2006 Volume 47 Issue 1 Pages 20-24
The B2⁄L21 order–disorder transition and ferromagnetic/paramagnetic transition temperatures in Co2(Cr1−xFex)(Ga1−yAly) alloys were determined by differential scanning calorimetry and transmission electron microscopy. It was found that spinodal decomposition cannot be suppressed by quenching in the Al-rich portion of Co2Cr(Ga1−yAly) alloys, leading to lowering of Curie temperature Tc. The transition temperature TtB2⁄L21 from the B2 to L21-type phase decrease with increasing y for both the Co2Cr(Ga1−yAly) and Co2Fe(Ga1−yAly) alloy systems. The Tc in the Ga-rich portion of the L21-type Co2Cr(Ga1−yAly) alloy system is almost constant at about 480 K, whereas that in the B2-type Co2Fe(Ga1−yAly) alloy system slightly increases from about 1100 K to about 1170 K. By extrapolation from the Ga-rich side of Co2Cr(Ga1−yAly) alloys, TtB2⁄L21 and Tc of the metastable Co2CrAl alloy were determined as 800 and 470 K, respectively. An optimal concentration area for obtaining excellent half-metallic properties and high stability of the L21-type phase in the Co2(Cr1−xFex)(Ga1−yAly) alloys is proposed.