Powder neutron diffraction studies for the L21 phase of Co2YGa (Y = Ti, V, Cr, Mn and Fe) Heusler alloys

Abstract Site occupancies of Co, Y ( Y  = Ti, V, Cr, Mn and Fe) and Ga atoms for the L 2 1 phase in Co 2 Y Ga alloys annealed at 773 K were precisely investigated by powder neutron diffraction measurement. While Co atoms in all the five alloys almost perfectly occupy the x  (2 a ) site, the occupancy of the z  (4 b ) site by Ga atoms depends on the kind of Y atom, and it decreases with increasing number of valence electrons except for Co 2 CrGa alloy. Degrees of long-range order on the z site occupancy of Ga atoms experimentally determined for all the alloys are in good agreement with those thermodynamically estimated from their order–disorder transition temperatures using the Bragg–Williams–Gorsky approximation.