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

Thin films of the magnetoelectric insulator α-Cr2O3 are technologically relevant for energy-efficient magnetic memory devices controlled by electric fields [1-3]. In contrast to single crystals, the quality of thin Cr2O3 films is usually compromised by the presence of point defects and their agglomerations at grain boundaries, putting into question their application potential. We experimentally investigated the defect nanostructure of magneton-sputtered 250-nm-thick Cr2O3 thin films prepared under different conditions on single crystals of Al2O3 (0001) and correlate it with the integral and local magnetic properties of the samples [4]. We evaluated the type and relative concentration of defects. For this purpose, positron annihilation spectroscopy (PAS) was used as a unique probe for open-volume defects in thin films. The results obtained for the thin-film samples are compared to single crystal data. Our analysis reveals that the Cr2O3 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 Cr2O3 samples capped with a thin layer of Pt relying on spin Hall effect [5]. 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 Néel temperature, which is one of the important technological metrics, is hardly affected by the formed defects in a broad range of deposition parameters.

References
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