3 years ago

Coupled Lattice Polarization and Ferromagnetism in Multiferroic NiTiO3 Thin Films

Coupled Lattice Polarization and Ferromagnetism in Multiferroic NiTiO3 Thin Films
Seokwoo Jeon, Libor Kovarik, Timothy C. Droubay, Yulan Li, Seungbum Hong, Tamas Varga, Vaithiyalingam Shutthanandan, Manjula I. Nandasiri, Dehong Hu, Bumsoo Kim, Scott A. Chambers
Polarization-induced weak ferromagnetism (WFM) was demonstrated a few years back in LiNbO3-type compounds, MTiO3 (M = Fe, Mn, Ni). Although the coexistence of ferroelectric polarization and ferromagnetism has been demonstrated in this rare multiferroic family before, first in bulk FeTiO3, then in thin-film NiTiO3, the coupling of the two order parameters has not been confirmed. Here, we report the stabilization of polar, ferromagnetic NiTiO3 by oxide epitaxy on a LiNbO3 substrate utilizing tensile strain and demonstrate the theoretically predicted coupling between its polarization and ferromagnetism by X-ray magnetic circular dichroism under applied fields. The experimentally observed direction of ferroic ordering in the film is supported by simulations using the phase-field approach. Our work validates symmetry-based criteria and first-principles calculations of the coexistence of ferroelectricity and WFM in MTiO3 transition metal titanates crystallizing in the LiNbO3 structure. It also demonstrates the applicability of epitaxial strain as a viable alternative to high-pressure crystal growth to stabilize metastable materials and a valuable tuning parameter to simultaneously control two ferroic order parameters to create a multiferroic. Multiferroic NiTiO3 has potential applications in spintronics where ferroic switching is used, such as new four-stage memories and electromagnetic switches.

Publisher URL: http://dx.doi.org/10.1021/acsami.7b04481

DOI: 10.1021/acsami.7b04481

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