ES22-Wadhwa

Author: Wadhwa, Payal - Department of Physics, University of Cagliari, Sardinia, Italy

Title: Doping induced ferromagnetism in EuTiO3 and STO/ETO/LAO heterostructures by ab-initio calculations

Abstract: The emergence of a quasi two-dimensional electron gas (2DEG) at the interface of two metal oxides as LaAlO3 (LAO) and SrTiO3 (STO) raised an immense interest in the community of oxide electronics, insofar as this system was found to be blessed with a plethora of outstanding properties such as field-effect driven superconductivity, high elec-tron mobility and magnetoresistance. An old dream of the spintronic community, remained substantially eluded so far, has been the possibility to inject magnetization in the 2DEG by introducing a magnetic layer at the interface of LAO/STO heterostructure. This may create spin-polarized 2DEG, and enable this system as a paramount material for spintron- ics and spin-orbitronic technology. A serious candidate as magnetic interlayer is EuTiO3 (ETO), proposed in recent years by experiments [1]. ETO has cubic perovskite crystal structure and has nearly identical lattice constant to STO. It is reported that bulk ETO has G-type AFM ground state below Tn = 5.3 K, while it becomes FM under tensile strain or doping [2, 3]. We have applied several ab-initio approaches (GGA, GGA+U, and HSE06 functionals) to study structural, electronic and magnetic properties of ETO bulk and the STO/ETO/LAO heterostructure. We found, for increasing electron doping, a progressive enhancement of the FM phase stability under doping. We also applied the Wannier function interpolation to explore the magnetic interactions in ETO. Our results show that Eu-Ti-Eu coupling is predominant over direct Eu-Eu coupling, while intra-Eu 4f -5d virtual excitations are fundamental to drive FM coupling under n-doping. In fact, for increasing electron doping, the whole charge entirely goes to fill majority Ti-3d t2g orbitals, while a small but significant residual magnetization ‚àº0.05 ŒºB is also present, even at zero doping, on the Eu-5d states, indicating strong 4f -5d hybridization. Overall, our results for n-doped ETO and STO/ETO/LAO heterostructures depict them to be potential candidates for electronic transport and magneto-transport applications.   

References 
[1] De Luca et al., Phys. Rev. B, 89, 224413 (2014). 
[2] T. Katsufuji et al., Phys. Rev. B, 60, R15021(R) (1999).  [3] J. H. Lee et al., Nature, 466, 954 (2010).

Other authors: Alessio Filippetti & Department of Physics, University of Cagliari, Sardinia, Italy