Change in the nature of exchange interactions in Heusler alloys with a replacement of Co for Cu

RCCI (the preasymptotic form) and Caroli-Blandin models are used for calculating the Fermi wave vector and the exchange integrals in $Cu_2MnAl$ and $Co_2MnAl$ alloys. The experimentally acquired values of the spin polarizations for the first and second coordinational spheres serve as the initial information. It is shown that the basic role in the $Cu_2MnAl$ alloy is played by a mechanism of d-resonance scattering, while it is played by sd-exchange in the $Co_2MnAl$ alloy.