  MgO-barrier magnetic tunnel junctions with half-metallic Heusler alloy
electrodes attracted much attentions for spintronics applications. However, a
couples of issues related to materials still remain to be resolved for
practical uses. Recently, quarterly equiatomic Heusler alloys attracted
attentions as advanced Heusler alloys. CoIrMnZ (Z = Al, Si, Ga, and Ge)
half-metallic Heusler alloys were designed and predicted to have moderate Curie
temperatures and to be a lattice-matched with the MgO barrier, being
advantageous to traditional Co2 Heusler alloys [T. Roy et al., J. Magn. Magn.
Mater. 498, 166092 (2020)]. Here we experimentally investigated structure and
magnetic properties for thin films of one of those alloys, CoIrMnAl with a
sputtering deposition. We successfully obtained the films with the B2 chemical
ordering even with no post-annealing process. The lattice constant for the
films annealed at 500-600$^\circ$C approximates the predicted values. The
magnetization at 10 K was near 500 kA/m and the Curie temperature was
approximately 400 K were observed, which were about 70% of the values predicted
for the fully ordered structure. The magnetic properties observed in those B2
ordered films were well explained by ferrimagnetism appeared in B2 ordered
CoIrMnAl with full-swap disorders of Co-Ir and Mn-Al and almost full-swap
disorder of Co-Mn, predicted from the first-principles calculations.
