Robust thermoelectric performance and high spin polarisation in CoMnTiAl and FeMnTiAl compounds

New quaternary Heusler materials, CoMnTiAl and FeMnTiAl, have been investigated. These alloys are found to be stable in a ferromagnetic phase in Y-1 type structure; the stability is also confirmed by various conditions of elastic constants. Both alloys show half-metallic (HM) ferromagnetic character with integer magnetic moments and they present a metallic nature. The values of the minority band gap in CoMnTiAl and FeMnTiAl are found to be 0.50 eV and 0.25 eV respectively. These alloys also possess excellent thermoelectric behaviour with Seebeck coefficients for CoMnTiAl (FeMnTiAl) as 31 mu V K-1 (20 mu V K-1) at room temperature. Here we report that CoMnTiAl achieves a figure of merit of 0.62 in a wide temperature range while FeMnTiAl achieves 0.77. Thus these new quaternary Heusler alloys can prove to be ultimate candidates for spin valves and for the best thermoelectric applicability over an ample temperature range.