Atomic- and Nanoscale Magnetism (eBook)

Roland Wiesendanger studied physics at the University of Basel, Switzerland, where he received his Ph.D. in 1987 and his habilitation degree in 1990, working in the field of scanning tunnelling microscopy and related techniques. In 1992 he accepted a Full Professor position at the University of Hamburg, related to the launch of the Microstructure Advanced Research Center Hamburg. In Hamburg, Roland Wiesendanger initiated the Center of Competence in Nano-scale Analysis, the Interdisciplinary Nanoscience Center Hamburg, the Collaborative Research Center of the German Research Foundation entitled "Magnetism from single atoms to nanostructures", and the Free and Hanseatic City of Hamburg Cluster of Excellence "Nanospintronics". Since the late 80s, Roland Wiesendanger has pioneered the technique of spin-polarized scanning tunnelling microscopy (SP-STM) and spectroscopy, which allowed the first real-space observation of magnetic structures at the atomic level. He also contributed significantly to the development of magnetic force microscopy (MFM) and magnetic exchange force microscopy (MExFM). Roland Wiesendanger is author or co-author of about 600 scientific publications and 2 textbooks, and editor or co-editor of 8 monographs. He has received numerous scientific awards and honours, including the American Vacuum Society’s Nanotechnology Recognition Award in 2010, the first Heinrich Rohrer Grand Medal and Prize in 2014, and the Julius Springer Prize for Applied Physics in 2016. He is an elected member of the German Academy of Sciences "Leopoldina", the Hamburg Academy of Sciences, the German Academy of Technical Sciences "acatech", the Polish Academy of Sciences, and the European Academy of Sciences "EURASC". Additionally, he is a Fellow of the American Vacuum Society and the Surface Science Society of Japan. In 2015 he received an Honorary Doctor degree from the Technical University of Poznan.

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