  Order-disorder phase transition in Ni$_{2+x}Mn_{1-x}$Ga Heusler alloys has
been studied. It was found that the $L2_1 \to B2^{\prime}$ phase transition in
Ni2+xMn1-xGa (x = 0.16 - 0.20) Heusler alloys is of second order and the
temperature of this transition decreases with Ni excess.
