  Heusler compounds offer potential as spintronic devices due to their
spin-polarization and half-metallicity properties, where electron spin-majority
(minority) manifold exhibits states (band gap) at the electronic chemical
potential, yielding full spin-polarization in a single manifold. Yet, Heuslers
often exhibit intrinsic disorder that degrades its half-metallicity and
spin-polarization. Using density-functional theory, we analyze the electronic
and magnetic properties of equiatomic Heusler ($L$2$_{1}$) CoMnCrAl and
CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder
(thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl
undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained
for a limited range. Antisite disorder between Co-Al pairs in CoMnCrAl and
Co-Ge pairs in CoFeCrGe is energetically the most favored, and retain
half-metallic character in Co-excess samples. However, Co-deficient samples
undergo a transition from half-metallic to metallic, with a discontinuity in
the saturation magnetization. For binary swaps, configurations that compete
with the ground state are identified and show no loss of half-metallicity;
however, the minority-spin bandgap and magnetic moments vary depending on the
atoms swapped. For single binary swaps, there is a significant energy cost in
CoMnCrAl but with no loss of half metallicity. Although a few configurations in
CoFeCrGe energetically compete with the ground statei, however the
minority-spin bandgap and magnetic moments vary depending on the atoms swapped.
These informations should help in controlling these potential spintronic
materials.
