FePdSe: Magnetic Spin-Glass Polymorph of FeSe and PdSe Stable at Ambient Pressure.

We report the synthesis and characterization of FePdSe with a pyrite-type structure. FePdSe was synthesized using ambient pressure flux crystal growth methods even though the space group Pa3 is high-pressure polymorph for both FeSe and PdSe. Combined experimental and theoretical analysis reveal magnetic spin glass state below 23 K in 1000 Oe that stems from random Fe/Pd occupancies on the same atomic site. The frozen-in magnetic randomness contributes significantly to electronic transport. Electronic structure calculations confirm dominant d-electron character of hybridized bands and large density of states near the Fermi level. Flux-grown single crystal alloys in Pd-Fe-Se atomic system therefore open new pathway for exploring different polymorphs in crystal structures and their novel properties.