Emergence of exchange bias and giant coercive field enhancement by internal magnetic frustration in La0.67Sr0.33MnO3 thin films
Résumé
We have studied the influence of controlled defects on the magnetic properties of La0.67Sr0.33MnO3 (LSMO) thin films. We used 100 nm thick epitaxial LSMO films, which were grown on SrTiO3 substrates and introduced stoichiometry changes and defects using oxygen ion irradiation through nanoporous alumina masks. Oxygen irradiation through the mask creates cascades of defects in spatially-modulated regions in the plane of the LSMO film. The magnetic properties of the samples were compared before and after the irradiation. We have found that irradiation reduces the ferromagnetic ordering temperature, decreases the total magnetization, enhances the coercivity, and induces exchange bias below 50 K. The coercivity enhancement is dramatically higher below 50 K and can be associated with exchange bias. These results can be explained by the formation of Mn-rich antiferromagnetic or ferrimagnetic phases within the bombarded regions that are exchange coupled to the non-irradiated - ferromagnetic host.
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