Periodic Reporting for period 1 - LICONAMCO (Light-controlled nanomagnetic computation schemes)
Berichtszeitraum: 2019-10-01 bis 2021-09-30
Nanomagnetic logic, in which the outcome of a computation is embedded into the energy hierarchy of magnetostatically coupled bistable nanomagnets, offers an attractive pathway to implement low-power in-memory computation. The computational operation in such artificial spin systems is driven by thermally activated reversals of magnetic moments, thus requiring little energy, and its result is retained afterwards due to the non-volatility of the nanomagnets, thus avoiding separate energy costs associated with the transport and storage of information that occur in the commonly-used von-Neumann computation architecture.
Spontaneous fluctuations and reversals of the individual nanomagnets allows an interacting system to relax to a state of lower energy, which can encode the result of a computational operation. Thermal energy increases the probability of such transitions, however, commonly used global heating schemes (e.g. via thermal contact to the sample substrate) have the disadvantage of slow operation speeds as well as lack spatial selectivity and are thus inherently wasteful. These disadvantages can be removed by employing local plasmon-assisted photo-heating in hybrid nanomagnetic-plasmonic metamaterials. These combine nanomagnetic elements with a thermoplasmonic heater that can be excited by laser light, leading to highly localised, fast, and sub-lattice specific heating up to several hundred Kelvin to enable magnetic switching.
Based on this approach, i.e. combining arrays of nanomagnets with local plasmonic heating, the LICONAMCO project aimed to develop optically reconfigurable computation schemes towards low-power ultra-fast computing, taking advantage of versatile plasmonic heating schemes by varying optical degrees of freedom, such as light polarisation, power, beam position, and short laser pulses.
Spontaneous fluctuations and reversals of the individual nanomagnets allows an interacting system to relax to a state of lower energy, which can encode the result of a computational operation. Thermal energy increases the probability of such transitions, however, commonly used global heating schemes (e.g. via thermal contact to the sample substrate) have the disadvantage of slow operation speeds as well as lack spatial selectivity and are thus inherently wasteful. These disadvantages can be removed by employing local plasmon-assisted photo-heating in hybrid nanomagnetic-plasmonic metamaterials. These combine nanomagnetic elements with a thermoplasmonic heater that can be excited by laser light, leading to highly localised, fast, and sub-lattice specific heating up to several hundred Kelvin to enable magnetic switching.
Based on this approach, i.e. combining arrays of nanomagnets with local plasmonic heating, the LICONAMCO project aimed to develop optically reconfigurable computation schemes towards low-power ultra-fast computing, taking advantage of versatile plasmonic heating schemes by varying optical degrees of freedom, such as light polarisation, power, beam position, and short laser pulses.
To achieve the project goals, hybrid nanomagnetic-thermoplasmonic metamaterials were fabricated and optimised using nanolithography methods, and their optical and magnetic properties characterised. To track and image the magnetic behaviour in response to the optical excitation different experimental setups, e.g. based on photoelectron emission microscopy (PEEM) and magnetic force microscopy (MFM), were devised. Finite-elements multiphysics and micromagnetic simulations gave insight into the involved time scales of magnetic switching, and how thermoplasmonic selective heating can be exploited to design reconfigurable nanomagnetic Boolean logic gates.
One notable outcome, published in two Open Access peer-reviewed articles, describes a so-far overlooked reduction of the energy barriers in interacting nanomagnetic systems arising from preferential chiral reversal modes. This results in significantly faster and more realistic time scales used in kinetic Monte-Carlo simulations to model the relaxation in artificial spin systems and nanomagnetic logic circuits. Furthermore, the modifications of the barrier energies also lead to changes in the emergent spatial correlations, understanding the consequences of this effect are work in progress.
Furthermore, the design of a hybrid logic circuit made from only four nanomagnets combined with selective plasmonic heating allowed to implement reconfigurable Boolean AND/OR gates. In these, the desired operation is set either by modifying the initialising field protocol or optically during operation, by changing the order in which horizontally and vertically polarised laser pulses are applied. The results of micromagnetic simulations show that this approach offers itself as a fast (up to GHz), energy-efficient (here, about 100 pJ per operation) and reconfigurable platform for in-memory computation that can be controlled via optical means.
The LICONAMCO project made a significant step towards the experimental implementation, modelling and exploring novel functionalities of hybrid plasmonic-magnetic metamaterials, with potential applications to nanomagnetic computation.
Furthermore, the design of a hybrid logic circuit made from only four nanomagnets combined with selective plasmonic heating allowed to implement reconfigurable Boolean AND/OR gates. In these, the desired operation is set either by modifying the initialising field protocol or optically during operation, by changing the order in which horizontally and vertically polarised laser pulses are applied. The results of micromagnetic simulations show that this approach offers itself as a fast (up to GHz), energy-efficient (here, about 100 pJ per operation) and reconfigurable platform for in-memory computation that can be controlled via optical means.
The LICONAMCO project made a significant step towards the experimental implementation, modelling and exploring novel functionalities of hybrid plasmonic-magnetic metamaterials, with potential applications to nanomagnetic computation.