Speaker
Description
Artificial magnetoelectric multiferroic heterostructures, which combine multiple ferroic orders, have high potential for next-generation electronic devices. With device downscaling, the interface plays an increasingly important role and deserves special consideration. Oxide films are especially well suited for such applications. We combined Co [1] and Ni [2] ferrite layers, which bring their ferrimagnetic long range order with pure and N-doped barium titanate, which is a cost-effective and environment friendly prototypical ferroelectric material.
All layers were grown epitaxially using plasma assisted molecular beam epitaxy. Oxygen plasma was used to grow the ferrite layers and pure BaTiO$_3$. We employed an original approach consisting in using the SrTiO$_3$(001) substrate as the oxygen supplier and atomic nitrogen plasma to incorporate a small amount of substitutional N atoms into the BaTiO$_3$ perovskite lattice [3, 4]. The layers were thoroughly characterized by in situ high energy electron diffraction, Auger and photoemission spectroscopies analysis and ex situ by piezo-force and high-resolution electron microscopies. More detailed investigations were conducted using synchrotron radiation and in particular X-ray diffraction and X-ray magnetic circular dichroism.
On pure oxide systems, we could determine the correlation between these properties with respect to the respective layer thicknesses. Although Co and Ni ferrites are close compounds, we obtain different behaviours in the very thin film regime when deposited on BaTiO$_3$. Ni ferrite shows an almost magnetic dead layer below $4$ nm and different growth strain. We could determine annealing conditions allowing to cure the lack of magnetism for the thin films [2] which is understood as due to the imperfect formation of the Ni ferrite spinel structure.
A comparative study of CoFe$_2$O$_4$ grown on pristine and N-doped BaTiO$_3$ demonstrates different plastic relaxation leading to substantial changes in the magnetic properties of the ferrite overlayer showing that N-doping can be used as a tuning parameter in multiferroics [5].
Acknowledgements
The authors gratefully acknowledge the “Agence Nationale de la Recherche (ANR)” for their funding through the MULTINANO project (grant no. ANR-19-CE09-0036).
References
[1] N. Jedrecy et al., “Cross-Correlation between Strain, Ferroelectricity, and Ferromagnetism in Epitaxial Multiferroic CoFe2O4/BaTiO3 Heterostructures,” ACS Applied Materials & Interfaces, vol. 10, no. 33. American Chemical Society (ACS), pp. 28003–28014, Aug. 07, 2018. https://doi.org/10.1021/acsami.8b09499
[2] H. Lin et al., “Unveiling and Optimizing Interface Properties of NiFe2O4/BaTiO3 Heterostructures,” ACS Applied Electronic Materials, vol. 6, no. 10. American Chemical Society (ACS), pp. 7286–7300, Oct. 10, 2024. https://doi.org/10.1021/acsaelm.4c01215
[3] A. Derj et al., “Properties of self-oxidized single crystalline perovskite N : BaTiO3 oxynitride epitaxial thin films,” Materials Advances, vol. 3, no. 7. Royal Society of Chemistry (RSC), pp. 3135–3142, 2022. https://doi.org/10.1039/d1ma01082d
[4] C. Blaess et al., “Nitrogen Doping in Epitaxial Self-Oxidized BaTiO3 Ferroelectric Thin Films,” The Journal of Physical Chemistry C, vol. 129, no. 7. American Chemical Society (ACS), pp. 3849–3861, Feb. 11, 2025. https://doi.org/10.1021/acs.jpcc.4c07538
[5] C. Blaess et al., “Manipulation of artificial multiferroics using doping-induced plastic strain relaxation,” Applied Surface Science, vol. 690. Elsevier BV, p. 162585, May 2025. https://doi.org/10.1016/j.apsusc.2025.162585
