INMA Impulso: High-resolution mapping of magnetic properties in oxide heterostructures and nanosystems

El miércoles 16 de febrero tendrá lugar una nueva sesión del ciclo de seminarios INMA-Impulso, un ciclo de conferencias que trata de acercar la investigación más puntera a la sociedad.

La próxima sesión correrá a cargo de la Dra. María Varela de la Universidad Complutense de Madrid, que presentará la sesión titulada: High-resolution mapping of magnetic properties in oxide heterostructures and nanosystems.

La conferencia tendrá lugar el miércoles 16 de febrero a las 12 horas. La sesión se podrá seguir a través de la plataforma zoom: https://zoom.us/j/92250594815?pwd=TXFidXZWZVR5VWhYaU5HejJ4Mi9NQT09, ID de reunión: 922 5059 4815. Código de acceso: 296302

Resumen de la charla:

Complex oxides with a perovskite structure show a wide range of interesting properties due to a strong interplay and competition between lattice, spin, and charge degrees of freedom. This is particularly the case when obtained in the form of thin films or heterostructures, where novel macroscopic functionalities may arise. In this talk we will apply atomic resolution aberration corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) to the study of the structure and properties of magnetic oxide heterostructures. A first example of application involves local measurements of electronic and magnetic properties of ferromagnetic manganite La0.7Sr0.3MnO3 (LSMO) epitaxial ultrathin films grown by high-pressure O2 sputtering on single crystal SrTiO3 (STO) substrates. We will combine STEM-EELS with density-functional calculations to study local structural distortions and electronic phenomena associated with interfacial magnetism. Atomic resolution images exhibit an increase of the out-of-plane lattice parameter at the LSMO/STO interface plane, pointing to a local reconstruction of the charge density and, hence, physical properties. We use energy-loss magnetic chiral dichroism (EMCD) [1], a technique directly sensitive to the local magnetic moment, to track magnetic quantities across the interface with sub-unit cell resolution. The dichroic signal at both the Mn L2,3 and the Ti L2,3 edges is enhanced near the interface, pointing to a local increase of the Mn and Ti magnetic moments. These results agree with density-functional theory simulations including interfacial oxygen vacancies, which enhance charge transfer and antiferromagnetic coupling between the Ti and the Mn. A second example can be found in the study of the electronic and magnetic properties of multiferroic interfaces where ultrathin ferroelectric BaTiO3 (BTO) barriers are sandwiched between ferromagnetic LSMO electrodes. Real space measurements of local polarization obtained through the analysis of atomic resolution annular bright field images [3] will be compared to magnetic quantities measured from spatially resolved EMCD. Finally, the magnetic properties of bimagnetic FeO/Fe3O4 core/shell nanoparticles will be discussed. In this system the magnetic arrangement at the interface can play a crucial role in the properties and performance of the nanoparticles, with the magnetic moment being largest at the surface and decreasing towards the inner part of the nanoparticle [4].

[1] P. Schattschneider et al., Nature 441 (2006) pp. 486-488.

[2] J. Salafranca et al., NanoLetters 12 (2012), pp. 2499-2503.

[4] G. Sanchez-Santolino et al., Nature Nanotechnolgy 12, (2017) 655-662.

[5] D. Del Pozo-Bueno et al., NanoLetters 21 (2021) pp. 6923-6930.