Magnetic semiconductors and half-metals in FeRu-based quaternary Heusler alloys

Phase stability, electronic structure and magnetic properties of the FeRu-based quaternary Heusler alloys, FeRuYZ (Y = Ti, V, Cr, Mn and Z = Al, Ga, In, Si, Ge, Sn), have been investigated theoretically. In one primitive unit cell, these alloys contain 24-26 valence electrons. The formation energy E(f )of FeRuYZ increases with increasing atomic number of Z when the Y or Z elements belong to the same group in the periodic table. And in the same period, group-IIIA Z element is not preferable for the stability of FeRuYZ compared with corresponding group-IVA element. This can be explained from the charge density difference. The 24-electron FeRu-based quaternary Heusler alloys are all paramagnets. Among them, FeRuTiSi (Ge, Sn) are all semiconductors with real band gap at the Fermi levels. These alloys may have potential applications as thermoelectric materials. High spin polarization ratio is observed in the 25-electron Heusler alloys, among which FeRuCrAl is predicted to have a 100% spin polarization ratio. The 26-electron FeRuCrSi is found to be a spin gapless semiconductor (SGS) with total spin moment of 2 mu(B). These materials can be interesting for the development of spintronic materials. The origin of SGS character in FeRuCrSi was discussed and compared with half-metallic Fe2CrSi, in which Ru and Fe are isoelectronic. These findings can help to design new SGSs in Heusler alloys.