  Quaternary Heusler alloys Co$_2$Cr$_{1-x}$Fe$_{x}$Al with varying Cr to Fe
ratio $x$ were investigated experimentally and theoretically. The electronic
structure and spectroscopic properties were calculated using the full
relativistic Korringa-Kohn-Rostocker method with coherent potential
approximation to account for the random distribution of Cr and Fe atoms as well
as random disorder. Magnetic effects are included by the use of spin dependent
potentials in the local spin density approximation.
  Magnetic circular dichroism in X-ray absorption was measured at the $L_{2,3}$
edges of Co, Fe, and Cr of the pure compounds and the $x=0.4$ alloy in order to
determine element specific magnetic moments. Calculations and measurements show
an increase of the magnetic moments with increasing iron content. Resonant
(560eV - 800eV) soft X-ray as well as high resolution - high energy ($\geq
3.5$keV) hard X-ray photo emission was used to probe the density of the
occupied states in Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al.
