Periodic Report Summary 1 - HIGHSPIN (Tunable, highly spin-polarised materials for spintronics and non-volatile memories)
The aim of the HIGHSPIN project is to incorporate tunable, highly spin-polarised (THSP) materials into spintronic devices and utilise them in new 2D and 3D nanomagnetic data storage architectures.
The field of spintronics, where both the spin and charge of the electron are used, is one of the most rapidly developing and exciting areas of nano-science. The discipline has already revolutionised the information technology industry and further technological applications, from data storage to microwave field generation, make it a hugely worthwhile investigation area. Crucial to all proposed schemes is the efficient creation and control of spin-polarised electric currents. THSP materials offer a means to tailor robust, completely polarised currents. As yet however their use has not been realised in spin transport measurements and spintronic devices.
Spin currents offer a fast, low power, electrical means to control magnetic switching which may be scaled along with future device minimisation. They are particularly well suited for emerging classes of 2D and 3D magnetic data-storage, which offer unparalleled densities in fast, low power and non-volatile memories. There is a very real need for a technological breakthrough in data storage technology, including hard disk drive read head technologies. Spintronics will be part of this revolution if it can help move storage architectures into the 3rd dimension and capitalise on control of the electron spin degree of freedom. Demonstrating a viable means to generate appreciable spin accumulations and thereby control magnetisation in a technologically relevant framework would greatly assist the realisation of such a breakthrough. The ultimate goal of the project is to provide the first demonstration of THSP materials in spintronic devices and develop a working means of pure spin-current mediated data writing in these storage schemes. Fundamentally, the results will greatly further understanding of spin transport and spin torques on magnetic switching, while technologically it would demonstrate directly the viability of this means of device control.
The goals of the HIGHSPIN project are summarised by the three technical work packages:
WP1. Investigate the underlying Physics and Materials Science of spin transport in metallic channels, using advanced channel materials.
WP2. Incorporate tunable spin polarised materials into non-local spin valve (NLSV) geometries.
WP3. Develop spin current based data-writing in emerging 3-D nano-magnetic data storage schemes.
The project divides into two phases: an outgoing phase centred at the University of Minnesota, under the supervision of Prof C Leighton; and a return phase under the supervision of Prof R P Cowburn, at the University of Cambridge. Currently the outgoing phase has been successfully completed. Drawing from the expertise in advanced materials synthesis and spin transport of the Leighton group, in this phase advanced NLSV devices were fabricated using a variety of channel materials to probe the role of specific mechanisms in limiting spin transport. Materials investigated ranged from transition metal ferromagnets (FMs) [Ni, Co, Fe, Ni80Fe20] and non-magnetic (para- or dia- magnetic) [Al, Cu] and also sulphide/sulphide-compatible materials [CoS2, CuS, Al]. Fabricated NLSV devices had typical channel dimensions of 150 nm x 200 nm cross sectional area. Spin signals were measured at FM separations up to 5 um. By selectively tuning impurity concentration, grain size and contact miscibility, four separate spin relaxation mechanisms were isolated and probed. By tuning grain size and impurity concentration, spin diffusion lengths from 300 nm to 1.5 um could be achieved, remarkably with little change to device conductivity. Identifying the relevant contributions from each defect in this way, considerable insight has been gained into the future materials design needed to enhance spin signals and the relevant importance of tuning channel microstructure and composition. Significantly, the work of this project has directly led to an understanding of the role of interdiffusion in spin transport and also explained one of the longest standing mysteries in NLSV research, establishing the role of the Kondo effect in spin relaxation.
In addition to the fundamental studies investigating the limiting factors for spin diffusion, THSP materials have been integrated into spintronic devices including thin film GMR heterostructures, AMR nanowires and NLSV devices using S compatible channel materials (both CoS2/Al and CoS2/CuS). These included devices evaluating the use of CoS2 in the NLSV geometry and the probing of the role of spin polarisation on device performance. Crucially this work established the importance of both magnetic anisotropy and magnitude of spin polarisation in ensuring maximum signal sizes. Routes to ensure coherent magnetic switching have been identified, giving promising options available for integrating pure spin current switching into future storage architectures.
These investigations have been supported by fundamental research into potential nanomagnetic data storage architectures, including soliton, domain wall and artificial spin ice devices. This research into the most viable storage architectures has been made to ensure a smooth transition during the return period and the success the final project work package (WP3). By capitalising on the return host organisation’s leading role in 2-D and 3-D nanomagnetic storage architectures this places the project in an ideal position to achieve the overall objectives of all WPs and demonstrate a working spin current controlled data writing mechanism.
