correlated Nanosystems (Alexander Lichtenstein, Maria Valentyuk, Roberto Mozara, Michael Karolak)....Pages 55-70 Local Physical Properties of Magnetic Molecules (Alexander Schwarz)....Pages 71-87 Magnetic Properties of One-Dimensional Stacked Metal Complexes (Tabea Buban, Sarah Puhl, Peter Burger, Marc H. Prosenc, Jürgen Heck)....Pages 89-116 Designing and Understanding Building Blocks for Molecular Spintronics (Carmen Herrmann, Lynn Groß, Bodo Alexander Voigt, Suranjan Shil, Torben Steenbock)....Pages 117-136 Magnetic Properties of Small, Deposited 3d Transition Metal and Alloy Clusters (Michael Martins, Ivan Baev, Fridtjof Kielgast, Torben Beeck, Leif Glaser, Kai Chen et al.)....Pages 137-161 Non-collinear Magnetism Studied with Spin-Polarized Scanning Tunneling Microscopy (Kirsten von Bergmann, André Kubetzka, Oswald Pietzsch, Roland Wiesendanger)....Pages 163-182 Theory of Magnetic Ordering at the Nanoscale (Elena Vedmedenko)....Pages 183-200 Magnetism of Nanostructures on Metallic Substrates (Michael Potthoff, Maximilian W. Aulbach, Matthias Balzer, Mirek Hänsel, Matthias Peschke, Andrej Schwabe et al.)....Pages 201-217 Front Matter ....Pages 219-219 Magnetization Dynamics on the Atomic Scale (Stefan Krause, Roland Wiesendanger)....Pages 221-248 Magnetic Behavior of Single Nanostructures and Their Mutual Interactions in Small Ensembles (Stefan Freercks, Simon Hesse, Alexander Neumann, Philipp Staeck, Carsten Thönnissen, Eva-Sophie Wilhelm et al.)....Pages 249-265 Fluctuations and Dynamics of Magnetic Nanoparticles (Elena Vedmedenko, Michael Potthoff)....Pages 267-284 Picosecond Magnetization Dynamics of Nanostructures Imaged with Pump–Probe Techniques in the Visible and Soft X-Ray Spectral Range (Philipp Wessels, Markus Drescher)....Pages 285-298 Magnetic Antivortices (Matthias Pues, Guido Meier)....Pages 299-323 Nonequilibrium Quantum Dynamics of Current-Driven Magnetic Domain Walls and Skyrmions (Martin Stier, Michael Thorwart)....Pages 325-342 Imaging the Interaction of Electrical Currents with Magnetization Distributions (Robert Frömter, Edna C. Corredor, Sebastian Hankemeier, Fabian Kloodt-Twesten, Susanne Kuhrau, Fabian Lofink et al.)....Pages 343-358 Electron Transport in Ferromagnetic Nanostructures (Falk-Ulrich Stein, Guido Meier)....Pages 359-383 Back Matter ....Pages 385-390