Giant spin Seebeck effect through an interface organic semiconductor

Abstract

Interfacing an organic semiconductor C-60 with a non-magnetic metallic thin film (Cu or Pt) has created a novel heterostructure that is ferromagnetic at ambient temperature, while its interface with a magnetic metal (Fe or Co) can tune the anisotropic magnetic surface property of the material. Here, we demonstrate that sandwiching C-60 in between a magnetic insulator (Y3Fe5O12:YIG) and a non-magnetic, strong spin-orbit metal (Pt) promotes highly efficient spin current transport via the thermally driven spin Seebeck effect (SSE). Experiments and first principles calculations consistently show that the presence of C-60 reduces significantly the conductivity mismatch between YIG and Pt and the surface perpendicular magnetic anisotropy of YIG, giving rise to enhanced spin mixing conductance across YIG/C-60/Pt interfaces. As a result, a 600% increase in the SSE voltage (V-LSSE) has been realized in YIG/C-60/Pt relative to YIG/Pt. Temperature-dependent SSE voltage measurements on YIG/C-60/Pt with varying C-60 layer thicknesses also show an exponential increase in V-LSSE at low temperatures below 200 K, resembling the temperature evolution of spin diffusion length of C-60. Our study emphasizes the important roles of the magnetic anisotropy and the spin diffusion length of the intermediate layer in the SSE in YIG/C-60/Pt structures, providing a new pathway for developing novel spin-caloric materials.