The field of spintronics, where both the spin and charge of the electron are used, is one of the most rapidly developing and exciting areas of nano-science. The discipline has already revolutionised the information technology industry and further technological applications, from data storage to microwave field generation, make it a hugely worthwhile investigation area. Crucial to all proposed schemes is the efficient creation and control of spin-polarised electric currents. THSP materials offer a means to tailor robust, completely polarised currents. As yet however their use has not been realised in spin transport measurements and spintronic devices.
Spin currents offer a fast, low power, electrical means to control magnetic switching which may be scaled along with future device minimisation. They are particularly well suited for emerging classes of 2D and 3D magnetic data-storage, which offer unparalleled densities in fast, low power and non-volatile memories. There is a very real need for a technological breakthrough in data storage technology, including hard disk drive read head technologies. Spintronics will be part of this revolution if it can help move storage architectures into the 3rd dimension and capitalise on control of the electron spin degree of freedom. Demonstrating a viable means to generate appreciable spin accumulations and thereby control magnetisation in a technologically relevant framework would greatly assist the realisation of such a breakthrough. The ultimate goal of the project is to provide the first demonstration of THSP materials in spintronic devices and develop a working means of pure spin-current mediated data writing in these storage schemes. Fundamentally, the results will greatly further understanding of spin transport and spin torques on magnetic switching, while technologically it would demonstrate directly the viability of this means of device control.
The goals of the HIGHSPIN project are summarised by the three technical work packages:
WP1. Investigate the underlying Physics and Materials Science of spin transport in metallic channels, using advanced channel materials.
WP2. Incorporate tunable spin polarised materials into non-local spin valve (NLSV) geometries.
WP3. Develop spin current based data-writing in emerging 3-D nano-magnetic data storage schemes.
The project divides into two phases: an outgoing phase centred at the University of Minnesota, under the supervision of Prof C Leighton; and a return phase under the supervision of Prof R P Cowburn, at the University of Cambridge. Currently the outgoing phase has been successfully completed. Drawing from the expertise in advanced materials synthesis and spin transport of the Leighton group, in this phase advanced NLSV devices were fabricated using a variety of channel materials to probe the role of specific mechanisms in limiting spin transport. Materials investigated ranged from transition metal ferromagnets (FMs) [Ni, Co, Fe, Ni80Fe20] and non-magnetic (para- or dia- magnetic) [Al, Cu] and also sulphide/sulphide-compatible materials [CoS2, CuS, Al]. Fabricated NLSV devices had typical channel dimensions of 150 nm x 200 nm cross sectional area. Spin signals were measured at FM separations up to 5 um. By selectively tuning impurity concentration, grain size and contact miscibility, four separate spin relaxation mechanisms were isolated and probed. By tuning grain size and impurity concentration, spin diffusion lengths from 300 nm to 1.5 um could be achieved, remarkably with little change to device conductivity. Identifying the relevant contributions from each defect in this way, considerable insight has been gained into the future materials design needed to enhance spin signals and the relevant importance of tuning channel microstructure and composition. Significantly, the work of this project has directly led to an understanding of the role of interdiffusion in spin transport and also explained one of the longest standing mysteries in NLSV research, establishing the role of the Kondo effect in spin relaxation.
In addition to the fundamental studies investigating the limiting factors for spin diffusion, THSP materials have been integrated into spintronic devices including thin film GMR heterostructures, AMR nanowires and NLSV devices using S compatible channel materials (both CoS2/Al and CoS2/CuS). These included devices evaluating the use of CoS2 in the NLSV geometry and the probing of the role of spin polarisation on device performance. Crucially this work established the importance of both magnetic anisotropy and magnitude of spin polarisation in ensuring maximum signal sizes. Routes to ensure coherent magnetic switching have been identified, giving promising options available for integrating pure spin current switching into future storage architectures.
These investigations have been supported by fundamental research into potential nanomagnetic data storage architectures, including soliton, domain wall and artificial spin ice devices. This research into the most viable storage architectures has been made to ensure a smooth transition during the return period and the success the final project work package (WP3). By capitalising on the return host organisation’s leading role in 2-D and 3-D nanomagnetic storage architectures this places the project in an ideal position to achieve the overall objectives of all WPs and demonstrate a working spin current controlled data writing mechanism.