The electronic structures were systematically calculated for Heusler alloys X 2 YZ (X and Y = 3d transition element, Z = IIIb, IVb, Vb element). The results show that alloys Fe 2 CrZ have the high density-of-state at the Fermi energy in the majority-spin state and show high spin polarization. The effects of chemical disorder on the half-metallicity and magnetic moment are discussed on the basis of the electronic structures. Considering three types of chemical disorder, we show that among the alloys Fe 2 CrZ, there are high spin polarized materials insensitive to chemical disorder and that Fe-Cr chemical disorder may occur.

Materials with high spin polarization at the Fermi energy (E F ) are searched by the systematic band calculation for Heusler alloys X 2 YZ. It is shown that materials with high density-of-state (DOS) for the majority-spin state at the E F tend to maintain high spin polarization against chemical disorder. Such materials are predicted, using the characteristics of DOS of Heusler alloys. As a candidates, X 2 (Cr x Mn 1Àx )Z will be proposed, where X is combination between transition elements including at least one of Fe, Ru and Os, and Z is combination among IIIb, IVb and Vb elements.

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We investigate the half-metallic properties and the stability of the ferromagnetic state in the alloys (Fe x Ru 1Àx ) 2 CrSi (0 x 1) with orderly and disorderly atomic arrangement based on the Heusler structure. It is predicted from the electronic structures that the ordered alloys are half-metals in the range of 1=3 < x < 3=4 and ferromagnets with high spin polarization in the range of 3=4 x 1. However, in the ferromagnetic state, the atomic arrangement with the Fe-Cr disorder tends to be energetically more favorable than the orderly arrangement, and the Fe-Cr disorder decreases the spin polarization of the ordered alloys. This is attributed to the fact that occupation of Cr sites by Fe destroys the gap near the Fermi energy in the minority spin state. But, because the Fe-Cr disorder shows a tendency to keep the spin polarization high as x increases, it is deduced that (Fe x Ru 1Àx ) 2 CrSi are materials with high spin polarization if x is high.