Magnetic and anomalous transport properties in spin-gapless semiconductor like quaternary Heusler alloy CoFeTiSn

Abstract

The magnetic and anomalous transport properties have been studied for the as-melted and annealed half-metallic ferromagnet CoFeTiSn. First-principles calculations suggest that CoFeTiSn presents band structure of the near spin-gapless semiconductor. The experiments show that the alloy’s phase purity, chemical ordering and grain size have been improved by annealing, which causes a different transport property. The as-melted sample shows a temperature coefficient of resistivity sign transition from positive to negative accompanying the ferromagnetic–paramagnetic transition, while the annealed sample only shows negative temperature coefficient resistivity in the whole temperature range. The calculated positive ordinary Hall coefficient suggest that transport properties are dominated by the hole carrier. The measured saturation magnetic moment at 5 K is lower but close to 1 μB/f.u, which is probably attributed to the inhomogeneous magnetic phase and the anti-site disorder between Co-Fe. The band structure of near spin-gapless semiconductor is another possible reason. The anomalous Hall conductivity changes from 20 S/cm to 27 S/cm after annealing due to the altered chemical ordering. The positive linear magnetoresistance indicates that the alloy appears to have spin-gapless semiconductor like behavior as predicted by its band structure.