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

TL;DR

This study investigates the structure and magnetic properties of epitaxial CoIrMnAl Heusler alloy films, demonstrating successful synthesis with B2 ordering and magnetic characteristics consistent with first-principles predictions, relevant for spintronics applications.

Contribution

First experimental realization and characterization of CoIrMnAl Heusler alloy thin films with B2 ordering, confirming theoretical predictions of magnetic properties.

Findings

Films exhibited B2 chemical ordering without post-annealing.

Lattice constants matched predicted values after annealing at 500-600°C.

Magnetization at 10 K was about 500 kA/m, with a Curie temperature around 400 K.

Abstract

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.