Epitaxial Growth of Ordered Co₂(Cr_1−xFe_x)Al Full-Heusler Alloy Films on Single Crystal Substrates

Abstract

We have investigated the structural and magnetic properties for Co₂(Cr_1−xFe_x)Al (x=0.4, 0.6 and 1.0) full-Heusler alloy films deposited on MgO(001), MgO(011) and sapphire (a-plane) substrates by magnetron sputtering. Substrate temperatures were varied from ambient temperature to 773 K. The XRD patterns reveal that the Co₂(Cr_1−xFe_x)Al films grow epitaxially with the (001), (112), and (011) orientations on MgO(001), MgO(110) and sapphire (a-plane) substrates, respectively. The Co₂(Cr_1−xFe_x)Al films deposited at room temperature (RT) crystallize into the A2 structure, whereas the films deposited at 673 K showed the B2 structure. Especially, for the Co₂FeAl (x=1) films deposited on an MgO(001) substrate at 773 K, the crystal structure is determined to be the L2₁ structure with a flat surface. The saturation magnetization of Co₂FeAl films with the B2 and L2₁ structures exhibits almost the 5 μ_B/f.u., whereas those of Co₂(Cr_1−xFe_x)Al (x=0.4, 0.6) show a reduction from the theoretical values. This reduction of the saturation magnetization might be due to the anti-ferromagnetic coupling between Cr–Cr atoms.