Nanoscale spin dynamics in ferromagnetic/normal-metal heterostructures for spin-logic
application
Engineering of spin torque efficiency in Co 2 FeAl/β -Ta and Ru/FeCo/Ru multi-layers
Rahul Gupta
Licentiate thesis
Abstract
In the present information age, people across the globe generate an enormous digital foot- print. Therefore, it is necessary to store and process the information in an elegant way. Spin- logic circuits are being considered potential candidates beyond CMOS integrated computing due to high clock speed, non-volatility, and higher logical efficiency. A basic building block for spin-logic circuits is ferromagnetic (FM) and normal-metal (NM) heterostructures. An example of a spin-logic data processing circuit is the spin-orbit torque (SOT) magnetic random access memory (MRAM). Energy efficient operation of such circuits depends on the interfacial elec- tronic and magnetic properties of the heterostructures. These properties are known as Gilbert damping of the FM layer, spin Hall angle of the NM layer, spin-mixing conductance and spin- memory loss at the interface. To reduce the power consumption of such circuits, we propose two methods; doping and interface engineering. In paper I, we use ultra-low damping Fe65Co35
thin films as the FM layer and Ru as the NM layer. The interfacial parameter, the spin-mixing conductance, of the FeCo/Ru heterostructure is enhanced by 98% with Re doping in the FeCo.
In paper II, we use Co2FeAl as the FM layer and β -Ta as the NM layer, and inserting a Cu continuous layer at the interface of Co2FeAl/β -Ta, yielding an enhancement of the spin-mixing conductance. In both cases, the enhancement in spin-mixing conductance can be linked to the increase in number of quantum conductance channels on the NM side, which helps to reduce the power consumption, and may provide a direction towards ultra-fast efficient operation of spin-logic circuits.
"Dedicated to my family"
List of papers
This thesis is based on the following papers, which are referred to in the text by their Roman numerals.
I Engineering of spin mixing conductance at Ru/FeCo/Ru interfaces:
Effect of Re doping.
R. Gupta, N. Behera, V. A. Venugopal, S. Basu, A. K. Puri, P. Strom, M. A. Gubbins, L. Bergqvist, R. Brucas, P. Svedlindh, and A. Kumar Phys. Rev. B 101, 024401 (2020).
II Spin pumping and spin torques in interfacially tailored Co2FeAl/β -Ta layers
A. Kumar, R. Gupta, S. Husain N. Behera, S. Hait, S. Chaudhary , R.
Brucas, and P. Svedlindh
Phys. Rev. B 100, 214433 (2019).
Reprints were made with the permission from the publishers.
List of additional papers
I Effect of seed layers on dynamic and static magnetic properties of Fe65Co35thin films
S. Akansel, V. A. Venugopal, A. Kumar, R. Gupta, R. Brucas, S.
George, A. Neagu, C.-W. Tai, M. Gubbins, G. Andersson, P. Svedlindh J. Phys. D: Appl. Phys., 51 305001 (2018).
II Multi-jump magnetization switching in Co2FeAl full Heusler alloy thin films: Experiments and simulations
S. Husain, V. Barwal, A. Kumar, R. Gupta, N. Behera, S. Hait, N. K.
Gupta, P. Svedlindh, S. Chaudhary
Jour. Mag. Mag. Mat., 486 165258 (2019).
III Direct observation of unusual interfacial Dzyaloshinskii-Moriya interaction in graphene/NiFe/Ta heterostructure
A. K. Chaurasiya, A. Kumar, R. Gupta, S. Chaudhary, P. K. Muduli, and A. Barman
Phys. Rev. B, 99 035402 (2019).
Reprints were made with the permission from the publishers.
Author contributions
The research area of experimental physics contains many facts including the service of experimental equipment, instrumentation development, sample prepa- ration, carrying through the measurements, and finally analysing and present- ing the data for the community. This work is usually not done by one person only. In the work presented here my role has more been active in the later steps, that is to carry through the experimental work and to extract physical information from the experimental data. My contribution in the published work is to some extent reflected by my position in the author list.
PaperI: Main author– coordinated the project, performed experiments, data analysis, led discussions and writing.
PaperII: Contributed equally with main author, performed part of the experiments, analyzed the data, participated in the discussions.
