65th Annual Conference on Magnetism and Magnetic Materials, MMM2020 - Strain induced magnetic transition in CaMnO 3 ultrathin films

Congress

Summary *

The effect of high tensile strain and low dimensionality on the magnetic and electronic properties of CaMnO 3 ultrathin films, epitaxially grown on SrTiO 3 substrates, are theoretically analyzed (Fig. 1). By means of ab initio calculations, we find that, both, the high strain produced by the substrate and the presence of the free surface contribute to the stabilization of an in-plane ferromagnetic coupling, giving rise to a non-zero net magnetic moment in the ultrathin films. Remarkably, the FM component of the magnetic structure is stabilized, not as a consequence of a direct electron doping, as it happens when substituting the divalent Ca by trivalent elements or in the presence of O vacancies, as reported in the past, but rather because of a self-doping charge redistribution due to, both, the strain and the absence of apical oxygens. A deeper analysis of this charge redistribution can be obtained from the partial densities of states (pDOS) depicted in Fig. 2, where we separate the contributions of different MnO 2 planes. From the total density of states projected onto each layer, we can see that the oxygens located at the surface are the ones which loose part of their charge, and this charge is redistributed in the Mn atoms located in inner layers, and begin to occupy the d x2-y2 orbitals. The self-doping electrons of this e g states, allow the presence of the FM double exchange and the AAF magnetic structure with more FM pairs becomes more stable. As it can also be seen from Fig.2, coupled with this change in the magnetic order we find an insulator- metal transition triggered by the quantum confinement and the tensile epitaxial strain. Information provided by the agent in SIGEVA