Influence of long- and short-range chemical order on spontaneous magnetization in single-crystalline...

We systematically investigate the long- and short-range chemical order, lattice volume, and spontaneous magnetization in single-crystalline Fe_0.6Al_0.4compound thin films. The vapor-quenching method based on a molecular beam epitaxy technique is utilized to fabricate the single-crystalline Fe_0.6Al_0.4compound 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, ∼4%, due to epitaxial strain were observed. The changes inSandVwere accompanied with the change in the magnetic moment per Fe,μ_Fe.μ_Feshowed the monotonic decrease as a function ofSwhereasμ_Femonotonically increases withV. With considering tetragonal distortion,μ_Fe-Vrelationship has a good agreement with the previous reports. Theμ_Fe-Srelationship showed the steep decrease ofμ_FearoundS∼ 0.6. In contrast toμ_Fe-Vrelationship,μ_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 inμ_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 lowμ_Fe. The results suggest that the transition from the long- to the SRO state plays the significant role onμ_Fe.