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

We systematically investigate the long- and short-range chemical order, lattice volume, and spontaneous magnetization in single-crystalline Fe(0.6)Al(0.4)compound thin films. The vapor-quenching method based on a molecular beam epitaxy technique is utilized to fabricate the single-crystalline Fe(0.6)Al(0.4)compound with the differentB2 long-range order parameterS. Swas varied by the deposition temperatureT(d,)and it increases with increasingT(d). The lattice volumeVdecreased with increasingT(d), while the tetragonal distortion, similar to 4%, due to epitaxial strain were observed. The changes inSandVwere accompanied with the change in the magnetic moment per Fe,mu(Fe).mu(Fe)showed the monotonic decrease as a function ofSwhereas mu(Fe)monotonically increases withV. With considering tetragonal distortion,mu(Fe)-Vrelationship has a good agreement with the previous reports. The mu(Fe)-Srelationship showed the steep decrease of mu(Fe)aroundS similar to 0.6. In contrast to mu(Fe)-Vrelationship,mu(Fe)-Srelationship 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 mu(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 mu(Fe). The results suggest that the transition from the long- to the SRO state plays the significant role on mu(Fe).