Selective and fast plasmon-assisted photo-heating of nanomagnetsElectronic supplementary information (ESI) available: Schematic for experimental setup for plasmonic-pump MOKE-probe measurements. Optical properties of 4-vertex structures. Time-dependent temperature increase under pulsed illumination. Plasmonic and magnetic properties of permalloy-only nanoislands. See DOI: 10.1039/c9nr01628g

Thermal relaxation of nanoscale magnetic islands, mimicking Ising macrospins, is indispensable for studies of geometrically frustrated artificial spin systems and low-energy nanomagnetic computation. Currently-used heating schemes based on contact to a thermal reservoir, however, lack the speed and spatial selectivity required for the implementation in technological applications. Applying a hybrid approach by combining a plasmonic nanoheater with a magnetic element, in this work we establish the robust and reliable control of local temperatures in nanomagnetic arrays by contactless optical means. Plasmon-assisted photo-heating allows for temperature increases of up to several hundred kelvins, which lead to thermally-activated moment reversals and a pronounced reduction of the magnetic coercive field. Furthermore, the polarization-dependent absorption cross section of elongated plasmonic elements enables sublattice-specific heating on sub-nanosecond time scales. Using optical degrees of freedom, i.e. focal position, polarization, power, and pulse length, thermoplasmonic heating of nanomagnets offers itself for the use in flexible, fast, spatially-, and element-selective thermalization for functional magnetic metamaterials. Hybrid plasmonic-magnetic elements facilitate contactless, fast, spatially-selective, and sublattice-specific control of temperature in functional magnetic metamaterials via optical degrees of freedom.