University of Groningen
Controlling spins in nanodevices via spin-orbit interaction, magnons and heat
Das, Kumar Sourav
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Publication date: 2019
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Das, K. S. (2019). Controlling spins in nanodevices via spin-orbit interaction, magnons and heat. University of Groningen.
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Controlling Spins in Nanodevices
via
Spin-Orbit Interaction, Magnons and Heat
Curved Nanomembranes for Topological Quantum Computation
Zernike Institute PhD thesis series 2019-15 ISSN: 1570-1530
ISBN: 978-94-034-1625-0
ISBN: 978-94-034-1624-3 (electronic version)
The work described in this thesis was performed in the research group Physics of Nanode-vices of the Zernike Institute for Advanced Materials at the University of Groningen, the Netherlands. This work was realized using NanoLabNL (NanoNed) facilities and is part of the Future and Emerging Technologies (FET) programme within the Seventh Framework Pro-gramme for Research of the European Commission, under FET-Open Grant No. 618083 (CN-TQC). This work is supported by the Zernike Institute for Advanced Materials and is (partly) financed by the NWO Spinoza prize awarded to Prof. B. J. van Wees by the Netherlands Or-ganisation for Scientific Research (NWO).
Typeset using LATEX.
Cover art: An illustration of a spinning electron at the heart of a microchip, representing the vision of spintronic-based microprocessors of the future.
Cover design: SVDH Media, background image from Adobe Stock. Printed by: Proefschriftmaken (www.proefschriftmaken.nl)
Controlling Spins in Nanodevices
via
Spin-orbit Interaction, Magnons and Heat
PhD Thesis
to obtain the degree of PhD at the University of Groningen
on the authority of the Rector Magnificus Prof. E. Sterken
and in accordance with the decision by the College of Deans.
This thesis will be defended in public on
Friday 17 May 2019 at 14.30 hours
by
Kumar Sourav Das
born on 18 October 1988 in Burdwan, India
Supervisor
Prof. B. J. van Wees
Co-Supervisor Dr. I. J. Vera-Marun Assessment committee Prof. G. E. W. Bauer Prof. A. Fert Prof. T. Jungwirth
Contents
1 Introduction 1
1.1 Spintronics . . . 1
1.2 Motivation and outline . . . 3
References . . . 5
2 Concepts 9 2.1 Electrical spin injection . . . 10
2.1.1 Spin injection from a ferromagnet into a non-magnetic material 10 2.1.2 Spin injection via spin-orbit effects . . . 10
2.2 Non-local spin valves . . . 13
2.2.1 1-dimensional diffusive spin transport . . . 15
2.2.2 Hanle spin precession measurements . . . 15
2.3 Thermoelectric effects . . . 17
2.3.1 The Seebeck effect . . . 18
2.3.2 The Peltier effect . . . 19
2.3.3 The anomalous Nernst effect . . . 19
2.4 Spin transport in a magnetic insulators . . . 20
2.4.1 Magnons . . . 20
2.4.2 The spin-mixing conductance . . . 22
2.4.3 Electrical injection and detection of magnons . . . 23
2.4.4 Thermal magnon injection via the spin Seebeck effect . . . 24
References . . . 25
3 Experimental methods 33 3.1 Device fabrication techniques . . . 34
3.1.1 Deep-UV lithography . . . 36
Contents
3.1.2 Electron beam lithography . . . 37
3.1.3 Focussed ion beam etching . . . 37
3.1.4 Physical vapour deposition . . . 38
3.2 Measurement setups . . . 39
3.3 Lock-in measurement technique . . . 39
4 Anisotropic Hanle line shape via magnetothermoelectric phenomena 43 4.1 Introduction . . . 44
4.2 Experimental details . . . 45
4.3 Results and discussion . . . 45
4.4 Conclusions . . . 52
4.5 Supporting information . . . 53
4.5.1 Device fabrication . . . 53
4.5.2 Anisotropic magnetoresistance measurements . . . 53
4.5.3 Hanle data fitting . . . 53
4.5.4 Extended Hanle dataset . . . 55
4.5.5 Analytical heat diffusion model . . . 55
4.5.6 Three-dimensional finite element simulation (3D-FEM) . . . 56
4.5.7 Additional experiments and modelling . . . 58
References . . . 63
5 Independent geometrical control of spin and charge resistances in curved spintronics 67 5.1 Introduction . . . 68
5.2 Non-local spin transport experiments in curved nanochannels . . . 69
5.3 Model for spin transport in inhomogeneous curved channels . . . 70
5.4 Independent geometrical control of spin and charge resistances . . . . 74
5.5 Conclusions . . . 74 5.6 Methods . . . 75 5.6.1 Sample fabrication . . . 75 5.6.2 Electrical characterization . . . 76 5.6.3 Modelling . . . 76 5.7 Supporting information . . . 78
5.7.1 Room temperature measurements . . . 78
5.7.2 Pure spin currents in inhomogeneous metallic channels . . . 79
5.7.3 Spin accumulation signal . . . 81
5.7.4 Effect of changing the total thickness and/or the channel length of a flat homogeneous channel . . . 82
5.7.5 Generalized advantage of a curved inhomogeneous nanochannel 85 References . . . 87
Contents
6 Temperature dependence of the effective spin-mixing conductance probed
with lateral non-local spin valves 91
6.1 Introduction . . . 92
6.2 Experimental details . . . 93
6.3 Results and discussion . . . 94
6.4 Conclusions . . . 98
References . . . 99
7 Spin injection and detection via the anomalous spin Hall effect of a ferro-magnetic metal 103 7.1 Introduction . . . 104
7.2 Experimental details . . . 105
7.3 Results and discussion . . . 106
7.4 Conclusions . . . 111
7.5 Supporting information . . . 113
7.5.1 Ruling out the effect of interfacial exchange interaction between YIG and Permalloy . . . 113
References . . . 117
8 Efficient injection and detection of out-of-plane spins via the anomalous spin Hall effect in permalloy nanowires 121 8.1 Introduction . . . 122
8.2 Experimental details . . . 124
8.3 Results and Discussion . . . 124
8.4 Conclusions . . . 131
8.5 Supporting information . . . 132
8.5.1 Determination of the Py and the YIG magnetization orientations 132 8.5.2 Modelling the first harmonic non-local resistance with an angle-dependent b-parameter . . . 135
8.5.3 Control device with Pt injector and Pt detector . . . 136
8.5.4 Device fabrication details . . . 137
8.5.5 Interfacial exchange interaction between the Py nanowires and the YIG thin film . . . 139
8.5.6 Spin current injection via the anisotropic magnetoresistance/the planar Hall effect of the Py nanowires . . . 141
8.5.7 Measurement of the third harmonic response of the non-local signal . . . 142
8.5.8 Reciprocity check in a control device with a Pt injector and a Py detector . . . 143
Contents
8.5.9 Different mechanisms contributing to the second harmonic
re-sponse of the non-local signal . . . 144
8.5.10 Finite non-local signal in the fully perpendicular case (φ = 89◦) 146 References . . . 147
9 Modulation of magnon spin transport in a magnetic gate transistor 151 9.1 Introduction . . . 152
9.2 Experimental details . . . 152
9.3 Results and Discussion . . . 153
9.4 Conclusions . . . 157 References . . . 157 Summary 159 Samenvatting 163 Acknowledgements 167 Publications 171 Curriculum Vitae 173 x
