In this paper, we report results of the first studies on the thermoelectric power (TEP) of the magnetic heusler alloy Ni$_{2.19}$Mn$_{0.81}$Ga. We explain the observed temperature dependence of the TEP in terms of the crystal field (CF) splitting and compare the observed behavior to that of the stoichiometric system Ni$_2$MnGa. The resistivity as a function of temperature of the two systems serves to define the structural transition temperature, T$_M$, which is the transition from the high temperature austenitic phase to low temperatures the martensitic phase. Occurrence of magnetic (Curie-Weiss) and the martensitic transition at almost the same temperature in Ni$_{2.19}$Mn$_{0.81}$Ga has been explained from TEP to be due to changes in the density of states (DOS) at the Fermi level.

12 pages, 4 figures, Accepted in Physical Review B vol 70, Issue 13