Magnetic stray-field studies of a single Cobalt nanoelement as a component of the building blocks of artificial square spin ice

•Focused Electron Beam Induced Deposition; combination with micro-Hall magnetometry.•Stray field study of a ferromagnetic Cobalt nanoisland's magnetization reversal.•Comparison to interacting nanoelements within a building block of square spin ice.•Thermally induced switching and metastable states during magnetization reversal.•Results supported by micromagnetic simulations.

We use Focused Electron Beam Deposition (FEBID) to directly write Cobalt magnetic nanoelements onto a micro-Hall magnetometer, which allows for high-sensitivity measurements of the magnetic stray field emanating from the samples. In a previous study [M. Pohlit et al., J. Appl. Phys. 117 (2015) 17C746] [21] we investigated thermal dynamics of an individual building block (nanocluster) of artificial square spin ice. In this work, we compare the results of this structure with interacting elements to the switching of a single nanoisland. By analyzing the survival function of the repeatedly prepared state in a given temperature range, we find thermally activated switching dynamics. A detailed analysis of the hysteresis loop reveals a metastable microstate preceding the overall magnetization reversal of the single nanoelement, also found in micromagnetic simulations. Such internal degrees of freedom may need to be considered, when analyzing the thermal dynamics of larger spin ice configurations on different lattice types.