- Stanislav Kamba: Making EuO multiferroic by epitaxial strain engineering
- 1. 12. 2021, 14:10
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Abstract:
Infrared spectroscopy is effective tool for the study of polar soft phonons driving the displacive ferroelectric phase transitions because it can reveal the phase transitions without any structural investigations or without any electrodes required for dielectric measurements.
We will demonstrate application of infrared spectroscopy for already published studies of strain-induced ferroelectric phase transition in SrTiO3 and EuTiO3 [1] and newly for investigation of strained EuO ferromagnet.[2]
Our first-principles density functional calculations using a hybrid functional predicted strain-induced ferroelectric phase transition in ferromagnetic EuO with a tensile strain superior to 5%. For that reason, we investigated different EuO films grown using molecular beam epitaxy on various substrates inducing strain from 0 to 6.4 %. To achieve strain higher than 5 %, we had to prepare and characterize (EuO)2/(BaO)2 superlattices on (001) LSAT substrates. In this case the EuO and BaO are nominally strained by +6.4 % and -1.2 %, respectively. We found that the EuO optical phonon is drastically shifted down in comparison with the phonon in unstrained EuO and exhibits softening towards 100 K and a hardening below this temperature. This is a typical phonon behavior near ferroelectric phase transition. The system remains ferromagnetic, i.e. the superlattice becomes multiferroic at low temperatures below 30 K.
1. S. Kamba. APL Materials 9, 020704 (2021).
2. V. Goian, R. Held, E. Bousquet, Y. Yuan, A. Melville, H. Zhou, V. Gopalan, P. Ghosez, N. A. Spaldin, D. G. Schlom, and S. Kamba, Commun. Mat.1, 74 (2020).