The metrology of low power computation

Smaller, faster, and more efficient electronic devices are a vital part of the UK’s economic growth and industrial innovation. This is directly evidenced by the recent publication of the Royce road mapping exercise for low loss electronics.

Spintronics, involves the utilisation of the intrinsic spin of electrons to process information in a way that is analogous to charge in traditional electronics. The benefits of this approach will lead to more efficient, low energy consumption devices that are faster than their charge-based counterparts.

One of the approaches on the way to implementation of green ICT is magnetic skyrmions. We are currently investigating how skyrmions can be utilised as next-gen information carriers in addition to developing the metrological framework associated with measurements of skyrmions.  Skyrmions are of interest due to their ability to be manipulated and moved with spin polarised electrical currents at very low current densities.

Additionally, their inherent stability which arises due to the unique topology, affords them particle like properties and nanoscale size. This makes them perfect candidates for novel logic/storage architectures for low loss electronic devices. It is also why they have received attention for their applicability to be incorporated into low loss neuromorphic inspired devices with skyrmion based synapse and neuron devices demonstrated.

Projects

TOPS a collaborative project with Euramet aims to progress topologically-protected spin structures (TSS) towards standardisation and support Europe’s continuing expertise and competitiveness in electronic device manufacturing.

The project will develop and validate measurement tools and techniques for describing TSS, helping to identify key parameters that determine the formation, size and stability.

Publications

Using a combination of controlled nucleation, single skyrmion annihilation, and magnetic field dependent measurements the thermoelectric signature of individual skyrmions is characterised. Thermoelectric Signature of Individual Skyrmions

Our recent research on the role of the underlying magnetic energy landscape and skyrmion-skyrmion interactions in chiral magnetic multilayer systems Diameter-independent skyrmion Hall angle observed in chiral magnetic multilayers

Demonstrating single skyrmion manipulation using local field gradients from a magnetic force microscopy probe. Individual skyrmion manipulation by local magnetic field gradients

Demonstration of skyrmion lattice formation via interaction with a magnetic force microspy probe. Direct writing of room temperature and zero field skyrmion lattices by a scanning local magnetic field

Artificial spin ice (ASI) are networks of coupled single domain nanomagnets (or "macro-spins") arranged on periodic or aperiodic lattices, which exhibit geometric frustration by design. As the lattices are lithographically defined, it is possible to tune the interactions within the arrays to probe a plethora of frustration physics including phase transitions, collective dynamics, and formation/manipulation of emergent monopoles.

Nanomagnets are promising for low-loss electronics as operations can be performed at energies close to the thermodynamic limit. The modular nature of ASI means they are versatile in application as models for understanding effects in more complex systems, and hardware realisations in areas including reconfigurable magnonics, and novel computation.

With complex structures comes complex behaviours, which must be characterised and understood through metrology as material systems are geared towards novel application.

We have focused our research efforts towards modified lattice designs to create hybrid systems that tune the lattice energies for application in novel computation. This includes the evaluation of the magnetostatic response of a quasi-hexagonal lattice, which creates a competition between geometric frustration and ferro- and antiferromagnetic coupling by inclusion of parallel nanomagnets in the lattice; and investigation of defects in a honeycomb lattice for controllable and low-power monopole propagation.

Publications

An artificial spin ice lattice that exhibits unique Ising and non-Ising behavior under field switching protocols due to inclusion of coupled nanomagnets into the unit cell. Modal Frustration and Periodicity Breaking in Artificial Spin Ice

Individual DW manipulation has the potential to enable a wide range of new devices.  From logic circuits that use DWs for information transfer, requiring only a fraction of the energy current computers use; to chips to manipulate individual MNPs and perform biological analysis such drug testing or cell manipulation. We perform combined to develop DW-based technologies.

Our electromagnetic laboratory enables measurement of electrical effects associated with changes in magnetization (such as magnetoresistance, anomalous Hall effect, anomalous Nernst effect), individual DW detection, and electrical manipulation of DW using current pulses. The MFM studies, which can be customised to allow simultaneous electrical measurements, has enabled imaging of DW dynamics including DW movement through electrically driven spin torque.

Publications

Simultaneous anisotropic magnetoresistance and magneto-optical Kerr effect measurements on Permalloy nanowires Simultaneous magnetoresistance and magneto-optical measurements of domain wall properties in nanodevices

Combined electromagnetic manipulation/sensing of DWs with MFM studies Anisotropic Magnetoresistance State Space of Permalloy Nanowires with Domain Wall Pinning Geometry

A novel nanosensor based on DW nucleation perpendicular anisotropic nanodevices Magnetic Particle Nanosensing by Nucleation of Domain Walls in Ultra-Thin CoFeB/Pt Devices

Metal/Ferromagnetic (Au/Py) nanojunctions are used to investigate magnetoresistance effects and track magnetization in L-shaped Py nanostructures
Hybrid normal metal/ferromagnetic nanojunctions for domain wall tracking

Anomalous Nerst effects as a simple and powerful tool to precisely track the position and motion of a single propagating DW
Nanoscale thermoelectrical detection of magnetic domain wall propagation

A study of domain walls in cylindrical nanowires consisting of cobalt and nickel
Current Controlled Magnetization Switching in Cylindrical Nanowires for High-Density 3D Memory Applications