Artificial fabrication and magnetic properties of non-equilibrium ordered alloys by monatomic layr control

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We have compared structural and magnetic properties of the Ll_0-type FeAu ordered alloy fabricated by monatomic layr control to those of Fe (x ML) /Au (x ML) superlattices, where ML represents monatomic layr thickness. X-ray diffraction peaks corresponding to the superlattice period of x+x=2x ML have been observed definitely both for x=integers and non-integers. The X-ray diffraction patterns can be simulated by the model assuming a complete layr-by-layr growth with strucutural coherence throughout the sample, indicating the formation of coherent layred structure. The perpendicular magnetic anisotropy energy has been estimated from the in-plane and perpendicular magnetization curves. The product of the perpendicular anisotropy energy K_* and the Fe layr thickness t_<Fe>, K_*・t_<Fe>, for x=integers, decreases linearly with increasing t_<Fe> as seen in many magnetic superlattices. The interface anisotorpy energy K_s evaluated from the linear relationship increases with x for 1<less than … More or equal>x<less than or equal>3, and saturates for x<greater than or equal>4, which is explained by an extended Neel model. For x=non-integers, on the other hand, K_*・t_<Fe> vs.t_<Fe> deviates from the linear relationship, and shows oscillatory behavior with a period of 1 ML.We consider that this is a consequence associated with the reduction in K_s due to the interface roughness for x=non-integers. This study provides the first discovery of the oscillatory perpendicular anisotropy in magnetic superlattices. Furthermore, FMR measurements have indicated that the in-plane fourfold anisotropy also oscillates as a function of t_<Fe> with a period of 1.ML.In order to elucidate the origin for the oscillatory magnetic anisotropies, more precise structure analyzes including high resolution TEM,EXAFS and in situ STM are necessary. Magnetooptical measurements also indicate the oscillation of the Kerr rotation for the photon energy less than 2.5 eV.For 1<less than or equal>x<less than or equal>8, in addition, prominent structure around 3-4 eV has been observed, suggesting the formation of quantum well states of 3d electrons in Fe layrs. Less