Hole doped La2/3Sr1/3MnO3 (LSMO) is an auspicious candidate for spintronic applications due to its high spin polarization 1 and colossal magnetoresistance 2. However, the growth of LSMO thin films on silicon, and other substrates important for applications, is extremely challenging due to their structural incompatibility and high reactivity with oxygen.
Here, we demonstrate the possibility to grow strain-free LSMO thin films on silicon substrates with magnetic, magneto-optical and optical properties comparable to epitaxial layers grown on SrTiO3 (STO). This growth was achieved using a two-dimensional Ca2Nb3O10 nanosheet (NS) seed layer which induces epitaxial stabilization of LSMO. The 20 and 40 nm thick films of LSMO were grown by pulsed laser deposition with identical conditions for both the silicon and STO substrates. X-ray diffraction characterization of the samples confirmed strained epitaxial LSMO layers on STO and relaxed fibre textured films with unified out-of-plane orientation on Si with NS seed layer. Magnetization measurements, shown in Fig. 1, revealed smaller saturation magnetization for samples grown on Si. This might be attributed to the textured nature of the samples. However, these samples exhibit a higher Curie temperature by more than 10 K, which is the result of strain relaxation. For a closer insight into the electronic structure of the material a combination of spectroscopic ellipsometry and magneto-optical spectroscopy experiments were performed. The results allowed to derive the full permittivity tensor of the material in the spectral range from 1.5 to 5 eV. The spectral dependence of the off-diagonal element of the permittivity tensor, shown in Fig. 2, revealed striking similarity between the LSMO samples grown on STO and Si. Three electronic transitions around 1.9, 2.9, and 3.5 eV were identified in the spectra, suggesting the main contribution to the optical response arises from Mn states 3.
1 M. Bowen, M. Bibes, A. Barthélémy, et al., Appl. Phys. Lett., Vol. 82, p.233–235 (2003)
2 A.P. Ramirez, J. Phys.: Condens. Matter, Vol. 9, p.8171–8199 (1997)
3 M. Zahradník, T. Maroutian, M. Zelený, et al., Phys. Rev. B, Vol. 99, p.195138 (2019)
Fig. 1: Temperature dependent magnetization of LSMO samples on STO and Si in saturation.
Fig. 2: Spectral dependence of the off-diagonal element of the permittivity tensor of LSMO samples on Si and STO.