Substantial enhancement of thermal spin polarization in Py/Cu interface

We investigated the temperature dependence of thermally excited spin current properties of ferromagnet Py $({\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20})$ by using a lateral spin-valve structure. The spin-dependent Seebeck coefficient at the Py/Cu interface was found to show a significant increase at low temperature while the charge Seebeck coefficient showed the ordinal reduction with decreasing temperature. This produces a crossover between the charge- and spin-dependent Seebeck coefficients, resulting in the thermal spin polarization greater than $100%$ below 125 K. From the first-principles calculation specially developed for the Py/Cu interfaces, the spin-dependent Seebeck coefficient is found to be highly susceptible to the magnetic disorder-induced scattering at the interface. The calculation with considering the temperature dependence of the magnetic disorder provides a consistent description for the significant enhancement of spin-dependent Seebeck coefficient in the Py/Cu interface. Our demonstration shows the importance of interface disorder and paves the way toward the development of conventional ferromagnetic metal for the practical application of thermo-spin energy conversion.