  In this paper, we investigate the half-metallicity of Heusler alloys
Fe2Co1-xCrxSi by first principles calculations and anisotropy magnetoresistance
measurements. It is found that, with the increase of Cr content x, the Fermi
level of Fe2Co1-xCrxSi moves from the top of valence band to the bottom of
conduction band, and a large half-metallic band gap of 0.75 eV is obtained for
x=0.75. We then successfully synthesized a series Heusler Fe2Co1-xCrxSi
polycrystalline ribbon samples. The results of X-ray diffraction indicate that
the Fe2Co1-xCrxSi series of samples are pure phase with a high degree of order
and the saturation magnetic moment follows half-metallic Slater-Pauling rule.
Except for the two end members, Fe2CoSi and Fe2CrSi, the anisotropic
magnetoresistance of Fe2Co1-xCrxSi (x=0.25, 0.5, 0.75) show a negative value
suggesting they are stable half-metallic ferromagnets.
