Optimal half-metal band structure for large thermoelectric performance

Half-metal ferromagnets were predicted [Cahaya, Tretiakov, and Bauer, IEEE Trans. Magn. 51, 1 (2015)] to give large thermoelectric performance in antiparallel spin valve configuration. Despite being metals that suffer from the Wiedemann-Franz law, the additional spin degrees of freedom allow for tuning of the thermoelectric properties due to the spin valve enhancement factor. We test this theory and find a mismatch of parameters that gives large thermoelectric performance and large spin valve enhancement factor. As a result, we show that the spin valve setup is useful only for half-metal ferromagnets with initially poor thermoelectric performance. To obtain the largest thermoelectric performance, one still needs to open the band gap.