Resolving the phase structure of nonstoichiometric Co2FeGa Heusler nanoparticles

Abstract

Heusler nanocrystals, i.e., Heusler compounds with dimensions in nanometer range are promising materials for next-generation spin-related devices. Recently, we have developed a chemical approach to prepare L21 ordered Heusler nanoparticles and characterized their size-related structure and magnetic properties. In this work, effect of precursor composition is investigated in terms of their importance in controlling the phase structure of Co2FeGa nanoparticles. The formation of the L21 ordered Co2FeGa phase is evidenced by combining X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy and Mössbauer spectroscopy measurements. From XRD, precursor compositions of low Co and high Fe are associated with decreasing amounts and even disappearance of fcc Co and fcc Fe impurities. We also find that, even though the XRD data indicate only pure Co2FeGa phase in sample with excess Fe, EXAFS and Mössbauer spectroscopy data unambiguously reveal the co-existence of bcc Fe with Co2FeGa main phase.