Crafting the magnonic and spintronic response of BiFeO3 films by epitaxial strain

• Published in: Nature materials Vol. 12; no. 7; pp. 641 - 646
• Main Authors: Sando, D., Agbelele, A., Rahmedov, D., Liu, J., Rovillain, P., Toulouse, C., Infante, I. C., Pyatakov, A. P., Fusil, S., Jacquet, E., Carrétéro, C., Deranlot, C., Lisenkov, S., Wang, D., Le Breton, J-M., Cazayous, M., Sacuto, A., Juraszek, J., Zvezdin, A. K., Bellaiche, L., Dkhil, B., Barthélémy, A., Bibes, M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2013; Nature Publishing Group
• Subjects: 639/301/119/996; Biomaterials; Condensed Matter Physics; Ferroelectrics; Magnetism; Materials Science; Nanotechnology; Optical and Electronic Materials; Photovoltaics; Physics; Thin films; Valves
• ISSN: 1476-1122; 1476-4660; 1476-4660
• DOI: 10.1038/nmat3629

Multiferroics are compounds that show ferroelectricity and magnetism. BiFeO 3 , by far the most studied, has outstanding ferroelectric properties, a cycloidal magnetic order in the bulk, and many unexpected virtues such as conductive domain walls or a low bandgap of interest for photovoltaics. Although this flurry of properties makes BiFeO 3 a paradigmatic multifunctional material, most are related to its ferroelectric character, and its other ferroic property—antiferromagnetism—has not been investigated extensively, especially in thin films. Here we bring insight into the rich spin physics of BiFeO 3 in a detailed study of the static and dynamic magnetic response of strain-engineered films. Using Mössbauer and Raman spectroscopies combined with Landau–Ginzburg theory and effective Hamiltonian calculations, we show that the bulk-like cycloidal spin modulation that exists at low compressive strain is driven towards pseudo-collinear antiferromagnetism at high strain, both tensile and compressive. For moderate tensile strain we also predict and observe indications of a new cycloid. Accordingly, we find that the magnonic response is entirely modified, with low-energy magnon modes being suppressed as strain increases. Finally, we reveal that strain progressively drives the average spin angle from in-plane to out-of-plane, a property we use to tune the exchange bias and giant-magnetoresistive response of spin valves. The ferroelectric properties of BiFeO 3 have been the subject of extensive study. Using a range of experimental tools and numerical modelling, it is now shown that its ferroic properties can also be manipulated by strain effects, giving rise to a variety of magnonic phenomena.