Seeking large Seebeck effects in LaX(X=Mn and Co)O3/SrTiO3 superlattice by exploiting high spin-polarized effect

The SrTiO3-based transition-metal oxides heterostructures with superconducting, ferromagnetic, ferroelectric, and ferroelastic properties exhibit high application potential in the field of energy storage, energy conversion, and spintronic devices. Meanwhile, the high effective (charge)-Seebeck coefficient composed of ferromagnetic layer and SrTiO3 insulator layer has been achieved but we still have blocks to pursuing high spin-Seebeck coefficient. Here, we use first-principles calculations combined with spin-resolved Boltzmann transport theory to investigate the spin- and effective- Seebeck coefficients in the LaX (X=Mn and Co) O3/SrTiO3 superlattice. Compared with the LaMnO3/SrTiO3 superlattice, LaCoO3/SrTiO3 with ferromagnetic ordering has high spin polarization, relatively low valence valley degeneracy but high effective mass. Utilizing these characteristics, the maximum spin-Seebeck coefficient of LaMnO3/SrTiO3 is -152 µV/K at 450 K along the cross-plane direction, while the LaCoO3/SrTiO3 reaches -247 µV/K at the same conditions. Interestingly, the spin- and effective-Seebeck coefficients are amazingly consistent with each other below 200 K, which indicate that one spin channel (spin-up or spin-down) dominates the carrier transport, and the other one (spin-down or spin-up) is filtered out. These characteristics are mainly associated with the two-dimensional confinement effect in the magnetic MnO2/CoO2 layers with distinct and orbitals near the Fermi level. Our results clarify the relationship of spin- and effective- Seebeck coefficients and indicate that SrTiO3-based transition-metal oxide heterointerfaces are a key valuable for the spin caloritronics.