Artificial spin ices (ASIs) are metamaterials consisting of arrays of dipolar-coupled nanomagnets arranged in complex frustrated geometries. They continue to be of significant interest because various fascinating phenomena that can be investigated at accessible temperatures and with microscopy methods. Initially, AC demagnetization protocols were applied as an effective thermal anneal to achieve the lowest energy state. However, it was immediately observed that demagnetization protocols did not provide a means to reach the lowest energy state. More recently, various research groups found ways to create materials where the nanomagnets are superparamagnetic at accessible temperatures and where a true thermal annealing protocol could be implemented. This breakthrough enabled the systematic study of thermally active ASI systems that allow the observation of how they relax towards the ground state.
Recently, it was shown that ferromagnetic nanomagnets support coherent coupling of photons to localized surface plasmon resonances (LSPs), which are collective free-like electron oscillations at the interface between a conductor and a dielectric. Hybrid structures combining noble and ferromagnetic metals, can improve further the efficiency of this coupling, i.e., the transfer of energy from an incident electromagnetic radiation to the nanostructure. As a consequence, the local temperature of the nanomagnet can be increased, even dramatically, and in a finely controlled manner. For example, the incident electromagnetic radiation can be focused in small spots in the order of 10 mm or even less at optical frequencies, in order to achieve thermal activation of selected portions of an ASI. Moreover, the energy transfer via excitation of LSPs occurs at a selected and narrow wavelength bandwidth that depends on the size and shape of the nanomagnet and the polarization of the incident radiation. This allows for a selective heating of a desired subset of nanomagnets within the illuminated area of an ASI, depending on their in-plane orientation.
In this paper, we present the results of our initial efforts, namely modeling of the electromagnetic and Plasmon-induced thermal behavior of nanomagnets as well as our first exploratory experiments, aiming at showing the viability and potential of this approach as a novel and improved tool to study the thermal behavior of artificial spin ice systems. Apart from the investigation of intriguing physic phenomena, this methodology can open a new path to the creation of new opto-thermally active nanomagnet devices suitable for low-power data transfer and computation.