Structural and magnetic properties of CoIrMnAl equiatomic quaternary Heusler alloy epitaxial films designed using first-principles calculations

Abstract

• CoIrMnAl was computationally designed as one of the advanced materials for spintronics. • We obtained B2 ordered CoIrMnAl thin films with the lattice constant similar to that predicted in fully ordered alloy. • Magnetization at 10 K and Curie temperature measured were about 70% of the predicted values in fully ordered alloys. • Experimental data were well explained with ferrimagnetism due to Co-Mn swap disorders predicted from ab-initio calculation. MgO-barrier magnetic tunnel junctions with half-metallic Heusler alloy electrodes have attracted considerable attention for spintronics applications. However, there remain a couple of issues related to materials that should be resolved before practical use. Recently, quarterly equiatomic Heusler alloys have attracted attention 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 lattice-matched with the MgO barrier, which is advantageous compared to traditional Co 2 Heusler alloys T. T [T. Roy et al., J. Magn. Magn. Mater. 498 (2020) 166092]. Here, we experimentally investigated the structure and magnetic properties of thin films composed of one of these alloys, CoIrMnAl, fabricated by sputtering deposition. We successfully obtained films with the B 2 chemical ordering, even without a post-annealing process. The lattice constants for the films annealed at 500–600 ∘ C were approximately equal to the predicted values. The magnetization at 10 K was close to 500 kA/m, and the Curie temperature was approximately 400 K, which were approximately 70% of the values predicted for the fully ordered structure. The magnetic properties observed in the B 2-ordered films were well explained by ferrimagnetism that appeared in the B 2-ordered CoIrMnAl with full-swap disorders of Co-Ir and Mn-Al and almost full-swap disorder of Co-Mn, which was predicted from the first-principles calculations.