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

Abstract

SrTiO₃-based transition-metal oxide heterostructures with superconducting, ferromagnetic, ferroelectric, and ferroelastic properties exhibit high application potential in the fields of energy storage, energy conversion, and spintronic devices. Meanwhile, high effective (charge)-Seebeck coefficient materials composed of a ferromagnetic layer and SrTiO₃ insulator layer have been achieved but we still have blocks to pursuing high spin-Seebeck coefficient materials. 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⁻¹ at 450 K along the cross-plane direction, while LaCoO₃/SrTiO₃ reaches −247 μV K⁻¹ under the same conditions. Interestingly, the spin- and effective-Seebeck coefficients are amazingly consistent with each other below 200 K, which indicates 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 magnetic MnO₂/CoO₂ layers with distinct d_xy and d_z² 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 candidate for spin caloritronics.