Influence of long- and short-range chemical order on spontaneous magnetization in single-crystalline Fe_0.6Al_0.4 compound thin films

Abstract

We systematically investigate the long- and short-range chemical order, lattice volume, and spontaneous magnetization in single-crystalline Fe0.6Al0.4 compound thin films. The vapor-quenching method based on a molecular beam epitaxy technique is utilized to fabricate the single-crystalline Fe0.6Al0.4 compound with the different B2 long-range order parameter S. S was varied by the deposition temperature T d, and it increases with increasing T d. The lattice volume V decreased with increasing T d, while the tetragonal distortion, ∼4%, due to epitaxial strain were observed. The changes in S and V were accompanied with the change in the magnetic moment per Fe, μ Fe. μ Fe showed the monotonic decrease as a function of S whereas μ Fe monotonically increases with V. With considering tetragonal distortion, μ Fe–V relationship has a good agreement with the previous reports. The μ Fe–S relationship showed the steep decrease of μ Fe around S∼ 0.6. In contrast to μ Fe–V relationship, μ Fe–S relationship does not match only from ours to previous studies but also among other reports. It implies the statistical number of the nearest-neighbor Fe–Fe bonds, i.e. S, cannot be an enough explanatory parameter. To clarify the structural origin of change in μ Fe, the short-range order (SRO) parameter inferred from the analysis of superlattice diffractions were introduced. They showed the clear difference for the films with high and low μ Fe. The results suggest that the transition from the long- to the SRO state plays the significant role on μ Fe.