Research Training in Materials Science
Spin dynamics and spin-orbit torque study in W/CoFeB heterostructure for energy efficient spin-logic operations
Why spin-based electronics? In the present digital world, our digital footprints generate enormous amount of data, which is stored in personal computer/device, clouds and data centres, and there is an ever-increasing demand of energy to process the information. Therefore, unless the currently used hardware based on semiconducting CMOS technology is replaced with a less energy consuming technology, the Information and Communication Technology sector (ICT) will become one of the largest energy consumers on the planet in near future. The utilization of the electron’s spin degree of freedom in logic devices have the potential to replace the existing ICT semiconducting CMOS based logics. The use of spin-logic-circuits not only have the potential to realize ultralow energy scaling, but can also increase the operational speed by several orders, which is beyond existing CMOS semiconducting technologies. The basic building blocks for spin-logic-circuits are magnetic and nonmagnetic (NM) thin films and their heterostructures, creating digital “0” or “1” states by switching the magnetization of the magnetic layer utilizing spin currents in spin-orbit torque (SOT) magnetoresistive random access memories (SOT-MRAM) (see Figure) and spin-torque-oscillators devices.
Aim: The project will provide a deep understanding of how to manipulate the magnetic state of the magnetic layer in heterostructures by utilizing spin currents. The samples in this project are W/CoFeB heterostructures and have already been characterized by XRD, XRR, FMR (ferromagnetic resonance) and planar Hall effect measurements; these data will be provided for the project. In addition, the project includes measurements of ST-FMR (spin-torque ferromagnetic resonance) measurements in W/CoFeB heterostructures and analyses of all results. The objective of the project is to determine the torques generated by spin currents in the heterostructures. The enhancement of spin-torques will result in more energy efficient manipulation of magnetic states for spin-logic operations
Credits: 15 ECTS (hp).
For whom: The project is open to bachelor/master students at Uppsala University, who should have a basic knowledge of solid-state physics, especially in magnetism. It is recommended to have previous experience in a programming language such as Python and/or Matlab.
Location: The experimental part will be performed at the division of solid state physics, Ångström Laboratory (House 4, floor 3), Uppsala University.
Upon completion of the course you should:
- understand the basic concepts of spin-based electronics.
- be able to find, evaluate and identify the parameters that are important for spin-based electronics.
- have gained knowledge of basic experimental tools for spin dynamics measurements and software to analyse the data.
- understand how to compile your research in a thesis format and the possibility exist to submit a research paper in a peer reviewed international journal.
To pass the project you need to:
- be present and perform the ST-FMR measurements in the laboratory. Otherwise, depending on the covid-19 situation the student can perform much of the work from home.
- perform the analysis of all data and compile a report for all measurements.
1. Luqiao Liu et al, Spin-Torque Ferromagnetic Resonance Induced by the Spin Hall Effect, Phys. Rev. Lett. 106, 036601 (2011).
2. Chi-Feng Pai et al, Spin transfer torque devices utilizing the giant spin Hall effect of tungsten, App. Phys. Lett. 101, 122404 (2012).
3. Ankit Kumar et al, Spin pumping and spin torques in interfacially tailored Co2FeAl/β-Ta layers, Phys. Rev. B, 100, 214433 (2019).
Direct measurement of the adiabatic temperature change: a step towards magnetic refrigeration
Credits: 15 ECTS (hp)
Requirements: Basic knowledge on LabVIEW programming.
Introduction: Magnetic refrigeration based on the magnetocaloric effect has the potential to replace the green-house gas emitting conventional vapour-compressor refrigerator1. The magnetocaloric effect is a simple thermodynamic phenomenon, where the temperature of a magnetic material will change upon application or removal of a magnetic field. However, to measure the temperature change of a material, the system should provide adiabatic conditions for the material2. Thus, we need to build up a system where we can measure the temperature change adiabatically upon application of magnetic fields. Currently the system looks like as in the picture below.
Tasks: (total time estimate; 30 working days)
The hardware (including cryostat, temperature controller, magnet and computer) is readily available.
1. Understanding the basic thermodynamics of the measurement system. (Time estimate: 5 working days including reading relevant research literature and discussion supervisors.)
2. LabVIEW interface with temperature controller and magnet. (Time estimate: 10 working days including writing and modification of LabVIEW programme.)
3. Measurement on a magnetocaloric material. (Time estimate: 7 working days.)
4. Supplementary measurement: The direct measurement data will be compared with an indirect measurement of heat capacity and isothermal entropy change in Quantum Design Physical Property Measurement System (PPMS) system; (Time estimate: 3 working days.)
5. Writing report (Time estimate: 5 working days.)
Location: The experimental setup is located at the division of solid-state physics, Ångström laboratory (house 4, floor 3), Uppsala University. However, most of the project tasks can be performed remotely in this covid-19 situation
Sagar Ghorai (email@example.com) profile: https://katalog.uu.se/profile/?id=N18-2129
Peter Svedlindh (firstname.lastname@example.org), profile: https://katalog.uu.se/profile/?id=N94-1074
1 R. Skini, S. Ghorai, P. Ström, S. Ivanov, D. Primetzhofer, and P. Svedlindh, J. Alloys Compd. 827, 154292 (2020).
2 S. Ghorai, R. Skini, D. Hedlund, P. Ström, and P. Svedlindh, Sci. Rep. 10, 19485 (2020).