Defect nanostructure and its impact on magnetism of α-Cr2O3 thin films.

Thin films of the magnetoelectric insulator Cr$_{2}$O$_{3}$ are technologically relevant for energy-efficient magnetic memory devices controlled by electric fields. We experimentally investigated the defect nanostructure of 250-nm-thick Cr$_{2}$O$_{3}$ thin films prepared under different conditions on single crystals of Al$_{2}$O$_{3}$ (0001) and correlate it with the integral and local magnetic properties of the samples. Positron annihilation spectroscopy (PAS) was used as a unique probe for open-volume defects in thin films. Analysis reveals that the Cr$_{2}$O$_{3}$ thin films are characterized by the presence of complex defects at grain boundaries, formed by groups of monovacancies, coexisting with monovacancies and dislocations. The concentration of complex defects can be controlled by the sample fabrication conditions. The defect nanostructure strongly affects the magnitude of the electrical readout, which is measured of the Cr$_{2}$O$_{3}$ samples capped with a thin layer of Pt relying on spin Hall effect. Furthermore, the presence of larger defects like grain boundaries has a strong influence on the pinning of magnetic domain walls in thin films. Independent of these findings, we showed that the N\'{e}el temperature, which is one of the important technological metrics, is hardly affected by the formed defects in a broad range of deposition parameters.